Kinetic study of reverse water-gas shift chemical looping on La-based perovskite

Abstract

This was a kinetic study on the reduction reaction with H2(g) and subsequent oxidation reaction with CO2(g) involved in a chemical looping reverse water-gas shift cycle (RWGS-CL) on lanthanum-based perovskites. The influence of particle size, gas flow rate, initial sample mass, temperature, and reactant gas partial pressure were analyzed for each reaction. The kinetic parameters of reduction reactions for LaCoO3 and LaCo0.50Fe0.50O3 were determined through isothermal reactions between 275 and 400 °C and hydrogen partial pressure between 1.67 and 5 pct. These reactions are well described by a contracting volume model. The activation energies found were 90.3 ± 2 and 71.6 ± 4 kJ mol−1, and for ln(A) 10.4 ± 0.4 and 8.3 ± 0.9, for LaCoO3 and LaCo0.50Fe0.50O3 reductions, respectively. Two kinetic regimes were identified for the reaction between reduced LaCo0.50Fe0.50O3 and CO2(g) with formation of CO(g), depending on particle size. The surfaces of the solid reactants serve as potential sites for initiating the conversion reaction due to their higher energy levels compared to those of the bulk material. This accounts for higher conversion rates observed in smaller particle sizes, where the surface-to-bulk ratio is higher. The second stage kinetics was analyzed, and the activation energy was determined to be 148.6 ± 9 kJ mol−1. For LaCo0.50Fe0.50O3, XPS measurements show that only Co changes its oxidation state during the redox reactions.