Abstract
We have developed a generalizable strategy to quantify the effect of surface barriers on zeolite catalysis. Isomerization of n‐pentane, catalyzed by Pt/Beta, is taken as a model reaction system. Firstly, the surface modification by chemical liquid deposition of SiO2 was carried out to control the surface barriers on zeolite Beta crystals. The deposition of SiO2 leads to a very slight change in the physical properties of Beta crystals, but an obvious reduction in Brønsted acid sites. Diffusion measurements by the zero‐length column (ZLC) method show that the apparent diffusivity of n‐pentane can be more than doubled after SiO2 deposition, indicating that the surface barriers have been weakened. Catalytic performance was tested in a fixed‐bed reactor, showing that the apparent catalytic activity improved by 51–131 % after SiO2 deposition. These results provide direct proof that reducing surface barriers can be an effective route to improve zeolite catalyst performance deteriorated by transport limitations.
Highlights
We have developed a generalizable strategy to quantify the effect of surface barriers on zeolite catalysis
Zeolites are an important class of microporous materials that are widely used as catalysts in the refining and petrochemical industries. Due to their well-defined, molecular-sized micropore networks, they possess the great advantage of shape selectivity in catalysis,[1] but they are heavily plagued by diffusion limitations that reduce catalytic activity, selectivity, and stability.[2]
Recent observations show that diffusion limitations still persist in zeolite crystals, even when their thickness is reduced to a few nanometers.[5,6]
Summary
We have developed a generalizable strategy to quantify the effect of surface barriers on zeolite catalysis. The XRD patterns of the two samples display modified by amorphous SiO2 after performing the chemical peaks at 2q = 7.88, 13.48, 21.58, 22.68, 25.48, 27.08, and 29.78 liquid deposition; this is not obvious, and the surface attributed to the typical Beta phase with a BEA-type modification is too slight to be observed in SEM and structure,[33] indicating that SiO2 deposition does not change HRTEM images.
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