First principles studies of vanadia-titania monolayer catalysts: mechanisms of NO selective reduction.
The selective reduction of NO with NH(3) catalyzed by isolated VO(x) species grafted onto TiO(2) (anatase) is studied by means of periodic density functional calculations. NH(3) is adsorbed molecularly by the bare support both as a Lewis-bonded complex at (101) 5-fold coordinated Ti sites, and as a H-bonded complex at (001) Ti-OH sites. Analogous interactions are predicted for stable submonolayer VO(x) species, which provide V(5+) Lewis acid sites and V-OH sites. Neither Ti-OH nor submonolayer V-OH groups act as Brønsted acids toward NH(3). Reaction pathways where both Lewis-bonded and H-bonded NH(3) complexes yield a NH(2)NO intermediate are found. In the former case, a (rate-determining) deprotonation step of NH(3) is required, whereas, in the latter, NH(2)NO is formed directly through a concerted mechanism. This suggests that many channels may contribute to the NO reduction process.
Vittadini
Andrea
A
Casarin
Maurizio
M
Selloni
Annabella
A