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

Abstract

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.