A study of "superacidic" MoO3/ZrO2 catalysts for methane oxidation

A series of zirconia-supported molybdenum oxide catalysts with different mo lybdenum loadings prepared using conditions reported to generate "superacid ity" have been evaluated for their performance as catalysts for methane oxi dation. A marked dependence of Mo content on activity has been observed, wi th the most active material being that with intermediate molybdenum content . 5 wt% MoO3/ZrO2 compares favourably with ZrxCe1-xO2 for methane combustio n. The presence of MoO3 is observed to stabilise the tetragonal polymorph o f ZrO2 and, as Mo content is increased, dispersed MoO3 crystallites are for med as evidenced by Raman spectroscopy. Temperature-programmed reduction st udies evidence differences in the reduction behaviour of the materials as a function of loading. The results indicate that molybdenum oxide supported on monoclinic zirconia gives rise to the most active catalyst. It is tentat ively suggested that the formation of a MoO3 monolayer during reaction may be of importance.