Highly Uniform Alkali Doped Cobalt Oxide Derived from Anionic Metal-Organic Framework: Improving Activity and Water Tolerance for CO Oxidation

Abstract

A sequence of alkali metal cation-exchanged Co metal-organic frameworks(Co-MOFs), therein after denoted as M@Co-MOF, M=Na+, K+, Rb+, and Cs+, was prepared and used as the precursors to obtain the corresponding alkali doped cobalt oxide(defined as M/Co3O4, M=Na+, K+, Rb+, and Cs+) through calcination under air atmosphere. The cobalt oxide modified by uniform alkali metals exhibited a significant promotion of catalytic activity for CO oxidation. The activity of M/Co3O4 decreased in the order of Cs+>Na+>K+>Rb+. Experimental and theoretical results revealed that the anionic skeleton of Co-MOF could facilely adsorb alkali metal cations and play a crucial role in the formation of highly uniform alkali doped cobalt oxide. The further characterizations, such as temperature-programmed reduction of H2(H2-TPR), oxygen temperature-programmed desorption(O2-TPD), X-ray photoelectron spectroscopy (XPS), and in situ diffuse reflectance infrared Fourier transform(DRIFT) spectra demonstrated that the enhanced catalytic activity is originated from the interfacial electron transfer as well as weakened the Co— O bond strength, which promoted oxygen desorption from Co3O4 and formation of cobalt species with the lower valence state. The Cs/Co3O4 catalyst was maintained for 60 h without deactivation and still showed a high activity in the presence of water.