Bimetallic PtGa/Al₂O₃ catalysts were prepared by successive impregnation of Pt (0.1, 0.5 and 1 wt.%) onto 5wt. %Ga/Al2O3 and characterized using ICP-OES, XRD, H₂-TPR, XPS, and FTIR. The results suggest that a fraction of Pt is stabilized in an oxidized state (Ptⁿ⁺) even after reduction at 650 °C, particularly at lower Pt loadings, due to strong interactions with Ga³⁺ species and the alumina support. This stabilization enhances Lewis acidity while reducing Brønsted acidity, as it was confirmed by pyridine-FTIR and 3,3-dimethylbut-1-ene isomerization. FTIR analysis under H₂ flow also demonstrates that the presence of Ptn+ enhances the formation of hydride species (Ga-H) suggesting a synergistic effect for H₂ activation. Catalytic tests for propane dehydrogenation reaction (PDH), performed at 575 °C with and without H₂ co-feed, show that bimetallic PtGa/Al₂O₃ catalysts outperform monometallic references for low platinum loading. The 0.1PtGa/Al₂O₃ and 0.5PtGa/Al₂O₃ catalysts achieve the best balance between propane conversion (up to ca. 40 %) and propylene selectivity (> 97 %). In contrast, the 1.0PtGa/Al₂O₃ catalyst, despite higher initial activity, suffers from rapid deactivation with H2 as co-feed due to the presence of metallic Pt⁰. The presence of unreducible Ptⁿ⁺ species and optimized Lewis/Brønsted acidity are identified as key factors for performance in PDH.

This study investigated the catalytic dehydrogenation of propane over uncalcined, calcined, or pre-reduced gallium-supported alumina catalysts. The effects induced by a reductive pretreatment and hydrogen cofeeding (5% and 50% in volume in the gas mixture) on the catalytic performance were evaluated. For comparison, a non-supported gamma-Ga2O3 sample was prepared. The catalysts were characterized by different methods, including XRD, TEM, SEM, NMR, TPR, FTIR, pyridine-FTIR, and the model reaction of 3,3-dimethylbut-1-ene isomerization. It was found that reductive pretreatment improved the propylene production in gas phase but decreased the initial conversion compared to the calcined sample. Hydrogen cofeeding positively impacted the catalytic stability of reduced catalysts, leading to a higher conversion after 240 min and reducing the deactivation of the catalyst up to 70% as the amount of H2 increased in the stream. Moreover, improvement in the carbon balance and reduction of carbon deposited were observed at a high H2 cofeeding ratio. The formation of gallium hydride species during the reduction pretreatment under H2 flowing was clearly identified, but their contribution in the PDH reaction can be considered as negligible compared to the positive effect induced by the decrease in acidity due to the reducing pretreatment.

We first optimized a simple and low-cost polyol-based synthesis route for the preparation of stable and monodisperse sub-10 nm copper nanoparticles. Building on this robust approach, we extended the method to tin and succeeded in producing tin nanoparticles that stabilized in an unconventional α-Sn phase, which is remarkable given the metastable character of this phase under ambient conditions. The resulting α-Sn nanoparticles exhibited excellent resistance to oxidation, together with long-term colloidal stability in air, enabling further processing for potential applications. In both cases, inexpensive commercial precursors and mild conditions (80 °C, aqueous or polyol solvents, ascorbic acid as the sole reducing agent, and no inert atmosphere or additional stabilizers) were employed. The nanoparticles were characterized using TEM, UV-visible spectroscopy, ATR-FTIR, ICP-OES, and XPS.

Oxidative dehydrogenation of hydrocarbons (ODH) converts propane and/or ethane into propylene and/or ethylene, which are important compounds in the chemical industry. Unlike steam cracking, ODH offers a high theoretical conversion to olefins and lower energy consumption. The ODH reaction of propane to propylene was studied using VO X /Al2O3 catalysts prepared by wet impregnation. The reaction conditions were widely varied, with temperatures ranging from 300 to 550 degrees C, the C3/O2 ratio from 1.6 to 3.3, and the vanadium content from 1 to 11 wt %. It was observed that these parameters are key experimental variables that influence the performance of the catalysts in ODH. Catalysts with intermediate vanadium loading exhibit an optimal amount of acidic sites due to the presence of monomeric and polymeric VO X species, resulting in high selectivity toward propylene. Temperature-programmed oxidation analyses showed that coke deposition is proportional to the degree of VO X polymerization.

Ir and IrSn catalysts with different Sn contents (0.5, 0.7 and 0.9 wt%) were prepared using MgAl2O4 supports synthesized using two different techniques (the citrate–nitrate combustion and coprecipitation methods). Both supports, with a spinel structure, presented low acidity and good textural properties. However, the support prepared by coprecipitation had higher specific surface area and pore volume than the one prepared by combustion, which would favor the dispersion of the metals to be deposited. Likewise, during the preparation of the catalytic materials, a very good interaction was achieved between the metals and both supports, which was confirmed by the presence of sub-nanometer atomic clusters in the mono- and bimetallic catalysts. Regarding the catalytic properties, while the monometallic Ir/MgAl2O4 samples lead to a very low conversion of n-butane and a selectivity towards hydrogenolysis products, the addition of Sn to Ir increases the conversion, decreases hydrogenolysis and therefore sharply increases the selectivity towards the different butenes. Catalysts with higher Sn loadings present better catalytic behavior. One of the roles of the Sn promoter would be to geometrically modify the Ir clusters, drastically decreasing the hydrogenolytic activity. This effect, added to the strong electronic modification of the Ir sites by the action of Sn, with probable Ir-Sn alloy formation, is responsible for the high catalytic performance of these bimetallic catalysts.

The conversion of methanol to olefins (MTO, T = 400 and 450 degrees C, WHSV=4 h(-1)) was studied using ZSM5, SAPO34 and amorphous silica-aluminas (different percentages of SiO2, 40%, 60% and 70%) (commercial catalysts) treated or not by HCl. All the catalysts studied present type IV adsorption/desorption isotherms of N-2. The incorporation of HCl decreased the surface area, increased the pore size, the total acidity and the quantity and strength of Br & oslash;nsted acid sites. The increase in the reaction temperature favors the yield of ethylene to a greater extent than that of propylene. The highest light olefins yield was obtained with catalysts containing 60% SiO2 at 400 degrees C. Its good performance is attributed to the combination of adequate acidity, high specific surface area, and small pore size. Catalysts with 40% SiO2 are not suitable for MTO. The addition of HCl to the aluminosilicates cause further deactivation.

Single atom alloy (SAA) clusters formed by anchoring single atoms in small supported host clusters are emerging as catalysts with high performance. In this work, density functional theory (DFT) calculations and ab-initio molecular dynamics (AIMD) simulations are performed to study the stability and the structure evolution of gamma-alumina-supported platinum/copper SAA clusters of sub-nanometer size in hydrogen environment. Due to the strong dynamic nature of both Cu cluster and anchored Pt single atom and their evolving interaction with the support, different isomers with different geometric and energetic properties are predicted. Extensive sampling through AIMD simulations reveals strong effect of hydrogen on the location of Pt single atom and strong variation of the cluster shape, evolving from 3D to concave and planar shapes wetting the alumina support. Interfacial site location of Pt single atom is found to be hydrogen coverage dependent. When the hydrogen coverage increases, the Pt single atom located preferentially at the interfacial site is pulled up by hydrogen atoms toward the upper surface Cu layers. The interaction of Pt/Cu cluster with alumina is predicted to decrease with increasing hydrogen coverage. Finally, electronic structure analysis reveals dramatic effect of hydrogen on the metallic nature of the catalysts.

In the general context of environmental air remediation, copper-oxide-based self-standing porous catalysts (MUB-103(x)) and their reduced homologues (Red MUB103(x)) have been synthesized and studied for the thermoconversion of CO to CO2. Catalytic experiments under dry air conditions reveal that for nonreduced catalysts, increasing the Cu content diminishes the light-off temperature T-50 (corresponding to 50% conversion). The catalytic performances exhibited by the CuO phase dispersed in the silica pores of MUB-103(x) samples are the highest reached to date despite the limitations of the experimental conditions used. After reduction with H-2, the native Red MUB103(x) catalysts offer CO conversion efficiencies significantly more increased, leading to a lowering of the T(50 )values equal to at least 100?. As such, the CO conversion reaches a T-50 value of 160 ? for Red MUB-103(2) with 1.81 wt % Cu; this catalyst displays a specific rate of 8.6 mmolCO gCu(-1) s(-1) at 175 ?, largely higher than those observed to date. The performances of the Red MUB103(2) sample were evaluated for CO oxidation under humid conditions with the addition of 5 vol % water vapor in the feed during four cycles, leading to the same efficiency when compared with that under dry experimental conditions, revealing robustness. A drastic increase in the CO conversion temperature was observed for the 4th cycle, i.e., after 8 h under humid conditions. Analyses of the spent Red MUB-103(2) catalyst after four cycles reveal a slight oxidation of copper, leading to Cu2O species. Importantly, after four cycles, the deactivated catalyst was able to partially recover its performance when reactivated through a 2 h reducing treatment under H2 at 400 ?.

Via integrative chemistry, the first CoOx-SiO2(HIPE) self-standing monoliths of cobalt nano-oxides embedded within silica macro-mesocellular hosts have been prepared. These binary CoOx-SiO2 porous nanostructure (MUB-100(x)) materials present an average of 95% porosity. We found out that high cobalt concentration maintains the hexagonal-2D organization of the mesoscopic voids when applying the thermal treatment at 700 degrees C. Their specific surface areas fall between 400 and 500 m(2) g(-1) when assessed by Ar physisorption measurements. At the microscopic length scale, as revealed through magnetic investigations, the low cobalt content foams MUB-100(1) and MUB-100(2) are made of the amorphous beta-Co(OH)(2) phase coexisting with the silica network, whereas increasing the cobalt concentration during the one-pot syntheses (MUB-100(3) and MUB-(4) materials) favors the formation of the spinel Co3O4 and olivine Co2SiO4 crystalline nanoparticles embedded within silica. When considering the CO oxidation catalytic performance, the MUB-100(4) is able to totally convert the CO flow before 200 degrees C (starting at 125 degrees C) while achieving 50% conversion for a light-off temperature (T-50) of 145 degrees C, revealing the good efficiency of the MUB-100(4) in CO oxidation with which up to 4 catalytic cycles have been performed without disrupting drastically the catalytic performance and reaching thermodynamic stability from cycle 2 to cycle 4.

Low-loaded Pt-based catalysts supported on gamma-Al2O3 (bare or modified by K) were studied for propane dehydrogenation. The alumina support was modified by adding 0.5 and 4 wt.% of K using potassium acetate as precursor. 0.5 wt.% of K is sufficient for suppressing the acidity of the alumina. Ultradispersed Pt supported catalysts (0.1, 0.2 and 0.3 wt.%) were obtained by ion exchange on Al2O3 or Al2O3-0.5 K. During propane dehydrogenation reaction, 0.3 wt.%Pt/Al2O3 strongly deactivates, mainly due to coke deposition. For the same Pt loading, the presence of K strongly decreases this phenomenon without modifying the initial turnover frequencies (TOF). On the series supported on Al2O3-0.5 K, there is no effect of the Pt content on the TOF values showing that whatever the sample, ultradispersed Pt entities present the same activity. Finally, the selectivity towards propene formation strongly depends on propane conversion and seems to be not affected by the change in K and Pt contents.

The development of a bimetallic catalyst for a given reaction requires not only the selection of the appropriate metals M1 and M2 but also the control as far as possible of the distribution of the two metals together and at the support surface in the case of supported catalysts. Preparation methods using redox reactions specifically enable the deposition of a second metal M2 at the surface of monometallic M1 nanoparticles, leading in most cases to core‐shell nanoparticles with strong metal‐metal interactions. Various methods are possible depending on the electrochemical potentials of the species involved: either a direct redox reaction, also named galvanic replacement, or the reduction of an intermediate reducing agent activated at the surface of M1. In this minireview, the fundamental bases of the preparation of bimetallic catalysts by both types of redox reactions and the recent advances in that domain are described.

Biogas upgrading by a catalytic process has been studied in order to obtain syngas using renewable source of methane. This work evaluates the influence of metal dopant (Gd, Sm, and Zr) on the CeO2 structure for the dry reforming of methane over Ni nanoparticle embedded catalysts. The doping with Zr improved the thermal stability of the catalyst, leading to the formation of small Ni nanoparticles, while Ni metal sintering was observed for Ni@CeO2, Ni@CeGdO2, and Ni@SmO2, according to in situ XRD under reduction conditions. The ceria reducibility was affected by the dopant nature, for which the addition of Zr caused distortions in the ceria lattice, promoting the diffusion of oxygen bulk to surface. The doping with Gd and Sm created oxygen vacancies by charge compensation, and the saturation of oxygen vacancies in the fresh samples decreased the degree of Ce reduction, according to TPR results. The larger Ni particles and poor redox behavior for Ni@CeGdO2 and Ni@CeSmO2 were responsible for the high carbon formation on these catalysts during the DRM reaction. The Ni@CeZrO2 catalyst did not present coke formation because of smaller Ni crystallite size and higher ceria reducibility. Therefore, the control of Ni particle size and the high oxygen mobility in the Ni@CeZrO2 catalyst inhibits carbon deposition and enhances the mechanism of carbon removal, promoting the catalyst stability.

Ni-based mesoporous mixed CeO2-Al2O3 oxide catalysts prepared by one pot Evaporation Induced Self Assembly (EISA) were tested in dry reforming of methane. The textural, structural and physicochemical properties of the catalysts were studied by N-2 adsorption-desorption, TEM-EDS, XRD and elemental analysis. The mobility of oxygen in the structure and the redox properties were investigated by OSCC measurements, TPR and in situ DRIFTS. Finally, the post-reaction samples were analyzed by TGA, RAMAN and TEM. The calcined catalysts prepared by EISA method present mesoporous structures with highly dispersed Ni in the form of NiAl2O4 spinel clusters. After reduction, small size metallic Ni particles are observed (< 5 nm). The presence of Ce in the structure interacting strongly with Al2O3 promotes the oxygen mobility and acts as sites for CO2 adsorption, increasing the activity of the catalyst and promoting the carbon removal mechanism. In absence of Ce in the mesoporous alumina support, the activity for carbon gasification is limited and C filaments accumulate inside the reactor. The same behavior occurs with CeO2-Al2O3 oxide prepared by EISA method when Ni is post-im-pregnated because of the presence of isolated larger Ni particles which promotes the decomposition of CH4. Therefore, Ni-based CeO2-Al2O3 catalysts prepared by one pot EISA method exhibited high activity and stability for the dry reforming of methane thanks to both properties which are the confinement of Ni particles and the inhibition of carbon deposition.

A series of Pt/Al2O3 catalysts with uniform Pt particle sizes ranging from 0.95 to 2.62 nm was synthesized using the refilling method to control the growing of Pt nanoparticles and evaluated in propane dehydrogenation. An effect of particle size on the initial propane activity and TOF was demonstrated, the smallest particles being the most active. A geometric model was developed to quantify the surface site concentration for any fcc metal particle size. Comparing the evolution of initial activity for propane dehydrogenation with the different surface site concentrations, it was shown that the active sites of Pt/Al2O3 catalysts corresponded to the combination of corner and edge atoms. To get further, the model was confronted with numerous data extracted from literature demonstrating that it is an efficient tool to predict the structure-activity relationship of fcc metal catalysts and determine the exact nature of active sites for a wide range of reactions and metals. (C) 2021 Elsevier Inc. All rights reserved.

This work investigated the effect of Pt nanoparticles embedded into CeO2 (Pt@CeO2) and CeZrO2 (Pt@CeZrO2) on the carbon removal mechanism for the dry reforming of methane, in comparison to impregnated Pt/CeO2. Morphological and structural characterization by TEM and Raman spectroscopy showed that Pt sintering is suppressed on both structures and the doping with Zr led to the CeZrO2 solid solution formation. A combination of TPR, oxygen isotopic exchange and DRIFTS measurements demonstrated that embedded Pt nanoparticles interact more strongly with ceria than supported Pt, and as a consequence, reactive lattice oxygen becomes more abundant on the catalyst surface, promoting the mechanism of carbon gasification over Pt nanoparticle. The low availability of oxygen species on Pt/CeO2 resulted in higher carbon formation, as demonstrated by TPO analysis. Therefore, the Pt@CeO2 and Pt@CeZrO2 catalysts were more resistant to coke formation due to the higher presence of reactive oxygen species at the metal-support interface, promoting the balance between the rates of carbon formation and carbon gasification over Pt nanoparticle.

The catalytic activity of Ni-bearing clay minerals obtained from natural nickel lateritic ores from Niquela<SIC>ndia, Brazil was evaluated in methane dry reforming reaction at 800 degrees C. These phyllosilicates materials are Ni/Mg smectites with a Ni content of about 23 wt %. The mineralogy and the crystallochemistry of the clay minerals were characterized using X-Ray diffraction and FTIR spectroscopy respectively. Prior to any catalytic test, the clay fraction was extracted from the lateritic ore to concentrate the smectites and remove primary minerals (quartz, pyroxenes) or impurities. In these samples, the Ni is localized in the octahedral layers (structural Ni) and in the interlayer space (exchangeable Ni). To evidence the impact of octahedral or exchangeable Ni, the clays were saturated either with Mg or with Ni. The activity in methane dry reforming is higher with the clay minerals saturated with Ni compared to those saturated with Mg. These results support the hypothesis that both octahedral and exchangeable Ni play a role in the conversion of CH4 and CO2 into H2 and CO. Finally, in situ XRD and TEM analyses were crucial to explain the strong influence of the reduction temperature on the H2 yield. In these natural nickel lateritic ores, the presence of Fe leads to strong interaction with Ni during the reduction step, which depending on its temperature can result in the loss of catalytic activity.

Presently, conventional technologies in water treatment are not efficient enough to completely mineralize refractory water contaminants. In this context, the implementation of catalytic processes could be an alternative. Despite the advantages provided in terms of kinetics of transformation, selectivity, and energy saving, numerous attempts have not yet led to implementation at an industrial scale. This review examines investigations at different scales for which controversies and limitations must be solved to bridge the gap between fundamentals and practical developments. Particular attention has been paid to the development of solar-driven catalytic technologies and some other emerging processes, such as microwave assisted catalysis, plasma-catalytic processes, or biocatalytic remediation, taking into account their specific advantages and the drawbacks. Challenges for which a better understanding related to the complexity of the systems and the coexistence of various solid-liquid-gas interfaces have been identified.

The influence of Ir content on sulphur tolerance for the selective ring opening of decalin was investigated. Ir/SiO2-Al2O3 catalysts (70 wt% and 80 wt% SiO2) were used. In the absence of sulphur, slight differences were observed on the yields according to the metallic content regardless of the support used. Although the results of cyclopentane hydrogenolysis showed that the metallic function acquires importance as the metal content increases, for these metal percentages the acid function limits the rate of decalin opening reaction. Products distribution are strongly modified using decalin with S content compared to pure decalin. The formation of dehydrogenated products is virtually null due to S adsorbed on the metal sites. The support has low influence on the thiotolerance. The results, related to the amount of S per Ir surface atom, showed that for a moderate S content (S/Ir-surf similar to 0.30), 1.5 Ir/Sy appears to be less poisoned than 1Ir/Sy and 2Ir/Sy.

This study proposes the steam reforming of a synthetic biogas stream containing 200 ppm of H2S, carried out in a non-commercial supported Pd-Au/Al2O3 membrane reactor (7-8 mu m selective layer thickness) at 823 K and 150 kPa over a non-commercial Rh(1%)/MgAl2O4/Al2O3 catalyst. This system is able to recover almost 80% of the total hydrogen produced during the reaction and shows good resistance to the H2S contamination, as confirmed by stable methane conversions for more than 400 h under operation. For comparison, the same reaction was carried out in a commercial self-supported Pd-Ag membrane (150 mu m wall thickness), yielding a hydrogen recovery equal to 40% at 623 K and 200 kPa, and presenting stable methane conversions for less than 200 h under operation due to the effect of the H2S contamination. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.