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Direct catalytic conversion of CO2 to methanol via renewable hydrogen has emerged as a promising technology among the various CO2 conversion techniques. However, efficient hydrogenation of CO2 using conventional Cu‐ZnO‐based catalysts, which are currently used for industrial methanol production from synthesis gas, remains a challenge due to inefficient energy conversion, poor stability and sluggish CO2 conversion kinetics. As the catalytic activity, stability and methanol selectivity of conventional Cu/ZnO catalysts are still insufficient for industrial applications, novel catalyst formulations using transition metals/metal oxides and supported noble metal nanostructures have emerged. Among them, intermetallic compounds are being explored for their unique electronic and crystalline structures, which can be tailored by controlled, precise, and seamless tuning of interatomic distances, specific arrangements and electronic structure to enhance their stability and activity for the selective hydrogenation of CO2 to methanol. In this context, intermetallic catalysts containing Pd, Cu and Ni combined with metal oxide nanoparticles (ZnO, Ga2O3, In2O3, etc.) have been shown to be more effective than the classical Cu‐ZnO‐Al2O3. This review analyses the progress made in the study of these intermetallic catalysts by analysing different aspects of their preparation, characterization, effects of promoters, support interactions, etc. Future research perspectives are discussed in the context of potential industrial applications of intermetallics for direct methanol production via CO2 hydrogenation. [ABSTRACT FROM AUTHOR]

This document is an editorial discussing the potential of photocatalysis as a technology for purifying air and water. Photocatalysis involves using catalysts to generate Reactive Oxygen Species (ROS) that can break down pollutants. However, there are challenges in scaling up photocatalytic systems for practical use, such as designing efficient reactors, optimizing energy efficiency, addressing environmental and safety concerns, and gaining societal acceptance. The document also highlights specific contributions in the field, including the degradation of pharmaceuticals and the development of new photocatalytic materials. Overall, photocatalysis has the potential to be a transformative solution for environmental remediation, but further research and innovation are needed. [Extracted from the article]

The performance of bifunctional hybrid catalysts based on phosphotungstic acid (H3PW12O40, HPW) supported on TiO2 combined with a Cu-ZnO(Al) catalyst in the direct synthesis of dimethyl ether (DME) from syngas has been investigated. In this work, different types of TiO2 were used as a support to study the effect of changes in the structure of the TiO2 support on the acidity and dispersion of HPW. Various TiO2 supports with different structural and surface characteristics have been studied and the results indicate that: (i) the crystallinity and crystallite size of the primary particles of the HPW units depend on the TiO2 support; (ii) the pore size distribution of the TiO2 support affects the surface segregation of the heteropolyacids; and (iii) changes in the supported HPW acid catalysts do not significantly alter the crystal structure of the CuO and ZnO phases after contact with CZA in bifunctional catalysts. The activity results indicate that the variation in the intrinsic activity of the Cu-ZnOx centers in the bifunctional catalysts for direct DME synthesis is minimal due to the limited alteration of the crystal structure of the centers. [ABSTRACT FROM AUTHOR]

Mn-promoted bulk iron catalysts with a high specific surface area (82–211 m2·g−1) were synthesized by coprecipitation followed by drying under supercritical conditions. The catalysts were tested in the CO2 hydrogenation to valuable C2-C5 hydrocarbons. The Mn-promoted iron catalysts exhibited better textural properties than the bare Fe2O3 catalyst, allowing better dispersion of the active phase, easier reduction and carburization of iron oxides and, consequently, resulting in higher catalytic activity than the bare Fe2O3 catalyst. The best activity results were obtained by catalyst promotion with a very low amount of Mn (Mn/Fe atomic ratio of 0.05). Upon steady state conditions (T = 340 °C, total pressure of 20 bar and H2/CO2 = 3), this catalyst exhibited high CO2 conversion (44.2%) and selectivity to C2-C4 hydrocarbons (68%, olefin to paraffin ratio of 0.54), while the selectivity to C5+ hydrocarbons, CH4 and CO was about 3.2, 38.5 and 5%, respectively. A close correlation was found between catalyst textural properties and CO2 conversion. The most active MnFe-0.05 catalyst exhibited high stability during 72 h of reaction related to a low amount of soft coke formation and catalyst activation through the formation of the χ-Fe5C2 phase during the on-stream reaction. [ABSTRACT FROM AUTHOR]

To achieve sulfur content in gas oil at a near-zero level, new catalysts with improved hydrogenation functions are needed. In this work, new Ni-Mo-Mo hydrodesulfurization (HDS) catalysts supported by Al2O3-CeO2 materials were synthesized to evaluate their efficiency in the reaction of HDS with dibenzothiophene (DBT). Al2O3-CeO2 supports different CeO2 loadings (0, 5, 10 and 15 wt.%) and supported NiMoW catalysts were synthesized by sol-gel and impregnation methods, respectively. The physicochemical properties of the supports and catalysts were determined by a variety of techniques (chemical analysis, XRD, N2 physisorption, DRS UV-Vis, XPS, and HRTEM). In the DBT HDS reaction carried out in a batch reactor at 320 °C and a H2 pressure of 5.5 MPa, the sulfide catalysts showed a dramatic increase in activity with increasing CeO2 content in the support. Nearly complete DBT conversion (97%) and enhanced hydrogenation function (HYD) were achieved on the catalyst with the highest CeO2 loading. The improved DBT conversion and selectivity towards the hydrogenation products (HYD/DDS ratio = 1.6) of this catalyst were attributed to the combination of the following causes: (i) the positive effect of CeO2 in forcing the formation of the onion-shaped Mo(W)S2 layers with a large number of active phases, (ii) the inhibition of the formation of the undesired NiAlO4 spinel phase, (iii) the appropriate textural properties, (iv) the additional ability for heterolytic dissociation of H2 on the CeO2 surfaces, and (v) the increase in Brønsted acidity. [ABSTRACT FROM AUTHOR]

A series of BiVO4/TiO2 nanocomposites with high surface area have been synthesized by a sol–gel method combined with supercritical drying. BiVO4/TiO2 samples with different BiVO4 loadings were synthesized in order to study the effect of this variable on the structuration and development of BiVO4/TiO2 heterojunctions. Bare BiVO4/TiO2 composites are practically inactive for the photoproduction of hydrogen from ethanol under simulated solar light but their photoactivity notably improves after platinum (Pt) deposition. The photocatalytic activity of the Pt–BiVO4/TiO2 composites was determined by the BiVO4/TiO2 ratio that modifies the interfacial charge transfer efficiency between BiVO4 and TiO2 and also by the Pt loading that controls the dispersion and contact of the Pt particles with the composites. In particular, the composite with 0.5 wt% of Pt attained the optimal H2 evolution rate, which is more than 100 times higher than that of the pristine BiVO4/TiO2 composite. The photoactivity of the Pt–BiVO4/TiO2 composites was explained according to the Z-scheme mechanism in which the electrons from the CB of TiO2 reduced H+ to form H2 through the Pt particles preferentially deposited on it. [ABSTRACT FROM AUTHOR]

Palladium oxide nanoparticles of 9 nm stabilized on TiOx subnano-islets (SNI) in monodispersed mesoporous silica nanospheres (MSN) having a stellate morphology are found to be very active for methane combustion. The characterization at various steps of the catalysts elaboration was performed using a panel of techniques including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV-visble reflectance spectroscopy. The catalytic performances were measured from methane combustion light-off experiments showing a remarkably low temperature light-off (T10% ∼ 200 °C) of these particles in comparison to PdO nanophase on 2D TiOx anchors (T10% ∼ 280 °C) or those obtained without TiOx anchors (T10% ∼ 350 °C). The surprising performance of these new catalysts is attributed to a combination of parameters along with the stellate pore morphology likely favorable for high conversion and a diffusion-controlled regime. [ABSTRACT FROM AUTHOR]

The effect of temperature and water/thiourea ratio on the growth, crystallinity and morphological characteristics of CdS nanostructures synthetized by a solvothermal method using ethylenediamine as solvent were studied. The temperature and water/thiourea ratio used in the synthesis determine the surface area, shape, length and degree of crystallinity of the CdS nanostructures obtained. Nanowires of high crystallinity and length were obtained when the solvothermal synthesis was performed at 190°C, while nanorods with lower length and crystallinity were obtained as the solvothermal temperature decreased to 120°C. The change in the water/thiourea ratio affects the crystallinity and length of the CdS nanostructures to a lesser extent than temperature. Nevertheless an increase in the water/thiourea ratio used during the solvothermal synthesis resulted in CdS nanorods with higher crystallinity, lower aspect ratio and lower specific surface area. Textural, structural and surface properties of the prepared CdS nanostructures were determined and related to the activity results in the production of hydrogen from aqueous solutions containing SO32-+ S2- under visible light. [ABSTRACT FROM AUTHOR]

Abstract: An effective and versatile synthetic approach to produce well-dispersed supported intermetallic nanoparticles is presented that allows a comparative study of the catalytic properties of different intermetallic phases while minimizing the influence of differences in preparation history. Supported PdZn, Pd2Ga, and Pd catalysts were synthesized by reductive decomposition of ternary Hydrotalcite-like compounds obtained by co-precipitation from aqueous solutions. The precursors and resulting catalysts were characterized by HRTEM, XRD, XAS, and CO-IR spectroscopy. The Pd2+ cations were found to be at least partially incorporated into the cationic slabs of the precursor. Full incorporation was confirmed for the PdZnAl-Hydrotalcite-like precursor. After reduction of Ga- and Zn-containing precursors, the intermetallic compounds Pd2Ga and PdZn were present in the form of nanoparticles with an average diameter of 6nm or less. Tests of catalytic performance in methanol steam reforming and methanol synthesis from CO2 have shown that the presence of Zn and Ga improves the selectivity to CO2 and methanol, respectively. The catalysts containing intermetallic compounds were 100 and 200 times, respectively, more active for methanol synthesis than the monometallic Pd catalyst. The beneficial effect of Ga in the active phase was found to be more pronounced in methanol synthesis compared with steam reforming of methanol, which is likely related to insufficient stability of the reduced Ga species in the more oxidizing feed of the latter reaction. Although the intermetallic catalysts were in general less active than a Cu-/ZnO-based material prepared by a similar procedure, the marked changes in Pd reactivity upon formation of intermetallic compounds and to study the tunability of Pd-based catalysts for different reactions. [Copyright &y& Elsevier]

Mechanistic aspects of ethanol steam reforming on Pt, Ni, and PtNi catalysts supported on gamma-Al(2)O(3) are investigated from the analysis of adsorbed species and gas phase products formed on catalysts during temperature-programmed desorption of ethanol and during ethanol steam reforming reaction. DRIFTS-MS analyses of ethanol decomposition and ethanol steam reforming reactions show that PtNi and Ni catalysts are more stable than the Pt monometallic counterpart. Ethanol TPD results on Ni, Pt, and NiPt catalysts point to ethanol dehydrogenation and acetaldehyde decomposition as the first reaction pathways of ethanol steam reforming over the studied catalysts. The active sites responsible for the acetaldehyde decomposition are easily deactivated in the first minutes on-stream by carbon deposits. For Ni and PtNi catalysts, a second reaction pathway, consisting in the decomposition of acetate intermediates formed over the surface of alumina support, becomes the main reaction pathway operating in steam reforming of ethanol once the acetaldehyde decomposition pathway is deactivated. Taking into account the differences observed in the mechanism of ethanol decomposition, the better stability observed for PtNi catalyst is proposed to be related with a cooperative effect between Pt and Ni activities together with the enhanced ability of Ni to gasify the methyl groups formed by decomposition of acetate species. On the contrary, monometallic catalysts are believed to dehydrogenate these methyl groups forming coke that leads to deactivation of metal particles.