Synergistic Combination of Inorganic and Organic Promoters on Palladium Catalysts for Effective Acetylene Partial Hydrogenation

Abstract

Selective acetylene partial hydrogenation in an ethylene-rich stream plays a crucial industrial role in removing acetylene impurities from ethylene produced through hydrocarbon cracking. In this study, we investigated the distinct promotional effects of Ag and amorphous polyphenylene sulfide (Am-PPS) on Pd catalysts. The addition of Ag increased the electron density of Pd and reduced the size of the Pd ensemble, effectively inhibiting undesired side reactions, such as the overhydrogenation of ethylene to ethane and the hydro-oligomerization of acetylene into C-4 and heavier paraffins (green oil). However, alloying with inactive Ag resulted in a reduced number of surface-exposed active Pd atoms, leading to a significant decrease in catalytic activity. On the other hand, surface modification of Pd with Am-PPS was very effective in suppressing ethylene overhydrogenation without compromising acetylene hydrogenation activity. Furthermore, it facilitated the removal of green oil from the catalyst surface before its transformation into coke, significantly retarding the catalyst deactivation. This can be attributed to the rapid cleaning of ethylene and green oil from the Pd surface through the competitive adsorption of the Am-PPS polymer chains. The advantages of each promoter can be synergistically combined through dual promotion. The resulting catalyst exhibited moderate activity, along with exceptionally high ethylene selectivity, and suppressed formation of carbonaceous deposits (both green oil and coke). These findings demonstrate the unique potential to design advanced selective hydrogenation catalysts by leveraging the advantages of both inorganic and organic promoters.