Influence of the Binder Type on the Properties of Nanocrystalline Zeolite Beta-Based Catalysts for Benzene Alkylation with Propylene

Аннотация

The effect of different binders (aluminum hydroxide (sample K-1), silica gel (sample K-2), pseudoboehmite (sample K-3), a kaolin–silica sol mixture (sample K-4), and a kaolin–aluminum hydroxide mixture (sample K-5)) on the set of the textural, acidic, and catalytic properties of catalysts based on nanocrystalline zeolite Beta has been studied. It has been shown that the introduction of aluminum hydroxide, silica gel, and a kaolin–aluminum hydroxide mixture as binders does not lead to the blocking of the pore structure of the zeolite, while the introduction of pseudoboehmite and a kaolin–silica sol mixture into the catalyst composition leads to a decrease in the micropore volume. Using the NH₃ TPD method, it has been found that the use of aluminum hydroxide, pseudoboehmite, and a kaolin–aluminum hydroxide mixture as a binder leads to an increase in the number of acid sites of the catalyst compared with the respective parameter of the original BEA-25 zeolite. The observed changes are attributed to the migration of aluminum from the binder to the zeolite structure to form new acid sites, as evidenced by ²⁷Al MAS NMR data. It has been assumed that an increase in acidity for the K-4 sample is associated with the interaction of silica with the extra-framework aluminum of the Beta zeolite. With respect to activity in the benzene alkylation with propylene, the catalysts can be arranged in the following order: K-1 > K-3 > K-2 > K-5 ≈ BEA > K-4, which correlates with the number of acid sites in the samples. The best process parameters have been achieved in the presence of the K-1 sample exhibiting a stable on-stream behavior for 10 h and providing a selectivity for alkylation products (cumene + DIPB) of 99.7% and a cumene selectivity of 89.7 wt % at 100% propylene conversion.