Disentangling the Promotional Roles of Interfacial and Alloyed Sites in PtCr Catalysts for CO₂ Hydrogenation

Promotional effects are ubiquitous across catalytic processes involving supported nanoparticles, where additional elements, known as promoters, significantly enhance the catalytic performances (activity, selectivity, and/or stability) of nanoparticles. However, the inherent complexity of catalytic materials, comprising multiple species located both in the bulk and at the surface, makes it difficult to pinpoint the role of promoters at the molecular level. In this study, we disentangle the effect of alloying and interfacial sites in a low-temperature reverse water-gas shift (RWGS) reaction, a key process in the chemical industry, by precisely constructing catalysts featuring narrowly dispersed alloyed PtCr nanoparticles with or without Cr(III) interfacial sites. Notably, we show that a catalyst containing exclusively PtCr alloys, PtCr@SiO₂, displays a substantial increase in catalytic activity compared to monometallic Pt@SiO₂, while having additional Cr(III) interfacial sites (PtCr-Cr_int@SiO₂) further improves the catalyst performance. In situ spectroscopic results reveal that the PtCr alloy facilitates a redox reaction pathway, whereas the presence of Cr(III) interfacial sites greatly facilitates CO₂ adsorption and opens an additional formate-mediated pathway, further accelerating the reaction. These findings highlight the power of well-defined model systems in elucidating the promotional effects at the molecular level.