Sorption and catalysis on sodium-montmorillonite interlayered with aluminum oxide clusters

Abstract-The surface charges and the zeta potential ofa Na-montmorillonite (Na-mont) and two pillared montmorillonite (MP1 and MP2) samples with different aluminum contents were determined by potentiometric titrations and electrophoretic measurements. At pH > 9 the two pillared montmorillonite samples showed zeta potentials similar to those of Na-mont, but at pH <8, the negative zeta potential shifted to lower negative values as the aluminum content increased. Sample MP 1, which had a greater A1 content, showed an isoelectric point (IEP) of 5.0-5.5. Titration curves obtained by acid-base potentiometric titration for sample MP1 showed a well-defined cross-over point at pH = 5.0, whereas this point was not observed for sample MP2 in the pH range studied. The results indicate, in principle, that both techniques can be used to characterize surface charges in this type of material. An attempt was also made to relate the data obtained from electrophoretic mobility and potentiometric titrations.

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Study of Some Physicochemical Properties of Pillared Montmorillonites: Acid-Base Potentiometric Titrations and Electrophoretic Measurements

Avena

1990

“…These modified clay minerals have attracted considerable attention as acid catalysts for petroleum refining (Occelli 1983) and other acid-catalyzed reactions (Occelli et al 1985;Burch and Warburton 1986). Hydroxyl groups on the surface of the layer aluminosilicates are very important with respect to the use of these solids in catalysis or adsorption.…”

Section: Introductionmentioning

confidence: 99%

Properties and Catalytic Activity of Acid-Modified Montmorillonite and Vermiculite

Ravichandran

Sivasankar

1997

124

Abstract--The acidic properties of acid-modified montmorillonite and vermiculite were determined by pyridine and ammonia adsorption to correlate with the alkylating and dehydrating activity of the activated samples. Treatment of the minerals with different concentrations of hydrochloric acid results in the variation of overall acidity and density of acidic sites. Infrared (IR) spectral and differential scanning calorimetric analyses have revealed the presence of Bronsted and Lewis acid sites on the activated samples. The catalytic activity towards the above reaction has been correlated to the acid strength and density of Lewis acid sites. Treatment of montmorillonite with hydrochloric acid in the range of 0.1 and 0.3 M and vermiculite with 0.2 to 0.3 M seemed to be suitable for the conversion of methanol into olefin-rich hydrocarbons. Acid-activated montmorillonite catalyzed the isopropylation of benzene to a maximum extent of 16%, whereas acid-activated vermiculite gave a maximum conversion of only 4%.

“…Well-defined pore structures in the range 1-2 nm can be obtained. A great variety of catalysts have, thus, been prepared that are active for cracking (Vaughan et al, 1979(Vaughan et al, , 1981, alkylation (Occelli et al, 1985;Matsuda et al, 1986), dehydrogenation , or epoxidation (Choudary et at., 1990a(Choudary et at., , 1990b, according to the nature of the pillars.…”

Section: Introductionmentioning

confidence: 99%

Preparation and Characterization of Montmorillonites Pillared by Cationic Silicon Species

Fetter

Tichit

Massiani

et al. 1994

Abstract--The hydrolysis of 2-(2-trichlorosilylethyl)pyridine (TCSEP) or 3-aminopropyltrimethoxysilane (APTMS) yields a complex mixture of oligomers, the composition of which is a function of time. zgSi NMR measurements show that the same oligosilsesquioxanes can be obtained from both compounds after prolonged hydrolysis. Ion exchange by monlmorillonite with the pillaring solution obtained from TCSEP results in partial intercalation, with a noticeable fraction of the clay exchange sites occupied by protons not by the Si cationic species. Calcination of this pillared clay results in a mixture of phases showing 1.86 or 1.56 nm basal spacings. Pillaring of the same montmorillonite by the solution obtained by partial hydrolysis of APTMS results in a homogeneous solid with a basal spacing of 2 nm, which reduces to 1.65 nm upon calcination above 773 K. The microporous volume (pores < 1 nm) of these Siclays, determined after calcination at 773 K, 0.15 ml/g for the PILC obtained from TCSEP, and 0.186 ml/g for the PILC obtained from APTMS is comparable to that measured for AI or Zr pillared clays. A better thermal stability is observed for the clay pillared by APTMS, which retains a large microporosity (0.167 ml/g) up to 973 K in air. These Si-pillared clays show a small number of weakly acidic sites and some strongly acidic sites retaining ammonia up to 723 K, which are most likely localized on the clay layers.