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Simultaneous Evaluation of Reaction and Diffusion over Molecular Sieves for Shape-Selective Catalysis
journal contribution
posted on 2020-07-22, 17:35 authored by Jingfeng Han, Zhiqiang Liu, Hua Li, Jiawei Zhong, Wenna Zhang, Jindou Huang, Anmin Zheng, Yingxu Wei, Zhongmin LiuShape
selectivity is the critical issue of molecular sieve catalysis.
As an important aspect of shape-selective catalysis, the significance
of diffusion in conversion, deactivation, and product selectivity
over molecular sieve catalysts has been recognized but still has not
been interpreted quantitatively and explicitly. In the present work,
direct tracking molecular diffusion in the SAPO-34 catalyst during
the methanol-to-olefins (MTO) reaction is successfully realized by
combining the MTO reaction with the diffusivity evaluation by a pseudo-gas
chromatography method which was operated in one catalyst bed under
the real reaction condition. Diffusion behavior over the working catalyst
can be measured along with the reaction to reflect the evolution in
shape-selectivity catalysis in real time. For the first time, the
accessibility of the catalyst microporous surface for the reactant
was quantified during the reaction, which provided a rational understanding
of the reaction and deactivation of MTO over the catalyst with continuous
coke deposition. The evaluation of configurational diffusion hindrance
in SAPO-34, because of the accumulation of organic species retained
in the catalyst, corresponds well to the evolution of methanol conversion
and product distribution and provides the scientific basis for manipulating
the MTO reaction from the point of shape-selective catalysis.