Optimizing reverse water gas shift catalysis: Minimizing metal loading and enhancing performance with Pt/ZrO2 catalysts through Rh incorporation

Abstract

In this study, the optimization of catalysts for the reverse water gas shift reaction by minimizing metal loading and enhancing the performance of supported Pt catalysts through Rh incorporation was done. The catalysts were synthesized by the wet impregnation method, in which the metal noble load in bimetallic samples decreased by approximately one-third compared to the reference platinum catalyst, with varying Rh-Pt ratios. In all materials, m-ZrO₂, obtained by the hydrothermal method, was used as support. In the catalytic tests in a continuous packed-bed flow reactor at atmospheric pressure, all samples were active to catalyze CO₂ reduction between 200 and 300 °C. Bimetallic samples, particularly those with an Rh-Pt atomic ratio of 20–80, exhibited superior performance in the RWGS reaction despite their lower metal content. Based on the results of H₂-TPR, FTIR in situ, and XPS, we propose that the enhanced CO production in bimetallic samples compared to Pt/ZrO₂ catalysts can be attributed to Rh increasing the reduction extent of supported Pt. This enhancement facilitates the hydrogenation of bicarbonate species into formate species, which subsequently evolve into Pt⁰-CO and ultimately into CO. Additionally, Rh incorporation enables an alternative pathway for CO generation, where Pt⁰-carbonyls, known for their CO-producing capability, are formed via CO₂ dissociation on the Pt⁰ surface. However, higher Rh concentrations favor the CO₂ methanation rather than the RWGS reaction.