(360n) Elucidating Ethylene Hydrogenation on Site Isolated Intermetallic Catalysts

Selective hydrogenation of certain functionalities in molecules in mixed reactant streams are important in the chemical industry. By targeting specific functionalities unique to varying molecules, it is possible remove impurities in a stream without modifying the relevant reactants before continuing to further downstream processes. For example, selective hydrogenation of acetylene to ethylene can remove the acetylene impurity in ethylene prior to polymerization before the polymerization catalyst can be poisoned by acetylene. Currently in industry, Pd-based catalysts are used to catalyze the selective hydrogenation of acetylene, but the selectivity for ethylene is low.

Bimetallic catalysts are often used to improve selectivity performance as compared to single component catalysts. However, surface segregation of randomly distributed alloys is unavoidable in reaction conditions, which makes selective hydrogenation elusive. Intermetallics compounds can offer tunable site electronics and ensemble structure for selective hydrogenation catalysis. By tuning the composition of intermetallic compounds, it is possible to determine the site requirements needed for different functionalities. Pd-Zn γ-brass intermetallic compounds have been used to isolate the site requirements for ethylene hydrogenation varying from Pd-Zn-Pd to Pd-Pd-Pd by tuning the atomic composition. With these isolated active site ensembles, the ethylene hydrogenation mechanism on the Pd-Pd-Pd active site ensemble was fully enumerated allowing for a full detailed microkinetic modeled to be developed to predict reaction rates, surface coverages, and the degree of rate control. Herein, we expanded our work on Pd-Zn γ-brass intermetallic compounds to include a third coinage metal (M = Cu, Ag, Au) to further tune the active site ensemble to be (Pd-M-Pd), which has been shown to intermediate activity for ethylene hydrogenation when compared to the Pd-Zn γ-brass intermetallic compounds.