Subnanometric Pt clusters dispersed over Cs-doped TiO2 for CO2 upgrading via low-temperature RWGS: operando mechanistic insights to guide an optimal catalyst design

Abstract

The RWGS reaction is gathering momentum as an effective route for CO₂ valorisation and given its endothermic nature the challenge lies in the design of active low-temperature catalysts. Herein we have designed two catalysts based on subnanometric Pt clusters providing effective CO₂ conversion and, more importantly, high CO selectivity in the low-temperature range. The impact of Cs as a dopant in the catalyst's formulation is crucial leading to full selectivity at 300 °C. The reaction mechanisms for the studied systems namely Pt/TiO₂ and PtCs/TiO₂ are significantly different due to the presence of the alkali promoter. The presence of Cs neutralises the hydroxide groups of the TiO₂ surface, changing the reaction pathway. The Pt/TiO₂ catalyst follows a redox mechanism where CO₂ dissociates to CO in the oxygen vacancies, and then these vacancies are recovered by the migration of H₂ by spill over phenomena. On the other hand, the Cs doped catalyst has two possible mechanism pathways: the (ii) formyl/acyl pathway, where –CHO species are formed and, depending on the reaction conditions, evolve to CO gas or oxygenated compounds, and (ii) frustrated Lewis pair (FLP) assisted CO₂ reduction route, in which the FLP induces the heterolytic dissociation of H₂ and the subsequent hydrogenation of CO₂ to CO. The latter route enabled by Cs-doping combined with the subnanometric Pt domains seems to be responsible for the excellent catalytic behaviour leading to fully selective low-temperature RWGS systems and thus unlocking new possibilities for less energy demanding CO₂ valorisation units based on RWGS.