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

Author:
Vlasenko, Nina V., Kochkin, Yuri N., Telbiz, German M., Shvets, Oleksiy V., Strizhak, Peter E.
Source:
RSC advances 2019 v.9 no.62 pp. 35957-35968
ISSN:
2046-2069
Subject:
Fourier transform infrared spectroscopy, X-ray diffraction, active sites, adsorption, aluminum, ammonia, desorption, energy, ethanol, liquids, nitrogen, nuclear magnetic resonance spectroscopy, pyridines, silicon, stable isotopes, temperature, zeolites
Abstract:
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 (ENH₃ = 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.
Agid:
6762979