Selective catalytic reduction of nitric oxide with ammonia: A theoretical ab initio study

Ab initio quantum chemical studies at the HF/Lanl2dz level were carried out to investigate the interaction of ammonia, NO, and a mixture of the two with vanadia/titania. It was found that the replacement of Ti_6c by V_6c is the only feasible way to form highly dispersed vanadia over the titania. The V?O species thus formed will be in octahedral symmetry with the axial distortions, and no tetrahedrally coordinated V species can be formed. Ammonia fully covers the catalyst surface either through the associative interaction with the Lewis acid site of Ti_5c or the dissociative adsorption channels. The dissociation of ammonia on the O site bridging the Ti_6c and V_6c octahedra and on the V?O group can proceed with the highest gain in energy. The formation of an adsorbed ammonium ion was found to be an energetically highly unfavorable process. The V?O group is no longer expected to play a major role in the stabilization of the surface ammonium ion. NO can be activated on the Ti_5c site of the catalyst containing predissociated ammonia on the bridging O site and V?O group. It can be expected that the SCR reaction products are formed through the reactions of both adsorbed NO and NH₂ or the desorbed NH₂ group with NO in the gas phase. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001