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Abstract

We discuss the details of important steps of the selective catalytic reduction (SCR) of NO_x at model V₂O₅(010) substrate. First, diffusion processes at the substrate surface are considered where hydrogen and ammonium, NH₄, are used as examples. Hydrogen diffusion, a prerequisite for water formation involving substrate oxygen, is described by diffusion paths between adjacent surface oxygen sites. Corresponding energy barriers are determined mainly by the flexibility and the amount of distortion of the oxygen atoms which participate in the O–H–O bridge formation at the transition state. Further, diffusion of sub-surface oxygen to fill surface oxygen vacancies of the V₂O₅(010) substrate has been considered and results in reactive surface sites which have not been discussed so far. NH₄ diffusion at the V₂O₅(010) surface can be described as a combined tumbling and rotation process characterized by quite low diffusion barriers which make the adsorbate rather mobile. Finally, hydrogenation and dehydrogenation of different NH_x species at the V₂O₅(010) substrate surface are studied where special emphasis is given to the influence of surface reduction simulated locally by oxygen vacancies. The results confirm experimental findings of the presence of both NH₂ and NH₄ species after ammonia adsorption at the V₂O₅(010) surface.