Enhanced catalytic isomerization of α-pinene over mesoporous zeolite beta of low Si/Al ratio by NaOH treatment

Abstract

Small crystal zeolite beta with Si/Al ratio of 12 was subjected to post-synthesis treatment with NaOH solutions. The effect of alkaline concentration on the crystallinity, pore structures, compositions and acidic properties of zeolite beta was studied by XRD, N2 sorption, XRF, and FTIR techniques. The catalytic performance of zeolite beta before and after alkaline treatment was investigated in terms of liquid phase isomerization of α-pinene. No distinct change in the crystallinity was observed after the zeolite was treated by 0.1–0.4M NaOH solutions. However, mesoporosity was evidently developed; the mesopore surface area up to 349m2g−1 was obtained when 0.4M NaOH solution was employed. The acidic properties of zeolite beta were mostly preserved when it was treated by 0.1–0.2M NaOH solutions, but the amount of strong Brönsted acid sites was to some extent reduced when 0.4 and 0.7M NaOH solutions were employed. The catalytic activities of the samples increase with the development of mesoporosity. The best catalytic performance at 70°C and 30min reaction time was observed on zeolite beta containing the largest mesopore volume of 0.69cm3g−1: 100% conversion of α-pinene with 85.4% selectivity into camphene, terpinolene, α- and γ-terpinene as desired products. At the same conditions only 20.3% conversion was obtained over parent zeolite beta containing only 0.23cm3g−1 mesopore volume. This result indicates that the enhanced catalytic activity for α-pinene isomerization is mainly attributed to the mesopore formation resulting from alkaline treatment.