Acid site accessibility in sulfonated polystyrene acid catalysts: Calorimetric study of NH3 adsorption from flowing gas stream

Insight into the active site nature of zeolite H-BEA for liquid phase etherification of isobutylene with ethanol

The nature of active acid sites of zeolite H-BEA with different Si/Al ratios (15–407) in liquid phase etherification of isobutylene with ethanol in a continuous flow reactor in the temperature range 80–180 °C has been explored. We describe and discuss data concerning the strength and concentration of acid sites of H-BEA obtained by techniques of stepwise (quasi-equilibrium) thermal desorption of ammonia, X-ray diffraction, low-temperature adsorption of nitrogen, FTIR spectroscopy of adsorbed pyridine and solid-state ²⁷Al MAS NMR. The average values of the adsorption energy of NH₃ on H-BEA were experimentally determined as 63.7; 91.3 and 121.9 mmol g⁻¹ (weak, medium, and strong, respectively). In agreement with this, a correlation between the rate of ethyl-tert-butyl ether synthesis and the concentration of weak acid sites (E_NH3 = 61.6–68.9 kJ mol⁻¹) has been observed. It was concluded that the active sites of H-BEA for this reaction are Brønsted hydroxyls representing internal silanol groups associated with octahedrally coordinated aluminum in the second coordination sphere.

The active sites of H-BEA zeolites for ETBE synthesis are the weak Brønsted acid sites representing internal silanol groups.

Adsorption–desorption of ethanol on sulfonated resin catalysts for ethyl-tert-butyl ether synthesis

Ethanol adsorption on sulfonic resins of different morphological types, such as gel, macroporous sulfonic resin, mixed sample (1:1 mixture of gel-type sulfonic resin with aerosil) and sulfonic resin loaded on wide-porous mineral carrier was studied using the methods of quasi-equilibrium thermal desorption and quartz crystal microbalance. It has been observed that the faster ethanol adsorption proceeds on the macroporous sulfonic resin and the slower ethanol adsorption on the gel-type one. It is due to different swelling ability. It was found that the transfer of the ethanol molecules through the gel phase of sulfonic resin proceeds by means of the adsorption–desorption mechanism. The ratio of ethanol adsorption on sulfonic resin is one molecule per one acid site. During the ethanol adsorption on the gel and mixed sulfonic resin, one type of adsorbed complex is formed, whereas on the macroporous and loaded samples two adsorbed complexes with different energies are formed. This is probably because of the different localization of the acid sulfonic groups.