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An examination of the environment provided by the zeolite channels in high-silica zeolites, which have the MFI (ZSM-5), CHA (Chabazite), MOR (Mordenite), TON (ZSM-22), MTW (ZSM-12), FER (Ferrierite), and FAU (Faujasite) structures is presented. Result indicates that the heats of adsorption of physically adsorbed species changes due to the size and structure of zeolite cavities.

Microcalorimetry is used to investigate the interaction of CO and N2 with Bronsted acid sites on the zeolite H-MFI. Results show that 1:1 complexes are formed between CO and the Bronsted acid sites in the H-MFI at 195 K. The strength of the hydrogen bond is about 10.5 kJ/mol. The weakness of the interaction between N2 and Bronsted acid sites has also made it difficult to measure the interaction at 195 K.

The adsorption of acetonitrile on H-(Fe)ZSM-5 and H-(Al)ZSM-5 was investigated using microcalorimetry, temperature-programmed desorption and Fourier transform infrared spectroscopy. The aim was to characterize the differences between the Bronsted acid sites in the two materials. Experimental results showed that acetonitrile forms 1:1 stoichiometric adsorption complexes with Bronsted sites associated with framework Fe (FeOHSi) and framework Al (AlOHSi).

The different heats of adsorption of several alkylamine and substituted pyridine bases in two zeolites, namely, H-ZSM-5 and the dealuminated mordenite H-M, were determined via microcalorimetric measurements. The results proved the existence of a strong link between the gas-phase proton affinities of the basic adsorbates and differential heats of adsorption. However, no correlation between the differential heat of adsorption and aqueous base strengths was found.

Zeolites are a potentially suitable medium for a large range of selective catalytic reactions and absorptive separations. The study of acid-catalyzed reactions in zeolites based on realistic potentials requires that demarcation between acidity, an equilibrium thermodynamic concept, and activity, a composite kinetic concept should be made clear. Methods for characterizing zeolite acidity, including spectroscopy, alkane cracking, amines, and stochiometric complexes are described.

Efforts to estimate the differential heats of adsorption for simple amines in H-ZSM-5 as a function of coverage, using microcalorimetry, illustrate the advantages of applying a gas-phase reference condition to an analysis of the acid-base attributes of zeolites. Correlation between heats of adsorption and solution-phase acidity is feeble, while that with gas-phase acidity scales is very good.