Enhanced chemical looping CO2 conversion activity and thermal stability of perovskite LaCo1−xAlxO3 by Al substitution†
Abstract
The reverse water–gas shift chemical looping (RWGS-CL) process that utilizes redox reactions of metal oxides is promising for converting CO2 to CO at low temperatures. Metal oxides with perovskite structures, particularly, perovskite LaCoO3 are promising frameworks for designing RWGS-CL materials as they can often release oxygen atoms topotactically to form oxygen vacancies. In this study, solid solutions of perovskite LaCo1−xAlxO3 (0 ≤ x ≤ 1), which exhibited high CO production capability and thermal stability under the RWGS-CL process, were developed. Al-substituted LaCo0.5Al0.5O3 (x = 0.5) exhibited a 4.1 times higher CO production rate (2.97 × 10−4 CO mol g−1 min−1) than that of LaCoO3 (x = 0; 0.73 × 10−4 CO mol g−1 min−1). Diffuse reflectance infrared Fourier transform spectroscopy studies suggested that an increase in CO2 adsorption sites produced by the coexistence of Al and Co was responsible for the enhancement of CO production rate. Furthermore, LaCo0.5Al0.5O3 maintained its perovskite structure during the RWGS-CL process at 500 °C without significant decomposition, whereas LaCoO3 decomposed into La2O3 and Co0. In situ X-ray diffraction study revealed that the high thermal stability was attributed to the suppression of phase transition into a brownmillerite structure with ordered oxygen vacancies. These findings provide a critical design approach for the industrial application of perovskite oxides in the RWGS-CL processes.
- This article is part of the themed collection: Dalton Transactions HOT Articles