Identification of Active Sites for Reverse Water–Gas Shift Reactions on Pt/TiO2 Cluster Catalysts

The reverse water–gas shift (RWGS) reaction is a key process for CO₂ conversion and sustainable fuel production, yet the nature of the active sites on Pt/TiO₂ cluster catalysts remains elusive. Using first-principles microkinetic simulations, we systematically investigated the catalytic behavior of Pt clusters on TiO₂ under operational reaction conditions. We studied three distinct catalytic sites─Pt cluster surfaces, oxygen vacancies (O_V) on TiO₂, and Pt–O_V–Ti interfaces─and revealed that the Pt–O_V–Ti interface exhibited the highest RWGS activity via a redox mechanism. This synergy enhances CO₂ activation and facilitates oxygen reduction more effectively than the isolated O_V on TiO₂, which show 4-fold lower activity. In contrast, CO-covered Pt clusters show minimal CO₂ activation but serve as H₂ dissociation sites, enabling hydrogen spillover to adjacent O_V on TiO₂, thereby sustaining the RWGS process. Kinetic analysis revealed OH reduction to H₂O as the rate-determining step on both interfacial Pt–O_V–Ti and at the O_V on the TiO_2–X support. These findings highlight the pivotal role of the Pt–O_V–Ti interface in driving the RWGS and offer a design strategy for optimizing high-temperature CO₂ hydrogenation catalysts by maximizing the number of interfacial active sites.