Journal of Colloid and Interface Science, Vol.581, 964-978, 2021
Sintering- and oxidation-resistant ultrasmall Cu(I)/(II) oxides supported on defect-rich mesoporous alumina microspheres boosting catalytic ozonation
Supported copper oxides with well-dispersed metal species, small size, tunable valence and high stability are highly desirable in catalysis. Herein, novel copper oxide (CuOx) catalysts supported on defect-rich mesoporous alumina microspheres are developed using a spray-drying-assisted evaporation induced self-assembly method. The catalysts possess a special structure composed of a mesoporous outer layer, a mesoporous-nanosphere-stacked under layer and a hollow cavity. Because of this special structure and the defective nature of the alumina support, the CuOx catalysts are ultra-small in size (1 similar to 3 nm), bivalent with a very high Cu+/Cu-2(+) ratio (0.7), and highly stable against sintering and oxidation at high temperatures (up to 800 degrees C), while the wet impregnation method results in CuOx catalysts with much larger sizes (similar to 15 nm) and lower the Cu+/Cu-2(+) ratios (similar to 0.29). The catalyst formation mechanism through the spray drying method is proposed and discussed. The catalysts show remarkable performance in catalytic ozonation of phenol wastewaters. With high-concentration phenol (250 ppm) as the model organic pollutant, the optimized catalyst delivers promising catalytic performance with 100% phenol removal and 53% TOC removal in 60 min, and a high cyclic stability. Superoxide anion free radicals (center dot O-2(-)), singlet oxygen (O-1(2)) and hydroxyl radicals (center dot OH) are the predominant reactive species. A detailed structure-performance study reveals the surface hydroxyl groups and Cu+/Cu-2(+) redox couples play cooperatively to accelerate O-3 decomposition generating reactive radicals. The plausible catalytic O-3 decomposition mechanism is proposed and discussed with supportive evidences. (C) 2020 Elsevier Inc. All rights reserved.