III International Conference

PP-II-12catalysts. A good correlation between their presence and concentration, and the catalyticactivity in butane isomerization has been observed [2].We investigated in detail the formation and parameters of hexamethylbenzene (HMB)radical cations after HMB adsorption from different organic solvents on various sulfatedalumina catalysts. We observed the values of the hyperfine constant in the HMB radicalcations to depend on the choice of solvent, temperature and catalyst pretreatment. At anytemperature, the hyperfine constant was found to increase following an increase in the solventionization potential. We believe that this is caused by fast electron exchange between HMBradical cations and the solvent molecules, which becomes more and more significant as theionization potential of the solvent goes down and approaches that of HMB. Also we havefound that an increase of sulfur concentration up to monolayer coverage leads to considerableincrease in the concentration of HMB radical cations and decrease of their hyperfine constantreflecting the growing strength of acceptor sites.Cu-ZSM-5 zeolites attract world-wide attention of researchers due to their high activity inselective catalytic reduction of NO by hydrocarbons. Samples with Si/Al =17 and Cuconcentration ranging from 0 to 3.41 wt.% were used in the study. The starting H-ZSM-5zeolite used for synthesis of Cu-exchanged samples was found to have one-electron acceptorsites capable of ionizing adsorbed benzene to its radical cations. After the copper introductionthe acceptor sites were found to grow both in number and strength.All Cu-ZSM-5 samples were found to ionize chlorobenzene, which is not ionized over H-ZSM-5 samples. The concentration of sites capable of ionizing chlorobenzene wasapproximately proportional to the copper concentration at low exchange levels up toCu/Al at = 0.35. Although the concentration of very strong acceptor sites continues to growafter further increase of the copper concentration, the rate of such growth becomes slower. So,Cu-ZSM-5 has very strong one-electron acceptor sites comparable to those of sulfatedzirconia. Further studies are needed to evaluate their role in the catalytic activity of Cu-ZSM-5.Financial support by the Russian Foundation for Basic Research (Grants 06-03-32712and 06-03-33107) is acknowledged with gratitude.References1. H. Garcia, H. D. Roth, Chem. Rev. 102 (2002) 3947.2. A. F. Bedilo, A. S. Ivanova, N. A. Pakhomov, A.M. Volodin, J. Molec. Catal. A 158 (2000) 409.184