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Herein, a Mott-Schottky heterojunction catalyst was developed by incorporating nickel (Ni) nanometallic particles supported on nitrogen-doped carbon-coated TiO 2 , enabling full-spectrum light absorption and facilitating a robust metal-support interface. This catalyst demonstrated exceptional performance in photo-thermal catalysis. Specifically, the Ni/0.5-TiO 2 @NC catalyst achieved a CO 2 hydrogenation rate of 65.3 mmol/(g cat ·h) with a CH 4 selectivity exceeding 99% under full-spectrum illumination. Remarkably, the catalyst exhibited excellent stability, maintaining its performance over two reaction cycles. The strong metal-support interface of the Mott-Schottky heterojunction catalyst enhanced photo-generated electron-hole separation efficiencies, leading to a substantial rise in catalyst surface temperature. Consequently, this phenomenon accelerated the reaction kinetics and lowered the activation energy, thereby improving overall efficiency. [Display omitted] • Mott-Schottky heterojunctions consisting of TiO 2 @NC-support and highly dispersed Ni NPs catalysts were successfully prepared. • The Mott-Schottky heterojunction catalysts exhibit rapid interface electron transfer, leading to superb carrier separation efficiencies. • The Ni/0.5-TiO 2 @NC catalyst demonstrates exceptional photo-thermal co-catalytic effects, resulting in outstanding performance in the RWGS reaction. • The in-situ DRIFTS analysis revealed that the mechanism governing the photo-thermal co-catalytic RWGS reaction follows the *HCOO pathway. Photo-thermal co-catalytic reduction of CO 2 to synthesize value-added chemicals presents a promising approach to addressing environmental issues. Nevertheless, traditional catalysts exhibit low light utilization efficiency, leading to the generation of a reduced number of electron-hole pairs and rapid recombination, thereby limiting catalytic performance enhancement. Herein, a Mott-Schottky heterojunction catalyst was developed by incorporating nitrogen-doped carbon coated TiO 2 supported nickel (Ni) nanometallic particles (Ni/x-TiO 2 @NC). The optimal Ni/0.5-TiO 2 @NC sample displayed a conversion rate of 71.6 % and a methane (CH 4) production rate of 65.3 mmol/(g cat ·h) during photo-thermal co-catalytic CO 2 methanation under full-spectrum illumination, with a CH 4 selectivity exceeding 99.6 %. The catalyst demonstrates good stability as it shows no decay after two reaction cycles. The Mott-Schottky heterojunction catalysts display excellent efficiency in separating photo-generated electron-hole pairs and elevate the catalysts' temperature, thus accelerating the reaction rate. The in-situ experiments revealed that light-induced electron transfer effectively facilitates H 2 dissociation and enhances surface defects, thereby promoting CO 2 adsorption. This study introduces a novel approach for developing photo-thermal catalysts for CO 2 reduction, aiming to enhance solar energy utilization and facilitate interface electron transfer. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ni phyllosilicate was firstly synthesized by a modified microwave synthesis method. • Surfactant modification led to ultrahigh specific surface area of 535 m2 g−1 and ultrathin layer of Ni phyllosilicate of only 1.43 nm. • Hexadecyl trimethyl ammonium bromide showed higher promotion effect compared with P123 and F127. • The special structure resulted in competitive catalytic activity for CO 2 methanation. • This catalyst could exhibit high stability for 100 h in a long-term test. The traditional techniques for the synthesis of nickel phyllosilicates usually time-consuming and energy-intensive, which often lead to the formation of layers with excessive thickness due to uncontrolled crystal growth. In order to overcome these challenges, this work introduces a microwave-assisted synthesis strategy to facilitate the synthesis of Ni-phyllosilicate-based catalysts within an exceptionally short duration of only five minutes, attaining a peak temperature of merely 102 °C. To enhance the specific surface area and to increase the exposure of active sites, an investigation was conducted involving three surfactants. The employment of hexadecyl trimethyl ammonium bromide (CTAB) has yielded remarkable results, with an ultrahigh specific surface area reaching 535 m2 g−1 and an ultrathin lamellar thickness of 1.43 nm. The catalyst exhibited an impressive CO 2 conversion of 81.7 % at 400 °C, 60 L g−1 h−1, 0.1 MPa. It also demonstrated a substantial turnover frequency for CO 2 (TOF CO2) of 5.4 ± 0.1 × 10−2 s−1, alongside a relatively low activation energy (E a) of 80.74 kJ·mol−1. Moreover, the catalyst maintained its high stability over a period of 100 h and displayed high resistance to sintering. To further elucidate growth temperature gradient of the catalyst and concentration gradient of the materials involved, COMSOL Multiphysics (COMSOL) simulations were effectively utilized. In conclusion, this work breaks the limitation associated with traditional, laborious synthesis methods for Ni-phyllosilicates, which can produce materials with high surface area and thin-layer characteristics. [ABSTRACT FROM AUTHOR]

[Display omitted] • High loading Ni/SiO 2 with high dispersion was prepared by sol–gel method. • 79% CO 2 conversion with 96% CH 4 selectivity could be reached at 300 °C. • Formate pathway, RWGS + CO hydrogenation pathway and C-O bond cleavage pathway were identified over the Ni/SiO 2 catalyst. • RWGS + CO hydrogenation pathway is dominant at low temperature (>250 °C). In the power-to-gas scenario, surplus renewable electricity is stored in the form of methane, by reacting green hydrogen with waste CO 2 through the Sabatier reaction. Low-cost catalysts that feature a high activity at low temperature are needed. We disclose the sol–gel preparation of high-loading mesoporous Ni/SiO 2 catalysts. (HR)-TEM, XRD, N 2 physisorption, and H 2 chemisorption show that small Ni particles (<5 nm) are obtained, even at loading up to 38 wt%. The best catalyst reached a specific activity of 10.2 µmol CH4.g−1.s−1 at 250 °C (TOF = 0.0155 s−1; almost 3 times higher than a reference catalyst prepared by impregnation). Being based on inert silica, these catalysts are ideal model materials to elucidate the reaction mechanism on nickel. Combining CO 2 -TPD, in-situ CO 2 -DRIFTS, and TPSR with DFT calculations, we show that CO 2 methanation follows mostly the RWGS + CO-hydrogenation and the formate pathways, the former being dominant at low temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] • MgO addition improves the CH 4 selectivity of a Ni/SiO 2 catalyst. • MgO partly covers metallic Ni, forming an MgO/Ni interface. • The rate determining step for methanation is formyl group conversion. • MgO/Ni interface facilitates the formyl group conversion due to a lower energy barrier. CO 2 methanation is a promising carbon–neutral process to produce synthetic natural gas. Ni is a cost-effective catalyst, but needs improved selectivity to compete with noble metal catalysts. Herein, MgO-promoted Ni/SiO 2 is investigated as model system and compared to unpromoted Ni/SiO 2. The catalysts are characterized with chemisorption, transmission electron microscopy and in situ quick X-ray absorption spectroscopy. After reduction, MgO partly covers metallic Ni forming an MgO/Ni interface, which proves to be critical to the reaction through metal oxide-metal interaction. Combining kinetic and in situ diffuse reflectance infrared Fourier transform spectroscopy, formyl group hydrogenation was found to be the rate determining step for both catalysts. The enhanced CH 4 selectivity after MgO addition is attributed to facilitated conversion of the key intermediates - formyl groups - due to a lower energy barrier. This work provides unambiguous experimental proof for the role of the MgO/Ni interface in the reactivity for CO 2 methanation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Well-defined Fe x O y C z compositions promoted with Li, Na, K, Rb or Cs were prepared. • They were tested in CO 2 hydrogenation to higher hydrocarbons. • Stationary phases and their spatial distribution depend on alkali metal type. • Steady-state Fe 5 C 2 /Fe 3 C ratio determines the selectivity to C 2+ -hydrocarbons. • The kind of alkali metal affects reaction pathways of CH 4 formation. A series of catalysts for CO 2 hydrogenation to higher (C 2+) hydrocarbons were prepared through controlled decomposition of iron (II) oxalate dihydrate impregnated with Li, Na, K, Rb or Cs carbonate. They consist of Fe 3 O 4 , Fe 5 C 2 , Fe 3 C and Fe. Their steady-state spatial phase distribution is, however, affected by the presence and the kind of the promoter. These structural characteristics determine catalyst activity and product selectivity. Fe 3 C seems to favor CH 4 formation, while C 2+ -hydrocarbons are formed over Fe 5 C 2. A positive relationship between the rate of C 2+ -hydrocarbons formation and the rate constant of dissociation of adsorbed CO 2 was established, while an opposite dependence is valid for the rate of CO 2 methanation. The rate constant of this reaction increases in the presence of alkali metal and with an increase in its atomic number. Therefore, CH 4 is mainly formed over Rb- or Cs-doped catalysts through CO hydrogenation, while CO 2 methanation prevails over the remaining catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Non-noble Ni catalyst for the coupling of primary amines into secondary amines. • Facile control of Ni nanoparticle size by Ni salt precursors. • Ni particle size controlled catalytic efficiency. • High yields with wide scope of substrates at base-free conditions. Earth-abundant metal catalysts, especially Ni, are highly favourable in heterogeneous reactions compared with noble metal ones. Herein, Ni nanoparticle catalysts supported on Vulcan carbon (VCX) support were prepared through a simple impregnation-reduction method and utilized for the acceptorless dehydrogenation of primary amines to secondary amines. The best performance was achieved with Ni (A) /VXC with Ni particle size of 11.9 nm at 150 °C. Smaller or larger particle sizes resulted in a lower TOF, indicating a structure-sensitive activity. This work may serve as inspiration for further investigation into acceptorless dehydrogenation using non-noble metal catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Highly dispersed Ni 2 P catalyst was prepared from nickel phyllosilicate precursor. • Nickel phyllosilicate facilitated the formation of nanosized Ni 2 P particles. • (2 0 1) plane of Ni 2 P gave more coordinately-unsaturated active sites. • Ni 2 P/SiO 2 -DP exhibited high performance in hydrodesulfurization of 4,6-DMDBT. • Highly dispersed Ni 2 P catalysts were obtained on MCM-41, S-1, and TS-1. Highly dispersed Ni 2 P catalysts were prepared from nickel phyllosilicate precursor, which was generated on the support by the deposition–precipitation (DP) method. Si-containing materials, including SiO 2 , MCM-41, S-1, and TS-1, were used as the supports. The strong interaction between Ni and Si species in nickel phyllosilicate effectively suppressed the agglomeration of nickel species. Highly dispersed Ni 2 P catalyst (Ni 2 P/SiO 2 -DP) was obtained by subsequent temperature-programmed hydrogen reduction, and the size of Ni 2 P crystallites was smaller than that of Ni 2 P/SiO 2 -IM prepared from conventional impregnation precursor (7.7 nm vs 14.2 nm). HRTEM observation demonstrated that a large fraction of (2 0 1) planes were present in Ni 2 P/SiO 2 -DP whereas (1 1 1) planes were predominant in Ni 2 P/SiO 2 -IM. The strong metal-support interaction and the smaller particle size, along with the higher degree of coordinately unsaturated sites facilitated the hydrogen spillover and the hydrogenation activity. As a result, Ni 2 P/SiO 2 -DP exhibited significantly higher performance than Ni 2 P/SiO 2 -IM in hydrodesulfurization of 4,6-dimethyldibenzothiophene. Similarly, highly dispersed Ni 2 P catalysts supported on Si-containing molecular sieves (MCM-41, S-1, and TS-1) were obtained from the in situ generated nickel phyllosilicate as well. It seems that the strong interaction between Ni and Si species in nickel phyllosilicate precursor played a decisive role in the formation of highly dispersed and (2 0 1) plane-exposed Ni 2 P catalysts. [ABSTRACT FROM AUTHOR]

Small nano-sized Ni/CeO 2 -S catalyze air-level CO 2 hydro-methanation. Here, Ni/CeO 2 -S has double defect synergistic effect, highly dispersed active Ni species, enhanced H spillover and efficient CO 2 adsorption and activation capability. [Display omitted] • Ni/CeO 2 -S (<5 nm) shows superior CO 2 methanation performance. • Enhanced CO 2 methanation due to Ni-O x -Ce interfaces, O vacancies, dispersed Ni, and H spillover. • In-situ DRIFTS reveals a unique Formate pathway on Ni/CeO 2 -S. • Ni/CeO 2 -S shows excellent durability in 100-h continuous CO 2 methanation. Smaller nano-sizes typically result in supported catalysts with abundant interfacial and intrinsic oxygen vacancies for better adsorption and activation of small molecules, including CO 2 , leading to improved efficiency of CO 2 methanation. Here, Ni/CeO 2 -S with the smaller nano-size of around 4.2 nm is used to catalyze CO 2 methanation, which exhibits significantly enhanced activity compared to larger nano-sized Ni/CeO 2 -L catalyst, even surpassing the most majority of previously reported catalysts using CeO 2 as the support or Ni as the active metal. The coexistence of interfacial defects and intrinsic oxygen vacancies allows for enhanced adsorption and activation of CO 2 molecules as well as H spillover, resulting in such improved CO 2 methanation. In-situ DRIFTS demonstrate a nearly sole Formate pathway on Ni/CeO 2 -S for efficient CO 2 hydrogenation. This research provides valuable insights into the reaction mechanism over a small nanosize supported catalyst. [ABSTRACT FROM AUTHOR]

Propionate is a model substrate for studying energy-limited syntrophic communities in anaerobic digestion, and syntrophic bacteria usually catalyze its degradation in syntrophy with methanogens. In the present study, metagenomics and metatranscriptomics were used to study the effect of the supportive material (e.g., hydrochar) on the key members of propionate degradation and their cooperation mechanism. The results showed that hydrochar increased the methane production rate (up to 57.1%) from propionate. The general transcriptional behavior of the microbiome showed that both interspecies H 2 transfer (IHT) and direct interspecies electron transfer (DIET) played essential roles in the hydrochar-mediated methanation of propionate. Five highly active syntrophic propionate-oxidizing bacteria were identified by genome-centric metatranscriptomics. H85pel, a member of the family Pelotomaculaceae , was specifically enriched by hydrochar. Hydrochar enhanced the expression of the flagellum subunit, which interacted with methanogens and hydrogenases in H85pel, indicating that IHT was one of the essential factors promoting propionate degradation. Hydrochar also enriched H162tha belonging to the genus of Thauera. Hydrochar induced the expression of genes related to the complete propionate oxidation pathway, which did not produce acetate. Hydrochar and e-pili-mediated DIET were enhanced, which was another factor promoting propionate degradation. These findings improved the understanding of metabolic traits and cooperation between syntrophic propionate oxidizing bacteria (SPOB) and co-metabolizing partners and provided comprehensive transcriptional insights on function in propionate methanogenic systems. • Addition of hydrochar enhanced by 57.1% methane production rate from propionate. • One putative SPOB H85pel was specifically enriched by hydrochar. • IHT and DIET were key pathways in hydrochar-mediated methanation of propionate. • H162tha might encode a novel syntrophic propionate oxidation pathway. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ni/CeO 2 (10 wt%) catalysts for CO 2 methanation were modified by altering calcination temperature/atmospheres. • Characterisation was performed to evaluate the importance of properties such as Ni crystallite size, availability and oxygen vacancies. • Ni availability (i.e. catalytically accessible Ni), determined from crystallite size and SMSI extent, affects the number of interfacial sites. The structure of a catalyst has a strong impact on its performance. Here we investigate the physicochemical properties of Ni/CeO 2 in an attempt to draw structure–activity relationships for CO 2 methanation. A combination of characterisation methods (X-ray diffraction (XRD), 4D Scanning Transmission Electron Microscopy (4D-STEM), CO chemisorption and oxygen storage capacity study etc.) clearly demonstrates the effect of Ni crystallite size, Ni availability (i.e. catalytically accessible Ni) and oxygen vacancies at the Ni-CeO 2 interface in Ni/CeO 2 during CO 2 methanation. Among them, the role of exposed Ni active sites is highlighted, and two possible optimisation schemes i.e. changing the support calcination temperature and the final calcination atmosphere are proposed to obtain a better dispersal of Ni NPs (nanoparticles) on CeO 2. Both modification methods do not affect the reaction route, and the activity differences of Ni/CeO 2 can be explained by the various hydrogenation rate of formate species, as confirmed by in situ diffuse-reflectance infrared Fourier-transform spectroscopy (DRIFTS) measurements. [ABSTRACT FROM AUTHOR]

[Display omitted] • BiVO 4 @TiO 2 shows high selectivity and activity for CO 2 -to-CH 4 conversion. • S-scheme heterojunction was identified by DFT and KPFM. • Effective separation and directional migration of electrons are achieved. • Achieving efficient CO 2 conversion by reinforcing reaction process factors. • A solar-to-fuels efficiency of ∼ 0.46 ‰ is obtained under UV-enhanced light sources. Herein, a unique structure BiVO 4 @TiO 2 nanograss/needle arrays S-scheme heterojunction photocatalyst for CO 2 photoreduction reaction was created. The photocatalyst can drive electrons to the reactive spots spontaneously and continuously, which effectively tackles the problem of severe recombination and disordered migration of photogenerated carriers. Theoretical calculations and experimental results demonstrate that adding BMIM-BF 4 ionic liquid to generate BMIM-*CO 2 intermediate promotes CO 2 activation and enrichment of reactants concentration around the catalytic sites. Benefiting from the sufficient electron supply of catalytic sites and reinforced reactants supply in the interfacial microenvironment, the BiVO 4 @TiO 2 photocatalyst shows high selectivity and activity of CO 2 -to-CH 4 conversion. The CH 4 selectivity increased to 57.3 % (132.7 μmol m-2h−1) and the methanation activity was increased by 8.6 times in the 5.0 % BMIM-BF 4 aqueous solution. Significantly, the BiVO 4 @TiO 2 NNAs catalyst obtains a solar-to-fuels energy efficiency of ∼ 0.46 ‰ under ultraviolet-enhanced light sources without any sacrificial agent or co-catalyst. This work displays the relationship between reaction process factors (electron supply, CO 2 molecule, and proton supply) and CO 2 photoreduction activity and selectivity, giving new insight into achieving efficient CO 2 photoreduction conversion. [ABSTRACT FROM AUTHOR]

[Display omitted] • Carbon removal rate-limiting for Fe-carbide in the Fischer-Tropsch (FT) reaction. • C deposits decrease FT activity and increase CH 4 selectivity. • SSITKA investigations used as function of amount of C deposits. • Slow sites mainly responsible for CH 4 formation via MvK mechanism. • Higher H 2 /CO ratio or total pressure removes C deposits and decreases deactivation. A well-known observation in the Fe-catalyzed Fischer-Tropsch (FT) reaction is that Fe-carbide catalysts deactivate due to carbon deposition. In comparison, the influence of such carbon deposits on the product distribution has been less widely reported. The present work investigates the relationship between the kinetics of the FT reaction for a carburized Raney-Fe model catalyst and the composition of the catalytic surface with a focus on carbon deposits. The deposition of carbon during the ongoing FT reaction at low pressure decreases the FT activity and increases the CH 4 selectivity. Steady-state transient isotopic kinetic analysis (SSITKA) at low pressure shows that the buildup of C deposits affects fast CO conversion sites on the Fe-carbide surface, mainly responsible for C C coupling via a Langmuir-Hinshelwood mechanism, more than slow sites that mainly produce CH 4 via a Mars-Van Krevelen mechanism. Hindrance of migration of chain-growth monomers by C deposits decreases the amount of longer hydrocarbons. Nevertheless, SSITKA shows that C 2 products form faster, which is likely since their formation increasingly depends on monomers formed at proximate CO dissociation sites when the amount of carbon deposits increases. Carbon deposition can be suppressed and reversed by increasing the H 2 /CO ratio at constant pressure or by increasing the total pressure at constant H 2 /CO ratio. As such, the FT performance can be stabilized by operating at elevated pressure, even if initially the reaction was started at low pressure. Nevertheless, prolonged operation at low pressure leads to a less reactive character of the C deposits that cannot be removed anymore during high-pressure operation. [ABSTRACT FROM AUTHOR]

The O-deficit SiC-Co 3 O 4 -CuFe 2 O 4 surface area available for gas–solid reactions exhibited high oxidation potential and remarkably CO 2 -splitting capacities with a total CO yield of 1919.33 µmol/g at 1300 °C. The significance of exploiting the synergy between CuFe 2 O 4 and Co 3 O 4 layers provided fundamental insights useful for the solar thermochemical process. [Display omitted] CO 2 -splitting and thermochemical energy conversion effectiveness are still challenged by the selectivity of metal/metal oxide-based redox materials and associated chemical reaction constraints. This study proposed an interface/substrate engineering approach for improving CO 2 -splitting and thermochemical energy conversion through CuFe 2 O 4 and Co 3 O 4 two-layer coating SiC. The newly prepared material reactive surface area available for gas–solid reactions is characterized by micro-pores CuFe 2 O 4 alloy easing inter-layer oxygen micro mass exchanges across a highly stable SiC-Co 3 O 4 layer. Through a thermogravimetry analysis, oxidation of the thermally activated oxygen carriers exhibited remarkably CO 2 -splitting capacities with a total CO yield of 1919.33 µmol/g at 1300 °C. The further analysis of the material CO 2 -splitting performance at the reactor scale resulted in 919.04 mL (788.94 µmol/g) of CO yield with an instantaneous CO production rate of 22.52 mL/min and chemical energy density of 223.37 kJ/kg at 1000 °C isothermal redox cycles. The reaction kinetic behavior indicated activation energy of 30.65 kJ/mol, which suggested faster CO 2 activation and oxidation kinetic on SiC-Co 3 O 4 -CuFe 2 O 4 O-deficit surfaces. The underlying mechanism for the remarkable thermochemical performances was analyzed by combining experiment and density functional theory (DFT) calculations. The significance of exploiting the synergy between CuFe 2 O 4 and Co 3 O 4 layers and stoichiometric reaction characteristics provided fundamental insights useful for the theoretical modeling and practical application of the solar thermochemical process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Doping Mn or In in Ni/CeO 2 significantly effects its CO 2 hydrogenation performance. • NiMn(4)/CeO 2 produces mainly CH 4 , while NiIn(4)/CeO 2 gives dominant CO. • Mn promoter enhances Ni reduction and promotes HCOO* and CH 3 * species formation. • Introduction of In hinders Ni reduction and facilitates formation of COOH* species. Conversion of CO 2 into value-added chemicals is a potential way for achieving carbon neutrality. A challenge is to controllably tune its product distribution. Thus, Ni/CeO 2 catalyst is modified here by doping Mn or In by the sol–gel method. NiMn(4)/CeO 2 shows CO 2 conversion of 35.3% and CH 4 selectivity of 86.6%, whereas NiIn(4)/CeO 2 produces dominant CO with selectivity of 99.1% and CO 2 conversion of 23.9%. Such catalytic results are highly comparable to those of previously reported Ni-based catalysts, but loading smaller amounts of Ni (1.7 wt%). Addition of Mn or In in Ni/CeO 2 significantly promotes formation of surface oxygen vacancies, influences Ni reducibility and enhances catalytic stability. Various characterizations, in situ spectroscopy and DFT calculation results reveal that high CH 4 selectivity of NiMn(4)/CeO 2 is due to formation of more HCOO* intermediates, whereas introduction of In significantly promotes formation of COOH* species, but inhibits generation of HCOO*, and thus resulting in dominant CO product. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bimetallic NiCo catalysts show an anti-synergistic effect for the CO 2 + H 2 reaction. • CH 4 and CO are formed through parallel routes with different RDS. • Strongly and weakly adsorbed CO are involved in the reaction mechanism. • It is proposed a mechanism and L-H model that accurately describe the kinetic data. • It is obtained a lumped parameter, which determines the selectivity at the surface. The mechanistic understanding of the CO 2 hydrogenation reaction is essential for the rational design of active and selective catalysts for this process, nevertheless, there are still important controversies related to the structural requirements, the sequence of elementary steps and the reaction intermediate involved in the formation of CH 4 and CO (g). Hence, a detailed mechanistic study was performed on SiO 2 -supported mono- and bimetallic NiCo catalysts by combining kinetic, spectroscopic and isotopic measurements under methanation conditions, to explain the effect of catalysts composition on the CO 2 hydrogenation rate and selectivity toward CO (g) and CH 4. It was observed an anti-synergistic effect for the CO 2 hydrogenation turnover rate on the NiCo bimetallic catalysts, which is attributed to the inhibition of the CH 4 formation pathway on the bimetallic surfaces; on the other hand, the CO (g) formation turnover rate values resulted close to the weighted average values and increases linearly with the cobalt content in the catalysts. The results suggest that the two reaction products are formed through parallel routes with different rate-determining steps, involving two types of active sites where carbonyl species adsorb differently: strongly adsorbed species (CO*) lead to CH 4 formation via the H-assisted C O bond dissociation while weakly adsorbed (CO⊕) desorbs to produce CO (g). This was consistent with the inverse H/D kinetic isotopic effect (KIE) observed for methane formation and the KIE values close to unity for CO (g) formation over all catalysts. Operando-infrared measurements suggested that weakly and strongly adsorbed carbonyl species are in quasi-equilibrium at the catalyst surface. It was proposed a sequence of elementary steps for CO 2 methanation reaction on Ni, Co and NiCo catalysts, from which a Langmuir-Hinshelwood models for CO (g) and CH 4 formation rates were derived. These models properly represent the kinetic data for products formation rates, and content physiochemically-consistent parameters, which point out that the CH 4 formation from CO 2 hydrogenation can be boosted over a catalytic surface that strongly adsorbs CO, hampers its transformation into CO⊕ and shows a high hydrogenation rate of carbonyl species. [ABSTRACT FROM AUTHOR]

Site-specified RuO 2 nanoparticles on the TiO 2 /palygorskite matrix can be prepared through a simple pH adjustment in aqueous conditions. The product showed very good catalytic CO 2 methanation performance (upto 88% efficiency and ∼100% CH 4 seletivity) and very high stability after 60h tests at 450 °C. [Display omitted] • Site-specified RuO 2 nanoparticles on the TiO 2 /palygorskite matrix was prepared by strong electrostatic absorption route. • Palygorskite with abundant hydroxyl groups significantly disperses the Ru species and yielded very fine nanoparticles. • Excellent catalytic CO 2 methanation performance (up to 88% efficiency and ∼100% CH 4 selectivity) were reached. • The product showed very high stability after 60 h catalytic tests at 450 °C. Here a site-specifically assembled Ru nanoparticles (2–8 nm) on palygorskite (Pal) loaded TiO 2 catalyst (TiO 2 /Pal) is reported to trigger the CO-radical mediated CO 2 methanation reactions. The catalyst was prepared by the strong electrostatic adsorption (SEA) method based on the interactions between the metal source and the TiO 2 support, which have successfully prevented the Ru nanoparticles (NPs) from aggregation. The optimized Ru(4%)-TiO 2 /Pal sample showed fairly good catalytic activities (μ max = 88.7%) to CO 2 and selectivity of CH 4 (C max ∼ 100%). The catalyst also demonstrated excellent stability: no obvious decedent in CO 2 conversion and no carbon deposition were detected after 60 h methanation test. In situ FTIR measurement showed the CO species were an intermediate state, which reacted with the adsorbed hydrogen to produce hydro carbonate, bidentate or monodentate formate species, and finally reached the methane molecular. The SEA method has proven to be an effective way to produce site-specified nano-composites under delicately controlled conditions. Nanofibrous Pal acted as TiO 2 carrier and separator, surface hydroxyls supplier, and origin of repulsive force to the Ru species, which finally resulted in outstanding catalytic performance. [ABSTRACT FROM AUTHOR]

[Display omitted] The incipient wetness impregnation (IWI) method is widely used in the preparation of supported transition metal catalysts for its high throughput and cost-effective synthesis, yet suffers from poor metal-support interaction, restricting its further application at an industrial scale. Herein, a universal strategy of chelation coupled impregnation (CCI) is presented. The as-prepared Ni/CeO 2 (CCI) showed superior catalytic performance for CO 2 conversion (84.3%) and CH 4 selectivity (100%) under the experimental conditions (WGHSV = 24,000 mL g−1 h−1 and H 2 /CO 2 = 4:1) even at low temperatures (T = 275 °C). The surface characterization results confirmed that the agglomeration of metal active sites in Ni/CeO 2 (CCI) was restricted and more surface oxygen vacancies were generated on CeO 2. Further, the in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) analysis suggested that the surface oxygen vacancies that served as active sites could facilitate the direct dissociation of CO 2 more favorably than the associative route, thus significantly promoting CO 2 methanation activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • CO and CO 2 methanation share the same rate-determining step. • Formate species are spectators that hinder the CO 2 hydrogenation on NiCo catalyst. • CO 2 formation involves the CO dissociation and the rejection of O* with CO* • CO is formed through the desorption of carbonyl species from weak sites. Although CO and CO 2 hydrogenation reactions have been extensively studied, there is still significant controversy regarding the mechanism of methane formation and the routes for byproducts, especially when both carbon sources are simultaneously present. This work combines kinetic, operando-spectroscopic, isotopic techniques and DFT calculations to elucidate the relationships between CO and CO 2 hydrogenation over mono Ni, Co and bimetallic NiCo catalysts with similar metal dispersion. The bimetallic catalysts showed a slight synergistic effect for methane formation from CO, while from CO 2 the effect was opposite, showing a negative shift of activity as compared with those observed on the monometallic catalysts. The kinetic analysis shows similar apparent order with respect to H 2 (∼0.5) and an inverse secondary isotope kinetic effect (<1) for both methanation reactions, suggesting that CH 4 formation proceeds via C-O bond breaking in an H*-assisted mechanism, where the rate-determining step was not shown to be sensitive to the carbon source. The anti-synergistic effect observed on the bimetallic catalysts during CO 2 hydrogenation is explained by the formation of unreactive HCOO* species (spectator), which generate a lower density of methane intermediates. On the other hand, the formation of the undesired products, i.e., CO or CO 2 during CO 2 or CO hydrogenation, respectively, shows relevant differences since the CO formation during CO 2 hydrogenation proceeds through the desorption of the carbonyl species adsorbed on weak sites, meanwhile the CO 2 formation from CO hydrogenation is due to a minority route of direct dissociation of CO, allowing the rejection of O* with CO* to produce CO 2. This study contributes to elucidate the routes that determine the selectivity and reactivity for CO and CO 2 hydrogenation and their mechanistic relationship. This information is valuable for the rational design and development of new materials with high performance during hydrogenation processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • A simple and efficient one-pot combustion method was employed to synthesize the 10Ni-0.1Ce/Al catalyst with a unique structure. • Ni nanoparticles are selectively coated by CeO 2 promoter, which promotes the generation of the Ni-O-Ce interface active sites. • The decomposition of b-HCOO- into *CO is the rate-limiting step in the CO 2 methanation. • The activity of b-HCOO- at the Ni-O-Ce interface sites is higher than on the Al 2 O 3 support. The methanation of CO 2 is crucial for resource utilization, however, achieving excellent CO 2 methanation performance with Ni-based catalysts at low temperatures remains highly challenging. In this study, a high-performance 10Ni-0.1Ce/Al catalyst was synthesized using a simple and efficient one-pot combustion method. Unlike other catalysts with the same components, this catalyst exhibits a unique feature where a small amount of the CeO 2 promoter is dispersed on the support, while the majority selectively binds to and coats the Ni nanoparticles. This distinctive structure allows it to achieve approximately 80 % CO 2 conversion and 99.9 % CH 4 selectivity under conditions of 260 °C, 0.1 MPa, and a GHSV of 48,000 mL·g−1·h−1. The high catalytic performance is attributed to the unique structure of Ni nanoparticles and CeO 2 , which promotes the formation of numerous Ni-O-Ce interface active sites. These Ni-O-Ce interfaces enhance the reducibility and increase the content of weak basic sites in the catalyst. The combination of in-situ DRIFTS and TPSR reveals that the decomposition of bridged HCOO– to *CO is the rate-determining step. The presence of Ni-O-Ce interface active sites in the 10Ni-0.1Ce/Al catalyst facilitates the generation of abundant bridged HCOO– intermediates with higher activity than the 10Ni/Al catalyst, leading to a substantial enhancement in catalytic performance. [ABSTRACT FROM AUTHOR]

The hydrogenation of CO 2 to CH 4 has gained considerable interest in terms of sustainable energy and environmental mitigation. In this regard, the present work aims to investigate the adsorptive concentration and CO 2 methanation performance over CoFe and NiFe bimetallic catalysts supported on fumed alumina-silica SA96 support at 170–450 °C and under atmospheric pressure. The catalysts were prepared by wet impregnation method, subjected to calcination and further reduced with hydrogen, and their performance in CO 2 methanation was investigated in a hydrogen-rich 2%CO 2 –55%H 2 –43%He gas mixture. In this study, we describe the crystal and mesoporous structures of the prepared catalysts by in-situ XRD and ex-situ nitrogen adsorption, evaluate the NiFe and CoFe metal surface states before and after catalysis by XPS, visualize the surface morphology by SEM, estimate the catalytic activity by gas chromatography, and investigate the adsorbed surface species, showing the presence of *HCOO/*HCO and *CO intermediates, determine two possible pathways of CH 4 formation on the studied catalysts by temperature-programmed desorption mass spectrometry, and correlate the structural and surface properties with high CO 2 conversions up to 100% and methanation selectivities up to 72%. The latter is related to changes in the elemental chemical states and surface composition of CoFe and NiFe nanocatalysts induced by treatment under reaction conditions, and the surface reconstruction during catalysis transfers the part of active 3d transition metals into the pores of the SA96 support. Our thorough characterization study with complementary techniques allowed us to conclude that this high activity is related to the formation of catalytically active Ni/Ni 3 Fe and Co/CoFeO x nanoscale crystallites under H 2 reduction and their maintenance under CO 2 methanation conditions. The successfully applied combination of CO 2 chemisorption and thermodesorption techniques demonstrates the ability to adsorb the CO 2 molecules by supported NiFe and CoFe nanocatalysts and the pure alumina-silica SA96 support. • Efficient NiFe and CoFe nanocatalysts are supported on a fumed alumina-silica, SA96. • CO 2 methanation over NiFe/SA96 and CoFe/SA96 catalysts at 375–450 °C and 1 atm. • Ni/Ni 3 Fe and Co/CoFeO x nanocrystals are formed on the surface of alumina-silica. • *HCOO/*HCO and *CO indicate the concurrent pathways of CH 4 formation. • CO 2 methanation reorganizes the surface layer of NiFe/SA96 and CoFe/SA96 catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • ITQ-6-based catalysts showed smaller Ni NP's and H 2 uptake than the FER-based ones. • Al-containing catalysts exhibited higher Ni dispersion and OH group concentration. • ITQ-6-based catalysts showed higher CO 2 conversion and CH 4 selectivity (>90 %). • E a calculations indicated that the associative mechanism is favored in ITQ-6 catalysts. • 15Ni/ITQ-6 (Si/Al = 30) exhibited high CO 2 conversion and CH 4 selectivity (79 % and 98 %, respectively, at 400 °C). Ni-based catalysts supported on delaminated ITQ-6 zeolite with different Si/Al ratios, 30 and ∞, were tested in the methanation of CO 2 and CO. ITQ-6 supports exhibited high surface areas (> 590 m2/g), and the catalysts based on them presented elevated CO 2 and CO conversion values, turnover frequencies (TOF), and CH 4 selectivity (> 90 %). Comparing the ITQ-6 catalyst and its precursor ferrierite (FER)-based catalyst, H 2 -chemisorption results confirmed higher metallic dispersion for the former, which resulted in improved H 2 uptake and efficient interaction of reaction intermediates via the associative pathway. Combined kinetic studies indicated that their higher available metallic surface contributed to lower apparent activation energies towards CH 4 formation, accounting for the higher selectivity values. A 15 wt% Ni-based catalyst supported on ITQ-6 zeolite (Si/Al = 30) exhibited catalytic results (X CO2 = 79 % y S CH4 = 98 %) comparable or even superior to some of the best zeolite-based catalysts reported so far. [ABSTRACT FROM AUTHOR]

[Display omitted] • Inverse MO x /Ni catalysts with abundant interfaces are successfully constructed. • MO x /Ni interface is proved as the active sites of CO 2 methanation. • Electronegativity of M atoms in MO x /Ni interface is CH 4 selective descriptor. • Electronegativity modulates selectivity by regulating CO adsorption capacity. Identifying the parameters influencing the selectivity of products is prominently significant for fabricating efficient catalysts. However, little progress has been made in describing the regulation rule of CH 4 selectivity toward the CO 2 methanation reaction, which is considered a vital process for CO 2 emission and conversion. Herein, we disclosed the integral role of the electronegativity of M atoms in Ni-MO x supported catalysts to producing CH 4 molecules, which the satisfactory catalytic performance stemmed from the regulated ability to capture CO 2 molecules and CO intermediates. More importantly, alongside the extensively studied descriptor of particle size, we uncovered a strong correlation between the electronegativity of M atom and CH 4 selectivity, in which the CO/CO 2 adsorption capacity upon the Ni/NiO x /MO x interfaces exhibited a volcanic trend based on the electronegativity of M atoms in MO x supports. The screened Ni-Y 2 O 3 composite catalysts demonstrated excellent CO 2 methanation performance, suggesting the powerful practicability of the electronegativity of M atoms in MO x supports as a descriptor. These findings not only shed fundamental insight into the reaction pathway but also paved the way for the rational design of Ni-based catalysts based on the simple descriptor of electronegativity. [ABSTRACT FROM AUTHOR]

[Display omitted] • HNO 3 gas-phase treatment introduced oxygen groups into Ru/C catalyst. • The presence of oxygen groups facilitates H 2 desorption. • Oxygen groups alleviate the ill effects of carbon methanation and hydrogen poisoning. • Ru/C catalyst with oxygen groups shows superior ammonia synthesis activity. Carbon-supported ruthenium catalysts are very promising application in ammonia synthesis. Here we show that the oxygen functional groups can be introduced into carbon preloaded with Ru species by HNO 3 gas-phase oxidation treatment. The results reveal that the presence of oxygen functional groups facilitates the desorption of hydrogen species. Moreover, the decomposition of barium nitrate is accelerated, and the ill effects of carbon methanation and hydrogen poisoning are effectively alleviated. The combination of the change in the existing form of Ba promoter, the acceleration in the desorption and exchange of hydrogen species accounts for the superior ammonia synthesis activity of Ru catalyst with HNO 3 gas-phase treatment. Understanding the role of oxygen functional groups provides design rules for the rational design of carbon-supported Ru catalyst with highly activity and stability for ammonia synthesis or other hydrogen-involved reactions. [ABSTRACT FROM AUTHOR]

[Display omitted] Herein, a novel Ru-doped bimetal phosphide (Ru-NiCoP) heterostructure electrocatalyst on Ni foam is successfully synthesized through a multi-step hydrothermal reaction, ion exchange, and phosphorization method for efficient overall water splitting in alkaline media. The doping of Ru and P can effectively optimize the electronic structure and expose more active sites. The unique 3D interconnected nanowires not only ensures the uniform distribution of Ru coupled with NiCoP, but also endows the Ru-NiCoP/NF with the large ECSA, the fast electron transport and the favorable reaction kinetics attributes. Benefiting from the compositional and structural advantages, Ru-NiCoP/NF catalyst exhibits significantly enhanced catalytic activities along with excellent stability, only needing 32.3 mV at 10 mA cm−2 for HER and 233.8 mV at 50 mA cm−2 for OER. In particular, when Ru-NiCoP/NF is employed as both cathode and anode electrodes, a small voltage of 1.50 V is required to reach 30 mA cm−2 for overall water splitting with an impressive stability. This study provides an alternative strategy on the design and development of high performance catalysts for overall water splitting and other energy conversion fields. [ABSTRACT FROM AUTHOR]

[Display omitted] • Versatile synthesis of bimetallic M x Ru 100−x @SILP (M = Fe, Co) catalysts. • Systematic comparison of catalytic performances in hydrogenation. • Activity and selectivity depend on the M:Ru ratios, with clear synergistic effects. • For a given selectivity, Co x Ru 100−x more active than Fe x Ru 100-x while requiring less Ru. • Crucial influence of the nature of the "diluting" 3d metal. Bimetallic iron-ruthenium and cobalt-ruthenium nanoparticles with systematic variations in the Fe:Ru and Co:Ru ratios are prepared following an organometallic approach and immobilized on an imidazolium-based supported ionic liquid phase (SILP). Resulting M x Ru 100-x @SILP materials are characterized by electron microscopy, X-ray diffraction and X-ray absorption spectroscopy, confirming the formation of small, well-dispersed and alloyed zero-valent bimetallic nanoparticles. A systematic comparison of the performances of Fe x Ru 100−x @SILP and Co x Ru 100−x @SILP catalysts is made using the hydrogenation of benzilideneacetone as model reaction. The M:Ru ratio is found to have a critical influence on activity and selectivity, with clear synergistic effects arising from the combination of the noble and 3d metals. Co x Ru 100−x @SILP catalysts are significantly more reactive to reach a given selectivity at a systematically higher content of the 3d metal as compared to the Fe x Ru 100−x @SILP catalysts, evidencing a remarkable influence of the nature of the "diluting" 3d metal on the overall performance of the M x Ru 100−x @SILP catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effects of feed impurities on CO 2 methanation over Ni/ZrO 2 were investigated. • Trace amounts of O 2 facilitate the conversion of intermediates during methanation. • More *OH groups can be generated on the catalyst surface after addition of trace O 2. • The generated *OH groups promoted CO 2 methanation. Feed composition is crucial for gas-phase catalytic reactions but has rarely been studied in CO 2 methanation. In this work, we studied the effect of impurities (i.e., N 2 , steam, and O 2) on the activity of Ni/ZrO 2 in CO 2 methanation. The reducible ZrO 2 favored the formation of oxygen vacancies, which enhanced CO 2 adsorption and subsequent hydrogenation into methane. Interestingly, trace O 2 enhanced CO 2 methanation over Ni/ZrO 2 due to the generation of more *OH groups facilitating the conversion of intermediates to methane. [ABSTRACT FROM AUTHOR]

[Display omitted] • Doped/co-doped iron ferrites were tested for HT-WGS at high pressure conditions. • Incorporated Cr or Co decreased the sintering and coke formation during WGS. • Cr or Co ion were entered into the octahedral sites of spinel framework. • Cr- or Co-codoping resulted in the reduced surface Fe3+/Fe2+ ratio of the ferries. • No obvious surface structural changes occurred for the ternary ferrites after WGS. In this work, Ce and Cr/Co co-doped iron oxide (FeCeMO x , where M = Cr or Co) ferrites were investigated for high-temperature water-gas shift (HT-WGS) under industrially relevant pressures (20 bars). The Ce and Cr/Co bi-doping has greatly promoted the catalytic performance in comparison to the single Ce-doping. Especially, the FeCeCoO x ferrite demonstrated the best HT-WGS activity without any deactivation at a steam to CO ratio of 3.5. The ternary FeCeCrO x and FeCeCoO x catalysts also exhibited reasonably stable performance with a slight methanation activity (<2.5%) even under low steam to CO ratio of 1.5. The hematite phase (Fe 2-x Ce x/2 M x/2 O 3 , where M = Cr or Co and × = 0.33) of the fresh (calcined) catalysts became [A (1-δ) B δ ]T[A δ B (2-δ) ]OO 4 type magnetite spinel structure (Fe 3-x Ce x/2 M x/2 O 4 , where M = Cr or Co and × = 0.5) during the activation process, which is regarded as the active phase for the WGS reaction. The co-doping of Cr or Co increased the stability of the active magnetite phase against sintering and suppressed the coke formation during the WGS reaction, which should be responsible for the stable activity. The addition of Cr or Co to iron oxide also delays the formation and over-reduction of active magnetite phase. Mössbauer spectra confirmed that the Cr or Co ions were incorporated into the octahedral sites of [A (1-δ) B δ ]T[A δ B (2-δ) ]OO 4 spinel framework during the activation and modifies the local structure. The superparamagnetic behavior of the spinel ferrites has significantly enhanced upon the co-doping of Ce and Cr/Co into the iron oxide lattice, indicating a high fraction of nanoparticles in the ternary spinel ferrites. The Cr or Co addition resulted in the decreased surface Fe3+/Fe2+ ratio which could be due to the replacement of Fe3+ ions by Cr or Co ions. Most importantly, no evident change was observed in the surface structure of ternary spinel ferrites even after the reaction, which could be responsible the stable performance of the catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • MoS 2 with a stable single-layered structure was prepared. • Single-layered MoS 2 exhibits high catalytic activity in the methanation of syngas. • The structural effect of MoS 2 on the catalytic activity is revealed. • Activity for different sites is attributed to the ability of CO/H 2 adsorption. MoS 2 is an attractive sulfur-resistant catalyst for directly converting sulfur-containing syngas to high value-added chemicals. However, the effect of the layered structure on the catalytic activity for CO hydrogenation reactions is far from clear. Herein, MoS 2 /carbon composite catalysts with 1–8 stacking layers in MoS 2 crystallites are synthesized, and the impact of the layer numbers on the catalytic performance is probed for the low-temperature methanation of sulfur-containing syngas. The results indicate that the turnover frequency of CO methanation increases from 2.4 × 10-3 to 3.7 × 10-3 s−1 with decreasing layer numbers of MoS 2 crystallites from 8.3 to 1.1. This result is thoroughly explained by the fact that the higher ratio of rim sites in MoS 2 crystallites with fewer layer numbers enhances the catalytic activity, which originates from the facilitated activation of CO and H 2. These understandings are important for the rational design and development of more efficient MoS 2 -based catalysts for CO hydrogenation. [ABSTRACT FROM AUTHOR]

[Display omitted] • TiO 2 particle size can control selectivity of Ru/TiO 2 catalysts in CO 2 reduction. • Larger TiO 2 particle favor CO 2 methanation vs. CO formation after HT treatment. • O-vacancy formation upon high-temperature (HT) treatment. • O-vacancy formation is preferred on catalysts with smaller TiO 2 particles. • Formation of charged Ru sites due to electronic metal–support interactions (EMSIs). Aiming at a better understanding of the functioning of oxide-supported Ru catalysts in the reduction of CO 2 , a highly attractive reaction from ecologic reasons, we systematically investigated the influence of the support particle size on the performance of highly active Ru/TiO 2 catalysts. Employing mixed rutile-anatase supported catalysts with different TiO 2 particle size, but similar Ru particle size and loading, we found that after a reductive high-temperature (HT) treatment their selectivity can be controlled by the TiO 2 particle size, from 100% methanation to 100% CO formation. Comprehensive characterization of the catalysts shows that the changes in reaction behavior are paralleled by significant modifications of their structural, chemical and electronic properties. We propose that the change in reaction characteristics is due to a HT-induced increase in O-vacancies and charge transfer to Ru interface atoms, which is more pronounced for high-surface-area catalysts. We see this approach as interesting strategy for tailoring catalyst properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electronic metal-support interactions (EMSIs) promote CO 2 methanation on Ru/ZrO 2. • Structural effects (SMSI) can be excluded. • EMSIs result from O-vacancy formation at ZrO 2 surface and charge transfer to Ru. • Charge transferred to Ru nanoparticles is localized at adjacent interface Ru atoms. • Negatively charged Ru sites stabilize CO adsorption, promoting CO methanation. Discrimination between electronic and structural effects in metal-support interactions (MSIs) is often hampered by contributions from either one. We report results of a combined experimental/theoretical study that directly demonstrate the action of electronic MSIs (EMSIs), while structural modifications like a partial overgrowth of metal nanoparticles by a partly reduced oxide due to SMSI, can be excluded. This is demonstrated for CO 2 methanation on Ru/ZrO 2 with small Ru NPs (~2nm), where a high-temperature reductive treatment results in a significantly increased methanation rate. Based on operando / in situ spectroscopies and other characterizations, SMSI induced structural modifications can be excluded; the enhanced activity results from charge transfer from O-vacancies in the ZrO x surface region to adjacent Ru nanoparticles. DFT calculations reveal that the transferred charge is localized at the interface, leading to stronger Ru-CO bonding and enhanced CO ad methanation. We believe that these trends are generally relevant for reactions in a reductive atmosphere. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ni n CeOx (n = 1–3) and Ni 2.5 Pd 0.1 CeO x nanofibers by electrospinning was reported. • For Ni 2.5 Pd 0.1 CeOx, CO 2 conv. = 90.4 % and CH 4 selec. = 99.6 % at 230 °C. • EPR, Raman, and O 1s XPS confirmed Pd2+ doping increased oxygen vacancies. • In-situ infrared indicated Ni 2.5 Pd 0.1 CeO x followed formate pathways. • DFT calculations suggested Pd2+ doping increased CO 2 adsorption energy. CO 2 methanation at low temperatures is still a challenge. Herein, Ni n CeO x (n = 1–3) and Ni 2.5 Pd 0.1 CeO x nanofibers by electrospinning is reported. The main advantage of this method is to obtain the highly dispersed precursor of palladium, nickel, and cerium, overcoming the difficulty of uniform mixing in conventional preparation methods. The Ni 2.5 Pd 0.1 CeO x nanofiber catalyst exhibited outstanding catalytic performance at low temperatures (CO 2 conversion rate = 90.4 %, CH 4 selectivity = 99.6 % at 230 °C) along with exceptional stability over 300 h. EPR, Raman, and O 1s XPS confirmed that Pd2+ doping increased oxygen vacancy concentration. In-situ infrared spectroscopy indicated that CO 2 methanation on Ni 2.5 CeO x and Ni 2.5 Pd 0.1 CeO x catalysts followed the formate pathways. Pd2+ doping increased the number of surface oxygen vacancies and hydroxyl groups, thus increasing the amount of bicarbonates and formates. DFT calculations suggested that Pd2+ doping increased CO 2 adsorption energy, and confirmed surface hydroxyl groups and bicarbonate being beneficial for CO 2 methanation, consequently enhancing the activity of Ni 2.5 Pd 0.1 CeO x catalyst especially at low temperatures. [ABSTRACT FROM AUTHOR]

[Display omitted] The conversion of CO 2 driven by solar energy into carbon-containing fuel has huge potential applications. However, most photocatalysts can only promote the two-electron reduction process to generate CO, and it is difficult to produce eight-electron CH 4 , which is more valuable and can store more solar energy. Herein, we prepared porous silver cyanamide nanocrystals with tunable morphologies via a facile synthesis strategy. Compared with ball/rectangular plate (RAP) and ball/leaf-like plate (SAP), the ball/porous leaf-like plate (LAP) can provide more internal reaction microenvironment, which is not only conducive to the transport of photoinduced charge carriers, but also can expand the active sites for photocatalytic CO 2 reduction. Moreover, the suitable band gap of LAP sample can capture more visible light to provide more photoinduced electron-hole pairs to participate in the reduction reaction. Consequently, the LAP sample can convert CO 2 to CH 4 with remarkable activity and high selectivity (nearly 100%) without cocatalyst and photosensitizer under visible light irradiation. This work provides a promising way to design new photocatalysts for various applications in solar energy conversion. [ABSTRACT FROM AUTHOR]

[Display omitted] • The catalytic activity of Ni/TiO 2 depends on the TiO 2 crystalline phases: Ni/TiO 2 -rutile ≫ Ni/TiO 2 -anatase. • A synergy occurs between Ni/TiO 2 -rutile and Ni/TiO 2 -anatase. • The synergy occurs even if the two catalysts are not in physical contact. • Hydrogen spillover is at the origin of the synergy observed for the Sabatier reaction. • TOF of 19.7 10-3 s−1 was measured, which is very high for Ni-catalyzed CO 2 methanation. The catalytic performances of TiO 2 -supported Ni catalysts for the methanation of CO 2 have been investigated using different crystalline phases of TiO 2 (rutile and anatase). The catalytic activity of Ni depends appreciably on the nature of the support. The rate for CO 2 hydrogenation decreases in the order of 10Ni/TiO 2 -rutile ≫ 10Ni/TiO 2 -anatase. The use of a mixture of catalysts containing 70% 10Ni/TiO 2 -anatase + 30% 10Ni/TiO 2 -rutile allows for a significant increase of the reaction rate related to 100% 10Ni/TiO 2 -rutile. Importantly, it has been demonstrated that the two catalysts do not need to be in direct contact for the synergetic effect to occur. DRIFTS operando analysis during the methanation reaction shows that adsorbed CO accumulates on Ni/TiO 2 -anatase and not on Ni/TiO 2-rutile , and that the role of the Ni/TiO 2-rutile is to assist the hydrogenation of this adsorbed CO on the Ni/TiO 2 -anatase. Increased CO 2 methanation is also observed by adding Ni-free TiO 2 -anatase to 10Ni/TiO 2 -rutile , indicating that CO x hydrogenation can also occur on bare TiO 2 -anatase if activated hydrogen can be supplied by another source. H 2 -TPD analyses and catalytic tests performed after dilution of the catalysts have shown that hydrogen spillover (mediated by surface or gas-phase species) is at the origin of the synergy observed between the two catalysts for the Sabatier reaction. [ABSTRACT FROM AUTHOR]

• A step-by-step synergistic stripping strategy was developed to prepare ultra-thin porous g-C 3 N 4 (THCN) with high conduction band position. • The THCN exhibits the best excellent separation and utilization efficiency of photo-generated carriers, supporting excellent conversion efficiency from CO 2 to CH 4 and CO fuels. • Our work provides a reference for preparation of other two-dimensional ultra-thin materials. The pristine g-C 3 N 4 (BCN) with a low conversion efficiency of CO 2 exits with small specific surface area, weak CO 2 adsorption and severe recombination of photo-generated charges. The stripping of few-layer g-C 3 N 4 represents excellent photocatalytic performance, which attracts extensive attention in photocatalytic CO 2 reduction. In the present study, the ultra-thin porous g-C 3 N 4 (THCN) with high specific surface area and high position of conduction band was prepared using step-by-step synergistic exfoliation. Further, we treated it with HCl-assisted hydrothermal stripping and successive thermal stripping/etching in air. Our results showed that the THCN exhibited the best CO 2 conversion efficiency from CO 2 to CH 4 and CO fuels, compared with g-C 3 N 4 (HCN) prepared by HCl-assisted hydrothermal stripping and g-C 3 N 4 (TCN) prepared by thermal stripping/etching in air. Further, the excellent photocatalytic performance for CO 2 reduction was mainly attributed to its high specific surface area and rich pores, excellent separation and utilization efficiency of photo-generated carriers, and upper position of conduction band. Due to its wide band gap and high specific surface area, the THCN also showed significantly better degradation for Rhodamine B than BCN, HCN and TCN. Nonetheless, using a simple two-step stripping strategy, we prepared and obtained an ultra-thin porous g-C 3 N 4 nanosheets with a high specific surface area for CO 2 conversion to CH 4 and CO fuels. This ultimately provided a reference for preparation of other two-dimensional ultra-thin materials for CO 2 reduction. [ABSTRACT FROM AUTHOR]

• Ni/SiO 2 catalyst is partially covered with Na 2 O species. • The Na 2 O covering the Ni surface can increase the positive charge on Ni. • Na 2 O additives on Ni/SiO 2 catalyst can influence the selectivity toward CO formation. • The formic acid is the major intermediate on the Ni/SiO 2 catalyst. • The hydrogen carbonate is the key intermediate on the NiNa x /SiO 2 catalysts. CO 2 hydrogenation over Ni/SiO 2 catalysts with and without Na additives was investigated in terms of the catalytic activity, selectivity of CO 2 methanation and reaction mechanism. Na additives could cause the formation of Na 2 O species that might deposit on the Ni surface of Ni/SiO 2 (NiNa x /SiO 2). When the Ni metal is partially covered with Na 2 O species, a highly positive charge on the Ni metal could occur compared to the original Ni/SiO 2 catalyst. The addition of Na to the Ni/SiO 2 catalyst could influence selectivity toward CO formation. The adsorbed formic acid is the major intermediate on the Ni/SiO 2 catalyst during CO 2 hydrogenation. The formic acid species might decompose into adsorbed CO complexes in the forms of linear CO, bridged CO and multibonded CO. CH 4 formation should be ascribed to the hydrogenation of these adsorbed CO complexes. The Ni/SiO 2 catalyst with the Na additive might have very weak ability for H 2 and CO adsorption, thus making it difficult for CO methanation to occur. The hydrogen carbonate species adsorbed on the NiNa x /SiO 2 catalysts were proposed to be the key intermediate, and they might decompose to CO or be hydrogenated to form CH 4. [ABSTRACT FROM AUTHOR]

[Display omitted] • 'Pt in CeO 2 ' was prepared from 'Pt on CeO 2 ' by the controlled reductive treatment. • 'Pt in CeO 2 ' displayed the high activity in the water-gas shift reaction. • The CH 4 formation was promoted on 'Pt on CeO 2 ' during the water-gas shift reaction. • 'Pt in CeO 2 ' was non-selective to CH 4 during the water-gas shift reaction. • Thin CeO 2 over-layers of 'Pt in CeO 2 ' catalyzed the water-gas shift reaction. Pt supported on CeO 2 (Pt/CeO 2) is known to be a good catalyst for the water-gas shift (WGS) reaction. However, Pt catalyzes the methanation reaction as a side reaction, which limits the usefulness of Pt/CeO 2 as a catalyst in the high-temperature (HT) WGS reaction. In this study, Pt nanoparticles (Pt NPs) were encapsulated in CeO 2 over-layers ('Pt in CeO 2 ') by using controlled reductive treatments to suppress the methanation reaction on Pt NPs. 'Pt in CeO 2 ' catalyst demonstrated the much lower CH 4 selectivity while showing the same high activity in the HT-WGS reaction compared to the conventional 'Pt on CeO 2 ' catalyst. Detailed characterizations revealed that the underlying Pt NPs promoted the WGS reaction on thin (<1 nm) CeO 2 over-layers by facilitating the formation of active oxygen vacancies. The present contribution to catalyst modification via simple thermal treatments will provide additional way to control metal-support interactions to improve catalytic performance. [ABSTRACT FROM AUTHOR]

• Mechanochemical ball milling incorporate Ni to MgO forming a "Mg-Ni-O" structure. • Ni incorporation on MgO promotes adsorption and activation of H 2 and CO 2 molecules. • Ni-incorporated MgO surface offers electropositive H+ (1 s 0) for CO 2 to CO* species. • Electronegative H− (1 s 2) benefits C-terminal hydrogenation of CO* species to CH 4. • Selective hydrogenation via specific hydrogen species improves CO 2 methanation. The conversion of CO 2 to CH 4 has great significance to energy supply and environment protection. For the first time, we report a Ni-incorporated MgO/MgH 2 material synthesized via a facile mechanochemical ball-milling method for thermo-catalytic CO 2 methanation. The Ni-incorporated MgO/MgH 2 material achieves the hydrogenation of CO 2 to CH 4 with a space–time yield (STY) of 944.6 g kg−1 h−1 and a selectively of 99.5% at 300 °C under 1.0 MPa H 2 /CO 2 /N 2 , which are comparable to traditional catalysts and much better than Ni/MgO or Ni/MgH 2 mixtures. This facile mechanochemical ball milling can in-situ incorporate Ni to MgO surface generating a stable "Mg-Ni-O" structure, which can promote the activation of H 2 and CO 2 molecules. DFT calculations suggest that Ni-incorporated MgO(1 1 0) can offer electropositive H+ (1 s 0) for the O-terminal hydrogenation of CO 2 to CO* species, while the following C-terminal hydrogenation to CH 4 is performed on MgH 2 (0 0 1) with electronegative H− (1 s 2) as hydrogen source. This selective hydrogenation via specific hydrogen species on Ni-incorporated MgO/MgH 2 can inspire catalysts design for the conversion of CO 2 to value-added chemicals. [ABSTRACT FROM AUTHOR]

• Enhanced CO 2 conversion by NiFe alloy catalysts at suitable Fe content. • NiFe alloy accelerated CO 2 activation and conversion via HCOO formation. • Proposed reaction mechanism of CO 2 methanation via formate pathway. Bimetallic NiFe catalysts have emerged as a promising alternative to the traditional Ni catalysts for CO 2 methanation. However, the promoting effect of Fe on the bimetallic catalysts remains ambiguous. In this study, a series of NiFe catalysts derived from hydrotalcite precursors were investigated. In situ x-ray diffraction (XRD) analysis revealed that small NiFe alloy particles were formed and remained stable during reaction. When Fe/Ni = 0.25, the alloy catalysts exhibited the highest CO 2 conversion, CH 4 selectivity and stability in CO 2 methanation at low temperature of 250–350 °C. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) study indicated that the formate pathway was the most plausible reaction scheme on both Ni and NiFe alloy catalysts, while a moderate addition of Fe facilitated the activation of CO 2 via hydrogenation to *HCOO. Density functional theory (DFT) calculations further demonstrated that the overall energy barrier for CH 4 formation was lower on the alloy surface. [ABSTRACT FROM AUTHOR]

• TOF CH4 (s−1) is independent of d Co (10–20 nm) but largely decreases with TOS. • θ CO and θ CHx increase but θ CxHy (inactive) remains the same with increasing d Co. • θ CHx decreases and θ CO remains constant but θ CxHy (inactive) increases with TOS. • An inverse D-KIE was estimate using a novel 13CO/D 2 -SSITKA experiment. • Deactivation is due to accumulation of -C x H y that largely reduces θ CHx and k CHx. SSITKA coupled with transient isothermal (TIH) and temperature-programmed hydrogenation (TPH) were used to investigate the influence of Co particle size (d Co = 11–21 nm) and time-on-stream, TOS (up to 25 h) on important kinetic parameters of CO methanation at 230 °C on Co/γ-Al 2 O 3. TOF CO and TOF CH4 were independent of d Co and decreased with TOS. The θ CO and θ CHx (active CO-s and CH x -s) slightly increased with d Co as opposed to θ CxHy (inactive species), which remained practically constant. On the contrary, θ CHx and θ CxHy largely decreased and increased, respectively, while θ CO stayed practically constant with TOS. An inverse D-KIE independent of d Co was estimated by a novel 13CO/D 2 -SSITKA experiment, reported for the first time to the best of our knowledge. The reason of catalyst deactivation was the decrease of k CHx (hydrogenation of -CH x) likely because of the influence of -C x H y on the bonding of active species and on θ H (a decrease was determined). [ABSTRACT FROM AUTHOR]

• Mn modification increases reducibility of Co-aluminates. • Mn modified catalysts allow hydrogen spillover and leads to mechanism shift. • Strongly improved CO 2 methanation activity due to increased catalytic active surface area. Mixed metal oxides as solid solutions are promising catalyst precursor species, due to their atomic dispersion of metals within an oxide matrix. Upon activation by pre-reduction highly dispersed metal nanoparticles grow on the surface of a functional mixed metal support. Herein, the impact of different amounts of structure distorting manganese that is integrated in CoMn x Al 2-x O 4 spinel phase on the reducibility as a measure for the ability for pre-activation was investigated. The reducibility of the spinel increases with increasing Mn content. By using the Sabatier reaction (CO 2 methanation) as model reaction it was shown that the activity depends on the low temperature reducibility of the spinel. The highest catalytic productivity of 0.65 mol/(mol·min) at 400 °C was obtained with CoMn 0.5 Al 1.5 O 4 as a precursor in line with a highly improved selectivity (S(CH 4) = 97%) towards methane as compared to manganese free CoAl 2 O 4. In addition, the activation energy drops from 107 kJ/mol to 69 kJ/mol upon Mn incorporation. Intense surface analysis via CO & H 2 pulsed titration, BET, CO 2 -TPD, CO 2 DRIFTS, as well as operando DRIFTS analysis revealed, that the integration of Mn into the spinel support decreases the overall surface basicity and enables, potentially due to its Mn3+/Mn2+ redox pairs, spillover of hydrogen from the metallic sites towards the surface of the support. This leads to an altered reaction mechanism via formate species without production of CO as reaction intermediates. This in combination with the ability to transfer the CO 2 conversion from the metal sites only towards the surface of the support due to hydrogen spillover leads to the observed increase in catalytic performance. This work demonstrates the high potential of specific modification of typically highly stable mixed metal oxides as valuable catalyst precursor species. [ABSTRACT FROM AUTHOR]

• Mn-promoted Ni catalysts on silica-modified alumina (SA) prepared. • Increasing Mn/Ni ratio yields more active and stable methanation catalysts. • Ni/SA methanation performance promoted by MnO at 1 bar and 20 bar. • Mn addition improves Ni reducibility and dispersion, CO 2 adsorption and activation. • Mn present as MnO clusters on Ni active phase in reduced catalysts. The viability of the Power-to-Gas (PtG) concept is strongly dependent on the development of highly active and stable methanation catalysts obtained from cheap and abundant elements. In this paper, the promotional effect of MnO on Ni catalysts supported on silica-modified γ-Al 2 O 3 (SA) was investigated in CO 2 and CO methanation on catalysts with Mn/Ni atomic ratios between 0 and 0.25. Significantly higher methanation rates and CH 4 selectivities were obtained for Mn-promoted compositions compared to Ni-only catalysts. The optimal NiMn/SA (Mn/Ni = 0.25) catalyst exhibited improved stability compared with unpromoted Ni/SA at 20 bar. The nature of the catalyst precursor and active catalyst was studied with STEM-EDX, XPS, and X-ray absorption spectroscopy (XAS). Evidence of a mixed Ni-Mn oxide in the catalyst precursor was obtained by EXAFS. EXAFS measurements revealed that the reduced catalyst consisted of metallic Ni particles and small oxidic Mn2+ species. Moreover, Mn addition improved the Ni dispersion and enhanced the Ni2+ reducibility by weakening the interaction between the Ni-oxide precursor and the support. A mechanistic study involving IR spectroscopy and steady-state isotopic (13CO 2) transient kinetic analysis (SSITKA) showed that the presence of Mn enhanced CO 2 adsorption and activation. [ABSTRACT FROM AUTHOR]

A direct spectroscopic observation of CO 2 methanation over the Re cluster edge sites, where CO 2 was reduced to CO via redox pathway followed by hydrogenation to methane. [Display omitted] • A direct spectroscopic observation of CO 2 methanation over the Re cluster edge sites, where CO 2 reduce to CO via redox pathway followed by hydrogenation to methane. • Identified and explain the size dependent activity of CO 2 methanation. • The rate-determining step in CO 2 methanation relates to the reactivity and stability of intermediate CO, rather than the activation of CO 2 or H 2. CO 2 methanation on heterogeneous catalysts holds great significance in achieving the net-zero emission target. However, understanding the atomic-scale relationship between reactivity and active site has been a subject of debate. The study investigated CO 2 methanation reaction catalyzed by Re/TiO 2 catalysts and identified the active site distribution and its relationship with reactivity. The low-coordinated edge sites of Re nanoparticle were found to be the active sites where CO 2 dissociated into CO via a carbide pathway and subsequently hydrogenated to form methane. Furthermore, the study revealed that the size of Re nanoparticle influenced the distribution of active edge sites and affected the reactivity and stability of the CO intermediate, which was the rate-determining step in CO 2 methanation reaction. Controlling the size and structure of Re nanoparticle can, therefore, enhanced the activity and efficiency of CO 2 methanation reaction. The identification of these active sites and the insights gained from this study have significant implications for the mechanistic understanding and optimization of CO 2 methanation over Re/TiO 2 catalysts. It provides a basis for designing more effective catalysts to facilitate the conversion of CO 2 to methane, thereby contributing to the goal of achieving net-zero emissions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mesopores in BEA catalysts facilitate small Ni particle formation. • Small Ni species boost the conversion of CO 2 to CO. • Larger Ni species promote the conversion of CO 2 to methane. • Ni-5A and Ni-13X, with larger Ni particles externally, demonstrate heightened CO 2 methanation activity. • TOF- CO2 and TOF- CH4 show a correlation with Ni particle size up to 8.8 nm. Ni catalysts supported on 4A, 5A, 13X, ZSM-5, and BEA zeolites were prepared using the vacuum-heating method for CO 2 methanation. These support materials play a pivotal role in shaping the catalysts' properties and their catalytic performance. High-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectroscopy (EDS) mappings suggest a significant concentration of Ni nanoparticles situated on the external surfaces of catalysts with low Si/Al ratios zeolites (Ni-4A, Ni-5A, and Ni-13X). These Ni nanoparticles exhibit characteristics of weaker metal-support interaction, lower metal reduction temperatures, and moderate H 2 adsorption activity. Moreover, these low Si/Al ratio zeolites demonstrate robust CO 2 adsorption activity. These properties endow Ni-5A and Ni-13X catalysts with heightened CO 2 conversion (70.4–70.9%) and methane selectivity (92.4–96.4%). In contrast, high Si/Al ratio zeolite-based catalysts (Ni-ZSM-5 and Ni-BEA) exhibit smaller Ni particles, strong metal-support interaction and weaker CO 2 adsorption activity, resulting in reduced CO 2 methanation activity and decreased methane selectivity (71.2–73.4%). The normalized CO 2 conversion rate presents a correlation with the average Ni particle size. [ABSTRACT FROM AUTHOR]

[Display omitted] • Propane oxidation to propene oxide and propene on V-silicas with intrinsic microporosity. • High and stable activity ruled by facilitated diffusion over 3D V/MCF. • Oligomeric V-species located in micropores responsible for propene formation as evidenced by o perando UV–vis. • A crucial role of N 2 O oxidant in the epoxidation reaction. • The reaction pathways of coproduction of propene and propene oxide with N 2 O/O 2. The present study investigated the influence of silica support texture on the catalytic performance of VO x /silica catalysts in the selective oxidation of propane. Two- and three-dimensional mesoporous materials, SBA-15 and MCF, were synthesized using hydrothermal methods to create different pore structures. Vanadium (approximately 5 wt%) was incorporated into the silica matrices (MCF, SBA-15) and SiO 2 (used as a reference system) through impregnation. The surface composition, valence state, and reducibility of the VO x species accommodated in VO x /silica catalysts were characterized using X-ray diffraction (XRD), diffuse reflectance ultraviolet–visible spectroscopy (UV–vis DRS), temperature-programmed reduction with hydrogen (H 2 -TPR), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR) techniques. The catalytic properties of the catalysts were evaluated in the propane selective oxidation conducted at 470 °C, utilizing a mixture of oxidants (N 2 O and O 2). Propane oxidation resulted in propane conversion of 34 %, propene selectivity of 49 %, and propene oxide selectivity of 20 %, corresponding to space–time yield of propene reaching 37 g C3H6 kg cat −1·h−1and propene oxide equal to 20 g PO kg cat −1h−1. The textural properties of the support materials noticeably influenced the stability of the catalysts. The vanadium catalysts supported on three-dimensional mesocellular silica foams (MCF) demonstrated superior activity, achieving turnover frequency (TOF) values of 9.0 × 10−4 s−1 for propene and 6.67 × 10−4 s−1 for propene oxide (PO). The unique three-dimensional ultra-large pores of the MCF material facilitated the generation of significant amounts of propene oxide, along with propene, while minimizing the formation of CO, CO 2 , and other oxygen-bearing by-products. Operando UV–vis studies supported by two-dimensional correlation analysis (2D COS) were employed to explain the diversity in the catalytic performance of VO x /silica catalysts. It has been found that the oligomeric vanadium species are the active sites in propane oxidative dehydrogenation, whereas the monomeric forms participate in propene oxide formation. Moreover, the reduction of V5+ to V4+ and even V3+ was identified as a crucial step in the reaction. A reaction scheme has been proposed based on catalytic experiments and spectroscopic insights. [ABSTRACT FROM AUTHOR]

[Display omitted] • Atomically dispersed Ru/Mg-CeO 2 catalyst was prepared and possessed excellent catalytic performance for photo-thermal catalytic CO 2 methanation reaction. • The photo-electron excitation/migration path and the surface structure changes induced by light were systematically characterized by operando experiments. • All potential micro-reaction steps and light intensification steps were determined by in situ DRIFTs experiments. • The reversible dynamic structural evolution between Ru-O-Ce structure and Ru-O v -Ce structure could be induced by light. It is a promising green technology to reduce CO 2 to CH 4 by using renewable solar energy driving photo-thermal catalysis route. However, the efficiency of photo-thermal catalytic CO2 methanation remained to be improved, and the mechanism of this reaction still required further investigation. In this paper, a Ru/Mg-CeO 2 catalyst was designed based on the concepts of single atom catalyst and photo-thermal catalysis concept. The catalyst achieved the CH 4 formation rate of 469 mmol·gcat−1·h−1 at 400 °C under photo-thermal conditions with good catalytic stability. Besides, the superiority of the single-atom of Ru, Ru-O-Ce structure and doping of alkaline metals in catalytic process was proved by a series of physicochemical and optical characterization, and electron migration direction from Ce and Mg elements to Ru sites through Ru-O-Ce and Ru-O-Mg path under photo-thermal catalysis was determined by ISI-XPS experiment. Finally, the comprehensive reaction mechanism and reversible dynamic structural evolution process between Ru-O-Ce and Ru-O v -Ce structures were investigated by in situ DRIFTs experiments, and the source of the excellent performance and structure-function relationship of the catalyst was explored, which provided the theoretical and practical basis for the development of catalyst and industrial application of the reaction. [ABSTRACT FROM AUTHOR]

Biogas methanation emerges as a prominent technology for converting biogas into biomethane in a single step. Furthermore, this technology can be implemented at biogas plant locations, supporting local economies and reducing dependence on large energy producers. However, there is a lack of comprehensive studies on biogas methanation, particularly regarding the technical optimization of operational parameters and the profitability analysis of the overall process. To address this gap, our study represents a seminal work on the technical optimization of biogas methanation obtaining an empirical model to predict the performance of biogas methanation. We investigate the influence of operational parameters, such as reaction temperature, H 2 /CO 2 ratio, space velocity, and CO 2 share in the biogas stream through an experimental design. Based on previous research we selected a nickel supported on ceria-alumina catalyst; being nickel a benchmark system for methanation process such selection permits a reliable data extrapolation to commercial units. We showcase the remarkable impact of studied key operation parameters, being the temperature, the most critical factor affecting the reaction performance (ca. 2 to 5 times higher than the second most influencing parameter). The impact of the H 2 /CO 2 ratio is also noticeable. The response surfaces and contour maps suggest that a temperature between 350 and 450 °C and an H 2 /CO 2 ratio between 2.5 and 3.2 optimize the reaction performance. Further experimental tests were performed for model validation and optimization leading to a reliable predictive model. Overall, this study provides validated equations for technology scaling-up and techno-economic analysis, thus representing a step ahead towards real-world applications for bio-methane production. • An empirical model to predict the performance of biogas methanation was built. • The influence of the main operational parameters was studied. • The temperature is the most critical factor affecting the reaction performance. • The impact of the H 2 /CO 2 ratio is also noticeable. • Temperature of 350–450 °C and H 2 /CO 2 ratio of 2.5–3.2 optimize the reaction. [ABSTRACT FROM AUTHOR]

A Ni 1 Co 1 O x catalyst with lattice distortions was prepared by a modified hard template method. Elemental analysis shows that Ni tends predominantly to disperse on the surfaces of the nanoparticles. Under the optimum reaction conditions (80 °C, 20 h, and 1.5 g NaOH), Ni 1 Co 1 O x catalyst could exhibit optimum catalytic performance (78.5% conversion, 66.5% GLYA selectivity, and recycling for four times). • A lattice-distorted Ni 1 Co 1 O x catalyst was synthesized by a modified hard template method. • High selectivity toward glyceric acid was obtained on the Ni 1 Co 1 O x catalyst. • Electron transfer from Ni cations to Co cations results in the generation of surface oxygen vacancies. • The oxygen vacancies of Co and Ni species promote the oxidation of glycerol to glyceric acid. Developing cheap and highly efficient catalysts for the selective oxidation of glycerol to value-added carboxylic acids still remains a challenge. Here, non-noble-metal Ni–Co oxide catalysts with lattice distortions are reported for the first time as highly efficient and stable catalysts for the oxidation of glycerol to glyceric acid. The Ni 1 Co 1 O x catalyst, prepared by a modified hard template method, exhibits superior activity (1.5 × 10−3 s−1), excellent glyceric acid selectivity (66.5%), and good stability under mild conditions (80 °C, 1 MPa O 2). Multiple characterizations demonstrated that the nanosized Ni 1 Co 1 O x catalyst (2.3 nm) contains lattice distortion Ni–Co structures with nickel-rich surfaces. This morphology induces electron transfer from Co cations (mainly Co3+) to Ni cations (mainly Ni3+), resulting in the generation of surface oxygen vacancies. Density functional theory calculations and catalytic kinetics demonstrated that oxygen vacancies on Co species could improve glyceric acid selectivity by preventing the cleavage of C C bond, and oxygen vacancies on the Ni species could promote the activation of C H bonds, which results in the exceptional catalytic performance of Ni 1 Co 1 O x. The novel Ni–Co oxide catalyst with lattice distortions synthesized here may provide some guidance for the rational design of inexpensive and highly efficient catalysts for the catalytic oxidation of biopolyols. [ABSTRACT FROM AUTHOR]

• Biojet fuel was produced from triglycerides by a single-step reaction over PtRe/USY. • PtRe/USY showed ideal hydrocracking even in the presence of in situ produced CO. • H 2 O and CO selectively suppressed undesired hydrogenolysis activity of PtRe/USY. • CO-tolerance of PtRe/USY is attributed to weak CO binding and fast methanation. The direct hydroconversion of triglycerides into biojet fuel (i.e., cascade reactions including hydrogenation, deoxygenation, and hydrocracking) is challenging, even though it is beneficial in terms of process intensification. This is because the minute amount of CO produced during deoxygenation can poison the metal component of various metal–acid bifunctional catalysts, causing undesired overcracking and rapid catalyst deactivation through coke formation. To overcome this problem, we synthesized a CO-tolerant catalyst by supporting bimetallic PtRe on ultra-stable Y (USY) zeolite as acidic support. Compared to conventional catalyst (e.g., Pt/USY), PtRe/USY showed markedly enhanced tolerance to CO because it had weakened interaction with CO and also could rapidly convert the chemisorbed CO into less harmful methane and H 2 O through methanation. Consequently, overcracking and catalyst deactivation were greatly suppressed during the direct triglyceride hydroconversion. It is remarkable that PtRe/USY is intrinsically a much poorer hydrocracking catalyst than Pt/USY under pure H 2 atmosphere because of its high hydrogenolysis activity. However, H 2 O and CO produced in situ during the deoxygenation of triglycerides selectively poisoned the active sites for undesired hydrogenolysis, thereby making PtRe/USY a highly stable and selective catalyst for producing biojet fuel. Under the optimum condition, 41 wt% of biojet fuel with respect to palm oil could be produced through direct hydroconversion, which satisfied all the required fuel specifications. [ABSTRACT FROM AUTHOR]

• FA pre-activation can convert Cu2+ to Cu+ in Cu-containing hydrotalcite. • Cu 2 O has a weak interaction with support oxides in Cu-based catalysts. • ZnO exhibits a synergetic effect with dispersed Cu in CO 2 hydrogenation. • FA pre-activation is helpful to improving catalytic activity of methanol catalyst. Formaldehyde (FA) was introduced into precursor slurries of CuZnAlZr catalysts (CZAZ) from co-precipitation in order to improve its catalytic performance in CO 2 hydrogenation to methanol. The obtained CZAZ catalysts with and without FA pre-activation were characterized by X-ray photoelectron spectroscopy, H 2 temperature-programmed reduction, X-ray diffraction, N 2 O-H 2 titration, N 2 adsorption-desorption, scanning electron microscopy and transmission electron microscope, respectively. The results indicated that FA pre-activation led to Cu2+ reduction to Cu+ in CZAZ precursors. After calcination in N 2 the copper components existed in state of Cu 2 O, which could provide highly-dispersed active Cu0 particles with a weak interaction between metal and supports. Meanwhile, FA pre-activation also gave rise to more crystallized semiconductor ZnO phase especially calcination in N 2 at a high temperature. Therefore, the obtained CZAZ catalysts with FA pre-activation on precursor exhibited better catalytic performance in CO 2 hydrogenation due to the synergistic effect of Cu0 particles and crystallized semiconductor ZnO phase. [ABSTRACT FROM AUTHOR]

• MoO x -decorated Ni-based catalysts were fabricated via a single-source precursor route. • As-fabricated Ni-based catalyst was highly active for γ-valerolactone hydrogenolysis. • Surface defective MoO x species facilitated the activation of carbonyl group. • A cooperation between Ni0 species and surface defects contributed to high efficiency. Currently, highly efficient biomass upgrading over non-noble metal catalysts is of vital importance for reducing equipment and operation expenses in biorefinery industries. In this respect, the related heterogeneous catalysis demands the design and construction of mutual cooperative microstructure of catalysts to improve their catalytic performances. Here, an efficient catalytic process for selective hydrogenolysis of biomass-derived γ-valerolactone (GVL) to produce 1,4-pentanediol (1,4-PDO) and 2-methyltetrahydrofuran (2-MTHF) was developed by earth-abundant nickel-based catalysts, which were derived from a molybdate intercalated Ni-Al layered double hydroxide precursor. It was found that with the elevated reduction temperature, the amount of surface defective MoO x species (0 < x < 3) was gradually increased. Especially, as-fabricated Ni-MoO x /Al 2 O 3 catalyst obtained at the reduction temperature of 600 °C delivered a 94.0% combined yield of 1,4-PDO and 2-MTHF under mild reaction conditions. It was demonstrated that over the present Ni-MoO x /Al 2 O 3 catalyst system, surface defective MoO x species could greatly facilitate the adsorption and activation of carbonyl group in GVL and thus significantly promote the cleavage of C O bond and its adjacent C O bond. This finding opens a promising door to engineer surface defective structure of high-performance supported metal catalysts. [ABSTRACT FROM AUTHOR]