Surface modification of ACo2O4 (A = Mn, Ni, Zn) spinel catalysts by H2/Ar-plasma etching: improving oxygen vacancies and low-valence state species to promote toluene combustion

In this work, a series of ACo2O4 (A = Mn, Ni, Zn) spinel catalysts were prepared by a sol-gel method, which were further promoted through H2/Ar plasma treatment. Activity test results have shown that the plasma-treated MnCo2O4-p exhibits excellent low-temperature activity (T90 = 218 °C). The XPS, H2-TPR, 18O2-TPSR-MS, EPR and NH3-TPD results have verified that H2/Ar plasma treatment can raise the proportion of low-valent metal ions, thus facilitating the synchronized generation of abundant surface oxygen vacancies, as well as active oxygen (O2-, O22-) and acidic sites beneficial to the reaction. The in-situ DRIFTS and toluene-TPSR-MS results have demonstrated that though plasma treating does not change the reaction pathway, the catalysts become more conducive to the ring-opening of the key benzoic acid intermediates, thus promoting toluene deep oxidation. This work provides a feasible strategy for rational design of high-efficiency catalysts in low-temperature toluene combustion.