Chitosan -NH₂ derived efficient Co₃O₄ catalyst for styrene catalytic oxidation: Simultaneously regulating particle...

In this study, a Co₃O₄ catalyst is synthesised using the chitosan-assisted sol-gel method, which simultaneously regulates the grain size, Co valence and surface acidity of the catalyst through a chitosan functional group. The complexation of the free -NH₂ complex inhibits particle agglomeration; thus, the average particle size of the catalyst decreases from 82 to 31 nm. Concurrently, Raman spectroscopy, hydrogen temperature-programmed reduction, electron paramagnetic resonance spectroscopy and X-ray photoelectron spectroscopy experiments demonstrate that doping with chitosan N sources effectively modulates Co²⁺ to promote the formation of oxygen vacancies. In addition, water washing after catalyst preparation can considerably improve the low-temperature (below 250 °C) activity of the catalyst and eliminate the side effects of alkali metal on catalyst activity. Moreover, the presence of Brønsted and Lewis acid sites promotes the adsorption of C₈H₈. Consequently, CS/Co₃O₄-W presents the highest catalytic oxidation activity for C₈H₈ at low temperatures (R_250 °C = 8.33 μmol g^-1 s^-1, WHSV = 120,000 mL hr^-1∙g^-1). In situ DRIFTS and ¹⁸O₂ isotope experiments demonstrate that the oxidation of the C₈H₈ reaction is primarily dominated by the Mars-van Krevelen mechanism. Furthermore, CS/Co₃O₄-W exhibits superior water resistance (1- and 2- vol% H₂O), which has the potential to be implemented in industrial applications.