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SAPO-11 zeolite-supported PtSn bimetallic catalysts (PtSn/SAPO-11) were prepared using a co-impregnation method for simultaneous selective hydrodeoxygenation of methyl palmitate and isomerization of deoxygenated hydrocarbons. The PtSn catalyst exhibited high isomerization activity and hydrodeoxygenation selectivity, and was superior to the monometallic Pt/SAPO-11 catalyst. The Pt/SAPO-11 catalyst was more active for C C bond cleavage, resulting in a considerable formation of C 15 hydrocarbons. The PtSn/SAPO-11 catalyst was more efficient for C O bond hydrogenation, affording higher selectivity to C 16 hydrocarbons. In the studied PtSn catalyst, the platinum content was constant at 0.3 wt% and the atomic ratio of Sn/Pt was varied from 1 to 3. The result of the catalytic test suggests that it is necessary to control tin surface density in order to obtain a well-balanced Pt–SnO 2− x function and a Pt–Sn alloy as well. The highest performance in the tandem hydrodeoxygenation–isomerization of methyl palmitate was observed at the Sn/Pt ratio of 2; for this catalyst, the isomerization yield obtained at 375 °C was 4 times higher than the monometallic Pt catalyst. After tin addition, Pt nanoparticles were highly dispersed on the support with an average size of ∼4 nm. HRTEM observations and FT-IR studies of CO adsorption indicate that a portion of Sn interacted with Pt, forming Pt–Sn alloys; other Sn species were formed in the form of tin oxides, likely SnO 2− x (0 < x < 2), and were mainly present on the periphery of Pt nanoparticles. The occurrence of SnO 2− x species is crucial for the hydrodeoxygenation pathway; however, excessive addition of tin would block the Pt and PtSn active sites, resulting in a decrease in the catalytic activity. The presence of Pt–Sn alloys is the most remarkable reason for its high isomerization activity. [ABSTRACT FROM AUTHOR]

To obtain diesel fuels with high combustion properties from hydrotreatment of vegetable oils, inhibiting the formation of multibranched isomers (MuBI) is highly desirable. A core@shell structural ZSM-22@SiO 2 zeolite was designed to passivate external acid sites and promote the formation of monobranched isomers (MoBI), which have much higher cetane numbers than MuBI (>85 vs. <60). A series of ZSM-22@SiO 2 zeolites with different amounts of shell silica were synthesized through a facile crystal growth method. External acid sites could be successfully inactivated using the proposed method. Synthesized zeolites were used as supports for bifunctional catalysts in hydrodeoxygenation of methyl palmitate. The effects of the shell silica amount and SiO 2 /Al 2 O 3 ratio of the core zeolite were investigated. The MoBI percentage in total isomers increased from 71% to 95% at a reaction temperature of 300 °C. However, deoxygenation activity and isomerization selectivity decreased gradually with increasing amount of shell silica. Fourier transform infrared spectroscopy of CO adsorption combined with transmission electron microscopy demonstrated that Pt particles exposed more Pt(1 0 0) facets than Pt(1 1 1) facets in silica-coated catalysts. This could be the most likely reason for the decreased deoxygenation activity. The decrease in the number of Brønsted acid sites could be responsible for the lowered isomerization selectivity. Catalytic performance could be enhanced by reducing the SiO 2 /Al 2 O 3 ratio of core ZSM-22. Catalysts with lower SiO 2 /Al 2 O 3 ratios favored smaller Pt particles and exposed more active Pt(1 1 1) corner sites. Additionally, acid sites played an important role in the adsorption of oxygenates. [ABSTRACT FROM AUTHOR]

The effect of the Cs addition on the H2S inhibition and subsequently on the DBT HDS activity over Ru-based catalysts was investigated. In good agreement with a previous study, the HDS activity over a Ru catalyst containing cesium was much higher than that over the same Ru catalyst without cesium. On the other hand, the HDS activity of the Ru&z.sbnd;Cs catalyst was more inhibited by H2S than that of the Ru catalyst at 260 °C. Thus, kinetic parameters were calculated using a Langmuir–Hinshelwood model to determine the mechanism of the H2S inhibition over Ru and Ru&z.sbnd;Cs catalysts. We found that the heats of adsorption of DBT and H2S on the Ru&z.sbnd;Cs catalyst were higher than on the Ru catalyst, indicating that the sulfur-containing species adsorb more strongly on the catalyst containing cesium. Subsequently, the role of cesium in the Ru&z.sbnd;Cs catalyst on the DBT HDS activity was investigated by using 35S-tracer experiments. The results suggested that while the Ru&z.sbnd;Cs catalyst was more inhibited by H2S, the Ru&z.sbnd;S bonds were more stable on this catalyst than on the Ru catalyst. This Ru&z.sbnd;S bond stabilization was responsible for the stabilization of the active phase, which allowed creation of a greater amount of sulfur atoms potentially labile. Thus, that explained the better HDS activity over the Ru&z.sbnd;Cs catalyst than over the Ru catalyst, despite a greater H2S inhibition on the former. [Copyright &y& Elsevier]

Alumina-supported ruthenium–cesium catalysts were presulfided using [35S]H2S pulse tracer method to evaluate their sulfidation state. Subsequently, using these previously 35S-labeled catalysts, HDS reactions of dibenzothiophene (DBT) were performed and the mobility of 35S introduced during the presulfidation stage was investigated. The results showed that the amount of labile sulfur (S0) was much smaller than the total amount of sulfur accommodated on the catalyst (Stotal). DBT conversion and Stotal increased linearly with Ru content. In a second part, labile sulfur amount was also determined under the catalyst working conditions and different results were obtained. Indeed, when the catalysts were marked with [35S] and with [35S]DBT under HDS reaction conditions, the obtained labile sulfur quantities (S0A) were significantly higher than the ones measured during the presulfidation stage (S0). These results showed that the labile sulfur is not formed on RuCs catalysts until the HDS reaction proceeds, which is quite different from that reported before for Mo, Pt, or Pd systems. [Copyright &y& Elsevier]