Effect of Fe on the activity of Au/FeO x -TiO2 catalysts for CO oxidation

Abstract

A thorough characterisation of Au/TiO2 and Au/FeOx-TiO2 catalysts was conducted in order to get a better understanding of the effect of Fe on the Au/TiO2 catalysts and link it to differences observed in their activities for CO oxidation. Several techniques including HRTEM, temperature-programmed reduction (TPR), UV-Vis and temperature-programmed desorption (TPD) of isopropyl amine, CO and CO2 were used to characterise the catalysts. Au/FeOx-TiO2 (300 °C), which was found to be the most active catalyst for CO oxidation, had the highest number of Bronsted acid sites, although its concentration of Lewis acid sites was similar to all other tested catalyst systems. X-ray photoelectron spectroscopy (XPS) revealed that the Fe species on the Au/FeOx-TiO2 catalyst is Fe2+ with a very small amount of Fe3+. Fe2+ is comprised of both FeO and Fe3O4 species, and according to TPR, the ratio (FeO/Fe3O4) between these two species increases with increasing calcination temperature. The presence of Fe on the Au/TiO2 catalyst seems to stabilise the Au nanoparticles from agglomeration. The activation energy of desorption (Ed) of CO from Au/FeOx-TiO2 (300 °C) was 82.7 kJ/mol, whilst on Au/TiO2, the Ed for CO was 108.8 kJ/mol. On both catalysts, the Ed for CO2 was ca. 99 kJ/mol.