from first principles PP-I-1

PP-III-86FTIR Study of Adsorption and Transformations of HCN on OxideAdsorbentsPetrov S.N. 1 , Tsyganenko A.A. 1 , Rudakova A.V. 1 , Smirnov K.S. 21 St. Petersburg State University, St. Petersburg, Russia2 UST de Lille Villeneuve d’Ascq Cedex, Francesergeypspb@mail.ruIn spite of a great importance of HCN for organic synthesis, the mechanism if its adsorption andtransformations on the surface of oxide catalysts is far of being understood. It has been shownearlier that 13 C- and 15 N- isotopic substitution can be helpful to distinguish the products of HCNdissociation on silica [1] and alumina [2], while DCN adsorption enables us to clarify the structureof molecular complexes of hydrogen cyanide [2, 3]. In the present work isotopic substitution wasused to determine the forms of HCN adsorption on TiO 2 , γ-Al 2 O 3 and MgO. Experimental resultswe compared with calculated isotopic shifts for model structures.Spectra of adsorbed DCN enable us to distinguish between the bands of molecular adsorptionand those of dissociation products. Using of 13 C and 15 N substitution, we have proved thatcoordinately adsorbed on TiO 2 and γ-Al 2 O 3 cyanide has HCN configuration, but not isomericHNC form. Both quantum mechanicalcalculation and normal coordinate analysis ofa model system show that C- and N-bondedforms of CN - ion should have deviations inthe isotopic shifts on 13 C and 15 N substitutionfrom the value predicted of the reduced massratios. This was used for band assignment inthe spectra of dissociated HCN.Spectra of adsorbed H 13 CN on MgO are shown in the figure. Bands at 2063.2 and 2022.1 cm -1(curve 1) are the first to appear after heating the sample with adsorbed isotopic mixture aboveroom temperature. Their separation is about 2 cm -1 smaller than follows from the reduced masses,while for the 2198.6 and 2140.8 cm -1 bands, growing on further heating (curve 2) or higher, on thecontrary, the shift is about 10 cm -1 above the predicted value. This means that HCN dissociationfirst leads to N-bonded CN - ions with further isomeric transition to C-bonded form. Analogousresults, obtained for alumina, are in accordance with the earlier interpretation [2].References:[1] Morrow, B.A.; Cody, I.A. J. Chem. Soc., Faraday Trans.1 1975, 71, 1021.[2] Kim, J. Sunhee; Sorescu, D.C.; Yates, J. T. J. Phys. Chem. C, 2007, 111, 5416.[3] Tsyganenko, A. A.; Chizhik, A. M.; Chizhik, A. I. PCCP. 12 2010, 6387-6395.243