Octahedral surface vanadium oxide species

The replacement of vanadia-based catalysts in the reduction of NOx with ammonia is of interest due to the toxicity of vanadium. Tentative investigations on the use of noble metals in the NO + NH3 reaction have been nicely reviewed by Bosch and Janssen [85], More recently, Seker et al. [86] did not completely succeed on Pt/Al203 with a significant formation of N20 according to the temperature and the water composition. Moreover, 25 ppm S02 has a detrimental effect on the selectivity with selectivity towards the oxidation of NH3 into NO enhanced above 300°C. Supported copper-based catalysts have shown to exhibit excellent activity for NOx abatement. Recently Suarez et al and Blanco et al. [87,88] reported high performances of Cu0/Ni0-Al203 monolithic catalysts with NO/NOz = 1 at low temperature. Different oxidic copper species have been previously identified in those catalytic systems with Cu2+, copper aluminate and CuO species [89], Subsequent additions of Ni2+ in octahedral sites of subsurface layers induce a redistribution of Cu2+ with a surface copper enrichment. Such redistribution... 

In a similar way as that used by Kucherov and Slinkin [92,1911, Huang et al. [192-194] prepared vanadium-containing ZSM-5 and mordenite via SSIE between V2O5 and the zeolites mentioned above. The products were characterized by XRD, XPS, and determination of their surface areas. At variance with the interpretation given by Kucherov and Slinkin, Huang et al. [192] and Shan et al. [193] claimed from their ESR results that the vanadyl species existed in two different coordination structures both in ZSM-5 and mordenite, viz., in a compressed hexacoordinated octahedral and a pentacoordinated pyramidal symmetry. Furthermore, the authors studied the acidity of the zeolites after SSIE with V2O5 by FTIR of adsorbed pyridine and titration with butylamine in apro-tic solution. In addition, the capacities for adsorption as well as the activities and selectivities for oxidation of toluene to benzaldehyde were investigated. The authors showed that the differences in adsorptive and catalytic behavior were related to the differences in acidity of the materials produced by SSIE [193]. 

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