CO Oxidation at 20 °C on Au Catalysts Supported on Mesoporous Silica: Effects of Support Structural Properties and Modifiers.

In this work we report the effects of support structural properties and its modification with some metal oxides modifiers on the catalytic behavior of Au catalysts in the total CO oxidation at 20 °C. Au catalysts were supported on mesoporous silica materials (MSM) having different structural properties: Channel-like (SBA-15), cage-like (SBA-16), hexagonal (HMS), and disordered (DMS-1) structures. The effect of the modifier was evaluated by comparison of the catalytic response of the SBA-15-based catalysts modified with MgO, Fe₂O₃, TiO₂, and CeO₂. The chemical, structural, and electronic properties of the catalysts were investigated by a variety of techniques (metal content analysis by ICP-OES, N₂ physisorption, XRD, UV-vis DRS, DRIFTS of adsorbed CO and OH regions, oxygen storage capacity (OSC), HR-TEM, and XPS). The activity of calcined catalysts in the CO oxidation reaction were evaluated at steady state conditions, at 20 °C, atmospheric pressure, and when using, as feed, a 1%CO/1%O₂/98% gas mixture. The work clearly demonstrated that all Au catalysts supported on the mesoporous silicas modified with metal oxides were more active than the Au/SBA-15 and Au/MgO reference ones. The support structural properties and type of dopant were important factors influencing on the catalyst behavior. Concerning the support textural properties, it was found that the HMS substrate with the wormhole-structure offers better porosity and specific surface area than their silica counterparts having channel-like (SBA-15), cage-like (SBA-16), and disordered (DMS-1) mesoporous structures. Concerning the effect of modifier, the best catalytic response was achieved with the catalysts modified with MgO. After activation by calcination at 200 °C for 4 h, the Au/MgO/HMS catalyst exhibited the best catalytic performance, which was ascribed to the combined effects of the best structural properties, a large support oxygen storage capacity and homogeneous distribution of gold particles on the support (external and inner). Implications of the type of active sites (Au or Au⁰), support structural properties and role of modifier on the catalytic activity are discussed.