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Growth of zeolite a on rutile, sapphire and quartz
H.G. Karge and J. Weitkamp (Eds.) Zeolite Science 1994: Recent Progress and Discussions Studies in Surface Science and Catalysis, Vol. 98 9 1995 Elsevier Science B.V. All rights reserved.
GROWTH OF ZEOLITE A ON RUTILE, SAPPHIRE AND QUARTZ A.Erdem-~enatalar*, H. van Bekkum* and J.C. Jansen* * Istanbul Technical University, Department of Chemical Engineering 80626 Maslak, Istanbul, Turkey. * Delft University of Technology, Laboratory for Organic Chemistry and Catalysis Julianalaan 136, 2628 BL, Delft, The Netherlands.
SUMMARY Single crystals of zeolite A have been grown on essentially fiat single crystal surfaces of 001 futile and sapphire and on single crystals of quartz. Two events of nucleation were observed, one initially on the support surface directly from dilute solution, and the other from a gel layer which formed later on the surface, resulting in a bimodal size distribution. Type of the support was seen to influence both events as was reflected in the orientation of the crystals. Formation of a monolayer of randomly oriented crystals of A was followed by time experiments on quartz surfaces.
INTRODUCTION
Recently, thin films and coatings of zeolites have been prepared for catalysis, separation and sensor applications. In particular, continuous monolayers of silicalite-1 crystals were grown on silicon wafer as support, the orientation of the crystals being a function of the presence of a continuous gel layer preceeding the crystallization [1]. In the case of low SilAI zeolites, however, nonuniform multilayers of randomly oriented crystals were reported [2].
The purpose of this work is to gain more insight on whether a particular gel phase can be formed or excluded in order to prepare a monolayer of zeolite A crystals either from a precursor phase or directly on the support surface. For this purpose, we followed the growth of single crystals of zeolite A on essentially flat single crystal supports of rutile, sapphire and quartz, which have physical and/or chemical framework matching properties with the zeolite A crystals. EXPERIMENTAL
Single crystal essentially flat 001 wafers of futile and sapphire and quartz single crystals were used as supports. Synthesis mixtures of different compositions were prepared using sodium aluminate, sodium hydroxide and sodium silicate solutions. PET bottles containing the supports, precleaned and placed in teflon inserts, were kept in a preheated oven at 65, 80 or 100 ~ for various periods. The surfaces, after being cooled and cleaned, were studied with optical microscopy, SEM and XRD. The 001 single crystal surfaces of the rutile and sapphire wafers were sampled for at least 100 single crystals of zeolite A, with SEM , using equal areas of I00 l~m2, selected randomly from different sections of the wafers.
3]
RESULTS AND DISCUSSION After the preliminary experiments with typical zeolite A synthesis mixture compositions, it was found to be necessary to strongly dilute the synthesis mixture in order to obtain a monolayer of zeolite A crystals. In a particular series of experiments from synthesis mixtures having a molar oxide composition of 10 Na20:0.2 AI203:1.0 SiO2:200 H20, growth of single crystals of zeolite A could be observed on the surfaces, much earlier than any crystal formation was observed in the bulk solution by conventional techniques. Two events of nucleation were indicated by the bimodal crystal size distribution of zeolite A, especially on rutUe and quartz surfaces. After the initial nucleation which started on the support surface in the dilute synthesis mixture resulting in relatively large crystals with enriched morphology, a continuous thin gel layer was formed on the surface initiating an explosion of small crystal formation. Type of the support surface was seen to influence both events. Of the large crystals born at an early stage on the support surface when still no gel phase was present, a substantial part (60 %) was edge oriented on futile whereas a fiat orientation was preferred on sapphire. No absolute orientation relation occurred though, despite the presence of local lattice matching units, for example in the case of 001 futile. The small crystals were mainly face oriented on futile. However, like the large crystals they were not alligned, which excludes epitaxy. It is therefore concluded that as soon as the crystallites growing in the gel layer touch the support surface, they become face oriented by electrical and surface tension forces, in this case. The absence of small crystals on the sapphire surface and the fact that their fiat orientation was not observed on quartz, indicate that the formation
and
physical/chemical nature of the gel layer are determined by the type of the support surface used. The formation of a monolayer, fiat on one side, of zeolite A crystals could be followed by time experiments at 65 ~
on quartz surfaces. The initial rate of nucleation is strongly
dependent on the surface topology and/or orientation of the support surface in the reaction mixture, as was seen from the markedly different larger crystal populations on different faces of the single quartz crystals. The growth rate, on the other hand, estimated to be 0.8 i~m/h for the initial crystals formed on the surface, was much higher than that for the second crop of smaller crystals growing from the gel, which was on the order of 0.3 l~m/h.
REFERENCES
1. J.C.Jansen, W.Nugroho and H. van Bekkum, Proc. 9th. IZC, Montreal (1992), R. von Ballmoos, J.B.Higgins and M.M.J.Treacy (Eds.), 247. 2. M.W.Anderson, K.S.Pachis, J.Shi and S.W.Carr, J.Mater.Chem., 2(1992), 255.
GROWTH OF ZEOLITE A ON RUTILE, SAPPHIRE AND QUARTZ A.Erdem-~enatalar*, H. van Bekkum* and J.C. Jansen* * Istanbul Technical University, Department of Chemical Engineering 80626 Maslak, Istanbul, Turkey. * Delft University of Technology, Laboratory for Organic Chemistry and Catalysis Julianalaan 136, 2628 BL, Delft, The Netherlands.
SUMMARY Single crystals of zeolite A have been grown on essentially fiat single crystal surfaces of 001 futile and sapphire and on single crystals of quartz. Two events of nucleation were observed, one initially on the support surface directly from dilute solution, and the other from a gel layer which formed later on the surface, resulting in a bimodal size distribution. Type of the support was seen to influence both events as was reflected in the orientation of the crystals. Formation of a monolayer of randomly oriented crystals of A was followed by time experiments on quartz surfaces.
INTRODUCTION
Recently, thin films and coatings of zeolites have been prepared for catalysis, separation and sensor applications. In particular, continuous monolayers of silicalite-1 crystals were grown on silicon wafer as support, the orientation of the crystals being a function of the presence of a continuous gel layer preceeding the crystallization [1]. In the case of low SilAI zeolites, however, nonuniform multilayers of randomly oriented crystals were reported [2].
The purpose of this work is to gain more insight on whether a particular gel phase can be formed or excluded in order to prepare a monolayer of zeolite A crystals either from a precursor phase or directly on the support surface. For this purpose, we followed the growth of single crystals of zeolite A on essentially flat single crystal supports of rutile, sapphire and quartz, which have physical and/or chemical framework matching properties with the zeolite A crystals. EXPERIMENTAL
Single crystal essentially flat 001 wafers of futile and sapphire and quartz single crystals were used as supports. Synthesis mixtures of different compositions were prepared using sodium aluminate, sodium hydroxide and sodium silicate solutions. PET bottles containing the supports, precleaned and placed in teflon inserts, were kept in a preheated oven at 65, 80 or 100 ~ for various periods. The surfaces, after being cooled and cleaned, were studied with optical microscopy, SEM and XRD. The 001 single crystal surfaces of the rutile and sapphire wafers were sampled for at least 100 single crystals of zeolite A, with SEM , using equal areas of I00 l~m2, selected randomly from different sections of the wafers.
3]
RESULTS AND DISCUSSION After the preliminary experiments with typical zeolite A synthesis mixture compositions, it was found to be necessary to strongly dilute the synthesis mixture in order to obtain a monolayer of zeolite A crystals. In a particular series of experiments from synthesis mixtures having a molar oxide composition of 10 Na20:0.2 AI203:1.0 SiO2:200 H20, growth of single crystals of zeolite A could be observed on the surfaces, much earlier than any crystal formation was observed in the bulk solution by conventional techniques. Two events of nucleation were indicated by the bimodal crystal size distribution of zeolite A, especially on rutUe and quartz surfaces. After the initial nucleation which started on the support surface in the dilute synthesis mixture resulting in relatively large crystals with enriched morphology, a continuous thin gel layer was formed on the surface initiating an explosion of small crystal formation. Type of the support surface was seen to influence both events. Of the large crystals born at an early stage on the support surface when still no gel phase was present, a substantial part (60 %) was edge oriented on futile whereas a fiat orientation was preferred on sapphire. No absolute orientation relation occurred though, despite the presence of local lattice matching units, for example in the case of 001 futile. The small crystals were mainly face oriented on futile. However, like the large crystals they were not alligned, which excludes epitaxy. It is therefore concluded that as soon as the crystallites growing in the gel layer touch the support surface, they become face oriented by electrical and surface tension forces, in this case. The absence of small crystals on the sapphire surface and the fact that their fiat orientation was not observed on quartz, indicate that the formation
and
physical/chemical nature of the gel layer are determined by the type of the support surface used. The formation of a monolayer, fiat on one side, of zeolite A crystals could be followed by time experiments at 65 ~
on quartz surfaces. The initial rate of nucleation is strongly
dependent on the surface topology and/or orientation of the support surface in the reaction mixture, as was seen from the markedly different larger crystal populations on different faces of the single quartz crystals. The growth rate, on the other hand, estimated to be 0.8 i~m/h for the initial crystals formed on the surface, was much higher than that for the second crop of smaller crystals growing from the gel, which was on the order of 0.3 l~m/h.
REFERENCES
1. J.C.Jansen, W.Nugroho and H. van Bekkum, Proc. 9th. IZC, Montreal (1992), R. von Ballmoos, J.B.Higgins and M.M.J.Treacy (Eds.), 247. 2. M.W.Anderson, K.S.Pachis, J.Shi and S.W.Carr, J.Mater.Chem., 2(1992), 255.