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Abstract: Alkane oxyhalogenation has emerged as an attractive catalytic route for selective natural gas functionalization to important commodity chemicals, such as methyl halides or olefins. However, few systems have been shown to be active and selective in these reactions. Here, we identify a novel and highly efficient TiC–SiC composite for methane and ethane oxyhalogenation. Detailed characterization elucidates the kinetics and mechanism of the selective activation under reaction conditions to yield TiO2–TiC–SiC. This catalyst outperforms bulk TiO2, one of the best reported catalysts, reaching up to 85 % selectivity and up to 3 times higher titanium‐specific space‐time‐yield of methyl halides or ethylene. This is attributed to the fact that the active TiO2 phase generated in situ is embedded in the thermally conductive SiC matrix, facilitating heat dissipation thus improving selectivity control. [ABSTRACT FROM AUTHOR]

Commercial two-step processes to convert glycerol into epichlorohydrin are more benign compared to the predominant industrial route starting from propene in terms of materials requirements and CO2 emissions. Still, the use of alkali hydroxides in stoichiometric amounts in the second reaction, i.e., the dehydrochlorination of the dichloropropanol intermediate, leads to the formation of large amounts of salt wastes, thus limiting the greenness of the technology. Here, we show for the first time that the latter transformation can be selectively conducted in the gas phase in the presence of a heterogeneous hydrotalcite-derived mixed oxide of Al and Mg. Upon reaction, the lamellar solid is rehydrated to a hydrotalcite-like compound, which can effectively activate the alcoholic group of dichloropropanol owing to its strong Brønsted basic character and moderately high surface area. In-depth characterisation of the porous, compositional, structural and acid/base properties demonstrates that the HCl formed during the reaction causes the progressive exchange of interlayer OH groups by Cl atoms, thus gradually diminishing the reactivity of the material. Facile calcination restores the original mixed oxide structure and is shown to enable three equivalent consecutive reaction runs. Since the HCl evolved along with water upon regeneration can be recycled in the first step of the process, i.e., glycerol hydrochlorination, our approach paves the way for a waste-free and more atom efficient biobased epichlorohydrin production process. [ABSTRACT FROM AUTHOR]

The gas-phase aldol condensation of propanal, taken as model for the aldehyde components in bio-oils, has been studied with a combined operando set-up allowing to perform FT-IR & UV-Vis diffuse reflectance spectroscopy (DRS) with on-line mass spectrometry (MS). The selected solid base catalysts, a cesium-exchanged X zeolite (Cs-X), a calcium hydroxyapatite (Ca-HA) and two alkaline metal-grafted ultrastable Y (Na- and Rb-USY) zeolites, were characterized ex-situ by FT-IR after CO (CO-IR) and pyridine (Py-IR) adsorption and subsequent desorption. The combined operando spectroscopy study shows that alkaline metal-grafted USY zeolites are the most selective catalysts towards aldol dimer product formation, while the hydroxyapatite was more selective for successive aldol condensation reactions. For Na-USY and Rb-USY, the C-C coupling seems to be the rate-determining step during the surface reaction, which is the limiting stage of the overall catalytic process. In contrast, for the two more basic catalysts, i.e., Cs-X and Ca-HA desorption is limiting the overall catalytic process. Furthermore, the combined operando FT-IR & UV-Vis DRS methodology allowed monitoring the formation of carbonaceous deposits as a function of reaction time. In particular, for Cs-X and Ca-HA the rapid formation of carbonaceous deposits was observed consisting of (poly-)aromatics and highly conjugated structures, respectively. The physicochemical properties of Ca-HA with strong basic sites and moderate acidity limit its deactivation despite the observed coke formation. On the other hand, both USY catalysts were more efficient in suppressing coke formation likely due to the moderate strength of their active sites. [ABSTRACT FROM AUTHOR]

Ethylene and propylene are the key building blocks of the chemical industry, but current processes are unable to close the growing gap between demand and manufacture. Reported herein is an exceptional europium oxychloride (EuOCl) catalyst for the selective (≥95 %) production of light olefins from ethane and propane by oxychlorination chemistry, thus achieving yields of ethylene (90 %) and propylene (40 %) unparalleled by any existing olefin production technology. Moreover, EuOCl is able to process mixtures of methane, ethane, and propane to produce the olefins, thereby reducing separation costs of the alkanes in natural gas. Finally, the EuOCl catalyst was supported on suitable carriers and evaluated in extrudate form, and preserves performance for >150 h under realistic process conditions. [ABSTRACT FROM AUTHOR]

Ethylene and propylene are the key building blocks of the chemical industry, but current processes are unable to close the growing gap between demand and manufacture. Reported herein is an exceptional europium oxychloride (EuOCl) catalyst for the selective (≥95 %) production of light olefins from ethane and propane by oxychlorination chemistry, thus achieving yields of ethylene (90 %) and propylene (40 %) unparalleled by any existing olefin production technology. Moreover, EuOCl is able to process mixtures of methane, ethane, and propane to produce the olefins, thereby reducing separation costs of the alkanes in natural gas. Finally, the EuOCl catalyst was supported on suitable carriers and evaluated in extrudate form, and preserves performance for >150 h under realistic process conditions. [ABSTRACT FROM AUTHOR]

Indium oxide catalyzes acetylene hydrogenation with high selectivity to ethylene (>85 %); even with a large excess of the alkene. In situ characterization reveals the formation of oxygen vacancies under reaction conditions, while an in depth theoretical analysis links the surface reduction with the creation of well-defined vacancies and surrounding In3O5 ensembles, which are considered responsible for this outstanding catalytic function. This behavior, which differs from that of other common reducible oxides, originates from the presence of four crystallographically inequivalent oxygen sites in the indium oxide surface. These resulting ensembles are 1) stable against deactivation, 2) homogeneously and densely distributed, and 3) spatially isolated and confined against transport; thereby broadening the scope of oxides in hydrogenation catalysis. [ABSTRACT FROM AUTHOR]

Indium oxide catalyzes acetylene hydrogenation with high selectivity to ethylene (>85 %); even with a large excess of the alkene. In situ characterization reveals the formation of oxygen vacancies under reaction conditions, while an in depth theoretical analysis links the surface reduction with the creation of well-defined vacancies and surrounding In3O5 ensembles, which are considered responsible for this outstanding catalytic function. This behavior, which differs from that of other common reducible oxides, originates from the presence of four crystallographically inequivalent oxygen sites in the indium oxide surface. These resulting ensembles are 1) stable against deactivation, 2) homogeneously and densely distributed, and 3) spatially isolated and confined against transport; thereby broadening the scope of oxides in hydrogenation catalysis. [ABSTRACT FROM AUTHOR]

The recent development of amorphous silica-alumina catalysts for the heterogeneously-catalyzed production of methylenedianiline (MDA) has resulted in an economically and environmentally attractive alternative to the industrially employed HCl catalyst. However, the quantitative kinetic description of the complex reaction network, a key prerequisite for reactor choice and process assessment, is unfeasible when using classical power-law based models due to the wealth of components and interactions involved. Based on high throughput batch experiments coupled with a detailed product analysis, we herein reveal that all possible reactions in an MDA mixture can be represented in terms of interactions between a small number of reoccurring functional groups. A corresponding categorization of all mixture components enables the description of the reaction network using population balance equations, an approach previously applied to polymerization, aggregation, and cell-growth processes. Thereby, every possible binary interaction between two molecules in the system can be accounted for, resulting in an unprecedented resolution regarding oligomeric species and improved predictive capabilities based on a small number of parameters. The translation of the deepened mechanistic understanding into advanced kinetic models enables to circumvent previous limitations, and is expected to accelerate the industrial realization of the sustainable process. [ABSTRACT FROM AUTHOR]

The industrialization of bromine-mediated natural gas upgrading is contingent on the ability to fully recycle hydrogen bromide (HBr), which is the end form of the halogen after the activation and coupling of the alkanes. Europium oxybromide (EuOBr) is introduced as a unique catalytic material to close the bromine loop via HBr oxidation, permitting low-temperature operation and long lifetimes with a stoichiometric feed (O2:HBr=0.25)-conditions at which any catalyst reported to date severely deactivates because of excessive bromination. Besides, EuOBr exhibits unparalleled selectivity to methyl bromide in methane oxybromination, which is an alternative route for bromine looping. This novel active phase is finely dispersed on appropriate carriers and scaled up to technical extrudates, enhancing the utilization of the europium phase while preserving the performance. This catalytic system paves the way for sustainable valorization of stranded natural gas via bromine chemistry. [ABSTRACT FROM AUTHOR]

Keywords: CO2 hydrogenation; flame spray pyrolysis; oxygen vacancies; sustainable methanol; ZnZrOx catalysts EN CO2 hydrogenation flame spray pyrolysis oxygen vacancies sustainable methanol ZnZrOx catalysts 1 1 1 04/17/23 20230413 NES 230413 B Methanol Synthesis b In article number 2204122, Javier Pérez-Ramírez and co-workers apply flame spray pyrolysis to design superior ZnZrO SB I x i sb catalysts for methanol synthesis from CO SB 2 sb . Design of Flame-Made ZnZrOx Catalysts for Sustainable Methanol Synthesis from CO2 (Adv. CO2 hydrogenation, flame spray pyrolysis, oxygen vacancies, sustainable methanol, ZnZrOx catalysts. [Extracted from the article]

The establishment of suitable processes for the conversion of glycerol into allyl alcohol is hindered by the fast deactivation of solid acids in the dehydration of the substrate to acrolein and by the requirement of hydrogen donors to enhance the selectivity of the subsequent reduction step. In this work, silver nanoparticles deposited onto a hierarchical ZSM-5 zeolite are proved to be an effective bifunctional catalyst to conduct the two reactions in the gas phase and in the presence of hydrogen by using a continuous fixed-bed reactor. The acidic function was accomplished by using a ZSM-5 zeolite modified by facile alkaline and acid treatments, which decreased the amount of Lewis acid centers while preserving the amount of Brønsted acid centers, and introduced an auxiliary network of intracrystalline mesopores, thus boosting the selectivity to acrolein (62 %) and the resistance to coking. Upon screening of various metals supported on the aluminosilicate, silver was identified as a superior hydrogenation catalyst, enabling a relatively high activity with >50 % allyl alcohol selectivity. Tuning of the metal loading, temperature, pressure, and contact time led to 15 % yield of allyl alcohol, thus approaching the state-of-the-art transfer hydrogenation systems, and stable behavior for 100 h on stream. Our results highlight the advantage of conducting the two transformations over a bifunctional material rather than over two separate single-function solids. [ABSTRACT FROM AUTHOR]

Gamma-valerolactone (GVL), a versatile renewable compound listed among the top 10 most promising platform chemicals by the US Department of Energy, is produced via hydrogenation of levulinic acid (LA). The traditional high-loading ruthenium-on-carbon catalyst (5 wt% Ru) employed for this transformation suffers from low metal utilisation and poor resistance to deactivation due to the formation of RuOx species. Aiming at an improved catalyst design, we have prepared ruthenium nanoparticles modified with the water-soluble hexadecyl(2-hydroxyethyl)dimethylammonium dihydrogen phosphate (HHDMA) ligand and supported on TiSi2O6. The hybrid catalyst has been characterised by ICP-OES, elemental analysis, TGA, DRIFTS, H2-TPR, STEM, EDX, 31P and 13C MAS-NMR, and XPS. When evaluated in the continuous-flow hydrogenation of LA, the Ru-HHDMA/TiSi2O6 catalyst (0.24 wt% Ru) displays a fourfold higher reaction rate than the state-of-the-art Ru/C catalyst, while maintaining 100% selectivity to GVL and no sign of deactivation after 15 hours on stream. An in-depth molecular analysis by Density Functional Theory demonstrates that the intrinsic acidic properties at the ligand–metal interface under reaction conditions ensure that the less energy demanding path is followed. The reaction does not obey the expected cascade mechanism and intercalates hydrogenation steps, hydroxyl/water eliminations, and ring closings to ensure high selectivity. Moreover, the interfacial acidity increases the robustness of the material against ruthenium oxide formation. These results provide valuable improvements for the sustainable production of GLV and insights for the rationalisation of the exceptional selectivity of Ru-based catalysts. [ABSTRACT FROM AUTHOR]

The porosity of layered hydroxides can be greatly enhanced by thermal activation. Despite intense interest in the associated structural transformations, porosity changes have been almost exclusively described in terms of primitive bulk descriptors (surface area, pore volume, and average pore size), providing limited insight into the pore architecture (i.e., the geometry, location, and connectivity of the pores). This article maps porosity upon thermal activation of well-crystallized Mg(OH)2 (brucite) and isostructural layered double hydroxide {LDH, [M2+1-xM3+x(OH)2]x+(An-x/n)•mH2O} materials through novel characterization approaches such as transmission electron microscopy (TEM) coupled with in situ heating, differential hysteresis scanning (DHS) by high-resolution argon sorption, and positron annihilation lifetime spectroscopy (PALS). Despite exhibiting comparable surface area enhancements, arising from the formation of micro- and mesoporosity upon activation up to 873 K, the findings highlight striking differences in the structure of the developed pore networks. As visualized by TEM, the substitution of trivalent metals like aluminum into the brucite-like sheets restricts the growth and improves the thermal stability of the pores, which form abundantly throughout the sample. Quantitative analysis by DHS reveals that the geometry of mesopores in the most highly porous samples is significantly constricted. This is supported by low-temperature measurements (55 K), which permits precise assessment of the small mesopores (approximately 2-3 nm) in the LDH. Complementary insights are obtained by PALS, which evidences the asynchronous development of micro- and mesopores and readily distinguishes differences in the transport properties. The complexity of the pore evolution demonstrated by this approach illustrates the scope for improving the mechanistic understanding of the design of porous materials derived from layered hydroxides. [ABSTRACT FROM AUTHOR]

Furan derivatives, such as 5-hydroxymethylfurfural (HMF) and furfural, obtained from renewable feedstocks are sustainable alternatives to petroleum-based building blocks for the manufacture of chemical products. This study shows for the first time the applicability of the catalytic fast pyrolysis (CFP) of glucose over tailored zeolites for the production of HMF and furfural. In particular, we demonstrate that Lewis-acid-containing faujasite zeolites attained by alkali metal-cation exchange exhibit combined yields to these platform molecules of 17 %. Despite the fact that further research is required on the process assessment at a larger scale and under more realistic conditions, CFP has potential for the production of biomass-derived commodity chemicals. [ABSTRACT FROM AUTHOR]

Higher alcohols are important compounds with widespread applications in the chemical, pharmaceutical and energy sectors. Currently, they are mainly produced by sugar fermentation (ethanol and isobutanol) or hydration of petroleum-derived alkenes (heavier alcohols), but their direct synthesis from syngas (CO + H2) would comprise a more environmentally-friendly, versatile and economical alternative. Research efforts in this reaction, initiated in the 1930s, have fluctuated along with the oil price and have considerably increased in the last decade due to the interest to exploit shale gas and renewable resources to obtain the gaseous feedstock. Nevertheless, no catalytic system reported to date has performed sufficiently well to justify an industrial implementation. Since the design of an efficient catalyst would strongly benefit from the establishment of synthesis–structure–function relationships and a deeper understanding of the reaction mechanism, this review comprehensively overviews syngas-based higher alcohols synthesis in three main sections, highlighting the advances recently made and the challenges that remain open and stimulate upcoming research activities. The first part critically summarises the formulations and methods applied in the preparation of the four main classes of materials, i.e., Rh-based, Mo-based, modified Fischer–Tropsch and modified methanol synthesis catalysts. The second overviews the molecular-level insights derived from microkinetic and theoretical studies, drawing links to the mechanisms of Fischer–Tropsch and methanol syntheses. Finally, concepts proposed to improve the efficiency of reactors and separation units as well as to utilise CO2 and recycle side-products in the process are described in the third section. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-C3N4) exhibits unique properties as a support for single-atom heterogeneous catalysts (SAHCs). Understanding how the synthesis method, carrier properties, and metal identity impact the isolation of metal centers is essential to guide their design. This study compares the effectiveness of direct and postsynthetic routes to prepare SAHCs by incorporating palladium, silver, iridium, platinum, or gold in g-C3N4 of distinct morphology (bulk, mesoporous and exfoliated). The speciation (single atoms, dimers, clusters, or nanoparticles), distribution, and oxidation state of the supported metals are characterized by multiple techniques including extensive use of aberration-corrected electron microscopy. SAHCs are most readily attained via direct approaches applying copolymerizable metal precursors and employing high surface area carriers. In contrast, although post-synthetic routes enable improved control over the metal loading, nanoparticle formation is more prevalent. Comparison of the carrier morphologies also points toward the involvement of defects in stabilizing single atoms. The distinct metal dispersions are rationalized by density functional theory and kinetic Monte Carlo simulations, highlighting the interplay between the adsorption energetics and diffusion kinetics. Evaluation in the continuous three-phase semihydrogenation of 1-hexyne identifies controlling the metal-carrier interaction and exposing the metal sites at the surface layer as key challenges in designing efficient SAHCs. [ABSTRACT FROM AUTHOR]

Nanoparticles are applied in a variety of industrially relevant transformations as heterogeneous catalysts typically with the help of an external force (pressure, temperature, or voltage) to steer the chemistry. The modification of platinum nanoparticles by a phosphate-amino surfactant enables catalysis without external energy supply in the hydrogenation of nitrobenzene to aniline. This can be attributed to the complex surfactant/metal interface which is able to split hydrogen into protons and electrons. The subsequent hydrogenation process mimics the electrochemical reduction described by Haber. The surfactant decorated Pt catalyst is two orders of magnitude more active than the state-of-the-art Pb-poisoned Pt catalyst. Our study provides a new approach to understand the functionality of emerging catalytic systems and can be applied to design new materials with optimal interfaces. [ABSTRACT FROM AUTHOR]

Ligand-modified palladium nanoparticles deposited on a carbon carrier efficiently catalyze the direct synthesis of H2O2 and the unique performance is due to their hybrid nanostructure. Catalytic testing demonstrated that the selectivity increases with the HHDMA ligand content from 10 % for naked nanoparticles up to 80 %, rivalling that obtained with state-of-the-art bimetallic catalysts (HHDMA=C20H46NO5P). Furthermore, it remains stable over five consecutive reaction runs owing to the high resistance towards leaching of the organic moiety, arising from its bond with the metal surface. As rationalized by density functional theory, this behavior is attributed to the adsorption mode of the reaction intermediates on the metal surface. Whereas they lie flat in the absence of the organic shell, their electrostatic interaction with the ligand result in a unique vertical configuration which prevents further dissociation and over-hydrogenation. These findings demonstrate the importance of understanding substrate-ligand interactions in capped nanoparticles to develop smart catalysts for the sustainable manufacture of hydrogen peroxide. [ABSTRACT FROM AUTHOR]

Ligand-modified palladium nanoparticles deposited on a carbon carrier efficiently catalyze the direct synthesis of H2O2 and the unique performance is due to their hybrid nanostructure. Catalytic testing demonstrated that the selectivity increases with the HHDMA ligand content from 10 % for naked nanoparticles up to 80 %, rivalling that obtained with state-of-the-art bimetallic catalysts (HHDMA=C20H46NO5P). Furthermore, it remains stable over five consecutive reaction runs owing to the high resistance towards leaching of the organic moiety, arising from its bond with the metal surface. As rationalized by density functional theory, this behavior is attributed to the adsorption mode of the reaction intermediates on the metal surface. Whereas they lie flat in the absence of the organic shell, their electrostatic interaction with the ligand result in a unique vertical configuration which prevents further dissociation and over-hydrogenation. These findings demonstrate the importance of understanding substrate-ligand interactions in capped nanoparticles to develop smart catalysts for the sustainable manufacture of hydrogen peroxide. [ABSTRACT FROM AUTHOR]

A catalytic process is demonstrated for the selective conversion of methane into carbon monoxide via oxychlorination chemistry. The process involves addition of HCl to a CH4-O2 feed to facilitate C−H bond activation under mild conditions, leading to the formation of chloromethanes, CH3Cl and CH2Cl2. The latter are oxidized in situ over the same catalyst, yielding CO and recycling HCl. A material exhibiting chlorine evolution by HCl oxidation, high activity to oxidize chloromethanes into CO, and no ability to oxidize CO, is therefore essential to accomplish this target. Following these design criteria, vanadyl pyrophosphate (VPO) was identified as an outstanding catalyst, exhibiting a CO yield up to approximately 35 % at 96 % selectivity and stable behavior. These findings constitute a basis for the development of a process enabling the on-site valorization of stranded natural-gas reserves using CO as a highly versatile platform molecule. [ABSTRACT FROM AUTHOR]

A catalytic process is demonstrated for the selective conversion of methane into carbon monoxide via oxychlorination chemistry. The process involves addition of HCl to a CH4-O2 feed to facilitate C−H bond activation under mild conditions, leading to the formation of chloromethanes, CH3Cl and CH2Cl2. The latter are oxidized in situ over the same catalyst, yielding CO and recycling HCl. A material exhibiting chlorine evolution by HCl oxidation, high activity to oxidize chloromethanes into CO, and no ability to oxidize CO, is therefore essential to accomplish this target. Following these design criteria, vanadyl pyrophosphate (VPO) was identified as an outstanding catalyst, exhibiting a CO yield up to approximately 35 % at 96 % selectivity and stable behavior. These findings constitute a basis for the development of a process enabling the on-site valorization of stranded natural-gas reserves using CO as a highly versatile platform molecule. [ABSTRACT FROM AUTHOR]

The industrial manufacture of vinyl chloride relies on a two-step process involving CuCl 2 -catalyzed ethylene oxychlorination to ethylene dichloride followed by thermal cracking of the latter to vinyl chloride. This work evaluates a wide range of commercial and self-prepared lanthanide (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er) compounds for the one-step production of vinyl chloride from ethylene in a fixed-bed reactor at 623–773 K and 1 bar using feed ratios of C 2 H 4 :HCl:O 2 :Ar:He = 3–6:1–9.6:1–7:3:80–92 and space times of 6–252 g h mol −1 (based on ethylene). Ex situ characterization by X-ray diffraction, electron microscopy, and X-ray photoelectron spectroscopy reveals that the oxide forms of all compounds, except CeO 2 , transform into their respective (oxy)chloride. Among all studied systems, CeO 2 shows the highest activity but suffers from combustion forming CO x , while europium oxychloride (EuOCl) leads to the best vinyl chloride selectivity of 96% at 20% C 2 H 4 conversion for over 100 h on stream. Temperature-programmed reduction with H 2 , temperature-programmed desorption of NH 3 , and oxidation tests (C 2 H 4 , CO, and HCl oxidation) unravel the unique balance of mild redox and enhanced acid properties of EuOCl compared to CeO 2 , which suppress over-oxidation and boost ethylene dichloride dehydrochlorination. Strategies to couple the excellent selectivity of EuOCl with the high activity of CeO 2 are demonstrated through the synthesis of homogeneous europium-cerium mixed oxides, combining two functions on a single surface. In addition, the engineering of a dual-bed reactor, integrating a CeO 2 bed first to produce ethylene dichloride in high yield which is subsequently transformed to vinyl chloride over EuOCl leads to vinyl chloride yields of up to 30% per pass. These very promising findings constitute a crucial step for process intensification of polyvinyl chloride production and exploring the potential of rare-earth compounds in industrially-relevant reactions. [ABSTRACT FROM AUTHOR]

Ceria has been very successfully employed in oxidation catalysis, whereas its application in other reactions has been less intensively investigated. The catalytic activity of ceria can be further enhanced by the use of dopants, and it exhibits structure sensitivity for numerous processes. The rich chemistry of cerium oxide is gathered and discussed in the present work, where the nature of each step of the most common reactions performed on it is assessed. Chemically intuitive computational and experimental descriptors, namely acid-base, redox, and structural features, are put forward to correlate the observed trends among the different doped and undoped facets. We have attempted to generate a robust framework that maps the chemically sound descriptors to the experimental fingerprints and theoretically calculated parameters. [ABSTRACT FROM AUTHOR]

The emergence of synergistic effects in multicomponent systems opens new opportunities to design improved catalysts for the electrochemical CO 2 reduction reaction (eCO 2 RR). Targeting the selective formation of CO, we have evaluated a comprehensive set of silver–indium electrocatalysts with different architectures, ranging from bulk intermetallic compounds to Ag nanoparticles supported on In 2 O 3 and In(OH) 3 . This approach allowed the design of a supported electrocatalyst with maximized performance. Despite very different bulk compositions, XPS analyses on Ag–In alloy electrodes revealed a near-surface indium enrichment, leading to a comparatively poor electrocatalytic performance. In contrast, the presence of oxidized indium deposits on the surface of bulk silver had a positive effect on the selectivity for CO at moderate overpotential. Based on these findings, we studied the interactions between silver and oxidic indium phases by preparing sets of In 2 O 3 - and In(OH) 3 -supported Ag catalysts, which were characterized with XRD, N 2 sorption, H 2 -TPR, CO 2 -TPD, STEM and EDX. With respect to the pristine supports and to similarly prepared Ag catalysts on carbon black, these nanostructured systems exhibited an enhanced current efficiency for CO at moderate overpotential, evidencing a synergistic effect between the metal nanoparticles and the supports. This effect was particularly marked at higher Ag loadings and with In(OH) 3 as support which, unlike In 2 O 3 , was stable against reduction under eCO 2 RR conditions. As a final step, the selectivity enhancement achieved in Ag/In(OH) 3 was combined with the known activity-promoting role of P25 TiO 2 by depositing Ag on a composite support. The Ag/In(OH) 3 –TiO 2 catalyst showed concurrent gains in selectivity and activity for CO. The findings highlight the potential of stable metal (hydr)oxide supports to act as promoters in the eCO 2 RR and the importance of the structural configuration in multicomponent electrocatalysts. [ABSTRACT FROM AUTHOR]

Optimal amounts of CO2 are added to syngas to boost the methanol synthesis rate on Cu-ZnO-Al2O3 in the industrial process. The reason for CO2 promotion is not sufficiently understood at the particle level due to the catalyst complexity and the high demands of characterization under true reaction conditions. Herein, we applied operando synchrotron X-ray powder diffraction and modulated-excitation infrared spectroscopy on a commercial catalyst to gain insights into its morphology and surface chemistry. These studies unveiled that Cu and ZnO agglomerate and ZnO particles flatten under CO/H2 and/or CO2/H2. Under the optimal CO/CO2/H2 mixture, sintering is prevented and ZnO crystals adopt an elongated shape due to the minimal presence of the H2O byproduct, enhancing the water-gas shift activity and thus the methanol production. Our results provide a rationale to the CO2 promotion emphasizing the importance of advanced analytical methods to establish structure-performance relations in heterogeneous catalysis. [ABSTRACT FROM AUTHOR]

Optimal amounts of CO2 are added to syngas to boost the methanol synthesis rate on Cu-ZnO-Al2O3 in the industrial process. The reason for CO2 promotion is not sufficiently understood at the particle level due to the catalyst complexity and the high demands of characterization under true reaction conditions. Herein, we applied operando synchrotron X-ray powder diffraction and modulated-excitation infrared spectroscopy on a commercial catalyst to gain insights into its morphology and surface chemistry. These studies unveiled that Cu and ZnO agglomerate and ZnO particles flatten under CO/H2 and/or CO2/H2. Under the optimal CO/CO2/H2 mixture, sintering is prevented and ZnO crystals adopt an elongated shape due to the minimal presence of the H2O byproduct, enhancing the water-gas shift activity and thus the methanol production. Our results provide a rationale to the CO2 promotion emphasizing the importance of advanced analytical methods to establish structure-performance relations in heterogeneous catalysis. [ABSTRACT FROM AUTHOR]

An exact knowledge of the architecture of complex pore networks and the impact on transport processes is critical to understand and optimize their integration in many functional solids. Here, a robust and versatile approach is demonstrated to quantitatively map pore constrictions within hierarchical faujasite-type (Y and USY) zeolites, the most widely applied zeolitic materials in industry. Differential hysteresis scanning measurements by high-resolution argon sorption coupled with an advanced modeling framework enable the derivation of the amount and size of pyramidal, constricted, and occluded mesopores. This yields unprecedented insight into the impact of widely practiced demetallation treatments on the porosity evolution and clearly highlights the interplay between the geometry of mesopores developed by a given treatment and those introduced by previously applied postsynthetic modifications. Based on the findings, the dynamic assessment by positron annihilation spectroscopy confirms the effectiveness of each mesopore type at enhancing the diffusion of ortho-positronium within the crystal. The quantitative descriptors attained by these complementary techniques can revolutionize the design of porous materials for a wide range of applications. [ABSTRACT FROM AUTHOR]

Active site coordination, bimetallic systems, cooperativity effects, single-atom catalysts By selectively occupying the most energetically favorable cavities in the carbon host, Pt atoms drive Ru atoms to assume a distinct, more active configuration. Keywords: active site coordination; bimetallic systems; cooperativity effects; single-atom catalysts EN active site coordination bimetallic systems cooperativity effects single-atom catalysts 1 1 1 12/27/22 20221222 NES 221222 B Bimetallic Single Atom Catalysts b In article number 2206513, Javier Pérez-Ramírez, Núria López and co-workers investigate cooperativity mechanisms between fully isolated Ru and Pt atoms via the hydrogen evolution reaction, demonstrating that catalytic synergies can arise in the absence of direct metal-metal interactions. [Extracted from the article]

The conversion of wet waste (e.g., food waste, sewage sludge, and animal manure) into bioenergy is a promising strategy for sustainable energy generation and waste management. Although experimental efforts have driven waste conversion technologies (WCTs) to various degrees of maturity, computational modeling has equally contributed to this endeavor. This review focuses on the application of modeling techniques, including computational fluid dynamics (CFD), process simulation (PS), and machine learning (ML) on WCTs including anaerobic digestion, hydrothermal carbonization, gasification, pyrolysis and incineration. It addresses in a concise manner on how CFD models aid in understanding of the complex process and their molecular kinetics; while PS and ML models help in understanding the reaction kinetics, variable-response relationship, techno-economic assessment and sensitivity analysis. Relevant modeling approaches with their pros and cons are summarized and case studies are presented for each WCT. Moreover, a comparative evaluation among the three modeling techniques, along with their recent and ongoing developments are highlighted. Hybrid frameworks derived by combining mechanistic and ML models are proposed, which are expected to advance future wet waste valorization strategies for sustainable clean energy production and waste management. [ABSTRACT FROM AUTHOR]

The Cover shows a hierarchically structured MnO2‐Co/C nanocomposite developed as a magnetically recoverable catalyst for the aerobic oxidation of alcohols. In their Communication, Zhi et al. demonstrate that these hybrid systems offer high catalytic activity, outperforming traditional oxidation systems using MnO2 as oxidant and rivalling the activity of Pd‐based catalysts, in addition to convenient separation by external magnets and excellent recyclability. More details can be found in the Communication by Zhi et al. on page 2585 in Issue 17, 2015. (DOI: 10.1002/cctc.201500549). [ABSTRACT FROM AUTHOR]

Methanol synthesis by CO2 hydrogenation is attractive in view of avoiding the environmental implications associated with the production of the traditional syngas feedstock and mitigating global warming. However, there still is a lack of efficient catalysts for such alternative processes. Herein, we unveil the high activity, 100 % selectivity, and remarkable stability for 1000 h on stream of In2O3 supported on ZrO2 under industrially relevant conditions. This strongly contrasts to the benchmark Cu-ZnO-Al2O3 catalyst, which is unselective and experiences rapid deactivation. In-depth characterization of the In2O3-based materials points towards a mechanism rooted in the creation and annihilation of oxygen vacancies as active sites, whose amount can be modulated in situ by co-feeding CO and boosted through electronic interactions with the zirconia carrier. These results constitute a promising basis for the design of a prospective technology for sustainable methanol production. [ABSTRACT FROM AUTHOR]

Methanol synthesis by CO2 hydrogenation is attractive in view of avoiding the environmental implications associated with the production of the traditional syngas feedstock and mitigating global warming. However, there still is a lack of efficient catalysts for such alternative processes. Herein, we unveil the high activity, 100 % selectivity, and remarkable stability for 1000 h on stream of In2O3 supported on ZrO2 under industrially relevant conditions. This strongly contrasts to the benchmark Cu-ZnO-Al2O3 catalyst, which is unselective and experiences rapid deactivation. In-depth characterization of the In2O3-based materials points towards a mechanism rooted in the creation and annihilation of oxygen vacancies as active sites, whose amount can be modulated in situ by co-feeding CO and boosted through electronic interactions with the zirconia carrier. These results constitute a promising basis for the design of a prospective technology for sustainable methanol production. [ABSTRACT FROM AUTHOR]

Iron phosphates comprise an important class of materials with a wide range of applications. We have designed novel routes for the controlled synthesis of iron phosphate dihydrates of varying crystallographic phases (monoclinic and orthorhombic) and morphologies. Our approach comprises the phosphation of β-FeOOH nanorods with aqueous phosphoric acid solutions. Through a systematic parametric study coupled to an array of characterisation techniques, including XRD, TEM, HAADF-STEM, AAS, N2 sorption, TGA-MS, FTIR, UV-Vis, XPS, EXAFS, EPR, and 57Fe Mössbauer spectroscopy, we unravel the complex synthesis chemistry on both the macroscopic and microscopic levels. It is found that the formation of iron phosphates occurs exclusively under acidic conditions and in general involves the dissolution of β-FeOOH which, upon reaction with H3PO4, precipitates as FePO4·2H2O. The pH of the treatment solution determines the crystallographic phase of the resulting product by regulating the rate of β-FeOOH dissolution and of the precipitation of the iron phosphates, while the treatment time is decisive for the preservation of the morphology. The formation of the monoclinic phase entails a fast iron dissolution and subsequent precipitation in the solution. The generation of the orthorhombic analogue involves an interfacial reaction between H3PO4 and β-FeOOH, forming an amorphous layer of iron phosphate, which crystallises into a pure phase with increasing treatment time. The thermal transformation of hydrated to anhydrous iron phosphates is dependent on the phase and morphology of the precursors. The rod shape of iron-rich orthorhombic FePO4·2H2O can be preserved even after annealing at 923 K, with the formation of mesopores. These novel nanostructures may widen the applications of iron phosphates and the routes developed herein can be anticipated to guide the fabrication of other metal phosphates. [ABSTRACT FROM AUTHOR]

This study investigates the design of mild base catalysts for the deoxygenation of bio-oil via aldol condensation paths. The first part rationalizes the active, selective, and stable performance of supported MgO catalysts in the vapor phase condensation of propanal, which is maximized upon the mechanochemical activation of a siliceous USY zeolite (Si/Al = 405) with 1 wt.% Mg(OH) 2 . Infrared spectroscopic studies of the interaction with CO and CO 2 , reveal that the presence of 4-coordinate Mg likely localized in framework defects on the zeolite surface, and the avoidance of MgO formation are key to moderating the basicity with respect to the bulk oxide. The second part compares the best‑performing MgO/USY catalyst with the most promising previously reported catalysts: K-grafted USY and Ca-hydroxyapatite. A detailed kinetic analysis of the conversion of individual bio‑oil constituents (propanal or acetic acid) and binary mixtures thereof (propanal with acetic acid, methanol, or water) provides insights into the reaction network, rate-limiting steps, and relative surface coverage of reactants and products over each catalyst. This enables the anticipation of the aldol-condensation performance in simulated and real bio–oil mixtures. A significant inhibitory effect is observed in the presence of acetic acid, but the K-grafted USY zeolite is found to preserve its stability and retain the highest activity due to the weaker adsorption of acidic compounds. The presence of water has no pronounced effect on the observed reaction rates, while methanol is found to selectively poison Ca-hydroxyapatite due to the competitive adsorption on the active sites. The attained results under real bio-oil conditions demonstrate the effectiveness of this simplified approach to bridge the complexity gap between the study of model compounds and real bio-oil. [ABSTRACT FROM AUTHOR]

The industrial viability of heterogeneous catalysts for the gas-phase conversion of lactic acid to acrylic acid will strongly depend on their selectivity and durability. Here, we initially screened various aluminum-rich zeolites confirming that NaY is the most efficient catalyst for this reaction. This material was modified by sequential dealumination and alkaline treatment attaining a solid featuring a hierarchical distribution of micro- and mesopores, reduced Lewis acidity, and increased basicity owing to the presence of well-dispersed sodium ions interacting with external siloxy groups, as evidenced by in-depth characterization. These properties were crucial for determining higher selectivity (75 %) and minimizing the activity loss in a 6 h run. Remarkably, the catalyst gained in selectivity and stability upon reuse in consecutive cycles. This was ascribed to the depletion of the stronger basic sites and the clustering of sodium into oxidic particles upon the intermediate calcination. [ABSTRACT FROM AUTHOR]

Ceria catalyzes the one-step production of the vinyl chloride monomer (VCM) from ethylene with a high yield because of its bifunctional character: redox centers oxychlorinate ethylene to ethylene dichloride (EDC), which is subsequently dehydrochlorinated to VCM over strong acid sites generated in situ. Nanocrystalline CeO2 and CeO2-ZrO2 lead to a VCM yield of 25 % in a single pass, outperforming the best reported systems and reaching industrially attractive levels. The use of CeO2 intensifies the current two-step process within PVC production encompassing CuCl2-catalyzed oxychlorination and thermal cracking. In addition, ceria-based materials offer stability advantages with respect to the archetypical CuCl2-based catalysts. [ABSTRACT FROM AUTHOR]

Ceria catalyzes the one-step production of the vinyl chloride monomer (VCM) from ethylene with a high yield because of its bifunctional character: redox centers oxychlorinate ethylene to ethylene dichloride (EDC), which is subsequently dehydrochlorinated to VCM over strong acid sites generated in situ. Nanocrystalline CeO2 and CeO2-ZrO2 lead to a VCM yield of 25 % in a single pass, outperforming the best reported systems and reaching industrially attractive levels. The use of CeO2 intensifies the current two-step process within PVC production encompassing CuCl2-catalyzed oxychlorination and thermal cracking. In addition, ceria-based materials offer stability advantages with respect to the archetypical CuCl2-based catalysts. [ABSTRACT FROM AUTHOR]

Selective hydrogenations lay at the heart of many industrial processes. The archetypal catalysts for this class of reactions are generally prepared by 'metal poisoning' strategies: the active metal is protected and selectively deactivated with various compounds. This approach has been applied for decades, with limited understanding. Low product selectivity and presence of toxic elements in the catalyst pose severe constraints in the utilization of these materials in the future. Thus, to develop more sustainable catalysts, this field has recently gained momentum. This Review analyzes the concepts and frontiers that have been developed in the last decade: from nanostructuring less conventional metals in order to improve their ability to activate H2, to the use of oxides as active phases, from alloying, to the ensemble control in hybrid materials, and site isolation approaches in single-site heterogeneous catalysts. Particular attention is given to the hydrogenation of alkynes and nitroarenes, two reactions at the core of the chemical industry, importantly applied in the manufacture of polymers, pharmaceuticals, nutraceuticals, and agrochemicals. The strategies here identified can be transposed to other relevant hydrogenations and can guide in the design of more advanced materials. [ABSTRACT FROM AUTHOR]

The impact of zirconia on the activity and stability of ceria has been investigated in the gas-phase oxidation of HBr and HCl to the corresponding halogens. Homogeneous and non-homogeneous ceria–zirconia catalysts with a Ce:Zr ratio of 75:25 were prepared and characterized by X-ray diffraction, temperature-programmed reduction in hydrogen, transmission electron microscopy, and X-ray photoelectron spectroscopy. Catalytic tests demonstrated that ZrO 2 promotes the activity of CeO 2 independently of the metal homogeneity in the mixed oxide. Upon cycling of the temperature and feed composition, no differences with respect to chlorine formation were observed. On the other hand, a hysteresis of the reaction rate was measured in HBr oxidation, which was more pronounced over the non-homogeneous mixed oxide due to the higher extent of bromination. A moderate degree of bromination was attained in the homogeneous mixed oxide, leading to an improved long-term stability. The impact of phase homogeneity on the halogenation properties of the catalysts, and thus on the lifetime, was further rationalized by the determination of the halogen uptake by operando prompt-gamma activation analysis. While the chlorine uptake under different reaction conditions was comparable over both materials, the bromine uptake on the non-homogeneous sample was up to 50% higher compared to the homogeneous counterpart. This indicates not only that the catalysts are more prone to bromination than chlorination, but also that their robustness depends on the intermixing of the Ce and Zr phases, suggesting that the mixed oxides are more stable than supported ceria catalysts. The degree of halogenation of the homogeneous ceria–zirconia catalysts can be controlled by tuning their Ce:Zr ratio, minimizing the halogen uptake at a Zr content in the range of 70–90 mol.%. [ABSTRACT FROM AUTHOR]

The hydrolytic hydrogenation of hemicellulose arabinogalactan was investigated in the presence of protonic and Ru (1–5 wt.%)-modified USY zeolites (Si/Al ratio = 15 and 30). The use of the purely acidic materials was effective in depolymerizing the macromolecule into free sugars. While the latter partly dehydrated into 5-hydroxymethylfurfural and furfural, the generation of high molecular-weight compounds (aggregates of sugars and humins) was not favored, in contrast to previous evidences over beta zeolites. Application of the bifunctional Ru/USY catalyst, comprising well-dispersed metallic nanoparticles on the aluminosilicate support, resulted in the formation of galactitol and arabitol, in the suppression of dehydration side products, and further inhibition of polymerization reactions, which only yielded low molecular-weight oligomers. Detailed analysis of the reaction pathways as well as kinetic modeling of hydrolytic hydrogenation was performed with an advanced reaction mechanism. [ABSTRACT FROM AUTHOR]

A literature survey reveals a prominent reduction in the concentration of Brønsted acid sites in hierarchically organized zeolites with increasing mesoporous or external surface area independent of the framework type or synthesis route; this suggests a common fundamental explanation. To determine the cause, nature, and impact of the underlying changes in aluminum speciation, this study combines a multitechnique analysis that integrates basic characterization, a detailed synchrotron XRD and multiple-quantum NMR spectroscopy assessment, and catalytic tests to correlate evolution of the properties with performance during successive steps in the preparation of hierarchical MFI-type zeolites by desilication. The findings, subsequently generalized to FAU- and BEA-type materials, identify the crucial impact of calcination on the protonic form, which is an integral step in the synthesis and regeneration of zeolite catalysts; on aluminum coordination; and the associated acidity trends. [ABSTRACT FROM AUTHOR]

We report the preparation and hydrogenation performance of a single-site palladium catalyst that was obtained by the anchoring of Pd atoms into the cavities of mesoporous polymeric graphitic carbon nitride. The characterization of the material confirmed the atomic dispersion of the palladium phase throughout the sample. The catalyst was applied for three-phase hydrogenations of alkynes and nitroarenes in a continuous-flow reactor, showing its high activity and product selectivity in comparison with benchmark catalysts based on nanoparticles. Density functional theory calculations provided fundamental insights into the material structure and attributed the high catalyst activity and selectivity to the facile hydrogen activation and hydrocarbon adsorption on atomically dispersed Pd sites. [ABSTRACT FROM AUTHOR]

Wir beschreiben die Herstellung und das Hydrierungsverhalten eines Einzelatom ‐ Palladiumkatalysators, geschaffen durch die Verankerung von Pd ‐ Atomen in den Mesoporen eines graphitischen Kohlenstoffnitridpolymers. Die Analyse des Materials bestätigt die atomare Dispersion der Palladium ‐ Phase über die komplette Probe. Gegenüber nanopartikelbasierten Vergleichskatalysatoren zeigte sich die hohe Aktivität und Selektivität deutlich bei Anwendung in der kontinuierlichen Drei ‐ Phasen ‐ Hydrierung von Alkinen und Nitroarenen in einem Durchflussreaktor. Dichtefunktionalrechnungen ermöglichten die Erarbeitung fundamentaler Erkenntnisse betreffend Materialstruktur und erlaubten, die hohe katalytische Aktivität und Selektivität auf die einfache Wasserstoffaktivierung und Kohlenwasserstoffadsorption auf den atomar verteilten Pd ‐ Strukturen zurückzuführen. Ein (geschütztes) Atom genügt: Die einzigartige Porenstruktur von Kohlenstoffnitriden ermöglicht die stabile Einlagerung isolierter Palladiumatome. Dieser heterogene „Single ‐ site”︁ ‐ Katalysator für selektive Hydrierungen übertrifft die modifizierten Palladium ‐ Nanopartikel, welche den derzeitigen Stand der Technik darstellen. [ABSTRACT FROM AUTHOR]

Ammonia Oxidation, Au/CeO2, Metal-Support Interface, Nitrous Oxide, Reaction Mechanisms Keywords: Ammonia Oxidation; Au/CeO2; Metal-Support Interface; Nitrous Oxide; Reaction Mechanisms EN Ammonia Oxidation Au/CeO2 Metal-Support Interface Nitrous Oxide Reaction Mechanisms 1 1 1 04/27/22 20220502 NES 220502 B A game of two halves b Direct ammonia oxidation unlocks a pathway towards affordable and efficient production of nitrous oxide, a highly promising agent for selective oxidation reactions, but necessitates the development of suitable catalysts. Back Cover: Ceria-Supported Gold Nanoparticles as a Superior Catalyst for Nitrous Oxide Production via Ammonia Oxidation (Angew. [Extracted from the article]

Keywords: Ammonia Oxidation; Au/CeO2; Metal-Support Interface; Nitrous Oxide; Reaction Mechanisms EN Ammonia Oxidation Au/CeO2 Metal-Support Interface Nitrous Oxide Reaction Mechanisms 1 1 1 04/27/22 20220502 NES 220502 B Ein Spiel zweier Hälften b Die direkte Oxidation von Ammoniak eröffnet einen Weg zur kostengünstigen und effizienten Produktion von Stickstoffoxid, einem vielversprechenden Reagens für selektive Oxidationsreaktionen. Rücktitelbild: Ceria-Supported Gold Nanoparticles as a Superior Catalyst for Nitrous Oxide Production via Ammonia Oxidation (Angew. Ammonia Oxidation, Au/CeO2, Metal-Support Interface, Nitrous Oxide, Reaction Mechanisms. [Extracted from the article]

The development of efficient CO 2 conversion catalysts is a long-lasting desire. Herein, we introduce an atomic Pd-promoted ZnZrO x solid solution catalyst (Pd-ZnZrO x), which shows markedly enhanced rate of methanol production compared to bare ZnZrO x , as well as excellent stability over 100 h on stream. Up to 0.8 at% (i. e. 0.6 wt%), Pd can be atomically dispersed in ZnZrO x , leading to more oxygen vacancies on the mixed oxide that foster methanol production. Kinetic analysis and in situ DRIFTS reveal that hydrogen activation is limited on ZnZrO x , but Pd doping facilitates H 2 dissociation as well as the consequent formation of HCOO*, thus boosting CO 2 conversion to methanol. DFT analyses suggest that the presence of atomic Pd enables a more exothermic H 2 dissociation, which increases the availability of surface H and facilitates CO 2 hydrogenation on adjacent Zn sites, providing rationale on the high activity and robustness of Pd-ZnZrO x in CO 2 hydrogenation. [Display omitted] • Coprecipitation of Zn, Zr, and Pd precursors forms atomically dispersed Pd on ZnZrO x. • Atomic Pd-doping leads to higher concentration of surface oxygen vacancies. • Atomic Pd-promoted ZnZrO x shows excellent CO 2 hydrogenation activity and lifetime. • Pd promotes H 2 splitting and the stabilization of key intermediates for CH 3 OH. [ABSTRACT FROM AUTHOR]

The transfer hydrogenation of sugars to alditols with biobased alcohol donors was studied over hydrotalcite-derived Cu6− xNi xAl2 catalysts prepared by coprecipitation at different pH and featuring variable Cu/Ni ratios. Their evaluation, after in situ activation in pure H2 at 773 K, in the ethanol-assisted upgrading of glucose in a continuous-flow fixed-bed reactor identified the solid synthesized at pH 9-10 and with Cu/Ni=1 as the best performer. Based on textural, structural, and redox analyses, this is related to an enhanced intermetallic interaction. Upon screening alternative donors, a sorbitol yield as high as 67 % was achieved with 1,4-butanediol. The catalytic system displayed a stable behavior during 48 h on stream and proved suitable to hydrogenate also fructose, mannose, xylose, and arabinose to the corresponding polyols (yields up to 65 %), thus standing as a more sustainable and economical alternative to Ru-based catalysts for sugar reductive upgrading. [ABSTRACT FROM AUTHOR]

The predominantly insulating nature of zeolites, as many classes of porous catalysts, can severely impair heat transfer and hence their performance in industrial processes. Strategies developed to engineer the thermophysical properties of technical zeolites for fixed-bed applications comprise the use of conductive secondary phases as structured catalyst supports or as inert diluents. However, the impact of integrating conductive additives into composite zeolite bodies (pellets, extrudates, or granules) has not been widely explored. Here, using a transient hot-plate technique to decouple the distinct contributions of porosity, sample hydration, and temperature, we quantify the impact of metallic (copper), ceramic (silicon carbide, aluminum nitride, boron nitride), and carbonaceous (graphite, carbon nanotubes) phases on the thermal conductivity of shaped zeolites at the body and packed-bed scales. The decisive role of particle morphology, dominating over the intrinsic conductivity of an additive, is corroborated through the three-dimensional reconstruction of data acquired by focused ion beam-scanning electron microscopy and X-ray microtomography coupled with in-situ thermographic studies. In particular, the order-of-magnitude improvement evidenced on application of graphite sheets stems from the extended paths of low thermal resistance created in the millimeter-sized catalyst ensemble. Through the identification of structure-property relations, our approach provides new insights into the rational design of composite porous materials with enhanced heat-transfer properties. [ABSTRACT FROM AUTHOR]

CeO 2 is a highly selective catalyst for the partial hydrogenation of alkynes. However, due to its limited H 2 splitting ability, a high operating temperature is required for the reaction, hampering the practical exploitation of this abundant oxide. In this work, we demonstrate that gallium promotes the activity of CeO 2 for the semi-hydrogenation of acetylene and methylacetylene, enabling a reduction of the operating temperature to 373 K, while maintaining an outstanding ethylene and propylene selectivity (80–97%), even in the presence of excess alkene in the feed. Oligomers comprised the main secondary product, while the selectivity to the corresponding alkane did not exceed 2%. The characterization of mixed Ce-Ga oxides reveals that the progressive incorporation of gallium into the ceria structure, forming a solid solution, boosts the oxygen storage capacity and the reducibility of the material. This is ascribed to the facilitated H 2 activation on the Ga-promoted samples, as confirmed by in situ infrared spectroscopy and density functional theory simulations. The interplay between the advantage brought by the decreased barrier for H 2 cleavage and the disadvantage due to the increased number of oxygen vacancies governs the reactivity of the CeGaO x catalysts in alkyne hydrogenation. The composition in the optimal catalyst, containing a molar Ce:Ga ratio of 95:5, was extrapolated to other trivalent cations. Indium incorporated in the ceria lattice favored the low-temperature H 2 activation and led to an activity enhancement that surpassed that of gallium. However, aluminum did not form a solid solution with ceria and caused no effect. This work comprises the first application of promoted cerias in hydrogenation catalysis and may prompt further developments in olefin purification. [ABSTRACT FROM AUTHOR]