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-beta zeolite was hydrothermally synthesized in the SiO2MnO2(TEA)(2)ONaFH2O system. The effect of the chemical composition of the precursor mixture to the crystallization of the Al-free Mn-beta zeolite was investigated. The synthesized Al-free Mn-beta zeolite was characterized by inductively coupled plasma (ICP), XRD, thermogravimetric/differential thermal analysis (TG/DTA), N-2 adsorptiondesorption, FT-IR, UVvis, X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM). The results show that the synthesized zeolite has a structure of beta zeolite with good crystallinity and Mn ions present in the framework of the zeolite. The synthesized Al-free Mn-beta zeolite shows great catalytic activity toward the phenol hydroxylation reaction using H2O2 as the oxidant. Approximately 35% of phenol conversion and similar to 98% of dihydroxybenzene selectivity can be obtained under the optimal conditions.