Electrical properties of zeolitic catalysts

The zeolites belong to the category of high surface area ceramics. Their exceptional catalytic properties and performance as solid electrolytes are linked with the composition pore geometry, the distribution of T-atoms, and the nature and mobility of the adsorbed phases. Parallel conductivity and dielectric relaxation studies, carried out mostly during the last three decades of growing scientific interest on zeolites, are utilised in the investigation of the necessary conditions for optimal catalytic activity and conductive behaviour. Their ionic conductivity and a number of dielectric relaxation phenomena, are strongly affected by the presence of various molecular and ionic species. The thermodynamic quantities related to the above processes show a marked dependence on the kind (size and charge), density (absolute number and relative partition in coordination site groups) and mobility of the current carriers since these parameters determine the strength of the electrostatic interactions, Moreover, the conduction mechanisms show dependence upon the three-dimensional matrix (channels' size and interconnection), which influences the cation jumping rate, as well as miscellaneous processes related to the conditions of material preparation and measurement (structure-directing templates, thermal treatments, vapour adsorption at controlled pressures with molecules of variable dimensions and polarisability, irradiation, clustering processes, etc).