Synthesis of Zeolite Y Nanocrystals from Clear Solutions
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Synthesis of Zeolite Y Nanocrystals from Clear Solutions Y. Shen, M.P. Manning, J. Warzywoda, and A. Sacco Jr. Center for Advanced Microgravity Materials Processing Northeastern University Boston MA 02115 USA
ABSTRACT Synthesis of zeolite nano-sized crystals has attracted much attention because of their properties, some of which maybe different from the normal sized crystals. A synthesis adopted by Voltchev and Mintova was used as the starting point: 0.078 Na2O: 4.35 SiO2: 1.0 Al2O3: 2.35 (TMA)2O: 248 H2O. Both the silicate and aluminum starting solutions were clear. Zeolite Y nanocrystals with zeolite A nanocrystals as an impurity were obtained with a size range of 20-100 nm through this synthesis technique. INTRODUCTION There has been considerable research over the years in synthesis of large zeolite crystals with sizes approaching the sub-millimeter range. This interest was driven by specific technological applications favoring larger crystals or because crystal structure – property relations could be better determined using larger crystals. Zeolite Y, in particular, plays an important role today in the field of cracking process catalysis - hence, this work focused on this zeolite. There have been several reports recently on the synthesis of small zeolite crystallites, such as zeolites A, X, L, Beta, ZSM-5 and Silicalite [1-7]. However, there are only few articles about synthesis of nano-sized zeolite Y [1,2]. Those articles explored the possibility of the synthesis of nano-sized particles [1] and the effect of Na2O/Al2O3 on the particle size [2]. The influence of the Si/Al ratio, aging time, the sodium content and TMA content in starting solution on the purity, crystal size, Si/Al ratio in crystals and yield of nano-sized zeolite Y was investigated. EXPERIMENTAL In this synthesis, zeolite Y nanocrystals were grown from clear aluminosilicate solutions with different composition. The following reagents were used: Ludox SM-30 colloidal silica (30 wt% SiO2, 0.56 wt% Na2O, 0.01 wt% NaCl, 0.03 wt% Na2SO4, 69.4 wt% H2O, Aldrich), aluminum isopropoxide (Al(OiPr)3, 98+%, Aldrich), tetramethylammonium hydroxide (TMAOH, 25 wt% aqueous solution, Aldrich), and deionized water. From the literature in which nanocrystals were obtained Ludox SM-30 has always been used as the silica source. Deionized water was filtered twice through 0.2 and 0.1 µm membrane filters to reduce the particulate sources of undesired ions. All other reagents were used as received. The synthesis mixtures were prepared from two clear precursor solutions. Solution I was prepared in a 60 ml HDPE bottle by adding Al(OiPr)3 into the double-filtered deionized water and TMAOH mixed solution. A white precipitate appeared in solution I upon addition of Al(OiPr)3, and therefore the mixture was stirred at room
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temperature using a magnetic stirrer until a clear solution formed. Solution II was formed by combining Ludox SM-30 with double-filtered deionized water in 30 ml HDPE bottle. The precursor solutions were mixed together in a 125 ml HDPE bo
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