Au/Co promoted CeO2 catalysts for formaldehyde total oxidation at ambient temperature: role of oxygen vacancies
Au catalysts with loading 1.5 and 3 wt% were dispersed over CeO2 and Co (9; 12 mol%) promoted CeO2, by deposition-precipitation method, followed by calcination at 350°C. The fresh supported Au catalysts were characterized by several techniques in order to investigate their morphological, structural as well as redox properties before to be tested in formaldehyde (HCHO) total oxidation. All the supported Au catalysts exhibit at 25°C HCHO oxidation into CO2 and have a great stability upon time on stream (40 h). While the 3 wt% Au catalysts demonstrate higher HCHO conversion than their low-gold counterparts (1.5 wt% Au), a remarkable improvement of HCHO conversion was observed using Co promoted ceria (9 mol%). Based on the HCHO amount (in µmol) converted into CO2 per gram of gold per second after 40 h on stream, 1.5Au/CeCo showed the best activity (~ 3.9) as compared to the other catalysts (≤ 2.0). XPS characterization of the fresh catalysts indicates Au species mainly in slightly ionic δ+ valence state without excluding the possibility of metallic gold. Furthermore, it is found no marked changes in gold dispersion when adding cobalt. Promotion of HCHO oxidation over gold supported on Co promoted ceria catalysts can be related to a higher oxygen vacancy concentration and an improvement of the redox properties which can contribute to a better activation of O2 and an enhancement of the oxygen mobility.