HYDROGENATION OF ACETYLENE IN ETHYLENE RICH FEEDSTOCKS - COMPARISON BETWEEN PALLADIUM CATALYSTS SUPPORTED ON PUMICE AND ALUMINA

The activity-selectivity patterns of Pd/pumice catalysts are compared with industrial and home prepared Pd/Al2O3 catalysts in the hydrogenat ion of acetylene in ethylene rich feedstocks (front-end and tail-end c uts). The iso-kinetic relationship (IKR) approach and a new mathematic al model, surface site evolution model (SSEM), are employed in this co mparison. Pumice and alumina supported Pd catalysts show different met al redox properties. A similar reaction mechanism is adequate to descr ibe the reaction pathway independently by the catalysts and the gas mi xtures considered. This mechanism involves the formation of surface po lymers during the catalytic reactions and different catalytic sites wh ich are discriminated on the basis of the different steric interaction s of the reagents with the surface species. Although the surface mecha nism appears to be analogous for all the Pd catalysts considered, indu strial Pd/Al2O3 and Pd/pumice catalysts show a different activity-sele ctivity pattern as a consequence of their different electron density a nd ensemble size. (C) 1998 Elsevier Science B.V. All rights reserved.