CO production from CO2 via reverse water–gas shift reaction performed in a chemical looping mode: Kinetics on modified iron oxide

Abstract

Carbon monoxide production from carbon dioxide via isothermal reverse water–gas shift chemical looping (RWGS-CL) is studied with a modified iron oxide oxygen carrier material (80wt% Fe2O3–Ce0.5Zr0.5O2). The material is characterized by TEM, XRD and thermogravimetry at temperatures from 750°C to 850°C and gas mole fractions of H2 and CO2 from 0.05 to 0.75, respectively. High temperature and high reactant concentrations favor the oxidation and reduction of the material during repeated redox cycles. The reaction rate of reduction is always faster than that of oxidation applying the same gas concentration of H2 and CO2, respectively. The long term stability of the material is investigated with 500 redox cycles in a plug flow reactor. The material shows gradual deactivation lowering the CO yield during the first 100 redox cycles. After that, a steady state CO yield is reached for the next 400 redox cycles. Deactivation is attributed to surface sintering which results in slower reaction kinetics. TG data was used for a kinetic analysis applying the master plot method. The experimental data for oxidation and reduction indicated reaction mechanisms, which are well described by a reaction order and a geometrical contraction model. After parameter estimation, a good agreement between the model and the TG data was achieved with the reaction order and geometrical contraction model for oxidation and reduction, respectively. The RWGS-CL process can be used for sustainable CO production from CO2 if the energy for the process and for H2 production is supplied by renewable sources.