Purification of exhaust gases from gasoline engine using adsorption-catalytic systems. Part 1: trapping of hydrocarbons by Ag-modified ZSM-5

In the present work, adsorptive-catalytic properties and thermal stability of the systems based on ZSM-5 zeolite and gamma-Al2O3, used as a binder, were studied. The zeolite was modified with silver, and the Ag loading used was 5 and 10 wt%. Characterization of the samples by a transmission electron microscopy has revealed that for the 5%Ag/ZSM-5 sample the predominant part of silver is represented by ion-exchanged forms. The 10%Ag/ZSM-5 sample contains also silver nanoparticles and clusters on the outer zeolite surface. As it was found by means of X-ray diffraction analysis, all these surface Ag species are roentgen-amorphous. Diffuse reflectance UV-vis spectroscopy confirms presence of the surface Ag clusters, which concentration increases after the high-temperature aging. The adsorption capacity of the samples was estimated using toluene as a model aromatic compound. The composition of the reaction mixture during the aging procedures was varied in order to elucidate the contribution of different silver sites to hydrocarbons sorption, their partial oxidation and oxidation of carbon monoxide.