Effect of Si/Al ratio on mesopore formation for zeolite beta via NaOH treatment and the catalytic performance in α-pinene isomerization and benzoylation of naphthalene

Small crystal zeolites beta with molar Si/Al ratios of 21, 30 and 40.5 were successfully obtained by treating parent beta (Si/Al = 14.5) with different oxalic acid concentrations. The influence of Si/Al ratio of zeolite beta on effective mesopore formation via NaOH treatment was studied by investigating the changes in crystallinity, morphology, chemical composition, acidity and textural property of zeolite beta before and after alkaline treatment. The catalytic performance was evaluated in terms of α-pinene isomerization and benzoylation of naphthalene with benzoyl chloride. Substantial mesoporosity could be developed for zeolites beta with molar Si/Al ratios of 14.5–30, coupled with better preserved microporosity. Though the largest mesopore surface area (488 m2 g−1) was achieved when Si/Al = 30, the crystallinity of zeolite beta was partly destroyed. The substantially improved catalytic activity of alkaline treated samples in α-pinene isomerization is mainly attributed to the developed mesoporosity, but the volcano curve change in catalytic activities of alkaline treated samples in benzoylation of naphthalene manifested that both mesoporosity and acid property play important role in a medium strong acid catalyzed reaction.

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► Zeolites beta with different Si/Al ratios were obtained by oxalic acid treatment.
► The Si/Al ratio of zeolite beta plays a vital role in mesopore formation by NaOH treatment.
► The optimal Si/Al ratio for alkaline treated zeolite beta should be less than 30.
► Alkaline treated zeolite beta showed enhanced catalytic activity in the two reactions.
► The higher activity is mainly due to the evidently developed mesoporosity.