Surface properties and performance of Ag- and Cu-promoted Pd/Al2O3 prepared by surface redox method in the selective hydrogenation of acetylene

摘要

The performance of Ag- or Cu-promoted Pd/Al2O3 catalysts in the selective hydrogenation of acetylene was compared for two types of catalysts that had been prepared by adding the promoter either by a surface redox method (SRM) or incipient wetness impregnation (IWI). Catalysts prepared by SRM showed higher acetylene conversions and ethylene selectivities than those prepared by IWI in both cases of Ag- and Cu-promotion. XPS and ethylene-TPD results indicated that the promoters introduced by SRM were in intimate contact with the Pd surface. CO-IR observation showed that Cu added by SRM was deposited preferentially on the low-coordinated sites of Pd, which are known to be responsible for the lowering in the ethylene selectivity. Consequently, Pd-Cu SRM exhibited improved ethylene selectivities even with small amounts of Cu compared with the case of Pd-Ag IWI