M'C HIGAN STATEU Will/l"Ill/Il””I///II// l’l Hi" mm 2 3 to 3 <2; 3% 321 LIERARY Michigan State University This is to certify that the thesis entitled Synthesis and Physical Properties of Imogolite Intercalated Mentmorillonite presented by Todd Allen Werpy has been accepted towards fulfillment of the requirements for M.S. degree in Chemistry Wprofessor Date Airy tyg /f/’/ 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before date due. F———.——_———_——_———_—_—'———' DATE DUE DATE DUE DATE DUE i II x | I i l l I! l _J MSU Is An Affirmative Action/Equal Opportunity Institution SYNTHESIS AND PHYSICAL PROPERTIES OF IMOGOLITE INTERCALATED MONTMORILLONITE BY Todd Allen Werpy A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Chemistry 1987 §5\ \31 ABSTRACT SYNTHESIS AND PHYSICAL PROPERTIES OF IMOGOLITE INTERCALATED MONTMORILLONITE BY Todd Allen Werpy The interest in smectite clays as catalysts and molecular sieves has been revitalized in recent years with the advent of pillared clays. Pillared clays, as opposed to exchanged clays offer larger interlayer spacings as well as higher thermal stability. The major goal of this dissertation was to synthesize and characterize a new pillared smectite clay using imogolite as a pillar. Imogolite is a tubular aluminosilicate with an external diameter of 23A and a length of approximately 1000A. The X-ray diffraction pattern indicated that this new imogolite-montmorillonite complex has a: d(001) spacing of 41A. This is the largest reported interlayer spacing of a pillared smectite to date. This complex also shows very reasonable thermal stability as evidenced by differential thermal analysis. Several other ‘techniques were also employed in the physical characterization imogolite intercalated montmorillonite. Based on the large interlayer spacings and good thermal stability of imogolite intercalated montmorillonite there appears to be several possible applications for this complex in the area of catalysis and as a molecular sieve. To Julie and Courtney ii ACKNOWLEDGEMENTS I would like to thank Dr. T. J. Pinnavaia for his- advice and patience during the undertaking of this project. I hope that we can continue this relationship through the completion of my graduate studies. I would also like to thank Dr. D. Nocera for his guidance in editing this thesis, as well as Dr. Dye for the useful suggestions he made during my oral. Finally, I would like to thank the past and present members of my research group for their assistance and knowledge. iii TABLE OF CONTENTS CHAPTER PAGE LIST OF TABLES .......................................... vi LIST or FIGURES .................................. .l ..... vii CHAPTER I-INTRODUCTION ................................... l Pillared Clays ...................................... 2 Objectives of Thesis Research ....................... 4 Structure of Smectite Clay Minerals ................. 5 Swelling Properties of Smectites .................... 9 Acidity ........................................... 10 Ion Exchange in the Interlayer .................... 11 Physical Properties of Imogolite .................. 14 Chemical Properties of Imogolite .................. 16 CHAPTER II-EXPERIMENTAL METHODS ......................... 18 Clay Preparation .................................. 18 X-Ray Powder Diffraction (XRD) Measurements ....... '20 Chemical Analysis ................................. 20 BET Surface Area Measurements ..................... 21 Adsorption Uptake Isotherms ....................... 21 Thermal Analysis .................................. 21 Infrared Spectrometry ............................. 22 Synthesis and Pillaring ........................... 22 CHAPTER III-RESULTS AND DISCUSSION ...................... 24 Introduction ...................................... 24 Characterization of Imogolite ..................... 24 iv CHAPTER PAGE Characterization of Imogolite Intercalated Montmorillonite ....... . ......... ..... .............. 26 X-Ray Diffraction....... ..... . ..................... 26 Surface Area Measurements .......................... 34 Elemental Analysis. ................................ 34 Thermal Analysis......................... .......... 36 Adsorption Isotherms........... ..... . .............. 42 Conclusions...... .......... ........ ............. ...50 CHAPTER IV-FUTURE STUDIES...................... ........ .53 Adsorption Properties of IIM ....................... 53 Acidity.............................. ....... . ...... 53 Catalysis....................... ....... ............54 New Imogolite-Smectite Complexes......... ....... ...55 LIST OF REFERENCES... ............. . ............ . ........ 56 N LIST OF TABLES PAGE Idealized Structural Formulas for Some Dioctahedral and Trioctahedral 2:1 Phyllosilicates... .......... ...... ................ 7 Surface Area Versus Outgassing Temperature. ...... 35 Elemental Analysis of Imogolite, Dialyzed IMM, Centrifuged IIM, and Na+-Montmorillonite for Si, Al, and Mg...................................37 Pore Volumes for Dialyzed IIM and Centrifuged IIM Based on Kinetic Diameter of Various MOle-CUleSoe ..... 00.0.0000... ..... O... ........... 51 vi LIST OF FIGURES Schematic Representation of a Pillared Clay (Pinnavaia,1983) ................................. 2 Schematic Representation of the Structure of Smectite ......................................... 6 Idealized Structure of Imogolite, Si02°A1203'3+X H20 .............................. 13 Infrared Spectrum of Imogolite. Sample Prepared as KBr Disk ............................ 25‘ X-Ray Diffraction Pattern of Imogolite Air Dried on a Glass Slide .......................... 27 X-Ray Diffraction Pattern of IIM Synthesized by Various Weight Ratios of Imogolite to Montmorillonite, Washed by Centrifugation: A=3:1, 382:1, C=l.3:l, D=1:1, E-0.67:1 .......... 28 X-Ray diffraction Pattern of IIM Washed by Centrifugation, Air Dried on Glass Slides, and Heated to: A=125°C, B=250°C, C=375°C, D=600°C ......................................... 31 X-Ray diffraction Pattern of IIM Washed by Dialysis, Air Dried on Glass Slides,and Heated to: A=125°C, B=250°c, c=375°c, D=600°C ......................................... 33 vii 10 11 12 l3 14 15 16 DSC of Dialyzed IIM(A), Centrifuged IIM(B), Dialyzed Imogolite(C), and Na+-Montmorillonite(D). All Samples Were Air Dried ......... ..... ............ ... ..... . ........ 39 DTA of Dialyzed IIM(A), Centrifuged IIM(B), Dialyzed Imogolite(C), and Na+-Montmorillonite(D). All Samples Were Air Dried ................. ...... .................... 41 TGA of Dialyzed IIM(A), Centrifuged IIM(B), Dialyzed Imogolite(C), and Na+-Montmorillonite(D). All Samples Were Air Dried..... ....... . ..... '. ........... .-.. ........ 44 Adsorption Isotherm of Water on Dialyzed IIM(O) and Centrifuged IIM( ) .................. 45 Adsorption Isotherm of Nitrogen on Dialyzed IIM(O) and Centrifuged IIM( )... ............... 46 Adsorption Isotherm of n-Butane on Dialyzed IIM(O) and Centrifuged IIM( ). ................. 47 Adsorption Isotherm of Benzene on Dialyzed IIM(O) and Centrifuged IIM( ) .................. 48 Adsorption Isotherm of Perfluorotribylamine on Dialyzed IIM(O) and Centrifuged IIM( ) ......... 49 viii CHAPTER 1 INTRODUCTION 1.1 W Pillared clays are smectite minerals in which alkali metal ions in the host mineral have been replaced by thermally stable, robust cations that act as molecular props. These molecular props allow the layers to be separated in the absence of the swelling solvent[1]. Various types of cations such as alkylammonium ions[2], bicyclic amines[3], and polynuclear hydroxy metal cations[4] have been used as pillaring agents. Figure 1 is a schematic representation of a pillared clay and shows the various pillaring agents used[1]. Barrer and Mcleod[5] introduced the concept of pillared clays more than 25 years ago when they showed that permanent porosity could be introduced into montmorillonite by replacing the interlayer alkali metal with tetra- alkylammonium ions. They were able to further demonstrate that pillared clays offered selective adsorption properties and could be thought of as two dimensional zeolites. Unfortunately, these materials were overshadowed by the advances being made in the synthesis and catalytic properties of zeolites. Pillared clays are now generating a renewed interest in the area of catalysis due to the development of pillars which allow the pore sizes to be larger than that of 1 Ammmfl.mam>mccamv .mmau nonmaafim m no cowumucmmmummm owumeonom H musmah +9232 4‘ x. ......r 229.: _ _ W I. r... A. m . _ fdv ABM L a/AV \m _ 1 ...... .l t”. _ fav. fine 9&1 _ m _ ”1 .I. ..l L T+ moot a 8.3202 3 faujasitic zeolite. In addition, the pore sizes can be made adjustable by varying the size of the pillar or the spacing between the pillars. The ability of pillared clays to have adjustable pore sizes makes them especially inviting for the catalysis of larger molecules such as those found in residual crude oil[1]. Thermal stability of pillared clays is also a very important issue. The pillaring agents illustrated in Figure 1 have very different thermal stabilities. Alkylammonium and bicyclic amine cations tend to decompose at temperatures below 250°C and metal chelates below 450°C[6]. Stability to temperatures above 500°C has been obtained by Brindley and co-workers[7,8]. They also reported hydroxy aluminum and hydroxy zirconium cations formed by base hydrolysis yielded thermally stable clays with surface areas of between 200 and 500m2/g. The hydroxy zirconium pillar is an Zr4 oligomer of the type Zr4(OH)X+16_x[8]. The hydroxy aluminum pillar was first suggested to be an A16 oligomer[7], however the structure of the pillaring cation is most likely to be the A113 oligomer related to the known cation A113O4(OH)247+[9]. This has also been reconfirmed by 27A1 NMR and potentiometric titration data[1]. The formation of metal' oxide clusters upon dehydroxylation of hydroxy cations is what generates this remarkable stability for the Zr and Al pillared clays. In the case of All3-montmorillonite the formation of the metal oxide may be shown as 11.11304 (on) 28m‘3‘n) + -H20 6.5 A1203 + (3-n)H+ where the aluminum is in small clusters. The exact location of the protons in the intercalate is still not known[l]. There are synthetic limitations to the preparations of oxometal species in pillared clays. These limitations are dependent upon the hydrolysis chemistry of the desired metal. The properties of the resulting clay intercalates are related to the hydrolysis chemistry and synthesis of the oxometal species[10]. 1.2 theetixes Qf Dissertation Research A variety of cations have been shown to permanently expand smectite-type layered silicates. Each new pillaring agent brings with it new physical and chemical properties. The purpose of this research is to evaluate an entirely new approach to the pillaring of smectite clays. This ‘new approach is based on the direct intercalation of a neutral, molecular sized oxide in the galleries of a smectite clay. The oxide selected for study is a tubular silicate mineral known as imogolite. The second objective is to examine the adsorption properties of the new tubular silicate—layered silicate complex as a potential molecular sieve. 5 1.3 Strummmm ' The term "clay" refers to a finely divided material with a particle size of less than two microns. The term "clay mineral" refers to silicate clays with definite stoichiometry and crystalline structure [11]. Figure 2 illustrates schematically the idealized structure of a smectite clay mineral layer. The oxygen atoms define upper and lower sheets of tetrahedral sites and a central sheet of octahedral sites. The relationship between the two tetrahedral sheets and one octahedral sheet within a layer allows the smectite clays to be classified as 2:1 phyllosilicates. Two tetrahedral sheets condensed to an octahedral sheet compose a clay layer. The distance between the top of one layer and the top of an adjacent layer, encompassing the thickness of the clay layer and the height of the interlayer gallery is defined as the basal spacing. Basal spacings are defined by the d(001) reflection and can be measured by X-ray diffraction. The different members of the smectite group of clays are distinguished by the type and location of the cations in the oxygen framework. A unit cell consists of 20 oxygen atoms and 4 hydroxyl groups, which hold eight tetrahedral sites and six octahedral sites. When two-thirds of the octahedral sites are occupied by cations, the clay is classified as a dioctahedral 2:1 phyllosilicate. If all of the octahedral sites are occupied by cations, the clay is labelled a trioctahedral 2:1 phyllosilicate. Table 1 lists 0 Oxygen e Hydroxyls oAluminum, Magnesium. Iron oSilicon, Occassionaly Alumlnum Figure 2 Schematic Representation of the Structure of Smectite. Ae.~_oum:x ..zeve~o.x_» The Bronsted acidity of hydrated cations in the clay galleries has been shown to be greater than that of the same cations in aqueous solution[13]. The acidity can be correlated with the cation polarizing power which increases with increasing charge-to-radius ratio. Inl addition, the acidity increases as the amount of interlamellar water decreases. 1.6 MW Interlayer cations can be replaced through ion exchange reactions with other cations, such as organic ions[11], metal complexes[14], silicates[15], or polyoxo-inorganic cations[l]. Several of these are robust cations that act as pillars and prop the clay layers apart even without a solvent. Ion exchange reactions in the clay minerals have several characteristics :hl common[6]. Reaction. rates generally are controlled by diffusion of the ions into the interlayer. This process occurs as the exchanging ions move against a concentration gradient. The second common characteristic is that the exchange is stoichiometric with respect to conservation of charge. Finally, ion exchange reactions are ion selective. Among homovalent cations, the smaller the effective radius, the more preferred is the binding. 11 The ability of clays to undergo cation exchange allows for the development of several unique intercalated compounds. 1.7 W The name and structure of imogolite was first introduced by Yoshinga and Aomine in 1962. They had limited data available however, and were essentially able to only propose a chemical formula for imogolite with little information about its structure. The chemical formula that they derived using elemental analysis was 1.SSi02°A1203'2.5H20. In 1966 Wada was able to elaborate on the structure of imogolite by obtaining a relatively pure sample of imogolite. The infrared spectrum suggested a unique structure, and chemical analysis verified the presence of an oxide consisting of only Sioz, A1203, and H20. Deuterium exchange showed the presence of surface hydroxyl groups on the fibers. In 1967 Wada proposed that imogolite was simply an end member of allophane and actually had a chemical composition ranging from Si02°A1203°2H20 to allophane 28i02°A1203°3H20. In 1969 Russel et al. used infrared and electron diffraction to further elucidate the structure of imogolite. The use of electron diffraction unambiguously showed that imogolite consisted of fibers with repeat units 8.4A parallel to the fiber axis and 23A perpendicular to it. These parameters could not be satisfied by the structure proposed by Wada in 1967. The use of infrared showed an adsorption band near 930cm"1 which could be interpreted in terms of the presence of Si207 units. 12 Based on this evidence Russel et al.[l7] proposed a layered chain structure for imogolite. However, in 1972 Cradwick, Farmer, and Russel proposed that imogolite was a hydrated aluminosilicate of tubular structure. The basis for their structure evolved from a combination of various pieces of evidence. They essentially used all of the previous data reported along with a new chemical technique which allowed them to differentiate between silicate anions with low degrees of polymerization. The technique is based on the conversion of the anion to a trimethyl silyl ether and then using gas chromatography for indentification. . The application of this technique to imogolite gave products of which 95% was the orthosilicate ether and 5% was the pyrosilicate ether. Since imogolite gave such a high yield of orthosilicate ether it suggested that there is indeed an orthosilicate group in imogolite. With this additional piece of information and the other available data Cradwick, Farmer, and Russel[18]proposed the structure shown in Figure 3. The resulting idealized chemical formula for imogolite was Si02°AlZO3°2H20 this formula was in very good agreement with the experimental formula of 1.1Si02'A1203'2.5H20. This structure depicts how an orthosilicate anion might be associated with a gibbsite sheet. The orthosilicate anion displaces hydrogen from the three hydroxyl groups surrounding a vacant octahedral site. The fourth Si-O bond would then point directly away from the sheet and react with a proton to form SiOH. When this happens there would be a shortening of about 0.2A in the 0-0 edges which define the basal plane of 13 Gibbsr'tc P. imogolite 2n/n gibbsite 1 imogolite £ Figure 3 Idealized Structure of Imogolite, Sioz-Alzo3-3+x H20 14 the tetrahedral Si site from about 3.2A in gibbsite to less than 3A in imogolite. This of edge lengths agrees with the shortening of the repeat unit from 8.6A in gibbsite to 8.4A in imogolite, as well as for the curling of the gibbsite sheet in imogolite to form a tube. These tubes would contain eleven repeat units in natural imogolite and twelve repeat units in synthetic imogolite with an outside diameter of 21 and 23A respectively[18]. This is now the accepted structure for imogolite and has since been confirmed by the use of magic angle spinning NMR[19]. The first successful synthesis of imogolite in the laboratory was performed by Farmer in 1981. Farmer synthesized imogolite by the digestion of hydroxy aluminum complexes formed at a pH of 3.2 to 5.5 in aqueous solutions with aluminum concentrations of less than 5.0 mmole per liter and silicon concentrations of less than 3.0 mmole per liter. To compare the structure of synthetic imogolite to natural imogolite Farmer used electron microscopy, electron diffraction, and infrared spectroscopy. The only difference that appeared. was that synthetic imogolite was 10 to 15 percent larger than natural imogolite as expected for 12 repeat units along the circumference of the tube[20]. 1.8 W The X-ray diffraction pattern of imogolite consists of several broad reflections. These reflections occur at 12-20, 7.8-8.0, and 5.5-5.6A[21]. The X-ray diffraction pattern along with the changes that occur upon heating serve as a 15 good criterion for distinguishing imogolite from other clay minerals, since it has very few similarities with these minerals. Thermal analysis is also a usful tool for characterizing imogolite. Imogolite gives a large endothermic peak between 50-300°C on the DTA curve due to a loss of large amounts of adsorbed water. Imogolite also gives an endothermic peak at 390-420°C due 'UD dehydroxylation. The appearance of an endothermic peak at 900-1100°C is caused by imogolite changing to nmllite or gamma alumina. On the TGA curve there is a continuous weight loss from 25°C to 300°C: This weight loss accounts for about 30% of the total mass of imogolite. At 300°C there is a more abrupt weight loss of about 10% due to dehydroxylation[22]. Infrared spectroscopy shows major broad adsorption in three regions, 2800-3800cm'1, 1400-1800cm'1,and 650-1200cm'1. The stretching frequency in the region 2800-3800cm"l is attributed to OH stretching of adsorbed H20 or surface OH groups. An adsorption band due to the HOH deformation vibration occurs around 1630-1640cm’1. Imogolite also shows an adsorption band at 930cm“1 due to the Si-O stretch from the SiO3OH group[17]. Electron diffraction of imogolite gave a series of ring reflections at 1.4, 2.1, 2.3(broad), 3.3(broad), 3.7 4.1, 5.7(broad), 11.8(broad), and 21-23A[10,15]. The 1.4 and 2.1A reflections were interpreted as higher order reflections arising from a repeat unit of 8.4A along the tube axis. The 5.7, 7.8, and 11.8A reflections were interpreted as higher 16 order reflections due to 21-23A interaxial separations of the tube unit[18]. The BET surface area of imogolite was reported to be 140-170 m2/g by N2 adsorption. This was determined by using a freeze dried sample of imogolite[17]. lawman Cation exchange capacity values for natural imogolite have been hard to establish due to impurities in the soil samples. The best results were obtained by equilibrating imogolite with 0.05N NaCH3COO at a pH of 7.0. The resulting value was 30 meq/lOOg. The cation exchange capacity of imogolite comes from the dissociation of surface hydroxyl groups[22]. The surface acidity of imogolite was determined by using Hammet indicators adsorbed on the clay and by titrating them in benzene suspension with n-butylamine. The H(Al) form of imogolite was found to be the most acidic while the Na-exchanged form was only slightly less acidic. Imogolite, as with most clays, was found to be more acidic at low relative humidities (ie, less than 8%). In comparison to other clays imogolite was more acidic than gibbsite, similar to Na-allophane and much less acidic than Na-montmorillonite or kaolinite. With regard to the effect of the cation on acidity it was found that H>A1>Fe>Mg>Ca>Ba>Na>NH4, this is do to the polarizing effect of the cation. The polarizing effect increases with increasing positive charge and with decreasing radius of the ion. Imogolite also shows an 17 increase in acidity upon heating. This is most likely due to dehydration and dehydroxylation. Imogolite reaches its most acidic state at around 500°C where dehydroxylation has essentially been completed. At 900°C there is a major loss in acidity due to new mineral formation. The acid sites of imogolite are generated by the dissociation of the surface hydroxyl groups[23]. CHAPTER II EXPERIMENTAL 2.1 Enumeration Imogolite was synthesized by the hydrolysis of Al(t-OBu)3 in HClO3 solution and the subsequent reaction of the resulting aluminum solution with Si(OEt)4 at 95°C. The general procedure has been provided previously by Farmer[l8]. The naturally occurring clay mineral montmorillonite contains impurities that must be removed before exchange reactions can be undertaken. The goal is to obtain a clay that is homogeneous and free of impurities. Impurities such as soluble salts and carbonates are removed from the clay in order to enhance flocculation of the clay. Calcium carbonate should also be removed from the clay since it may prevent intercalation. It may also interfere with CBC determination due to the following equilibrium: CaCO3 4.2+ Ca2++ 0032' Sodium acetate was buffered to a pH of 5.0 with acetic acid and was used to remove carbon dioxide upon digestion at 70°C according to the following: CaCO3(S) + 2H+ —> Ca2+ + H20 +COz(g) 18 19 The exact procedure for a 5 gram clay is as follows: (1) Add 50 ml of 1N sodium acetate buffered with HOAc to a pH of 5.0 and bring the clay into suspension. (2) Digest this suspension for 1 hour at 70°C with occasional stirring. (3) Centrifuge the solution discard the supernatant. (4) Repeat the preceding steps. Free (non-lattice) iron oxides which also inhibit exchange reactions are removed by treating the clay with sodium bicarbonate solution and subsequent low temperature (80°C) treatment with sodium thiosulfate. (1) Add 40 ml of 0.3N Na-citrate and 5 ml of 1N NaHCO3. The citrate chelates with ferric iron and prevents precipitation of FeS. The bicarbonate maintains neutrality and furnishes hydroxide ion when hydrolyzed. (2) Warm the suspension to 75-80°C and slowly add lg of Na28204. Do not exceed 80°C or FeS may precipitate out of solution. Digest for 15 minutes. This causes the reduction of ferric ions to ferrous ions which can be washed away. (3) The solution is then cooled and concentrated by centrifugation and the supernatant is discarded. Hydrogen peroxide is then added to remove organic impurities in the clay. The clay is then sodium saturated by the addition of NaCl. The flocculated particles are then 20 collected and washed free of chloride ion and air dried. 2.2 X:Ba¥_Eexder_Diffraetien A Phillips X-ray diffractometer with Cu K“ radiation where (l=l.5405A) was used to measure d(001) basal spacings. All samples were prepared by allowing approximately 1ml of 1% by weight clay suspensions to air dry on a glass or quartz slide. various samples were heated under vacuum for four hours at different temperatures. Samples which were heated over 450°C were placed on quartz slides. The Bragg angle 29 peak positions were converted to d-spacings by the use of a table relating 29 values to d-spacings. The entries in the table were calculated from the Bragg equation: nA:2dsin0. 2.3 ChemicaLAnalxais Elemental analysis of the clay samples was determined by the inorganic laboratory of the Department of Toxicology, Michigan State University. J.T. Baker instra-analyzed grade Si, Al, and Mg standards were used for for the calibration of the Jarnell-Ash auto-comp ICP emission spectrophotometer. NBS plastic clay 98a served as a clay standard. The clay samples were prepared by adding 0.05g of clay sample to 0.39 of lithium borate (Aldrich Gold Label). The samples were then mixed and fused at 1000°C for 12 minutes in preignited graphite fusion crucibles. The resultant glass was transferred to 50 ml of 6% nitric acid. This solution was mixed until complete dissolution of the glass was assured. Generally 10 minutes was a sufficient amount of time. The 21 solution was then diluted to 100 ml with deionized water. 2.4 W Surface area measurements were determined on a Quantachrome Quantasorb Jr. at liquid nitrogen temperature with nitrogen as the adsorbate and helium as the carrier gas. The three point BET method was used for surface area determinations. The samples were outgassed at temperatures of 100, 200, 300, 400, 500, and 600°C under dynamic vacuum for 24 hours prior to nitrogen adsorption. 2.5 W The adsorption of organicand inorganic molecules of various kinetic diameters was measured on a McBain balance using quartz glass buckets and springs. The samples were outgassed at 350°C for 24 hours under dynamic vacuum. The probe molecules used for the adsorption were water, nitrogen, n-butane, benzene, and perfluorotributylamine with kinetic diameters of 2.65, 3.64, 4.3, 5.85, and 10.2A, respectively. The probe molecules were stirred and equilibrated in a constant temperature bath at approximately 5 degrees below room temperature. This was done to insure no capillary condensation occurred and caused erroneously high readings. 2.6mm Differential thermal analysis, differential scanning calorimetry, and thermal gravimetric analysis were carried out on a DuPont 9900 thermal analyzer. Approximately 20 mg 22 of sample was used for each run. The sample was ground slightly prior to the experiment for convenience. The DTA and TGA runs were recorded to a maximum temperature of 1100°C, while the DSC runs were recorded to a maximum temperature of 550°C. The ramp rate was identical for all three instruments, 10 degrees per minute. Also, all samples were run under an inert atmosphere of nitrogen. 2.7 MW Infrared spectra were recorded on a Perkin Elmer model 599 spectrophotometer. The samples were KBr pellets of approximately 1% by weight. All samples were gently ground for three minutes and then pressed at 10,000 psi for 10 minutes. The scan time for recording spectra over the range from 4000cm’1 to 200cm'1 was 12 minutes. Samples for infrared spectroscopy were prepared by dialyzing a solution of imogolite for 5 days, followed by air drying. The dried imogolite was then made into a disk using KBr to dilute the sample. The KBr disk was approximately 10% imogolite by weight. 2-8 anthesiumularins Imogolite was synthesized by a method analogous to that described by Farmer and Fraser[25]. Al(t-OBu)3 was allowed to hydrolyze in an equivalent amount of HClO4 at room temperature for 6-12 hours. To the resulting aluminum solution was added a 10% stoichiometric excess of Si(OEt)4. The pH of the reaction mixture was adjusted to 5.0 by the 23 dropwise addition of 1.0M ‘NaOH and then the pH was immediately readjusted to 3.5 with 1.0M acetic acid. The reaction mixture was heated at 95°C for 2 days at which time it became clear, indicating' imogolite formation” 'The solution was then tested with NH4OH to obtain a gel which verified the presence of imogolite[ZO]. A series of imogolite-montmorillonite reaction products were obtained by the dropwise addition of a 1.0 weight% suspension of Na+-montmorillonite to imogolite at several ratios of smectite to imogolite. The solutions were stirred for 3-6 hours, and the products were washed either by centrifugation or by dialysis. The centrifugation procedure required a minimum of three washings to remove the excess imogolite and other impurities. Dialysis was done using SpectrophorTM membrane tubing having as molecular weight cutoff of 12,000-14,000. The dialysis was done for a minimum of 5 days with the water being changed every hour for the first 6 hours and then every 12 hours. The final pH in both cases was between 3.9-4.1. CHAPTER III RESULTS AND D ISCUSS ION 3.1 Introductien The synthesis of imogolite-intercalated montmorillonite has been recently claimed by Johnson and Pinnavaia[24]. A major objective of this work was to establish the optimum conditions for synthesis of this intercalated complex. A second objective was to determine whether or not the imogolite tubes were intercalated in the clay or somehow bound to the external surface. The final objective was to obtain some physical and chemical properties of this material and determine its potential use as a solid acid catalyst, or, possibly a shape selective catalyst. The reason for examining this material as a catalyst is because of the unique shape of imogolite and the potentially large d(001) spacings that would be obtained if the tubes are indeed intercalated. 3.2 WW: Imogolite was characterized by infrared spectroscopy, X-ray diffraction, and elemental analysis. The infrared spectrum is shown in Figure 4. There is an adsorption band at 980cm"1 indicating the presence of an orthosilicate group. There is a second adsorption band at 328cm‘1 which is a characteristic signature of imogolite[25]. The mode responsible for this band has not been defined. 24 25 OON .xmaa umx mm poummoum «Anamm .ouaaomoeu no Esuuooam poumuucu v unamwh ¢