Catalytic decomposition of formic acid on oxide catalysts - III. IOM model approach to bimolecular mechanism

In our previous paper [M.A. Borowiak, M.H. Jamroz, R. Larsson, J. Mol. Catal. A: Chem., 139 (1999) 97], an impulse-oscillation model (IOM) was used for a time description of catalytic acts in the reactions of catalytic decomposition of formic acid on oxide catalysts for unimolecular mechanism. In this paper: the bimolecular mechanism were modelled for the same reactions. The results of IOM calculation show the increase of the Selectivity of choice of the dehydrogenation path, in comparison to the unimolecular mechanism. The highest increase is for monodentate or bridged forms of adsorbed formats ions (the selectivity 60% in comparison to 42% for the unimolecular mechanism). The OCO bending mode in formate and the O-H surface stretching modes are not so important in the bimolecular mechanism as in unimolecular one. The conclusion can be explained from the point of view of the postulated [H. Onishi, T. Aruga, Y. Iwasawa, J. Am. Chem. Sec. 115 (1993) 10460; H. Onishi, T. Aruga, Y. Iwasawa, J. Catal. 146 (1994) 557; H. Onishi, Y. Iwasawa, Chem. Phys. Lett, 226(1994) 111; Y. Iwasawa, Stud. Surf. Sci. Catal. 101 (1996)21] mechanism which does not need strong deformation of OCO bond system and used as a source of acid proton from formic acid and not from surface hydroxyl group on catalyst. The best ranges of wavenumbers for the considered in IOM modes for the dehydrogenation reaction are proposed. (C) 2000 Elsevier Science B.V. All rights reserved.