Tuning Lewis acid sites in TS-1 zeolites for hydroxylation of anisole with hydrogen peroxide

Abstract

One-step direct hydroxylation of aromatics is an atom-economic way for phenols production. Ti-containing MFI zeolite is considered to be one of the most potential catalysts for hydroxylation of aromatics to phenols under mild condition with aqueous H 2 O 2 as the oxidant. However, the products are often a mixture of mono- or multi-phenols. Designing TS-1 zeolite catalyst with high yield and selectivity to the target phenols remains a challenging task. Here TS-1 zeolites are prepared by direct hydrothermal and post-synthetic methods. Multiple spectroscopic characterizations show that the crystallinity and Ti-Lewis acid sites (Ti-LASs) distribution of TS-1 zeolite can be controlled by the synthetic approach. The structure-activity relationship of TS-1 zeolite is established in the catalytic hydroxylation of anisole, revealing that Ti-LASs concentration determines the conversion of anisole, while both the crystallinity and Ti-LASs distribution significantly influence the selectivity to the desired product para -hydroxyanisole. •The Ti-Lewis acid properties of TS-1 zeolites can be precisely modulated by the sample preparation. •The concentration of Ti-LASs in TS-1 determines the conversion of anisole hydroxylation. •Introducing Ti-LASs into the well-crystalized TS-1 channels facilitates the selective production of para-isomers in the hydroxylation of anisole. •This work provides insights into the understanding of the catalytic properties of TS-1 zeolites towards the selective hydroxylation of anisole to phenols.