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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. [ABSTRACT FROM AUTHOR]

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/Irsurf ∼ 0.30), 1.5 Ir/Sy appears to be less poisoned than 1Ir/Sy and 2Ir/Sy. [ABSTRACT FROM AUTHOR]

Alumina and silica‐alumina supported Ru‐Pt catalysts were evaluated for the ring opening of naphthenes. Pt, Ru, and Ru‐Pt catalysts were prepared by the impregnation of inorganic precursors over γ‐alumina and silica‐alumina supports. The catalysts were evaluated by temperature programmed reduction (TPR), pyridine temperature programmed desorption (TPD), CO‐FTIR, and by test reactions of 33DM1B isomerization, cyclohexane dehydrogenation, cyclopentane hydrogenolysis, and the ring opening of decalin. The strong interaction between the metals (Pt‐Ru) was attributed to their reductions occurring simultaneously. The acidity and strength of the acid sites of the monometallic Ru catalyst were higher than those of the monometallic Pt catalyst. The total acidity (Lewis and Brønsted) and the strength of the acid sites were higher for the silica‐alumina supported catalysts. The silica‐alumina catalysts had 10 times more Brønsted acidity than the γ‐alumina ones and an increased activity and selectivity to decalin ring opening products. Supported monometallic Ru had the best performance for the ring opening reaction. [ABSTRACT FROM AUTHOR]

Abstract: The influence of gallium on the properties of Pt–Re/Al2O3 catalysts used in naphtha reforming was studied. The catalysts were prepared by the coimpregnation method. It was found that the addition of gallium to the Pt–Re/Al2O3 catalyst diminishes its acidity (Brønsted and Lewis). It also produces an inhibition of the metal function, i.e. dehydrogenation and hydrogenolysis activity. Activity tests for n-C5 isomerization showed that gallium addition decreases the total activity of the Pt–Re catalyst but increases its selectivity to i-C5 isomers. The selectivity to low value light gases (C1–C3) is particularly decreased. Catalytic tests for n-C7 reforming showed that addition of gallium increases both catalyst stability and selectivity to aromatics, and decreases the production of light gases. [Copyright &y& Elsevier]

Abstract: The deactivation and regeneration of naphtha reforming PtReGe/Al2O3 and PtReSn/Al2O3 catalysts prepared by catalytic reduction were studied. The extent and nature of coke deposition as determined by TPO were related to catalyst properties such as dispersion, acidity and Cl content. The PtReSn catalyst was the most resistant to coke deactivation. Regeneration was performed by calcination in oxygen at 450°C or ozone at 125°C at variable regeneration times. Regenerated catalysts were evaluated by cyclopentane hydrogenolysis, cyclohexane dehydrogenation and n-heptane reaction tests. Regeneration by oxygen burning-off was the most effective for decoking. However, oxygen combustion produced more segregation of the metal function than ozone regeneration. With the regeneration conditions used in this work, the original acidity of the catalysts cannot be recovered. [ABSTRACT FROM AUTHOR]

Sorbitol hydrogenolysis in aqueous medium was carried out over Ru-Pt based catalysts supported on SiO 2 -Al 2 O 3 and synthetized by three preparation methods (co-impregnation, successive impregnations or a surface redox deposition). These catalysts were characterized by N 2 isothermal adsorption desorption, transmission electron microscopy, H 2 chemisorption, temperature programmed reduction and by the model reaction in gas phase of cyclohexane dehydrogenation. The catalytic performances were compared to those of monometallic catalysts (Pt/SiO 2 -Al 2 O 3 and Ru/SiO 2 -Al 2 O 3 ) under hydrothermal conditions, in a batch reactor at 240 °C under 60 bar H 2 pressure. The main products were poly- and mono-oxygenated compounds in liquid phase and hydrocarbons in gaseous phase. The best yield of hydrocarbons was obtained in the presence of Ru-Pt bimetallic catalyst prepared by successive impregnations, for which a synergetic effect was observed. This effect can be explained by the existence of bimetallic particles of small size favoring an electronic exchange from Ru to Pt. Under the experimental conditions used in this study, it appeared that the reaction pathway of sorbitol transformation was not the same on Pt- or Ru-based catalysts. [ABSTRACT FROM AUTHOR]

Abstract: Pt-based catalysts supported on TiO2 and SIRAL 20 (Al2O3–20wt.%SiO2) were prepared and characterized by H2 chemisorption, FTIR of adsorbed pyridine and 3,3-dimethyl-1-butene isomerization. The catalysts were evaluated for the transformation under aqueous phase of glycerol and 1,2-propanediol at 210°C, under 60bar as total pressure (H2 atmosphere). Under similar conditions, 1,2-propanediol is easier converted than glycerol, indicating that in the glycerol transformation process in aqueous phase, the 1,2-propanediol reactivity is inhibited by the presence of glycerol. This behavior is explained by a strong adsorption of glycerol compared to 1,2-propanediol on the catalyst surface. [Copyright &y& Elsevier]

Graphical abstract Highlights • Platinum-based catalysts with size ranging from 0.91 to 2.41 nm were synthesized. • Pt particle size effect on methylcyclopentane ring-opening product distribution was evaluated. • Over-production of n -hexane was observed for smaller Pt particles. • Dedicated active sites were identified for the three reaction products. • A geometric model accounting for this product distribution was developed and validated. Abstract Hydrogenolysis of methylcyclopentane was studied in the presence of supported platinum catalysts, with particle sizes between 0.9 and 2.4 nm. The distribution of ring-opening products (n -hexane, 2-methylpentane, 3-methylpentane), which are virtually the only products at 573 K, mainly depended on the platinum particle size, with no effect of the methylcyclopentane conversion. This distribution was well described by the selective or non-selective mechanisms previously proposed in the literature except for the smallest particles (d < 1.5 nm), for which a very high yield in n -hexane was observed. A simplified model was developed combining a geometric approach, for counting the fraction of accessible surface of each superficial atom whatever the Pt particle size, to the knowledge of active sites for each product formation, as determined by DFT calculation. It was demonstrated that the sites responsible for n -hexane formation are corners and some edge sites, whereas 2-methylpentane and 3-methylpentane are formed on faces and a part of the edges. [ABSTRACT FROM AUTHOR]

Abstract: A series of platinum catalysts supported over various supports (Al2O3, Al2O3–SiO2 and TiO2) were prepared and characterized by X-ray diffraction, N2 sorption, H2 chemisorption, temperature programmed reduction, FTIR of adsorbed pyridine, 3,3-dimethyl-1-butene isomerization and cyclohexane dehydrogenation. These catalysts were evaluated for aqueous-phase process (APP) of glycerol at 210°C, under N2 or H2 atmosphere (60bar as total pressure). Among the tested catalysts, Pt/TiO2 was the most active and the most selective toward C3 products (propanediols, propanol) which can be further valorized into chemicals. TiO2 was identified as the support leading to the most stable Pt metallic phase, catalytic phase on which the hydrogenation/dehydrogenation reactions take place. The presence of acidic sites brought by the oxide support is necessary for the dehydration reactions (i.e. for Ces), but a too high quantity of these sites can promote the Ceavages via an acidic cracking mechanism. Among the various supported Pt-based catalysts studied in this work, Pt/TiO2 sample appears to be the most promising system for the transformation of polyol in aqueous phase. [Copyright &y& Elsevier]

Abstract: The influence of Sn addition by catalytic reduction method on the Pt-Re/Al2O3 properties for the n-C7 reforming reaction was studied. The Sn addition was performed in different media (HCl and H2O). It was found that trimetallic Pt-Re-Sn/Al2O3-Cl catalysts prepared in H2O or HCl medium present a good interaction between Sn and the catalytically active species (Pt-Re). This strong interaction of Sn with the active phase correlates with the lower hydrogenolytic and dehydrogenating activity of the trimetallic catalysts. Total acidity and Brønsted acidity decrease with the addition of Sn. The catalysts prepared in HCl have both higher Brønsted and total acidity in comparison to those prepared in H2O. In the case of catalysts prepared in HCl medium, the production of C2–C4 gases in the n-C7 reforming reaction also decreases upon Sn addition confirming that the cracking activity decreases when the acidity is decreased. In both trimetallic catalysts series a decrease in the toluene yield can be seen at high Sn contents. The production of toluene depends on the activity in dehydrocyclization reaction. Dehydrocyclization requires sites of lower acid strength than those needed for cracking. The addition of small amounts of Sn (≤0.2wt%) would enable the step of sulfidation of Pt-Re/Al2O3 catalysts to be spared. [Copyright &y& Elsevier]