{sup 15}N NMR study of the adsorption of NO and NH{sub 3} on titania-supported vanadia catalysts
- Rensselaer Polytechnic Institute, Troy, NY (United States)
The adsorption of nitric oxide (NO) by ammonia over a series of V{sub 2}O{sub 5}/TiO{sub 2} catalysts used for selective catalytic reduction (SCR) has been investigated by solid-state {sup 15}N NMR. The chemistry and the surface acidity are found to vary dramatically as the weight loading of vanadia is increased from 0 to 10%. NO reacts over evacuated TiO{sub 2} and V{sub 2}O{sub 5}/TiO{sub 2} at room temperature to form nitrous oxide (N{sub 2}O). Over the V{sub 2}O{sub 5}/TiO{sub 2} catalysts N{sub 2} is also produced upon room temperature adsorption. The chemical shift of the terminal nitrogen of N{sub 2}O adsorbed on the catalyst is an indicator of the Lewis acid character of the surface. The Lewis acidity of the surface is found to decrease with the loading of V{sub 2}O{sub 5} on the titania support. Ammonia adsorbs in two forms on evacuated TiO{sub 2} and V{sub 2}O{sub 5}/TiO{sub 2}. These two forms differ in their surface mobility. The reaction of NO with NH{sub 3} over the catalysts proceeds to a measurable degree at room temperature. N{sub 2} is the predominant product; however, N{sub 2}O is also produced by the partial reduction of NO. Following preadsorption of ammonia, the chemical shift of the terminal nitrogen of N{sub 2}O is similar to that of samples with a high V{sub 2}O{sub 5} loading regardless of the actual vanadia loading. This indicates that ammonia is adsorbed predominately on the Lewis acid sites of the catalyst, blocking the access of N{sub 2}O to these sites. 41 refs., 3 figs.
- OSTI ID:
- 223981
- Journal Information:
- Journal of Catalysis, Vol. 158, Issue 1; Other Information: PBD: Jan 1996
- Country of Publication:
- United States
- Language:
- English
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