Enhanced chemical looping CO 2 conversion activity and thermal stability of perovskite LaCo 1- x Al x O 3 by Al substitution

The reverse water-gas shift chemical looping (RWGS-CL) process that utilizes redox reactions of metal oxides is promising for converting CO to CO at low temperatures. Metal oxides with perovskite structures, particularly, perovskite LaCoO 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 LaCo Al O (0 ≤ ≤ 1), which exhibited high CO production capability and thermal stability under the RWGS-CL process, were developed. Al-substituted LaCo Al O ( = 0.5) exhibited a 4.1 times higher CO production rate (2.97 × 10 CO mol g min ) than that of LaCoO ( = 0; 0.73 × 10 CO mol g min ). Diffuse reflectance infrared Fourier transform spectroscopy studies suggested that an increase in CO adsorption sites produced by the coexistence of Al and Co was responsible for the enhancement of CO production rate. Furthermore, LaCo Al O maintained its perovskite structure during the RWGS-CL process at 500 °C without significant decomposition, whereas LaCoO decomposed into La O and Co . 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.