Abstract

Sb 2O 3/SiO 2 and Sb 2O 5/SiO 2 catalysts were prepared and characterized by N 2-adsorption, XRD, XPS, UV–vis DRS, UV Raman and H 2-TPR and investigated in methane-selective oxidation. No crystalline antimony oxide can be detected on catalysts even when antimony oxides loading reaches 20 wt.%. On Sb 2O 3/SiO 2 catalysts, the oxidation of highly dispersed Sb 3+ oxidic entities is more difficult than that of aggregated Sb 3+ oxidic entities. The concentration of Sb 5+ oxidic entities increases with Sb 2O 3 loading and about half the amount of Sb 3+ oxidic entities can be oxidized to Sb 5+ oxidic entities on 20 wt.% Sb 2O 3/SiO 2 catalyst. On Sb 2O 5/SiO 2 catalysts, SbOx species are all Sb 5+ oxidic entities and aggregated SbOx species emerge as Sb 2O 5 loading reaches 5 wt.%. In methane-selective oxidation, highly dispersed SbOx species are more active than aggregated SbOx species and the depression of deep oxidation towards CO 2 is more favorable on aggregated SbOx species than on highly dispersed SbOx species regardless of the oxidation state of Sb. Furthermore, highly dispersed Sb 3+ oxidic entities are more active than highly dispersed Sb 5+ oxidic entities. Such tendency is in line with that, for both Sb 2O 3/SiO 2 and Sb 2O 5/SiO 2 catalysts, the redox performance of aggregated SbOx species are poor compared to that of highly dispersed SbOx species. This results in their decreasing activity but increasing selectivity to CO and formaldehyde with increasing loading of antimony oxides in methane-selective oxidation.

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