期刊
JOURNAL OF CATALYSIS
卷 338, 期 -, 页码 227-238出版社
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcat.2016.02.025
关键词
ZSM-5; Particle size; Dimethyl ether synthesis; External surface acidity; Deactivation
资金
- ANR project CATSYN-BIOFUEL [ANR-12-BS07-0029-02]
- French National Research Agency
- China Scholarship Council
- Region of Lower Normandy
- Agence Nationale de la Recherche (ANR) [ANR-12-BS07-0029] Funding Source: Agence Nationale de la Recherche (ANR)
This paper reports on direct dimethyl ether synthesis from syngas on hybrid bifunctional copper-zeolite catalysts. Both laboratory synthesized and commercial zeolites were used in this work. The catalyst performance is evaluated under pressure in a continuous fixed bed milli-reactor. The relationships between zeolite particle sizes, acidity and catalytic performance of the hybrid catalysts in dimethyl ether synthesis have been studied. The catalysts and catalyst precursors were characterized using a wide range of characterization techniques: nitrogen adsorption-desorption measurements, X-ray diffraction, Al-27 NMR, scanning electron microscopy, transmission electron microscopy and Fourier transform infrared spectroscopy with adsorbed molecular probes. It is found that the reaction rate in direct dimethyl ether synthesis is strongly affected by the sizes of zeolite particles. The hybrid catalysts containing small individual nanosized zeolite particles (60-100 nm) were much active than their counterparts with intergrown crystal agglomerates. The phenomenon is interpreted in terms of enhanced transport of methanol from the copper catalyst to the acid sites in the small zeolite particles with a shift of the thermodynamic equilibrium. The catalyst deactivation was attributed to copper sintering in the presence of the acid sites on the external surface of zeolites. It is established that the catalyst deactivation is less significant with the catalysts containing ZSM-5 zeolites with lower concentration of acid sites on the zeolite external surface. A new methodology to enhance the catalytic performance and stability of copper-zeolite hybrid catalysts for direct dimethyl ether synthesis is proposed. (C) 2016 Elsevier Inc. All rights reserved.
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