Long-Time Stability vs Deactivation of Pd–Ag/Al2O3 Egg-Shell Catalysts in Selective Hydrogenation of Acetylene

Industrial relevant Pd–Ag/Al 2 O 3 egg-shell catalysts with varying Pd/Ag mole ratios were prepared, characterized (CO chemisorption, DRIFTS, EPMA, STEM, coupled with EELS and EDX, as well as TPR) and tested for selective hydrogenation of acetylene under tail-end conditions. Characterization suggests a reduction of the total number of Pd surface atoms n Pd,surf as well as an isolation of large Pd ensembles. The effect of silver addition on byproduct formation and deactivation behavior was investigated, representing a higher long time stability of Pd 5 –Ag 95 /Al 2 O 3 in comparison to silver free Pd 100 /Al 2 O 3 egg-shell catalysts, due to a decrease of green oil and coke formation. The selectivity to C 6 compounds is a fundamental indicator for long-term stability of palladium catalysts that is often overlooked in the literature. Furthermore, this study implicates selective hydrogenation of acetylene as a structure sensitive reaction originating from a geometric effect.