Effects of Hydrogen and Hydrothermal Pretreatments on a Silica-Supported Copper Catalyst for CO Oxidation: Copper Hydroxy Active Species

As an inert support, silica is appropriate to disperse active copper species to study the intrinsic structure–activity relationship for redox reactions including CO oxidation. Herein, a copper–silica catalyst (3 wt % Cu) was synthesized via a deposition–precipitation method, followed by a hydrogen and/or hydrothermal treatment. The sequential CO oxidation tests over the as-calcined samples show that the hydrothermal treatment effectively promoted the catalyst stability of Cu/SiO2. Hydrogen treatment can significantly increase CO conversion compared to oxygen treatment whose conversion rates are less than 10%. Multiple structural characterizations, including temperature-programmed reduction by hydrogen, temperature-programmed reduction by CO, X-ray absorption fine structure, and in situ diffuse reflectance infrared Fourier transform spectroscopy, were used to precisely determine the active species of small-sized copper catalysts. These analyses identify that the textural structure of silica and the coordination environment of the copper oxide species changed after the hydrothermal treatment, which make the catalysts more stable. The hydrogen pretreatment not only reduced copper oxide but also generated the copper hydroxyl species to make the adsorption of the CO reactant much easier. This work demonstrates the importance of hydrogen pretreatment in enhancing the catalytic activity of copper catalysts and the crucial role of copper hydroxyl groups in CO oxidation reactions for Cu-based catalysts.