Characterization and reactivity of V{sub 2}O{sub 5}--MoO{sub 3}/TiO{sub 2} de-NO{sub x} SCR catalysts
TiO{sub 2}-supported V{sub 2}O{sub 5}-MoO{sub 3} catalysts, having V and Mo loadings representative of commercial SCR catalysts, are considered in this study. The Mo and V oxide are present on the catalyst surface in the form of molybdenylic and vanadylic species, respectively, and the presence of polymeric Mo{sub x}O{sub y} species cannot be excluded. The features of the V and Mo surface oxide species closely resemble those observed over the binary V{sub 2}O{sub 5}/TiO{sub 2} and MoO{sub 3}/TiO{sub 2} catalysts, thus pointing out the vibrational independence of the V and Mo surface vanadyl and molybdenyl oxide species. However, in spite of their structural and vibrational independence, the presence of electronic interactions between the TiO{sub 2}-supported V and Mo oxides is also apparent. The catalyst surface is characterized by strong acidity, probed by NH{sub 3}-TPD and FT-IR. Ammonia is coordinatively held over Lewis acid sites (associated with Ti, V, and Mo surface cation species) and is protonated as NH{sub 4}{sup +} ions over Mo-OH or V-OH Broensted sites. The V{sub 2}O{sub 5}-MoO{sub 3}/TiO{sub 2} catalysts are very active in the reduction of NO by NH{sub 3}, and exhibit a higher reactivity with respect to the corresponding binary V{sub 2}O{sub 5}/TiO{sub 2} and MoO{sub 3}/TiO{sub 2} samples. On the basis of the characterization data, it is suggested that the observed synergism in the SCR reaction is related to the existence of the V-Mo electronic interactions. It is found that water addition in the feed improves the catalyst performance in that it preserves high NO conversions and high N{sub 2} selectivities at high temperatures: this is due to its strong inhibiting effect on the ammonia oxidation reactions occurring simultaneously with the SCR reactions.
- Research Organization:
- Politecnico di Milano, Milan (IT)
- OSTI ID:
- 20003842
- Journal Information:
- Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 2 Vol. 187; ISSN 0021-9517; ISSN JCTLA5
- Country of Publication:
- United States
- Language:
- English
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