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

Abstract

Industrial relevant Pd–Ag/Al2O3 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 nPd,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 Pd5–Ag95/Al2O3 in comparison to silver free Pd100/Al2O3 egg-shell catalysts, due to a decrease of green oil and coke formation. The selectivity to C6 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.