タイトル: Synthesis of [Al]-SSZ-31 Molecular Sieves using [Al]-Beta Zeolite ([Al]-BEA) as precursors
著者: Ahedi, Ranjeet Kaur; Kubota, Yoshihiro; Pusparatu; Sugi, Yoshihiro
抄録: The aluminosilicate version of SSZ-31 ([Al]-SSZ-31) zeolite was synthesized by a new route including phasetransformation,wherein an aluminosilicate analog of beta zeolite ([Al]-BEA) was used as a precursor and1,1,1,8,8,8-hexaethyl-1,8-diazoniaoctane dihydroxide was used as a structure-directing agent (SDA). [Al]-BEA precursorssynthesized by two routes, viz. the hydrothermal (HTS) and dry-gel conversion (DGC) method, were employed forthe synthesis. [Al]-SSZ-31 with a low output SiO2/Al2O3 ratio crystallized only when the precursor (SiO2/Al2O3 = 30),prepared by DGC method, was employed. Precursors synthesized by the HTS method produced highly crystalline samples,however, only in the high silica region. In general, [Al]-SSZ-31 samples over a wide range of SiO2/Al2O3 ratioscould be synthesized using a precursor route. During crystallization, a phase transformation from [Al]-BEA to [Al]-SSZ-31 was observed, indicating dissolution of the beta phase, followed by its redirection towards the SSZ-31 phasein the presence of SDA. An increase in gel water helped to produce pure [Al]-SSZ-31. [Al]-SSZ-31 was found to crystallizein NaOH/SiO2 window of 0.040?0.056. Scanning electron microscopy (SEM) showed plate-like crystals of about5 mm in size. 13CCPMASNMR indicated that the SDA was intact inside the pores during crystallization. Furthermore,the samples were also characterized by 29Si and 27Al MAS NMR in addition to X-ray diffraction (XRD), temperatureprogrammeddesorption of ammonia (NH3-TPD), SEM, etc.
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