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There is increasing interest in capturing H2 generated from renewables with CO2 to produce methanol. However, renewable hydrogen production is expensive and in limited quantity compared to CO2 . Excess CO2 and limited H2 in the feedstock gas is not favorable for CO2 hydrogenation to methanol, causing low activity and poor methanol selectivity. Now, a class of Rh-In catalysts with optimal adsorption properties to the intermediates of methanol production is presented. The Rh-In catalyst can effectively catalyze methanol synthesis but inhibit the reverse water-gas shift reaction under H2 -deficient gas flow and shows the best competitive methanol productivity under industrially applicable conditions in comparison with reported values. This work demonstrates a strong potential of Rh-In bimetallic composition, from which a convenient methanol synthesis based on flexible feedstock compositions (such as H2 /CO2 from biomass derivatives) with lower energy cost can be established.

Precisely tuning the nuclearity of supported metal nanoclusters is pivotal for designing more superior catalytic systems, but it remains practically challenging. By utilising the chemical and molecular specificity of UiO-66-NH2 (a Zr-based metal–organic framework), we report the controlled synthesis of supported bi- and trinuclear Cu-oxo nanoclusters on the Zr6O4 nodal centres of UiO-66-NH2. We revealed the interplay between the surface structures of the active sites, adsorption configurations, catalytic reactivities and associated reaction energetics of structurally related Cu-based ‘single atoms’ and bi- and trinuclear species over our model photocatalytic formic acid reforming reaction. This work will offer practical insight that fills the critical knowledge gap in the design and engineering of new-generation atomic and nanocluster catalysts. The precise control of the structure and surface sensitivities is important as it can effectively lead to more reactive and selective catalytic systems. The supported bi- and trinuclear Cu-oxo nanoclusters exhibit notably different catalytic properties compared with the mononuclear ‘Cu1’ analogue, which provides critical insight for the engineering of more superior catalytic systems., The controlled synthesis of novel bi- and trinuclear Cu-oxo nanoclusters supported on UiO-66-NH2 that show notably different catalytic properties in the photocatalytic formic acid decomposition reaction is reported.

Hydrodeoxygenation (HDO) of guaiacol over Ni metal supported on zeolites (H-Beta and H-ZSM-5) with different Si/Al ratios (12.5, 25, 175) and different metal loadings (2.3–23.4 wt%) was investigated in order to elucidate the role of catalyst acidity and the structure of Ni in the HDO reaction. Results show that the deoxygenation activity and product selectivity depend on the choice of support (acidity, pore size), level of metal loading, and reaction conditions. Guaiacol was deoxygenated in the presence of hydrogen with a maximum cyclohexane yield of 76% at a guaiacol conversion level of 100% over 15.7 wt% Ni/Beta-12.5 catalyst. Compared to Ni/ZSM-5 catalysts, Ni/Beta catalysts with mesopores facilitated the formation of coupling products (1,1′-bicyclohexyl). Under differential reaction conditions, we observed a linear relationship between deoxygenation activity and concentration of acid sites. Over catalysts containing small Ni particles, cyclohexane was formed as a result of a consecutive reduction of guaiacol to catechol and cyclohexane. At higher Ni-loading and consequently larger Ni particles, the selectivity towards cyclohexane increases with increased Ni loading. A higher concentration of nickel hydrides compared to smaller Ni sites was observed by H2-TPD and H2-FTIR over larger Ni species, and the nickel hydrides are believed to be crucial intermediates in the hydrogenation reaction. The 15.7 wt% Ni/Beta (Si/Al = 12.5) exhibits a promising HDO activity due to its good synergistic effect of hydrogenation and deoxygenation functions (high concentration nickel hydrides of and acid sites). In addition, based on the product distribution over catalysts containing mainly small Ni species and the Ni nanoparticles, two different reaction pathways were proposed, and the role of the acid sites and metal sites for each reaction route was discussed.

The adsorbate interactions of furans as probe molecules in H-ZSM-5 and H-USY with and without metal ion modification have been revealed by synchrotron X-ray powder diffraction (SXRD). The Rietveld refinements give both qualitatively and quantitatively the spatial arrangements and adsorption geometries of furan and 2,5-dimethylfuran (DMF) on the Bronsted acid sites (BAS) and metal Lewis acid sites (LAS). The bonding information between the adsorbate-framework can also be correlated with thermogravimetric findings. The use of probe molecule-SXRD can be used as a new characterisation tool which can spatially interrogate the acidity of crystalline porous catalysts, leading to molecular engineering of new catalytic systems.

At present, there is no low pressure methanol synthesis from CO2/H2 with high yield despite the presence of an upstream process of aqueous phase reforming (APR) of biomass derivatives on an industrial scale for CO2/H2 production at ca. 2 MPa. This is due to the intrinsic thermodynamics of the system which leads to particularly high CO levels at low pressure through reversed water gas shift reaction (RWGS) for most studied catalysts. Here we report a new Pd@Zn core-shell catalyst that offers a significantly higher kinetic barrier to CO/H2O formation in CO2 hydrogenation to reduce the CO levels but facilitates CH3OH formation at or below 2 MPa with CH 3 OH selectivity maintained at ca. 70% compared to ca. 10% over industrial Cu catalysts. The corresponding methanol yield at 2 MPa reaches 6.1 g methanol/g active metal *h which is comparable to the best reported value among a wide variety of catalysts under 5 MPa. It is thus believed that this active Pd based catalyst opens up a promising possibility for low pressure and temperature methanol production using a renewable biomass resource for fossil-fuel-starved countries.

The influence of catalyst pore size and shape selectivity on the catalytic hydrodeoxygenation (HDO) of biocrude oil has been investigated by comparing the activity of nickel catalysts on the supports of different pore sizes towards model compounds of increasing size. The catalysts (Ni/Beta and Ni/Y) with 3-dimensional structure containing 12 × 12-ring channels show a higher hydrogenation activity for phenanthrene compared to 10 × 10-ring and 12 × 8-ring channel catalysts (Ni/ZSM-5 and Ni/MOR), while only Ni/Y, possessed the largest pore limiting diameter (7.4 A), displays a good hydrogenation activity for pyrene (6.7 A), the model compound with the largest critical diameter studied in this work. While all catalysts display a good HDO activity for guaiacol conversion, the 10 × 10-ring channel catalyst (Ni/ZSM-5) exhibit a lower cyclohexane formation rate compared to catalysts containing 12-ring channels when the residence time was reduced, which could be attributed to the small pore diameter (5.0 A) of ZSM-5 that restricts the diffusion of guaiacol (~4.9 A). In addition, the Ni/Beta and Ni/ZSM-5 were also tested in HDO of biocrude oil. Ni/Beta catalyst displays higher conversion and high yield of cycloalkanes compared to Ni/ZSM-5, which confirms that the selection of catalyst support has a significant influence on the product distribution in HDO of biocrude.

A series of surfactant-free nickel-core and silver-shell (Ni@Ag) nanoparticles encapsulated within the mesopores of SBA-15 were synthesized and tested as catalysts for direct propylene oxidation by molecular oxygen. The influences of temperature, Gas Hour Space Velocity (GHSV) and Ni/Ag ratio on catalytic activity were systematically investigated. Among the prepared samples, Ni1Ag0.4/SBA-15 exhibited the best catalytic performance with selectivity of 70.7% and PO production rate of 4.4 nmol/g/s under 1 bar at 220 °C with GHSV of 192 h−1. High selectivity was attributed to longer Ag-Ag interatomic distance obtained by careful engineering the thickness of Ag shell over preformed Ni nanoparticles. In addition, all prepared new Ni@Ag core-shell catalysts presented excellent stability, which could maintain the conversion and selectivity for at least 10 h. These results suggest that new designs based on Ag surface atoms tailoring might pave the way to highly efficient and robust Ag catalysts for direct propylene oxidation using molecular oxygen as sole oxidant.

An increase in biodiesel production has seen a dramatic increase in the production of glycerol, the main by-product. To maintain biodiesel production as economically viable, processes for valorising the 10 wt% glycerol waste stream need to be developed. The content of this chapter discusses recent work which examines potential catalytic processes for producing value added chemicals using glycerol as a platform chemical. Significant research has focussed on catalytic reactions tailored to selectively convert oxygenates from biological resources to produce valuable chemicals. While homogenous and biological catalytic processes are important, heterogeneously catalysed reactions are considered to be more desirable and potentially more economically viable due to advantages in feedstock processing. The current transesterification process associated with biodiesel production results in a number of contaminants in the glycerol stream, such as free fatty acids and residual catalyst salts, which affects downstream processing. Special emphasis is given to understand how contaminants of various by-products interact with surfaces and identify robust catalysts while examining alternative catalytic processes for producing biodiesel with purer product streams.

Transition metal-doped nickel phosphide nanoparticles with metallic properties are prepared by a simple and facile wet-chemical method. It is shown for the first time that these transition metals: iron, cobalt, manganese, and molybdenum, can atomically substitute nickel in the parent hcp phosphide lattice as a single phase without significant change in its metallic structure and morphology. They are employed as electro- and photocatalysts for hydrogen evolution reaction, which show highly tunable activities dependent on electron filling of their metallic bands and H coverage according to our experimental and theoretical rationalizations. Molybdenum-doped nickel phosphide nanoparticle with lower H coverage exhibits the best hydrogen evolution performance in electrocatalytic hydrogen evolution reaction, which also shows excellent photocatalytic hydrogen production with organic photosensitizer. In addition, cobalt-doped nickel phosphide nanoparticle with higher H coverage with aqueous photosensitizer gives more superior hydrogen evolution rate.

Foreign transition metals are doped into the hexagonal nickel phosphide structure through a simple and facile bottom-up wet-chemical synthesis process via stabilization with oleylamine, trioctylphosphine (TOP), and trioctylphosphine oxide (TOPO): the as-prepared transition metal-doped nickel phosphide nanoparticles show a high level of doping but create no significant distortion of the crystal structure and morphology against pristine nickel phosphide nanoparticles, which exhibit excellent activity in the electrochemical oxygen evolution reaction (OER), having overpotential as small as 330 mV at 20 mA cm−2 with a low Tafel slope value of 39 mV dec−1.

Recently, the increasing level of atmospheric CO2 has been well noted due to its association with global warming, provoking growth in environmental concerns toward the continued use of fossil fuels. To mitigate the concentration of atmospheric CO2, various strategies have been implemented. Carbon capture and utilisation along with renewable hydrogen production to generate raw materials for methanol production are one of the options to turn waste CO2 into useful fuels and chemicals. In the 1960s, the highly active and cost-effective Cu/ZnO/Al2O3 catalyst was developed for the synthesis of methanol from carbon oxides and hydrogen derived from natural gas. Since then, metal nanoparticles and nanocomposites have been extensively investigated and applied to CO2 hydrogenation to methanol. Particularly, bimetallic catalysts have emerged as an important class of catalysts due to their unique properties and enhanced catalytic performances compared to their monometallic counterparts. In this mini review, after giving the introduction of the main motivation for the development of green methanol production via CO2 hydrogenation, we first summarise the recent promising research activities in the fields of generating renewable CO2/H2 sources from carbon capture technologies, green hydrogen production, and biomass-derived CO2/H2 mixtures. Then we provide an overview of the developments in the preparation of some new bimetallic catalysts for CO2 hydrogenation to methanol with emphasis on the synergistic effects and the enhancement of catalytic performances compared to their monometallic counterparts. Finally, the main conclusions are summarised and an outlook is presented for future development in this research area.

With the introduction of Ga 3+ into Cu/ZnO catalyst precursors, a series of catalysts have been prepared using a simple co-precipitation method and tested as catalysts for the synthesis of methanol from CO 2 hydrogenation. It is found that the presence of a small amount of Ga 3+ can facilitate thermal deep reduction of ZnO support to Zn atoms under hydrogen prior to catalysis; hence, a highly active CuZn bimetallic nanoparticle offering catalytic sites is generated. The effect of Ga 3+ incorporation is attributed to the formation of Ga-containing spinel, ZnGa 2 O 4 structure, which creates electronic heterojunction with excess ZnO phase to account for the facilitated reduction of Zn 2+ to Zn 0 to form CuZn when in contact with Cu nanoparticle. A correlation between Zn 0 concentration in the CuZn alloy nanoparticle to the catalytic performance can thus be clearly demonstrated, which shows CO 2 conversion and methanol selectivity can be significantly improved by increasing the Zn 0 content in these hetero-junctioned catalysts.

Ultrathin (1–3 cationic-layers) (CuZn)1–xGax-CO3 layered double hydroxide (LDH) nanosheets were synthesized following the aqueous miscible organic solvent treatment (AMOST) method and applied as catalyst precursors for methanol production from CO2 hydrogenation. It is found that, upon reduction, the aqueous miscible organic solvent treated LDH (AMO-LDH) samples above a critical Ga3+ composition give consistently and significantly higher Cu surface areas and dispersions than the catalysts prepared from conventional hydroxyl-carbonate phases. Owing to the distinctive local steric and electrostatic stabilization of the ultrathin LDH structure, the newly formed active Cu(Zn) metal atoms can be stably embedded in the cationic layers, exerting an enhancement to the catalytic reaction. The best catalyst in this study displayed methanol productivity with a space-time yield of 0.6 gMeOH·gcat–1 h–1 under typical reaction conditions, which, as far as we are aware, is higher than most reported Cu-based catalysts in the literature.

Surfactant-free bimetallic Ni@Ag nanoparticles in mesoporous silica, SBA-15 prepared by simple wet co-impregnation catalyse hydrogenation of dimethyl oxalate to methyl glycolate or ethylene glycol in high yield.

Near quantitative carbon yields of diesel-range alkanes were achieved from the hydrodeoxygenation of triglycerides over Pd/NbOPO4 under mild conditions with no catalyst deactivation: catalyst characterization and theoretical calculations suggest that the high hydrodeoxygenation activity originated from the synergistic effect of Pd and strong Lewis acidity on the unique structure of NbOPO4.

Mesoporous silica SBA-15-supported bimetallic silver–nickel catalysts (Ag–Ni/SBA-15) were prepared by a co-impregnation method for the chemoselective hydrogenation of dimethyl oxalate (DMO) to methyl glycolate (MG). The structure and physicochemical properties of the catalysts were characterized using N 2 adsorption–desorption, X-ray fluorescence spectroscopy, transmission electron microscopy, H 2 -temperature-programmed reduction, UV–vis light diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, fourier-transform infrared spectroscopy and ester temperature-programed desorption. Compared with monometallic Ag or Ni catalyst, the bimetallic Ag–Ni/SBA-15 catalysts exhibited enhanced catalytic performance for the chemoselective hydrogenation of DMO to MG. The optimized Ag–Ni/SBA-15 catalyst with a Ni/Ag atomic ratio of 0.2 presented the highest MG yield and excellent catalytic stability during the hydrogenation of DMO to MG for longer than 140 h. The characterization results suggested that the Ag and Ni bimetallic nanoparticles on the catalyst surfaces likely formed a segregation structure with more Ni species in the core and more Ag in the shell, and electron transfer from Ni to Ag possibly occurred. The interactions between the Ag and Ni species generated more active/adsorption sites and prevented the transmigration of bimetallic nanoparticles during hydrogenation.

It is demonstrated that light elements, including lithium and boron atoms, can take residence in the octahedral (interstitial) site of a Pd lattice by modifying the electronic properties of the metal nanoparticles, and hence the adsorptive strength of a reactant. The blocking of the sub-surface sites to H in the modified materials results in significantly higher selectivity for the partial catalytic hydrogenation of acetylene to ethylene.

Hydrated niobium oxides are used as strong solid acids with a wide variety of catalytic applications, yet the correlations between structure and acidity remain unclear. New insights into the structural features giving rise to Lewis and Brønsted acid sites are presently achieved. It appears that Lewis acid sites can arise from lower coordinate NbO5 and in some cases NbO4 sites, which are due to the formation of oxygen vacancies in thin and flexible NbO6 systems. Such structural flexibility of Nb–O systems is particularly pronounced in high surface area nanostructured materials, including few-layer to monolayer or mesoporous Nb2O5·nH2O synthesized in the presence of stabilizers. Bulk materials on the other hand only possess a few acid sites due to lower surface areas and structural rigidity: small numbers of Brønsted acid sites on HNb3O8 arise from a protonic structure due to the water content, whereas no acid sites are detected for anhydrous crystalline H-Nb2O5.\ud \ud

The conversion of oxygen-rich biomass into hydrocarbon fuels requires efficient hydrodeoxygenation catalysts during the upgrading process. However, traditionally prepared CoMoS2 catalysts, although efficient for hydrodesulfurization, are not appropriate due to their poor activity, sulfur loss and rapid deactivation at elevated temperature. Here, we report the synthesis of MoS2 monolayer sheets decorated with isolated Co atoms that bond covalently to sulfur vacancies on the basal planes that, when compared with conventionally prepared samples, exhibit superior activity, selectivity and stability for the hydrodeoxygenation of 4-methylphenol to toluene. This higher activity allows the reaction temperature to be reduced from the typically used 300 °C to 180 °C and thus allows the catalysis to proceed without sulfur loss and deactivation. Experimental analysis and density functional theory calculations reveal a large number of sites at the interface between the Co and Mo atoms on the MoS2 basal surface and we ascribe the higher activity to the presence of sulfur vacancies that are created local to the observed Co–S–Mo interfacial sites. Converting oxygen-rich biomass into fuels requires the removal of oxygen groups through hydrodeoxygenation. MoS2 monolayer sheets decorated with isolated Co atoms bound to sulfur vacancies in the basal plane have now been synthesized that exhibit superior catalytic activity, selectivity and stability for the hydrodeoxygenation of 4-methylphenol to toluene when compared to conventionally prepared materials.

International audience; Incorporation of CdS quantum dots is shown to significantly promote photocatalytic hydrogen production from water over singlelayer MoS2 in a remote manner via their dispersions on a carbon nanotube as a nanocomposite: the hydrogen evolution rate is found to be critically dependent on the content and structural integrity of the carbon nanotube such that the double-walled carbon nanotube shows superior H2 production to a single-walled carbon nanotube because the inner carbon tubules survive fromthe structural damage during functionalization.

Exfoliated crystalline niobium oxides that contain exposed but interconnected NbO 6 octahedra with different degrees of structural distortion and defects are known to catalyze Brønsted acid (BA), Lewis acid (LA), and photocatalytic (PC) reactions efficiently but their structure–activity relationships are far from clear. Here, three exfoliated niobium oxides, namely, HSr 2 Nb 3 O 10 , HCa 2 Nb 3 O 10 , and HNb 3 O 8 , are synthesized, characterized extensively, and tested for selected BA, LA, and PC reactions. The structural origin for BA is associated mainly with acidic hydroxyl groups of edge-shared NbO 6 octahedra as proton donors; that of LA is associated with the vacant band position of Nb 5+ to receive electron pairs from substrate; and that of PC is associated with the terminal Nb=O of NbO 6 octahedra for photon capture and charge transfer to long-lived surface adsorbed substrate complex through associated oxygen vacancies in close proximity. It is believed that an understanding of the structure–activity relationships could lead to the tailored design of NbO x catalysts for industrially important reactions.

Lindlar catalysts comprising of palladium/calcium carbonate modified with lead acetate and quinoline are widely employed industrially for the partial hydrogenation of alkynes. However, their use is restricted, particularly for food, cosmetic and drug manufacture, due to the extremely toxic nature of lead, and the risk of its leaching from catalyst surface. In addition, the catalysts also exhibit poor selectivities in a number of cases. Here we report that a non-surface modification of palladium gives rise to the formation of an ultra-selective nanocatalyst. Boron atoms are found to take residence in palladium interstitial lattice sites with good chemical and thermal stability. This is favoured due to a strong host-guest electronic interaction when supported palladium nanoparticles are treated with a borane tetrahydrofuran solution. The adsorptive properties of palladium are modified by the subsurface boron atoms and display ultra-selectivity in a number of challenging alkyne hydrogenation reactions, which outclass the performance of Lindlar catalysts.

Incorporation of Zn atoms into a nanosize Cu lattice is known to alter the electronic properties of Cu, improving catalytic performance in a number of industrially important reactions. However the structural influence of Zn on the Cu phase is not well studied. Here, we show that Cu nano-clusters modified with increasing concentration of Zn, derived from ZnO support doped with Ga3+, can dramatically enhance their stability against metal sintering. As a result, the hydrogenation of dimethyl oxalate (DMO) to ethylene glycol, an important reaction well known for deactivation from copper nanoparticle sintering, can show greatly enhanced activity and stability with the CuZn alloy catalysts due to no noticeable sintering. HRTEM, nano-diffraction and EXAFS characterization reveal the presence of a small beta-brass CuZn alloy phase (body-centred cubic, bcc) which appears to greatly stabilise Cu atoms from aggregation in accelerated deactivation tests. DFT calculations also indicate that the small bcc CuZn phase is more stable against Cu adatom migration than the fcc CuZn phase with the ability to maintain a higher Cu dispersion on its surface.

Graphitic-C3N4 is shown for the first time to catalyse photoacetalization of aldehydes/ketones with alcohols to acetals in high yields using visible light under ambient conditions; transient charge separation over the material is effective to catalyse the reaction in the absence of Lewis or Bronsted acids, giving a new green alternative catalyst.

Single layer MoS2 synthesized by exfoliation with Li is demonstrated to take up the dye molecule, Eosin Y, with strong binding affinity via sulfur vacancies. This dye-sensitized single layer MoS2 ensemble exhibits remarkable activity and stability for photocatalytic hydrogen production from water.