Integrated Cobalt Oxide Based Nanoarray Catalysts with Hierarchical Architectures: In Situ Raman Spectroscopy Investigation on the Carbon Monoxide Reaction Mechanism

Abstract Herein, a facile strategy for the in situ growth of a Co 3 O 4 ‐based precursor with unique hierarchical architectures oriented diagonal or perpendicular to Ni surfaces is reported. This strategy to prepare grafted ZIF‐67@Co 3 O 4 and MOF‐199@Co 3 O 4 precursor structures is based on a simple hydrothermal synthesis method to obtain the Co 3 O 4 precursor and the subsequent in situ growth of ZIF‐67 and MOF‐199, respectively. The morphologies of the Co 3 O 4 products can be tailored by controlling the solvent polarity and concentration of precipitants. CO is chosen as a probe molecule to evaluate the catalytic performance of the as‐synthesized Co 3 O 4 ‐based oxide catalysts, and the structure–activity relationships are confirmed by using TEM, H 2 temperature‐programmed reduction, X‐ray photoelectron spectroscopy, Raman spectroscopy and in situ Raman spectroscopy, and extended X‐ray absorption fine structure analysis. These analysis results demonstrate that irislike Co 3 O 4 exhibits a high catalytic activity for CO oxidation and contains an abundance of surface defect sites (Co 3+ species) to result in an excellent low‐temperature reducibility, oxygen vacancies and unsaturated chemical bonds on the surface. Moreover, we used in situ Raman spectroscopy to record the structural transformation of Co 3 O 4 directly during the reaction, which confirmed that CO oxidation on the surface of Co 3 O 4 can proceed through the Langmuir–Hinshelwood mechanism (<200 °C) and the Mars–van Krevelen mechanism (>200 °C).