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

Abstract

A series of alumina mixing phases were prepared as catalyst supports by heating commercial γ-Al2O3 at 900°C, 1000°C, 1050°C, and 1100°C. These supports were then impregnated stepwise and calcined to prepare 0.03wt% Pd and 0.09wt% 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: γ→(γ+δ+θ) (900°C)→(δ+θ) (1000°C)→(δ+θ) (1050°C)→(α) (1100°C). By increasing the heating temperature between 900°C and 1100°C, the surface area decreased from 244m2/g to 16.4m2/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°C. Ag shaped the strong adsorption multi-coordination sites and lowered the strength of adsorption linear active sites.