Chromium(III)-doped pillared clays (PILC's)

Abstract--Pillared bentonites were found to be efficient catalysts for the O-methyl bond cleavage of anisoles (e.g., m-methylanisole, guaiacol, and creosol) under very mild, static conditions (150"C, a few hours, inert atmosphere). The O-methyl bond cleavage led to phenolic products. Gas chromatographymass spectrometry and solid-state ~3C nuclear magnetic resonance (NMR) techniques used to probe '3C-labeled anisoles revealed that dealkylation and transalkylation reactions occurred to a large extent, and that conversion was efficient at > 95% after two days. Ortho-and para-isomers were observed exclusively, without any evidence of recta-substitution. Volatile products were determined by mass spectrometry to be '3CH3OH and ('3CH3)20. Magic-angle spinning 13C NMR experiments showed that the molecules were fairly mobile in the clay micropores prior to catalysis. After catalysis, cross-polarization NMR showed that molecular motion had decreased markedly. Ultraviolet-visible spectroscopy of the colored complexes suggested some quinone formation. The trend of clay reactivity was found to be: pillared bentonite >> acid-washed montmorillonite > untreated bentonite > pillared fluorhectorite -~ untreated fluorhectorite.

Section: Methodsmentioning

confidence: 99%

Reactivity of Anisoles on Clay and Pillared Clay Surfaces

Carrado

Hayatsu

Botto

et al. 1990

“…In principle, any metal oxide or salt forming polynuclear species upon hydrolysis can be inserted as a pillar. Most common ions used are polycationic species of AI (Shabtai et al, 1984;Pinnanvia et al, 1984;Suzuki et al, 1988;Sterte, 1991), Zr (Bartley and Buch, 1985;Burch and Warburton, 1986;Yang and Baksh, 1991), Ti (Sterte, 1986), Fe (Burch and Warburton, 1987;Yamanaka and Hattori, 1988), and Cr (Pinnavia et al, 1985;Carrado et al, 1986;Vaughan, 1987). These pillaring agents are prepared by hydrolysis of the corresponding salts in solution.…”

Section: Introductionmentioning

confidence: 99%

“…Another possible method to obtain pillared clays with mixed-oxide pillars is to use transition-metal ions by impregnation (Gil and Montes, 1997), with the pillared clay acting as a substrate. Pillared clays have been prepared also by cation exchange, either before or after initial pillaring of the clay (Suzuki et al, 1988;Carrado et al, 1986). In other cases, pillared clays were prepared by first combining the transition-metal ion with the pillaring agent and the resulting species subsequently used to pillar the clay (Occelli, 1986;Viera Coelho and Poncelet, 1991;Lee et al, 1989;Bergaya et al, 1993;Fetter et al, 1995;Cafiizares et al, 1999).…”

Section: Introductionmentioning

confidence: 99%

Enhanced Thermal Stability of Al-Pillared Smectites Modified with Ce and La

Valverde

Cañizares

Kou

et al. 2000

Abstract--A commercial bentonite (primarily smectite) from Fischer Scientific Company (F bentonite) and a natural bentonite from Peru (P bentonite) were used in the preparation of pillared clays with potyoxymetal cations of A1 that were subsequently modified with Ce and La. Several Al/metal ratios (5 and 9) were used to investigate the effects on the thermal and hydrothermal stability of these synthetic clays. The structure of these materials was studied by X-ray diffraction. Isotherms were determined by N2 adsorption. Thermal stability was determined using thermogravimetric (TG) measurements and ammonia-TPD (temperature programmedodesorption) was used to obtain acidity data. These materials exhibited basal spacings from 16 to 20 A, with surface areas from 239 to 347 m 2 g-~, with microporosity contributing from 50 to 80% of the total surface area. Pillared clays prepared from F bentonite generally showed larger basal spacings and surface areas than those prepared from P bentonite. Pillared clays modified with Ce or La did not show any apparent structural changes relative to the Al-pillared clays. Pillared clays modified with Ce and La had similar acid properties as Al-pillared clays. In contrast, the thermal and hydrothermal stabilities of these materials were greater than Al-pillared clays. However, Cepillared clay appears to be more effective than La-pillared clay in delaying the dehydroxylation of pillared clays with increasing temperature. The intercalation of Ce and La into Al-pillared clays improved the thermal stability, which may increase the utility of these materials as catalysts.

“…As the exact composition of the hydroxy-Cr polymers was not known, the structures of the interlayered species were not determined. Copyright 9 1994, The Clay Minerals Society Hydroxy-aluminochromium interlayers have been synthesized by those interested in the petrochemical applications of clays (Carrado et al, 1986). Upon calcination, the hydroxy polymers convert to fixed oxide pillars, which give the clay catalytic properties.…”

Section: Introductionmentioning

confidence: 99%

Properties of Hydroxy-Al and -Cr Interlayers in Montmorillonite

Dubbin

Goh

Oscarson

et al. 1994

Abstract-In environments contaminated with Cr, the interlayers of expandable layer silicates may serve as sinks for this potentially toxic element. As a means of determining the potential for smectites to serve as sinks for Cr, the precipitation products of A1 and Cr in the interlayers of a montmorillonite were examined. Five montmorillonite (SWy-1) day suspensions were treated with preweighed amounts of AIC13 and CrC13 to give five A1/(AI + Cr) molar ratios (1.0, 0.67, 0.5, 0.33, 0) with a total trivalent cation (M 3+ ) concentration of 600 cmol(+)/kg clay. The clay-cation suspensions were titrated with 0.1 N NaOH to give a NaOH/M 3+ molar ratio of 2.5. Analysis of the solid-phase reaction products showed that the cation exchange capacity and specific surface of all clays were reduced. Chromium reduced the exchangeability of the interlayers while A1 increased the thermal stability. X-ray diffraction analysis revealed that all Al-containing interlayer materials formed similar gibbsite-like polymers. Data from infrared spectroscopy indicated that both AI and Cr were present within the same polymer. Differential thermal analysis and thermogravimetric tracings showed that the rapid collapse of the interlayer in the Cr end-member upon heating was due to a low-temperature loss of hydroxyls. It was not possible to identify all interlayer structures in the Cr end-member. Data from X-ray photoelectron spectroscopy showed all Cr to be Cr(III). Displacement of the interlayer material became more difficult as Cr content increased. The least exchangeable interlayers, therefore, may be found in environments containing the most Cr.