Continuous Flow Synthesis of a ZSM-5 Film in Capillary Microchannel for Efficient Production of Solketal

Catalytic Enhancement of Cyclohexene Hydration by Ga-Doped ZSM-5 Zeolites

Ga-doped ZSM-5 zeolites were directly synthesized by a facile one-step hydrothermal method without organic templates and calcination and then investigated in the cyclohexene hydration reaction. The structure, component, textural properties, and acidity of the as-prepared samples were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), Brunauer-Emmett-Teller (BET), ammonia temperature-programmed desorption (NH₃-TPD), pyridine-chemisorbed IR (Py-IR), and ⁷¹Ga, ²⁷Al, ²⁹Si, and ¹H magic-angle spinning (MAS) NMR techniques. The characterization results showed that the introduction of Ga atoms into the ZSM-5 zeolite framework is much easier than Al atoms and beneficial to promote the formation of small-sized crystals. The number of Brønsted acid sites of Ga-doped ZSM-5 samples obviously increased compared with Ga0-ZSM-5. Additionally, the highest cyclohexanol yield (10.1%) was achieved over the Ga3-ZSM-5 sample, while the cyclohexanol yield of the Ga0-ZSM-5 sample was 8.6%. This result indicated that the improved catalytic performance is related to its larger external surface area, smaller particle size, and more Brønsted acid sites derived from Si-OH-Al and Si-OH-Ga of Ga3-ZSM-5. Notably, the green route reduces harmful gas emission and provides a basis for doping other heteroatoms to regulate the catalytic performance of zeolites, especially in industrial production.

Preparation of the WO X /MCM-41 Solid Acid Catalyst and the Catalytic Performance for Solketal Synthesis

In the present work, an efficient and stable WO _X /MCM-41 solid acid catalyst was prepared by the wet impregnation method. The characterization of powder X-ray diffraction, transmission electron microscopy, ultraviolet-visible, H₂ temperature-programmed reduction, X-ray photoelectron spectroscopy, NH₃ temperature-programmed desorption, and N₂ adsorption-desorption isotherms confirmed that the impregnation amount and calcination temperature of WO _X speciation affected the dispersity and acidity of the resulting catalyst. This WO _X /MCM-41 solid acid catalyst was subsequently applied in the ketalization reaction of glycerol and acetone to produce solketal. By catalyst screening and reaction condition optimization, WO _X /MCM-41 obtained by impregnating 20 wt % and calcining at 350 °C exhibited the highest solketal yield and catalytic stability.