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 2 to CO at low temperatures. Metal oxides with perovskite structures, particularly, perovskite LaCoO 3 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 1- x Al x O 3 (0 ≤ x ≤ 1), which exhibited high CO production capability and thermal stability under the RWGS-CL process, were developed. Al-substituted LaCo 0.5 Al 0.5 O 3 ( 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 LaCoO 3 ( x = 0; 0.73 × 10 -4 CO mol g -1 min -1 ). Diffuse reflectance infrared Fourier transform spectroscopy studies suggested that an increase in CO 2 adsorption sites produced by the coexistence of Al and Co was responsible for the enhancement of CO production rate. Furthermore, LaCo 0.5 Al 0.5 O 3 maintained its perovskite structure during the RWGS-CL process at 500 °C without significant decomposition, whereas LaCoO 3 decomposed into La 2 O 3 and Co 0 . 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.