The influence of alumina phases on the performance of the Pd-Ag/Al2O3 catalyst in tail-end selective hydrogenation of acetylene

A series of alumina mixing phases were prepared as catalyst supports by heating commercial gamma-Al2O3 at 900 degrees C, 1000 degrees C, 1050 degrees C, and 1100 degrees C. These supports were then impregnated stepwise and calcined to prepare 0.03 wt% Pd and 0.09 wt% Ag catalysts. The prepared samples were characterized by XRD, BET, NH3-TPD, ZP, CO-TPD, SEM, EDS, and UV-vis DRS, and their catalytic performances were evaluated for selective hydrogenation of acetylene. The phase transformation route of alumina was in: gamma -> (gamma + delta + theta) (900 degrees C) -> (delta + theta) (1000 degrees C) -> (delta + theta) (1050 degrees C) -> (alpha) (1100 degrees C). By increasing the heating temperature between 900 degrees C and 1100 degrees C, the surface area decreased from 244 m(2)/g to 16.4 m(2)/g, the number of acidic sites was decreased, especially for strong acid sites. The acetylene conversion of Pd/Al2O3 was between 15 and 80% and the best one was for the alumina heated at 1050 degrees C. Ag shaped the strong adsorption multi-coordination sites and lowered the strength of adsorption linear active sites. (C) 2015 Elsevier B.V. All rights reserved.