Conversion of CO2(g) to CO(g) via reverse water–gas shift cycle on mixed cerium/praseodymium oxides at 500 °C

Abstract

Reactions of cerium/praseodymium oxides under hydrogen atmospheres, and subsequently, carbon dioxide, involved in chemical looping reverse water–gas shift cycles (RWGS) at 500 ◦C were investigated by in-situ high- temperature X-ray powder diffraction, FTIR and thermogravimetry. The RWGS cycle is a critical chemical process for converting carbon dioxide into useful products, such as carbon monoxide, which can be used to synthesize fuels and chemicals. The mixed oxides exploit the redox properties of Ce and Pr, which can switch between oxidation states, making them suitable for oxygen incorporation and release during the RWGS process allowing them to react with H2(g), and subsequently with CO2(g), promoting their interaction and conversion into H2O(g) and CO(g). Pure cerium and praseodymium oxides showed poor CO2(g) conversion efficiency.However, we found that nanometric Ce/Pr mixed oxides exhibit enhanced oxyreduction performance suitable for this application, particularly with a composition of 75 mol% Ce and 25 mol% Pr, significantly improved performance, achieving an average CO(g) yield of 0.6 mmol/(goxide.cycle) and a maximum rate of 0.26 mmol/(goxide.min). Pr enhances oxygen mobility in CeO2, which improves the dissociation of C═O bonds in CO2(g). Thisis because the remaining oxygen atoms are delivered more quickly to the support sink, thereby cleaning up the vacant sites generated during the reduction step. These findings suggest that Ce/Pr mixed oxides are highly effective for CO2(g) conversion to CO(g) via RWGS cycle, offering a potentially viable option for industrial application.