CoOx supported on rice-husk derived SiO2 for styrene combustion: The balance of low temperature activity and thermal stability

In the current work, CoOx/SiO2 was engineered by using porous SiO2-16.3 %C derived from rice husk powder as the support. Pore restriction and Co valence adjustment were achieved respectively by the nanostructures and containing carbon of SiO2-16.3 %C during calcination. To be emphasized, cobalt species were distributed on different location sites of SiO2 by easily controlling the etching time, and their roles in styrene (C8H8) oxidation were disclosed by systematically physicochemical characterizations. Surface exposed CoOx provides Co3+ active sites for C8H8 activation and surface oxygen vacancies are beneficial for gaseous oxygen migration at low temperature, while the buried CoOx not only promote the transfer of lattice oxygen to the surface but also ensure thermal stability. Consequently, a quick channel for oxygen transfer is constructed. The optimised CoOx/SiO2-E4min, composed of 5.58 mmol/gcat surface exposed CoOx and 4.20 mmol/gcat buried CoOx, exhibited the best oxidation performance (TOF250 °C = 4.58 s−1). Moreover, good low-temperature activity and high thermal stability are guaranteed for CoOx/SiO2-E4min. The present study can provide new insights into the site-activity relationship of CoOx-based catalyst, which can also guide the preparation of other highly robust SiO2 supported metal oxide catalysts for VOCs oxidation.