CO oxidation on gold nanoparticles supported over titanium oxide nanotubes

Titanium oxide nanotubes (TN) were synthesized and used as support for Au nanoparticles obtained by deposition–precipitation with urea. The activity of Au/TN catalysts prepared under different conditions was tested in the oxidation of CO. The results indicate that titanium oxide nanotubes (TN) can be used as support for gold nanoparticles obtained by deposition–precipitation, since adequate gold nanoparticle sizes (<5 nm.) for CO oxidation can be obtained.Varying the preparation conditions of the catalysts it was found that the best catalyst performance is obtained by calcining the TN support at temperatures higher than 400 °C, temperature at which the trititanate phase obtained in the as-prepared material is completely transformed into TiO2-anatase. Higher calcination temperatures lead to a significant decrease in the surface area of TN.It was also observed that the activity of the Au/TN catalysts was negatively affected by long storage periods. This fact was evidenced by the significant increase in gold particle size, which is apparently due to the high mobility of gold nanoparticles on the support.Increasing the gold loading from 3 to 9 wt% does not improve the CO oxidation activity because, at 9 wt% Au the particle sintering increases leading to particles greater than 5 nm, which are not effective for CO oxidation.To obtain good catalytic activity it is necessary to pretreat the catalysts at least at 300 °C to assure the complete reduction of the gold precursor. The use of hydrogen or air in the catalyst pretreatment to obtain the reduction of the gold precursor did not affect the performance catalysts.