Effect of Calcination Temperature on CO2 Methanation Performance of LaCoO3 Perovskite Catalyst Precursors

Abstract

A series of lanthanum cobaltites (LaCoO3) calcined at different temperatures (600, 700, 800, and 900 degrees C) were investigated as catalyst precursors for the CO2 methanation reaction. Characterization data revealed that samples prepared at low calcination temperatures (i.e., 600 degrees C) exhibited a slightly distorted rhombohedral crystal structure, higher BET surface area, enhanced reducibility, and lower oxygen vacancy concentration as compared with catalysts calcined at higher temperatures. After additional reductive treatment at 400 degrees C following the calcination, the trend in oxygen vacancy concentrations was reversed, although the bulk crystal structure remained unchanged. Results of CO2-temperature-programmed desorption measurements indicated that the reduced samples, especially those calcined at low temperatures, exhibited better CO2 adsorption affinity, which is crucial for CO2 activation. The catalytic activity of the reduced samples was evaluated under both differential and high CO2 conversion conditions. Arrhenius plots showed little variation in the apparent activation energy, confirming XPS results that differences in the catalytic performance were attributed to the number of active sites rather than significant changes in the nature of the active sites. After successful activation of LaCoO3 prior to the reaction, the r-LaCoO3-600 catalyst demonstrated superior activity, achieving 73% CO2 conversion and 95% CH4 selectivity at a space velocity of 12,000 mL CO2 gcat -1 h-1, at 350 degrees C and 40 bar, using a CO2:H2 ratio of 1:4. Additionally, a 72 h stability test of the r-LaCoO3-600 catalyst under the same conditions showed slight deactivation, limited with only approximately 10% decrease in CO2 conversion while maintaining high CH4 selectivity. The methane space-time yield of 5959 gCH4 kgcat -1 h-1 offered by the r-LaCoO3-600 catalyst surpasses those of most of the ABO3-type perovskites. This high performance is linked to its higher surface area, increased oxygen vacancy concentration after H2 reduction, and greater cobalt dispersion post reaction. In contrast, samples calcined at higher temperatures developed larger Co species after reaction, attributed to the lower oxygen vacancy concentration in the reduced catalyst.