Influence of zeolite crystal size on selective conversion of n-alkane: Controlling intermediates’ diffusion distances inside the micropores

Abstract

In this work, the alkali-treatment with NaOH solution was used to reduce the crystal sizes of original zeolite Y. Acidic supports of two bifunctional catalysts consisted of γ-alumina binder and zeolite Y (original or alkali-treated) with different crystal size distributions. Most of metal platinum was selectively deposited on the γ-alumina component via the electrostatic adsorption method. Given the above, it can be deduced that (de)hydrogenation reaction occurred inside the zeolite micropores at a low probability, while active protonic acid sites catalyzing the skeletal conversions of alkene intermediates were exclusively located on zeolite Y. Therefore, the number of active protonic sites that intermediates potentially encountered between two metal sites can be regarded as being proportional to diffusion distances of intermediates within the zeolite micropore structures. Moreover, the above-mentioned diffusion distances were greatly associated with the zeolite crystal sizes. Isomerization reactions of n-decane (n-C10) on two bifunctional catalysts were investigated, and results indicated that the catalyst, with alkali-treated zeolite as the acidic component, performed better than the catalyst, for which original zeolite provided the acid function, in restraining the secondary reactions. This can be attributed to the shortened diffusion distances of intermediates inside the zeolite micropores, which was caused by reducing the zeolite crystal size.