Selective hydrogenation of highly concentrated acetylene streams over mechanochemically synthesized PdAg supported catalysts

Abstract

The selective hydrogenation of acetylene to ethylene in equimolar acetylene-ethylene streams is challenging due to the extreme exothermicity of the reaction. However, it could be necessary to convert the product stream of plasma-induced methane pyrolysis processes, where large amounts of acetylene are typically formed, to pure ethylene. This would allow a new production pathway for ethylene, but new catalyst materials need to be designed for this specific purpose. To this end, several Pd-Ag bimetallic catalysts supported on α-Al2O3 were obtained by ball milling and conventional wet impregnation, and their performance was compared. In general, higher amounts of Ag in the alloy were beneficial to attain high selectivity levels in the reaction, irrespective of the preparation method used. However, if the synthesis method little affected the selectivity, it greatly affected the stability of the catalysts under reaction conditions. While catalysts prepared via wet impregnation were typically stable for 5-10 h depending on the conditions, ball-milled catalysts exhibited no signs of deactivation for as long as tested (up to 15 h). The best performing formulation of the catalyst was reproduced with a mixed synthesis approach to understand possible underlying effects. This work shows that catalysts prepared by ball milling are the most suitable choice for such a challenging reaction.