An alumina-coated, egg-shell Pd/α-Al2O3@SiC catalyst with enhanced ethylene selectivity in the selective hydrogenation of acetylene

Abstract

For the selective hydrogenation of acetylene to ethylene, the selectivity of the palladium (Pd) catalyst is crucial. Pd is present as a skin distributed on the surface of Al₂O₃ supports and Pd active sites dispersed on the skin exhibit high activity for acetylene removal, which also inhibits over-hydrogenation of ethylene to ethane and the formation of oligomeric species on the catalyst. Therefore, it is significant to accurately control the distribution range of Pd active sites on the support by a feasible route. Herein, we demonstrate a facile approach to precisely control the Pd active-site distribution range on the support. An α-Al₂O₃ layer was prepared directly on the outside surface of a ring-like SiC substrate by one-step spray-coating, to obtain an egg-shell α-Al₂O₃@SiC support. The thickness of the α-Al₂O₃ layer could be freely tuned from 50 μm to 300 μm. The newly designed α-Al₂O₃@SiC support was used as the catalyst body in the selective hydrogenation of acetylene. As expected, the rational design of a Pd catalyst with this α-Al₂O₃@SiC composite material as the support has the ability to achieve higher ethylene selectivity than a conventional extrusive pellet Pd catalyst. In this work, the ethylene selectivity of the egg-shell Pd–Ag/α-Al₂O₃@SiC catalyst was 16% greater than that of a conventional pellet Pd–Ag/α-Al₂O₃ catalyst when achieving complete removal of acetylene in an ethylene-rich stream.