Elucidating the Role of Support Structure and Acid–Base Properties in Rh-Catalyzed CO2 Conversion via the Reverse Water Gas Shift Reaction

Abstract

The reverse water–gas shift reaction provides a viable pathway for CO2 valorization into CO, a key intermediate for the sustainable synthesis of fuels and chemicals. In this study, Rh catalysts supported on silica and aluminosilicate materials, including SiO2, MCM-41, Silicalite-1, ZSM-5, Zeolite X (13X Molecular Sieve), and kaolin were investigated to elucidate the effects of support structure, microporosity, and acid–base properties on catalytic activity and CO selectivity. Physicochemical characterization revealed that microporous frameworks enhanced Rh dispersion and strengthened metal–support interactions, while a balanced acidity-basicity profile promoted CO2 activation and suppressed secondary methanation pathways. Among the catalysts, Rh/Silicalite-1 and Rh/Zeolite X exhibited superior performance, achieving approximately 60% CO2 conversion greater than 97–99% CO selectivity, and negligible methane formation at 650 °C. Kinetic analysis demonstrated a clear correlation between the apparent activation energy and catalytic performance. Catalysts with lower activation energies, such as Rh/Silicalite-1 and Rh/ZSM-5, exhibited higher catalytic activity, as reflected by greater CO2 conversion, whereas the catalysts with higher activation energy values, namely Rh/Kaolin, Rh/Zeolite X, and Rh/SiO2 were generally associated with enhanced CO selectivity. These findings indicate an activity-selectivity trade-off governed by support-induced modulation of the reaction energetics. Time-on-stream testing confirmed excellent catalyst stability, with negligible deactivation. Overall, optimal RWGS performance was governed by the synergistic interaction between highly dispersed Rh sites and tailored support properties.