Hydrothermal Synthesis and Characterization of Aluminum-Free Mn‑β Zeolite: A Catalyst for Phenol Hydroxylation

Zeolite beta, especially heteroatomic zeolite beta, has been widely used in the industries of fine chemicals and petroleum refining because of its outstanding thermal stability, acid resistance, and unique 3-D open-frame structure. In this paper, aluminum-free Mn-β zeolite was hydrothermally synthesized in the SiO₂–MnO₂–(TEA)₂O–NaF–H₂O system. The effect of the chemical composition of the precursor mixture to the crystallization of the Al-free Mn-β zeolite was investigated. The synthesized Al-free Mn-β zeolite was characterized by inductively coupled plasma (ICP), XRD, thermogravimetric/differential thermal analysis (TG/DTA), N₂ adsorption–desorption, FT-IR, UV–vis, X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM). The results show that the synthesized zeolite has a structure of β zeolite with good crystallinity and Mn ions present in the framework of the zeolite. The synthesized Al-free Mn-β zeolite shows great catalytic activity toward the phenol hydroxylation reaction using H₂O₂ as the oxidant. Approximately 35% of phenol conversion and ∼98% of dihydroxybenzene selectivity can be obtained under the optimal conditions