Identification of the Active and Selective Sites over a Single Pt Atom-Alloyed Cu Catalyst for the Hydrogenation of 1,3-Butadiene: A Combined DFT and Microkinetic Modeling Study

Selective hydrogenation of butadiene to butenes is an important industrial process, and a single Pt atom alloyed with a Cu(111) surface shows superior activity and selectivity for this reaction. By utilizing density functional theory calculations combined with microkinetic modeling, herein, we systematically studied the hydrogenation of butadiene over the Pt/Cu(111) single-atom alloy (SAA) catalyst and identified the active sites and probed the product selectivity at different sites under reaction conditions. Although the structure of the SAA is found stable in vacuum, it is likely that aggregation of surface Pt atoms could be induced upon butadiene adsorption, and the aggregated structure shows lower activity than the single Pt site. In addition, we found that the Cu site shows almost identical hydrogenation activity with the Pt site, while considering the concentration of the surface Pt sites, which gives a good explanation on the experimental observations reported previously that the activity of the Pt/Cu(111) SAA catalyst was unaffected by the occupation of CO at Pt sites. Furthermore, all butene isomers produced would preferably desorb rather than being further hydrogenated to butane at the surface sites considered. Although the selectivity between butene isomers over the single Pt sites is different from that over the Cu sites, the overall SAA catalyst gives the same selectivity trend with the single Pt sites. Our work shows, at the molecular level, how different sites over the Pt/Cu(111) SAA catalyst contribute to the hydrogenation activity and product selectivity