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

Abigail Moreno-Martell,Barbara Pawelec,Noelia Mota,Luis Escamilla-Perea,Jose L.G Fierro,Rufino Nava,Rufino M Navarro

doi:10.3390/ma11060948

Abigail Moreno-Martell, Barbara Pawelec + Show 5 more

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https://doi.org/10.3390/ma11060948

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Abstract

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 (Au1+ or Au0), support structural properties and role of modifier on the catalytic activity are discussed.

Highlights

Concerning the support substrates, the Au catalysts supported on the transition metal oxides, such as Fe2 O3, CeO2, or TiO2, were the most extensively investigated because of their direct participation in the CO oxidation reaction mechanism linked with their ability to adsorb or store oxygen at low temperatures, lattice oxygen mobility, stabilization of the Au nanoparticles by inducing a stronger metal-support interaction, and/or the creation of ionic gold species [21]
Catalytic studies combined with characterization techniques demonstrated the key role of the support structural properties in CO oxidation reaction at 20 °C
Materials used as supports were: SBA-16 substrate (3D cage-like structure), SBA-15 (2D channel materials used as supports were: SBA-16 substrate (3D cage-like structure), SBA-15 (2D channel systems), hexagonal mesoporous silica (HMS), and disordered mesoporous silica (DMS-1)

Summary

Introduction

Since the discovery of the high activity of extremely fine gold nanoparticles in a low temperatureCO oxidation [1,2], the use of Au/oxide and inverse oxide/Au catalysts in different reactions have been extensively studied [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]. There is general consensus that the most important effect is related to the availability of low-coordinated sites on the surface of very small gold particles [26]. It is still not clear how the complex nature of the interface between Au and support may influence on the nature of active sites in the CO oxidation reaction [23,24]. On the contrary to metal oxides with variable valence states (Fe2 O3 , CeO2 , or TiO2 , etc.), the SiO2 , Al2 O3 , or MgO substrates are relatively difficult to be reduced

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