Hydrocarbon radicals and nitroxy complexes on the surface of HZSM-5 and CuZSM-5 zeolites: An ESR study

The conditions favorable for the formation of oligomer and benzene cation radicals upon C₂H₄, C₆H₆, and C₃H₆ adsorption on thermally activated HZSM-5 and CuZSM-5 zeolites were studied. In the case of isolated copper ions, the radicals were shown to be formed from C₃H₆ but not from C₂H₄ and C₆H₆. Paramagnetic nitroxy complexes, which were formed as a result of the interaction of adsorbed hydrocarbons C₂H₄, C₆H₆, and C₃H₆ with NO and NO₂, were revealed on HZSM-5 zeolite and Al₂O₃. Hydrocarbon radicals and nitroxy complexes are localized on different zeolite sites. Nitroxy complexes are formed on aluminum cations. The role of radicals and nitroxy complexes in the process of NO _x selective catalytic reduction by hydrocarbons on the zeolites was discussed on the basis of the temperature dependences of the concentrations of these species.