Effect of External Surface Diffusion Barriers on Platinum/Beta‐Catalyzed Isomerization of n‐Pentane

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.

Controlling Heterogeneous Catalysis with Organic Monolayers on Metal Oxides

“…Alkyl PAs were generally found to bind to the external surface of the zeolite, slowing transport of various gases into the zeolite crystals. By manipulating the chemistry of the PA tail groups to preferentially attract or repel particular gases, it may be possible to selectively retard transport to the interior of the zeolite, providing a new basis for selectivity control . More complex scenarios are also possible.…”

“…By manipulating the chemistry of the PA tail groups to preferentially attract or repel particular gases, it may be possible to selectively retard transport to the interior of the zeolite, providing a new basis for selectivity control. 51 More complex scenarios are also possible. For example, the shortchain methyl PA was found to penetrate the subsurface region of the 5A zeolite crystals, creating a structure that more dramatically influenced gas diffusion into the pores.…”

Molecular transport in zeolite catalysts: depicting an integrated picture from macroscopic to microscopic scales

“…12C, right). 35 They found that the surface barriers were reduced by surface deposition of a silica layer. As a result, the apparent catalytic activity was remarkably improved.…”

Synthesis of nanosheet epitaxial growth ZSM-5 zeolite with increased diffusivity and its catalytic cracking performance

“…16 The surface barrier, which may originate from surface defects, has been widely discussed and considered as another important diffusion mechanism. [17][18][19] Pure nanosheet zeolite with discontinuity along the b-axis direction produces a large amount of extraframework Al and external Si-OH, which may increase the surface barrier. It has been found that compared with bulk ZSM-5, the spent nanosheet zeolite deposits more coke after 100 h of n-heptane cracking.…”

“…21,22 The reduction of the surface barrier after silica deposition makes the Pt/Beta zeolite exhibit 131% increase in catalytic activity. 17 Although the two-dimensional nanosheets achieve an ultra-short diffusion pathlength, the external surface barrier may be another consideration for adjusting the catalytic performance of the nanosheet zeolite.…”