Ultrasound-assisted nanocasting fabrication and excellent catalytic performance of three-dimensionally ordered mesoporous chromia for the combustion of formaldehyde, acetone, and methanol

Rhombohedral chromia with three-dimensionally (3D) ordered mesopore structures were fabricated adopting the ultrasound-assisted nanocasting strategy with 3D ordered mesoporous silica (KIT-6) as hard template and chromium nitrate as metal source. The physicochemical properties of the materials were characterized by the XRD, TGA/DSC, BET, TEM/SAED, XPS, and H₂-TPR techniques, and their catalytic activities were evaluated for the oxidation of typical volatile organic compounds (VOCs), such as formaldehyde, acetone, and methanol. It is found that there were tri-, penta-, and hexavalent chromium ions in the 3D mesoporous structure. Compared to the bulk chromia, the mesoporous chromia materials were larger in surface area (69-124m²/g) and could be reduced at lower temperatures. Among the chromia catalysts, the meso-Cr-400 one obtained after calcination at 400°C showed the best performance. Over meso-Cr-400 at space velocity=30,000mL/(gh), formaldehyde, acetone, and methanol conversions achieved 90% at 117, 124, and 130°C, respectively; the corresponding apparent activation energies were 45.6, 49.7, and 50.8kJ/mol. It is concluded that the ultrasound treatment was a key step to improve the mesoporosity quality of the chromia materials during the nanocasting process, and the factors, such as low-temperature reducibility, 3D ordered mesoporous architecture, and high-surface area, were responsible for the excellent catalytic performance of meso-Cr-400.