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

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.