We report for the first time a novel and efficient synthesis of conventional-NaY (Con-NaY) and nano-crystalline Y aggregates (NM-NaY) by using structure directing agent (SDA) in extremely dense aqueous system.By modification of SDA, the regularity of the SDA species and its modulation of active structural unit have been enhanced, which leads to formation of the Y aggregate (NM-NaY). Comparatively, the NaY (Con-NaY) zeolite sample was synthesized by the non-modified SDA (Con-SDA), which exhibits typical octahedral morphologies and the crystal size ranges from 400 to 500 nm(Fig.1-left). However, zeolite samples (NM-NaY) synthesized by the modified SDA show nano-micro aggregates with particle size about 4μm, which are composed by numerous domains of interconnected nanocrystals(10-100nm) as shown in Fig.1-right. The N2 adsorption analysis shows Con-NaY has a type I isotherm, typical feature of microporous materials. In contrast, sample NM-NaY shows a pronounced typical IV isotherm with a hysteresis loop, possessing mesoporous characteristics. For sample NM-NaY, the BET external surface area is larger than that of NM-NaY (85.33 vs 26.80 m2g-1), the exhibiting more large mesoporous volume(0.42 vs 0.33 m3g-1). Pyridine Infrared spectra show that the stronger B acid amounts (higher than 350 oC) of NM-HY is more than Con-HY sample. Representative SAXS curves for samples before and after modification of SDA are shown in Figure 2. The remarkable feature is the presence of scattering shoulder at q = 0.8 nm-1 in the curve of modified SDA which is related to an average distance between nanoscopic domains, the long period. In brief, the homogeneity of particles are improved in the modified SDA compared to the Con-SDA, which is the critical factor to generate NM-NaY.A primary mechanism for Y aggregates was speculated.

Structure of directing agent and its effect on fabrication of nano-crystalline Y aggregates

253rd National Meeting (2017)

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