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

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 H2O2 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.