In situ pyrolysis of ZIF-67 with cobalt nitrate etching for the catalytic oxidation of methane: promoting surface lattice oxygen and molecular oxygen activation

Abstract

Oxygen species play an important role in the oxidation reactions of CH₄, but the specific mechanisms of different oxygen species and the strategy to enhance oxygen species activity still need to be further investigated. In this work, a Co₃O₄-X catalyst was obtained by pyrolyzing ZIF-67 etched using Co(NO₃)₂. The etching strategy significantly enhanced the activity of the catalyst for the complete oxidation of CH₄. The T₉₀ of Co₃O₄-0.1 was 345 °C, representing a decrease of 90 °C in comparison to the unetched Co₃O₄ catalyst. It was found that mild etching conditions could introduce abundant defect sites into the catalyst and promote the dual activation of surface lattice oxygen and molecular oxygen. The surface lattice was involved in the initial oxidation of CH₄, and the deep oxidation of intermediate products as well as the filling of surface oxygen vacancies depended on the activation of molecular oxygen. The results of temperature programmed experiments and in situ DRIFTS indicated that the promotion of oxygen molecule activation was the key factor for the catalyst performance enhancement. This work has significant implications for understanding the role of oxygen species in catalytic oxidation reactions and for designing more efficient catalysts.