Elucidation of the active phase in PtSn/SAPO-11 for hydrodeoxygenation of methyl palmitate

• PtSn/SAPO-11 shows high hydrodeoxygenation activity and isomerization selectivity.
• The active phase in Sn-promoted Pt/SAPO-11 in ester hydrogenation was identified.
• High hydrodeoxygenation activity is linked to a synergistic effect of Pt–SnO2−x.
• The presence of Pt–Sn alloys improves isomerization selectivity.

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 CC bond cleavage, resulting in a considerable formation of C15 hydrocarbons. The PtSn/SAPO-11 catalyst was more efficient for CO bond hydrogenation, affording higher selectivity to C16 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–SnO2−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 SnO2−x (0 < x < 2), and were mainly present on the periphery of Pt nanoparticles. The occurrence of SnO2−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.

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