CHEN Han-lin, LIANG Xiao-liang, LIU Peng^*

(1. CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;
2. Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou 510640, China;
3. University of Chinese Academy of Sciences, Beijing 100049, China)

Abstract: As volatile organic compounds (VOCs) are important precursors of photochemical ozone (O3) and fine particulate matters (PM2.5), their abatement is an important step in the air pollution control process. Perovskite-type composite oxides have a relatively good application prospective in the thermal catalytic oxidation of VOCs, due to their advantages of good catalytic oxidation activity, controllable chemical composition, and high thermal stability. In this study, a series of different Ca-substituted LaCoO3 products (La1-xCaxCoO3, x？=？0, 0.1, 0.2 and 0.3) were synthesized by using the sol-gel method to investigate the mechanism of constraint on the property of thermal catalytic oxidation of toluene by various Ca-substituted LaCoO3 products. The results show that the Ca-substitution has not resulted in the obvious change of the crystal structure of La1-xCaxCoO3, but has resulted in the significant enhancement of the thermal catalytic activity of La1-xCaxCoO3. In addition, the Ca-substitution has resulted in the decrease of grain sizes but the increases of specific surface areas and pore capacities of the La1-xCaxCoO3. These are beneficial to reduce the gas diffusion resistance. Putting the corresponding temperature (T50) for the 50% toluene degradation and the CO2 generation rate normalized by using specific surface area of sample series at reaction temperature of 200 ℃as the evaluation indicators, the increasing intensities of catalytic activities of the series samples are in following order: LaCoO3 (260 ℃, 0.094 μmol m-2 s-1) < La0.9Ca0.1CoO3 (232 ℃, 0.114 μmol m-2 s-1) < La0.7Ca0.3CoO3 (225 ℃, 0.118 μmol m-2 s-1) < La0.8Ca0.2CoO3 (212 ℃, 0.135 μmol m-2 s-1). With the increase of amount of the Ca-substitution, the catalytic activity of La1-xCaxCoO3 per unit specific surface area initially increased and then slightly decreased. The density of cationic vacancy absorption oxygen of the series samples did not change obviously, but the release rate of lattice oxygen increased significantly. This is favorable for the catalytic oxidation of toluene to CO2 and H2O. With the increase of amount of Ca-substitution, The activity of lattice oxygen enhanced firstly and then decreased, leading to a similar variation trend in catalytic activity among La1-xCaxCoO3 samples.

Keywords: Perovskite-type oxides; Ca-substituted LaCoO3; toluene; thermal catalytic oxidation

ACTA MINERALOGICA SINICA Vol. 40, No.3, 2020, page 330