Improving the Catalytic Selectivity of Reverse Water–Gas Shift Reaction Catalyzed by Ru/CeO2 Through the Addition of Yttrium Oxide

This study reports the synthesis, characterization, and catalytic performance of a series of catalysts of Ru supported on CeO2-Y2O3 composites (Ru/CeYX; X = 0, 33, 66, and 100 wt.% Y2O3) for CO2 hydrogenation. Supported material modification (Y2O3-CeO2), by the Y2O3 incorporation, allowed a change in selectivity from methane to RWGS of the CO2 hydrogenation reaction. This change in selectivity is correlated with the variation in the physicochemical properties caused by Y2O3 addition. X-ray diffraction (XRD) analysis confirmed the formation of crystalline fluorite-phase CeO2 and α-Y2O3. High-resolution transmission electron microscopy (HR-TEM) and energy-dispersive X-ray spectroscopy (EDS) elemental mapping revealed the formation of a homogeneous CeO2-Y2O3 nanocomposite. As the Y2O3 content increased, the specific surface area, measured by BET, showed a decreasing trend from 106.3 to 51.7 m2 g−1. X-ray photoelectron spectroscopy (XPS) of Ce3d indicated a similar Ce3+/Ce4+ ratio across all CeO2-containing materials, while the O1s spectra showed a reduction in oxygen vacancies with increasing Y2O3 content, which is attributed to the decreased surface area upon composite formation. Catalytically, the addition of Y2O3 influenced both conversion and selectivity. CO2 conversion decreased with increasing Y2O3 content, with the lowest conversion observed for Ru/CeY100. Regarding selectivity, methane was the dominant product for Ru/CeY0 (pure CeO2), while CO was the main product for Ru/CeY33, Ru/CeY66, and Ru/CeY100, indicating a shift towards the reverse water–gas shift (RWGS) reaction. The highest RWGS reaction rate was observed with the Ru/CeY33 catalyst under all tested conditions. The observed differences in conversion and selectivity are attributed to a reduction in active sites due to the decrease in surface area and oxygen vacancies, both of which are important for CO2 adsorption. In order to verify the surface species catalytically active for RWGS, the samples were characterized by FTIR spectroscopy under reaction conditions.