Structure and catalytic performances of nanocrystalline Co3O4 catalysts for low temperature CO oxidation prepared by dry and wet synthetic routes

The nanocrystalline Co3O4 catalysts were prepared via wet-chemical precipitation and dry-solid-state reaction, respectively. To assess the suitability of such Co3O4 as an oxidation catalyst, CO oxidation was taken as model reaction. The best catalyst was obtained by dry grinding route calcined at 300 °C, showing the 50% conversion of CO at −92 °C, under a stream of normal feed gas containing moisture. Comparing the reaction rate per cobalt oxide mass unit at room temperature (ca. 1.53 mmol g−1 s−1) with the Au-based catalyst in the current literature confirmed the exceptionally high activity of these new materials. The as-synthesized catalysts have been characterized by various techniques in a view of material characterization, as well as to investigate the mechanistic aspects of catalytic reactions. Examination of the surface nature of the materials by X-ray photoelectron spectra (XPS) and temperature-programmed desorption of oxygen (O2-TPD) shows that O− and lattice oxygen (O2−) are the predominant species at the oxidized surface. In addition, a close parallel between the catalytic activity and the concentration of O− oxygen species indicates that a large amount of more mobile and reactive O− species is the main reason for its enhanced CO oxidation activity.

Graphical abstractNanocrystalline Co3O4 prepared by wet-chemical precipitation and dry solid-state grinding route, respectively. The grinding-derived catalyst calcined at 300 °C was satisfying with the 50% conversion of CO at −92 °C, showing superior catalytic ability than that of the precipitation-derived sample (T50 = 35 °C). It was proved that pretreatment in O2 atmosphere of grinding-derived catalysts enhanced the formation of surface reactive oxygen species to react with CO.Figure optionsDownload full-size imageDownload high-quality image (97 K)Download as PowerPoint slideHighlights► Co3O4 prepared by different routes show distinct performances for CO oxidation. ► The grinding-derived catalyst exhibits higher catalytic activity (T50% = −92 °C). ► The process of mechanochemical activation promotes the formation of structural defect. ► The amount of weakly adsorbed O− species plays a key role in CO oxidation on Co3O4.