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

Herein, a facile strategy for the insitu growth of a Co3O4-based precursor with unique hierarchical architectures oriented diagonal or perpendicular to Ni surfaces is reported. This strategy to prepare grafted ZIF-67@Co3O4 and MOF-199@Co3O4 precursor structures is based on a simple hydrothermal synthesis method to obtain the Co3O4 precursor and the subsequent insitu growth of ZIF-67 and MOF-199, respectively. The morphologies of the Co3O4 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 Co3O4-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 insitu Raman spectroscopy, and extended X-ray absorption fine structure analysis. These analysis results demonstrate that irislike Co3O4 exhibits a high catalytic activity for CO oxidation and contains an abundance of surface defect sites (Co3+ species) to result in an excellent low-temperature reducibility, oxygen vacancies and unsaturated chemical bonds on the surface. Moreover, we used insitu Raman spectroscopy to record the structural transformation of Co3O4 directly during the reaction, which confirmed that CO oxidation on the surface of Co3O4 can proceed through the Langmuir-Hinshelwood mechanism (<200 degrees C) and the Mars-vanKrevelen mechanism (>200 degrees C).