ИСТИНА

Liquid acid catalysts are widely used by chemical industry. These acids generate significant amounts of toxic waste and there is a need to replace them with solid ones [1]. Solid acid catalysts have favorable characteristics such as efficient activity, high selectivity, long catalyst life and ease in recovery and reuse. Water has attracted considerable attention as a reaction medium in recent years. The selection of water as a solvent offers many benefits; beside low cost and abundance, the advantages are the fact that it is nonflammable, nontoxic and safe to the environment [2]. Therefore, for the development of green processes there is a need to replace the liquid with solid acids and to use water as reaction medium. However, when measuring acidity of solid catalysts the distinction between the “intrinsic” acidity as measured by adsorption of probe molecules from the gas phase on the catalyst and “effective” acidity displayed by the interaction of probe molecules with the catalyst in the liquid phase is important [3]. Relative acid strengths of solid materials depend markedly on whether a solvent is present, on the nature of the solvent, and may vary as the medium in which the acidity is measured is changing [4]. Moreover, it is known that some of the acidic groups at the surface can interact with the solvent molecules in a way that hinders their catalytic action. Therefore, in order to find valuable relationships between surface acidity of solid catalysts and catalytic activity, and to gain better understanding of heterogeneous processes in a liquid phase, characterization of surface active sites in a reaction medium is of prominent importance. In the present investigation, the surface acidity of some solid materials was investigated by following adsorption of 2-phenyl-ethylamine (PEA) from the aqueous solutions by calorimetry technique. Additionally, amount of adsorbed probe molecule was determined by UV-Vis spectrometry. In this way determination of the number of acid sites and differentiation of the sites by their acid strength was possible.