Synthesis of hierarchical Beta zeolite with uniform mesopores: Effect on its catalytic activity for veratrole acylation

Uniform mesoporosity has been effectively developed in hierarchical Beta zeolite by means of a hydrothermal treatment at 110 degrees C with an ammonia/surfactant solution. As a result, the broad pore size distribution, existing within the supermicropore-mesopore range in the parent hierarchical Beta sample, was rearranged into a uniform one centred at 40 A. In contrast, this treatment was less effective when applied to a conventional Beta zeolite sample with little secondary porosity. Neither amorphous phases nor MCM-41-like materials were detected after the mesopore narrowing treatment. Likewise, FTIR/pyridine measurements of the zeolite samples indicated that their acid properties were preserved after the ammonia/surfactant treatment, while just small variations were observed in the Si/Al ratio. Veratrole acylation tests were employed for assessing the catalytic properties of the samples. In spite of the reduction in the BET surface area produced by the mesopore narrowing treatment, the samples with uniform mesopores exhibited enhanced catalytic activity. In particular, the highest veratrole conversion was attained with the h-Beta (mnt) sample, obtained from the hierarchical Beta material. This result denotes the benefits derived from the presence of a high quality uniform mesoporosity on the catalytic performance of hierarchical Beta zeolite, as it increases the accessibility to the active sites and decreases the zeolite deactivation by product inhibition.