Template-Retained 2D Fe-PREFER Zeolite: A Green and Recyclable Catalyst for Highly Efficient Phenol Hydroxylation

Iron-based zeolites are promising catalysts for various selective oxidation reactions, yet conventional three-dimensional microporous zeolites suffer from significant mass-transfer limitations, which become particularly pronounced in liquid-phase catalytic systems. In this study, we optimized the synthesis strategy and successfully prepared highly crystalline two-dimensional Fe-PREFER zeolite from a silicon–iron precursor under fluoride-free conditions, reducing the crystallization time to 5 days, thereby improving both economic and environmental sustainability. Through comprehensive characterization techniques including XRD, SEM/TEM, UV–vis DRS, Raman, and EPR spectroscopy, it was confirmed that iron species are incorporated into the zeolite framework as isolated tetra-coordinated sites, which serve as the active centers for catalysis. By adopting a “structure-directing-agent-retained” strategy for catalytic evaluation, the detrimental effects of high-temperature treatment on active sites were avoided. The Fe80-PREFER catalyst exhibited excellent performance in phenol hydroxylation, achieving a phenol conversion of 52.9% and a dihydroxybenzene selectivity of 90.6% under mild conditions (50 °C, 3 h). Mechanistic studies revealed that the reaction proceeds via a hydroxyl-radical pathway, with surface-activated phenol species identified as the key intermediates. To address catalyst deactivation, an ethanol-washing regeneration method was developed. This room-temperature process, which consumes far less energy than conventional high-temperature calcination, effectively removes surface phenolic tar while preserving the zeolite framework structure and the stability of the active iron species, leading to full recovery of catalytic performance. The synthesis and regeneration strategies established for this two-dimensional Fe-PREFER zeolite can be extended to other liquid-phase oxidation systems involving small molecules, such as low-temperature methane oxidation and aromatic hydroxylation.