Tailoring Co3O4 active species to promote propane combustion over Co3O4/ZSM-5 catalyst

Co3O4 species in Co3O4/ZSM-5 catalyst can be tailored to smaller particle size and higher content of surface lattice O2- and Co3+ species by pre-reduction and pre-oxidation (labeled as Co3O4/ZSM-5-A catalyst), resulting in the enhanced catalytic activity for propane combustion. The 25Co3O4/ZSM-5-A catalyst gives a high reaction rate of 0.379 mu mol gcat-1 s-1, which is over two folds higher than that of the 25Co3O4/ZSM-5 catalyst (reaction rate of only 0.177 mu mol gcat-1 s-1). The higher content and reducibility of surface lattice O2- in the Co3O4/ZSM-5-A catalyst facilitated its activity for propane combustion through the Mars-Van Krevelen mechanism as evidenced by in-situ diffuse reflectance infrared spectra. The 25Co3O4/ZSM-5-A catalyst (Ea = 37.1 +/- 2.9 kJ mol- 1) gives much lower apparent activation energy than 25Co3O4/ZSM-5 catalyst (Ea = 85.5 +/- 6.7 kJ mol-1), suggesting the easier occurrence of propane combustion over the 25Co3O4/ZSM-5-A catalyst. The atmospheres (2% O2 + 0.2% C3H8 + N2; 9% O2 + 0.2% C3H8 + N2; Air) for pre-oxidation process also significantly affect the catalytic activity of the finally obtained catalysts (labeled as 25Co3O4/ZSM-5-A, 25Co3O4/ZSM-5-B, 25Co3O4/ZSM-5-C), which is attributed to their differences in Co3O4 species (nanoparticle size, and the content of surface lattice O2- and Co3+). Besides, the acid sites of ZSM-5 also play important role on the catalytic combustion propane.