Kinetic mechanism of CO oxidation on gold catalyst supported on TiSBA-15 previously treated in a hydrogen atmosphere

Abstract The CO oxidation by supported gold catalysts on TiSBA-15 was investigated experimentally as well as via construction of a kinetic model. Functionalization of the siliceous mesoporous SBA-15 with titanium (IV) isopropoxide (Si/Ti: 20, 40 and 80 M ratios) was carried out to prepare gold mesoporous catalysts with 2.5–2.9 Au wt.% through the deposition–precipitation method assisted by urea. The samples were characterized by X-ray diffraction, N2 adsorption–desorption and TEM. The gold amount was determined by chemical analysis (ICP-OES). Before the CO oxidation, the samples were pretreated in air or H2 atmosphere at 300, 400 or 500 °C. The functionalization of SBA-15 with Ti contributes to obtaining Au0 nanoparticle sizes lower than 4 nm. Both the H2 atmosphere for reducing Au species and Si/Ti molar ratio on the SBA-15 were crucial for increasing the catalytic activity. The catalytic evaluation showed that the highest CO conversion is achieved when the SBA-15 is enriched with a molar ratio of Si/Ti = 20 (Au/TiSBA20). Kinetic experiments over Au/TiSBA20 catalyst were then used to construct a series of kinetic models based on distinct mechanisms following a Langmuir-Hinshelwood-Hougen-Watson type. Statistical analysis addressing the physical meaning of the kinetic parameters allowed to elucidate two dual-site surface reactions with the adsorption of COx and O2 on Au0 nanoparticles (NPs) and in the periphery of the Au0 NPs with the support, respectively, as a dominant mechanism. The estimated CO, CO2 and O2 adsorption enthalpies amounted to −30, −39 and −13 kJ/mol, respectively, while the activation energies varied from 78.8 to 81.7 kJ/mol.