Preparation Of MCM-22 Zeolite Coatings On Cordierite

Zeolite coatings have potential applications in separation of different substances at molecular levels under the circumstances of high-temperature, chemical and biological corrosions and in integration of catalysis and separation processes. Zeolite MCM-22 possessing unique channel systems has been used widely as catalysts with good conversion and selectivity. So it is of significance to conduct preparation and application studies of MCM-22 zeolite coatings to obtain excellent-quality MCM-22 zeolite coatings.In this dissertation, using silica acid as silica source, sodium aluminate as alumina source, HMI as template, cordierite honeycomb as support, a synthesis of MCM-22 zeolite coatings was studied in detail respectively adopting different support pretreatment time and hydrothermal synthesis parameters, the zeolite coatings with continuous, compact and pure MCM-22 crystals were synthesized.The cordierite crystals were treated with oxalic acid and sodium hydroxide solution successively, and MCM-22 zeolite was synthesized in situ on cordierite honeycomb by a hydrothermal synthesis method. The performance of zeolite and cordierite were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), N₂ adsorption (BET) and X-ray fluorescence Spectrometry (XRF), and the effect of pretreatment of cordierite on coatings formation was explored. To this end, acid treatment destroyed cordierite crystals structure, dissolved Mg, Al, produced amorphous SiO₂ and enlarged BET surface area, pore volume and micro pores; succeeding alkali treatment dissolved amorphous SiO₂ and a little Al₂O₃, MgO without destroying the cordierite crystals, the pore volume was enlarged further more. As to no treatment, pretreatment of cordierite can prepare continuous and compact MCM-22 zeolite coatings, longer pretreatment time got larger firm load mass gain, and the morphologies, dimensions and congregate density of MCM-22 also varied.MCM-22 zeolite coatings was in situ prepared on pretreated cordierite honeycomb under different static hydrothermal parameters, XRD and SEM were used to characterize the coatings. The effects of H₂O-to-silica ratio (HSR), temperature, time, silica-to-alumina ratio (SAR) and silica-to-support ratio (SSR) on mass gain ratio and physics performance were studied. To this end, a lower HSR, higher temperature, a longer time and a higher SSR can get a higher mass gain ratio of support, overmuch time and SSR cannot enlarge mass gain ratio largely, SAR can not affect mass gain ratio clearly.