n-Hexane Hydrogenolysis Behavior of Alumina-Supported Palladium–Platinum Alloys

Abstract

The behavior of alumina-supported palladium-platinum catalysts in the reaction of n-hexane hydrogenolysis was analyzed. The monometallic Pt/Al 2 O 3 catalyst showed much higher activity than the rest of catalysts. The relationship between the catalytic activity of Pd-Pt/Al 2 O 3 catalysts and bulk Pd-Pt composition matched the accepted relation between the surface composition and bulk composition of Pd-Pt, confirming a high surface enrichment in palladium. A linear relation between the apparent activation energy and preexponential factor (compensation effect) suggests that the reaction mechanism is similar for all Pd-Pt catalysts. However, after very high temperature of catalyst reduction (at 600 °C), the behavior of monometallic Pd/Al 2 O 3 catalyst exhibited a considerable departure from the compensation plot, and drastic variations in C 1-C 5 products distribution. Such big changes are rationalized by assuming the transformation of Pd/Al 2 O 3 into Pd-Al alloy, occurring at very high temperature of reduction. Product distribution of n-hexane hydrogenolysis for Pt/Al 2 O 3 differs from that of Pd/Al 2 O 3 , showing more internal bond splitting than a terminal demethylation. However, bimetallic Pd-Pt/Al 2 O 3 catalysts showed even more 'internal bond splitting' character than the Pt/Al 2 O 3. Reasons for this synergism and changes in the behavior of Pd/ Al 2 O 3 catalysts are analyzed in terms of an electronic interaction between metals and alumina support.

Promotional Effect of Pd Addition on the Catalytic Activity of Composite Pt-Pd/AlSBA-15–β Catalyst for Enhanced n-Heptane Hydroisomerization

“…We believe that the answer can be found in the interaction not only between Pt-support and Pd-support but also within active phase components, i.e., between Pt and Pd clusters. The electronic effects were claimed to originate from the formation of electron-deficient Pt species in the bimetallic Pt-Pd particles [61]. However, the precise explanation for the changes in the acidity of Pt-Pd modified catalysts is probably more complicated.…”