In situ Raman spectroscopy during the partial oxidation of methane to formaldehyde over supported vanadium oxide catalysts
- Lehigh Univ., Bethlehem, PA (United States); and others
Vanadia was found to be well dispersed and present as a two-dimensional overlayer when supported on SiO{sub 2}, TiO{sub 2}, SnO{sub 2}, TiO{sub 2}/SiO{sub 2}, 3 wt% TiO{sub 3}/SiO{sub 2}, and 3 wt% SnO{sub 2}/SiO{sub 2}. Partial oxidation of methane by oxygen formed formaldehyde most selectively over the V{sub 2}O{sub 5}/SiO{sub 2} catalyst, but catalytic performance strongly dependent on vanadia coverage and autocatalytic behavior was observed. At very low conversions, the formaldehyde activity increased linearly with vanadia coverage, indicating that isolated V{sub 5}, species were responsible for the active sites. No significant structural changes were revealed by in situ Raman spectroscopy for the V{sub 2}O{sub 5}/SiO{sub 2} catalyst, which indicated that the fully oxidized surface sites were related to the high formaldehyde selectivity. This selectivity exhibited a maximum at 1 wt% V{sub 2}O{sub 5} content, and the lower selectivities at higher loadings appeared to be due to the increasing Lewis acidity of the catalysts. Space-time yields of 0.1-1.4 kg CH{sub 2}O/kg cat/hr and selectivities of 2-78% are reported herein for the V{sub 2}O{sub 5}/SiO{sub 2} catalysts. Deep oxidation products, CO and CO{sub 2}, were principally produced over the V{sub 2}O{sub 5}/TiO{sub 2} and V{sub 2}O{sub 5}/SnO{sub 2} catalysts. For the first time, in situ Raman analysis clearly showed that for these latter catalysts the surface vanadium(V) oxide species were partially reduced under the steady-state reaction conditions. The performance of the V{sub 2}O{sub 5}/TiO{sub 2}/SiO{sub 2} catalyst was similar to that of the V{sub 2}O{sub 5}/TiO{sub 2} catalyst, consistent with the earlier observation that vanadia was largely bound to the titania overlayer. It appears that formaldehyde selectivity decreased with increasing catalyst reducibility, but no direct correlation of catalyst activity with reducibility was observed. 36 refs., 12 figs., 2 tabs.
- DOE Contract Number:
- FG21-92MC29228
- OSTI ID:
- 476840
- Journal Information:
- Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 1 Vol. 165; ISSN JCTLA5; ISSN 0021-9517
- Country of Publication:
- United States
- Language:
- English
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