期刊
JOURNAL OF CATALYSIS
卷 377, 期 -, 页码 153-162出版社
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcat.2019.06.014
关键词
Methanol to olefins; SAPO-34; Pre-coking; Coke location; Ethene selectivity
资金
- National Natural Science Foundation of China [21703239, 91334205]
- Key Research Program of Frontier Sciences of Chinese Academy of Sciences [QYZDY-SSW-JSCO24]
- International Partnership Program of Chinese Academy of Sciences [121421KYSB20180007]
Control of product selectivity is a central yet challenging issue in catalysis chemistry, both in academia and industry. The ever-increasing market demand for ethene, together with relatively low ethene selectivity, necessitates the upgrading of the current methanol-to-olefins (MTO) industry to enhance ethene selectivity. We report here an operable strategy, 1-butene precoking technology, by which ethene selectivity has been unprecedentedly enhanced while the catalyst lifespan has been conserved. We also made effects to provide more insight into the long-standing controversies regarding the mechanistic origin of the increase in ethene selectivity. With the aid of a C-12-/C-73-methanol switch experiment, MD calculations, and FTIR analysis, it was demonstrated that ethene increase is neither simply-or solely-caused by the configurational diffusion effect, nor due to the transition-state shape selectivity or methylnaphthalene species, but rather to the spatial siting of the presituated coke. The relatively evenly distributed presituated coke extends the reaction zone toward the near-core of the SAPO-34 crystal, elongating the diffusion trajectories of molecules and allowing more acid sites to be utilized. The diffusion-hindered higher olefinic intermediates tend to evolve to active aromatic species, which, in turn, lead substantially to ethene. This mechanistic understanding could be also applicable to explaining ethene increase with time on stream (TOS) on parent SAPO-34. (C) 2019 Elsevier Inc. All rights reserved.
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