Effect of alkali/alkaline-earth-metal doping on the Co3O4 spinel structure and N2O decomposition

In this study, a series of alkali/alkaline-earth-metal doped Co3O4 spinel oxides was prepared for N2O catalytic decomposition. It was found that doping with alkali/alkaline-earth-metal ions essentially caused lattice distortion of M–Co3O4, decreased the crystal size, and increased the specific surface area and Co2+ (active sites) amounts. Physicochemical characterization of these as-prepared catalysts was performed, including Raman, XPS, H2-TPR, O2-TPD, and OIE, to indicate that M–Co3O4 has a high lattice oxygen mobility and is prone to form more oxygen vacancies. These oxygen vacancies were involved in N2O decomposition and synergistically promoted the reaction cycle of Co2+ sites. The catalytic activities were ranked in the order of Co3O4 < Mg–Co3O4 < Na–Co3O4 < Ca–Co3O4 < K–Co3O4 < Rb–Co3O4 < Cs–Co3O4, among which the best-performing sample (Cs–Co3O4) had a T90 that was nearly 200 °C lower than that of pure Co3O4, with the complete conversion of N2O achieved at 350 °C. In addition, the effects of alkali/alkaline-earth-metal doping on the lattice distortion, oxygen vacancy formation, N2O dissociation, and oxygen recombination and desorption of M–Co3O4 were verified using DFT calculations.