Effects of H2 and CO Concentrations on the Performance of PdAg/Al2O3 Catalysts in Selective Hydrogenation of Acetylene

This study compares Pd/Al2O3 and Pd1Ag5/Al2O3 catalysts for the front-end selective hydrogenation of acetylene, with a focus on how their catalytic performance correlates with the H2 : C2H2 ratio and CO concentration. A combination of physicochemical characterization methods demonstrated that single-atom Pd1 sites isolated from one another by Ag atoms were formed on the surface of the bimetallic sample. The acetylene hydrogenation rate increased with the H2:C2H2 ratio, a correlation that was more pronounced for Pd/Al2O3 than for Pd1Ag5/Al2O3. This was quantified by the apparent reaction order with respect to hydrogen (n(H2)), which was 1.5 and 1.0, respectively. While increasing the H2 : C2H2 ratio had a significant adverse impact on selectivity toward the target product, this was effectively counteracted by the addition of CO to the reaction mixture. Furthermore, promoting the Pd/Al2O3 catalyst with Ag eliminated any thermal runaway effect and facilitated precise temperature control.