Iron-loaded pure silica -SVR zeolite for the hydroxylation of phenol†

Abstract

Dihydroxybenzene compounds are a type of crucial fine chemicals used in daily life, but their production process is severely constrained by contamination and relatively low efficiency. In this work, the iron-containing pure silica -SVR zeolite was successfully developed and proven to be an efficient catalyst in the conversion of phenol into dihydroxybenzene compounds in a green way. Notably, in the presence of hydroperoxide, the heterogeneous-mediated oxidative process achieved a record-high conversion of 37% and selectivity of 99%. Combining physicochemical analysis and multiple spectroscopic techniques, the active species was confirmed to be the trivalent iron sites confined within the -SVR voids. Moreover, the accessible ordered silanol defects confined within the -SVR channel system are abundant, providing anchor points for grafting iron sites. The highly active iron species initiates the free radical-mediated reaction pathway, significantly facilitating the oxidative reaction process. As unveiled by the catalytic kinetics, the iron-containing zeotype catalyst affords a TON of 861 and TOF of 430.5 h⁻¹, and the apparent active energy E_a was determined as 26 kJ mol⁻¹. Overall, these results not only provide a highly effective heterogeneous catalyst for the conversion of phenol into dihydroxybenzene compounds in an eco-friendly manner but also open up new horizons for the effective utilization of pure silica zeolites listed in the IZA database.