Insights into the active surface species formed on Ta2O5 nanotubes in the catalytic oxidation of CO

Abstract

Freestanding Ta₂O₅ nanotubes were prepared by an anodizing method. As-anodized amorphous nanotubes were calcined at high temperature to obtain a crystalline phase. All materials were studied by means of BET analysis, XRD, TEM, SEM, XPS, and FTIR and were evaluated in the catalytic oxidation of CO. An XPS study confirmed the formation of different tantalum surface species after high temperature treatment of amorphous Ta₂O₅ nanotubes. Calcination at 800 °C generated Ta⁴⁺ while higher temperature (1000 °C) treatment led to the formation of Ta³⁺ species. These materials also showed significant differences in catalytic activity. Higher activity was observed for samples calcined at 800 °C than at 1000 °C, suggesting that Ta⁴⁺ species are active sites for CO oxidation.