N-Hexane Hydrogenolysis Behavior of Alumina-Supported Palladium\u2013Platinum Alloys

Abstract

The behavior of alumina-supported palladium-platinum catalysts in the reaction of n-hexane hydrogenolysis was analyzed. The monometallic Pt/Al2O3 catalyst showed much higher activity than the rest of catalysts. The relationship between the catalytic activity of Pd–Pt/Al2O3 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/Al2O3 catalyst exhibited a considerable departure from the compensation plot, and drastic variations in C1–C5 products distribution. Such big changes are rationalized by assuming the transformation of Pd/Al2O3 into Pd–Al alloy, occurring at very high temperature of reduction. Product distribution of n-hexane hydrogenolysis for Pt/Al2O3 differs from that of Pd/Al2O3, showing more internal bond splitting than a terminal demethylation. However, bimetallic Pd–Pt/Al2O3 catalysts showed even more ‘internal bond splitting’ character than the Pt/Al2O3. Reasons for this synergism and changes in the behavior of Pd/Al2O3 catalysts are analyzed in terms of an electronic interaction between metals and alumina support.Graphic