from first principles PP-I-1

PP-III-106Unusual DRIFT Spectrum of Ethane Adsorbed by Mo/Y Zeolite Preparedby CVD Method from Molybdenum HexacarbonylSokolova N.A., Subbotina I.R.N.D. Zelinsky Institute, RAS, Moscow, Russiasubbot@ioc.ac.ruRecently, we presented evidence that the intensity of IR bands of paraffins adsorbed byzeolite reflect the polarization and activation of a chemical bonds upon adsorption [1, 2]. Themost strongly perturbed vibrations are the initially fully symmetric C–H stretching vibrationsif paraffins adsorbed by isolated bivalent cationic forms of zeolites. The strongest polarizationof ethane by Zn 2+ /ZSM-5 leads to activation and the subsequent heterolytic dissociation ofethane at moderately elevated temperatures [3]. In presented work the adsorption andactivation of ethane by isolated, incorporated in Y zeolite molybdenum cations wereinvestigated by DRIFTS.Modification of Y zeolites with molybdenum cations was carried out by chemical vapourdeposition (CVD) method via chemical reaction of the hydrogen form of zeolite Y withmolybdenum hexacarbonyl vapor without oxygen atmosphere. Zero valency molybdenumspecies substitute acid protons removed as hydrogen, oxidize and stabilize as isolated cationsin cationic positions, more possible as Mo n+ (n=2 or 3). This preparation results in similarquantitative substitution of all acidic protons.Ethane adsorption by Mo/Y leads to appearance a very high relative intensity of lowfrequency band at 2734 cm -1 from initially symmetric C-H stretching vibration in comparisonwith other C-H bands in DRIFT spectra. The obtained spectrum is very similar to thespectrum of ethane adsorbed by Zn 2+ /ZSM-5 [3] and indicates strong polarization of ethane inthe result of interaction with molybdenum cations. Such strongest polarization of ethane leadsto chemical activation and to subsequent chemical transformations of ethane at moderatetemperatures resulting in the heterolytic cleaving of proton from ethane and formation ofacidic hydroxyl groups. Also new bands in the regions of C-H bands higher then 3100 cm -1appear. The appearance of these bands is connected with C-H bands of acetylenic fragment.This result cat be explained assuming that ethyl fragment obtained after cleaving of protonfrom ethane decomposed with simultaneous formation of molybdenum hydride fragments (viahomolytic oxidative addition of the hydrogen) and stable as acetylenic species coordinated tothe molybdenum.[1] Kazansky, V. B.; Subbotina, I. R.; Jentoft, F. C.; Schlögl, R.; J. Phys. Chem. B 110 (2006) 17468.[2] R. Subbotina, V.B. Kazansky, J. Kröhnert, F.C. Jentoft, J. Phys. Chem. A, 2009, V. 113, P. 839–844[3] V. B. Kazansky and E. A. Pidko; J. Phys. Chem. B 2005, 109, 2103-2108266