Pd Ensemble Sites Tuned Local Environment of Cu Catalysts for Matching Propyne Semi-Hydrogenation.

Tailoring local environments of active sites to match targeted configuration of key species is significant for controlling reaction pathways in selective hydrogenations. Herein, differently typed Pd sites are introduced onto Cu catalysts to tune the local environment of Cu sites for controlling the configuration of semi-hydrogenation pathway of propyne hydrogenation used in production of polymer-grade propylene. Detailed structure characterizations demonstrate the controllable construction of Pd single-atom and Pd ensemble sites modified Cu surfaces and PdCu alloy via fine tuning the Pd/Cu ratios. Catalytic tests, kinetics analysis, and temperature-programmed experiments demonstrate that the presence of Pd ensemble sites on Cu surface directly catalyzes the hydrogenation of propyne that occurs on the Cu sites in other cases, and enables a facile activation for hydrogen and simultaneously promotes the desorption of propylene against its hydrogenation. Accordingly, the selectivity to target propylene is up to 95.3% at the full conversion of propyne on the corresponding PdCu catalyst. In contrast, the C─C coupling pathway is quite facile on the Cu surface tuned by single-atom Pd sites, which is similar to that on the pristine Cu sites on the Cu catalyst, and the well-defined Pd─Cu coordination on PdCu alloy catalyst leads to facile over-hydrogenation process.