Insights into the effective inhibition of green oil formation on the PdMo bimetallic catalyst in the selective hydrogenation of acetylene

Abstract

Acetylene hydrogenation provides a novel route to produce ethylene from coal or natural gas. However, the high concentration of acetylene would lead to considerable oligomerization. This work delves into the PdMo bimetallic system and addresses the critical challenge of catalyst deactivation in high-concentration acetylene hydrogenation. By using a rigorous method of external analysis with the incorporation of volume change before and after the reaction, the Pd/Mo composition dependence (Pd/Mo=3:1, 1:1 and 1:3) is examined, and a proper addition of Mo (Pd/Mo=1:1) can simultaneously maintain the hydrogenation activity as well as alkene selectivity, and significantly suppress the green oil selectivity compared with Pd/SiO2. The surface modification by Mo induces a Mo(δ⁺)-Pd(δ⁻) dual-site synergistic effect evidenced by density functional theory (DFT) calculations, and the elementary reaction pathways of hydrogenation and C2 dimerization are compared over the Pd(111) and Pd1Mo1(111) model surfaces. Consistently with experimental results, the bimetallic structure could effectively suppress the 1,3-butadiene (green oil precursor) formation. Therefore, the stability could be greatly enhanced over the PdMo bimetallic catalyst. This combined experimental and theoretical study reveals the underlying mechanism of the Mo modification in the inhibition of oligomerization, and provides guidance for efficient and stable catalyst design in the novel production of ethylene from a high-concentration acetylene feed.