Promotional effects are ubiquitous across catalytic processes involving supported nanoparticles, where the addition of a second element – promoters – significantly improves the catalytic performance, such as activity, selectivity, and stability. However, the inherent complexity of these catalysts makes it difficult to pinpoint the roles played by promoters at the molecular level. In this study, we prepare well-defined PtCr bimetallic catalysts with or without Cr interfacial Lewis acidic sites via two different surface organometallic chemistry (SOMC) approaches.¹ Extensive characterizations are conducted to confirm the structural difference resulting from the different synthetic approaches. Notably, the catalyst containing exclusively PtCr alloys displays a substantial promotional effect in reverse water gas shift (RWGS) compared to monometallic Pt@SiO₂, while having additional Cr-interfacial sites further improves the catalytic activity. This difference in reactivity was explained by CO₂ adsorption IR and in situ spectroscopic studies, which reveal that PtCr alloy facilitates a redox reaction pathway, whereas an additional formate-mediated pathway takes place at the interface between PtCr alloy and Cr(III) Lewis acid sites. These findings highlight that both PtCr alloy formation and Cr interfacial sites contribute to improving the RWGS activity. The ability to synthesize well-defined bimetallic catalysts with SOMC approaches gives us the opportunity to dissect the roles of different species and establish a better understanding on the structure-activity relationship.

1. Christophe Copéret, Aleix Comas-Vives, Matthew P. Conley, Deven P. Estes, Alexey Fedorov, Victor Mougel, Haruki Nagae, Francisco Núñez-Zarur, Pavel A. Zhizhko, Chemical Reviews. 2016, 116, 323-421.