Copper doped ceria catalyst prepared by reverse microemulsion method for thermocatalytic conversion of carbon dioxide via reverse water gas shift

Abstract

High surface area CeO2/Al2O3 nano-catalysts were synthesized via the reverse microemulsion method and evaluated for reverse water gas shift. The effect of the active phase dispersion on the CeO2 nanoparticle growth was investigated via X-ray diffraction and gas adsorption. The 47.9wt% CeO2/Al2O3 catalyst showed complete selectivity to CO generation while attaining nearly equilibrium values for CO2 conversion at 600 °C and 8,000 mL/(g h). As compared to bulk CeO2, nanoparticle growth in the CeO2/Al2O3 catalyst was hindered significantly, resulting in a relatively stable catalytic performance, similar to that of the bulk CeO2. Our findings reveal that the reverse microemulsion synthesized Al2O3 support significantly decreases CeO2 nanoparticle growth and agglomeration. This reduction in nanoparticle sintering contributes to the enhanced catalytic performance and stability, facilitating efficient CO2 reduction. Copper-doped ceria (CuCeO2) catalysts with 0-26.5 Cu/(Cu+Ce) at% were synthesized via the reverse microemulsion method. X-ray diffraction analysis of freshly synthesized and spent (post-reaction) catalysts showed no separate phase of copper or copper oxide, indicating that Cu was incorporated into the CeO2 lattice, replacing Ce. Temperature-programmed desorption experiments showed that the activation energy of CO2 desorption increased for higher Cu loadings, indicating stronger CO2 adsorption. This phenomenon was attributed to the enhanced formation of oxygen vacancies due to Cu doping. X-ray photoelectron spectroscopy further confirmed the enhanced generation of oxygen vacancies due to Cu incorporation. The catalytic performance showed that all catalysts were 100% selective to CO generation, with higher Cu loadings resulting in CO2 conversion close to equilibrium values. The activation energy of the reaction, determined through reaction tests, exhibited a linear relationship with the activation energy of CO2 desorption. The relationship between these two energy barriers is explored, providing valuable insights into the catalytic mechanisms for RWGS.