Efficient Spinel Nanoparticle Catalysts ACo2O4(A?=?Cu, Ni, Mn) for Catalytic Oxidation of Toluene: Cation Substitution Effects

Co(2)O(4)has been applied in several catalytic fields as a favorite catalyst. However, its performance is still not enough to replace noble metal catalysts in the catalytic oxidation of toluene. Modifications are needed to enhance its activity. Herein, a series of spinel nanoparticle catalysts ACo(2)O(4) (A = Cu, Ni, and Mn) were synthesized by a simple template-free solvothermal process and applied to toluene oxidation. A fixed-bed reactor was used to investigate the catalytic activity. The CuCo(2)O(4)catalyst showed the best activity with T50 = 225 degrees C and T90 = 239 degrees C, which was much better than the other two catalysts. This dem-onstrated that tetrahedral A-site cation is crucial in determining the activity of ACo(2)O(4) catalysts. Higher Co3+ concentration (Co3+/Co2+ = 1.96), more surface-adsorbed oxygen species (Oads/O = 36.67%), and enhanced low-temperature reducibility, which are outcomes of cation substitution, are fundamental causes of efficient activity. In addition, the CuCo2O4 catalyst showed good long-term stability after 30 h of reaction, and the toluene conversion rate remained above 95% at 250 degrees C, which has considerable potential for practical application.