Supported Rucatalysts prepared by two sonication-assisted methods for preferential oxidation of CO in H2

Abstract

The preferential oxidation (PROX) of CO in the presence of H₂ is an important step in the production of pure H₂ for industrial applications. In this report, two sonochemical methods (S1 and S2) were used to prepare highly dispersed Ru catalysts supported on mesoporous TiO₂ (TiO₂(MSP)) for the PROX reaction, in which a reaction gas mixture containing 1% CO + 1% O₂ + 18% CO₂ + 78% H₂ was used. The supported Ru catalysts performed better than the supported Au and Pt catalysts, and the S1 and S2 methods are superior to the impregnation method. The Ru/TiO₂(MSP) catalysts were active for the PROX reaction below 200 °C and good for the methanation reactions of CO and CO₂ above 200 °C. The presence of residual chlorine in the catalysts severely suppressed their PROX reaction activity, and a higher dispersion of Ru particles led to better catalytic performances. The addition of Au in the Ru/TiO₂(MSP) catalyst also caused a poorer catalytic activity for both the PROX and the methanation reactions. TPR results showed that in the active catalysts prepared by the S1 and S2 methods, the well dispersed Ru particles, after calcination in air, had a stronger interaction with the support than those in the catalyst prepared by the impregnation method and in the Au-Ru/TiO₂(MSP) catalyst. In situ CO absorption experiments performed with the diffusion reflectance Fourier transform infra red (DRIFT) method showed that the bridged adsorbed CO species on isolated Ru⁰ sites correlated with the catalytic performances, indicating that these isolated Ru⁰ sites are the most active sites of the Ru/TiO₂(MSP) catalysts in the PROX reaction.