Theoretical and Experimental Studies of the Nature of the Catalytic Activity of VO x /TiO2 Systems |
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Authors: | Borovkov V Yu Mikheeva E P Zhidomirov G M Lapina O B |
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Institution: | (1) Russian Academy of Sciences, Zelinskii Institute of Organic Chemistry, Moscow, 119991, Russia;(2) Siberian Division of the Russian Academy of Sciences, Boreskov Institute of Catalysis, Novosibirsk, 630090, Russia |
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Abstract: | The states of supported vanadium and the nature of activation of ammonia adsorbed on vanadium sites of V
x
/Ti 2 catalysts are studied by 51V NMR spectroscopy and diffuse-reflectance IR Fourier-transform (DRIFT) spectroscopy using cluster quantum chemical calculations of N 3 adsorption. We employ the V
x
/Ti 2 catalyst of two types: the monolayer catalyst in which vanadium is located on the surface of well-crystallized anatase and the catalyst in which vanadium embedded in the anatase lattice at a rather great depth. It is shown that ammonia is predominantly adsorbed on Lewis acid sites of the monolayer catalyst, whereas most of N 3 adsorbed on the catalyst containing bulk vanadium is in the form of ammonium ions. Analysis of experimental and calculated data suggests that, in the monolayer catalyst, N 3 molecules in the selective reduction of nitrogen oxides are activated on Lewis acid sites. Ammonia activation involves the dissociation of the N–H bond in a coordinated molecule, which results in the formation of the amide V–N 2 group and a water molecule coordinated by a V5+ ion. It is likely that, in the case of the catalyst containing bulk vanadium, this reaction occurs with the predominant participation of ammonium ions. |
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