An improved route for the synthesis of Al13-pillared montmorillonite catalysts (original) (raw)
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Catalysis Today, 1999
A Ca 2 ±montmorillonite clay has been pillared with aluminium hydroxy polycations using ultrasonic technique. This pillared clay is compared with that obtained by conventional method of pillaring. XRD, FTIR in the framework region and surface area measurements elucidate that ultrasonically achieved pillaring is very homogeneous as compared to conventional technique. The uniform pillaring is responsible for the enhanced thermal and hydrothermal stability. However, the use of ultrasonics does not alter the inherent properties such as acidity of the pillared clays, as indicated by IR spectroscopy of adsorbed pyridine. The catalytic activities in the decomposition of propan-2-ol and cumene further con®rms the strong acidity of the pillared clays, obtained either by ultrasonic or conventional techniques. In the time on stream studies for both the reactions, slower deactivation was observed on pillared clay prepared by ultrasonication route. Thus, the pillared clay can be obtained via., ultrasonication method of intercalation within 20 min at ambient temperature, with improved textural properties leading to higher stability of the material, without compromising on acidity or catalytic activity of the pillared clay. # 1999 Elsevier Science B.V. All rights reserved.
Eurasian Chemico-Technological Journal, 2016
An accelerated diffusion of alumina precursor species in-between the gallery region of montmorillonite clays by the use of ultrasonic technique is described. This method offers a faster, efficient and attractive route for the synthesis of alumina-pillared clay catalysts. Out of the several preparative parameters studied, the role of pre-exchanged cations influenced the optimum duration of ultrasonic agitation and treatment for the pillaring process. By comparing ultrasonic route and conventional preparation procedure, it is revealed that uniform spacing of alumina pillars in the clay means homogeneously distributed acid centers. The influence of calcination temperature on the acidity and hence the catalytic activity is described. The choice of three different montmorillonite clays with different cation exchange capacities enables one to tune the pore dimensions of the pillared clays. The catalytic applications include studies on cumene cracking, dehydration of propan-2-ol and alkylation of benzene with linear olefins.
Factors affecting the preparation of alumina pillared montmorillonite employing ultrasonics
Microporous and Mesoporous Materials, 2000
In the preparation of alumina pillared clays, the intercalation step is shown to be completed within a few minutes using ultrasonics, and such materials show enhanced textural properties and improved thermal stability. The role of ultrasonics and various preparative parameters that govern the preparation of alumina pillared montmorillonite are presented. This includes the effect of exchangeable cations (Na, Ca, La), three different pillaring precursors, the concentration of pillaring species, and the concentration of the clay in suspension. It is shown that the exchangeable cations and their mode of binding influence the diffusional rates of the pillaring species. When different pillaring precursors are employed, not much variation in the textural properties of pillared clays is noticed. However, their optimum concentration is essential. It is also observed that this method can handle a concentrated clay suspension for pillaring with alumina. From the kinetics of calcium exchange experiments during pillaring, it was observed that the exchange under conventional conditions is completed instantaneously, while under ultrasonic treatment only 26% of Ca2+ exchange took place instantaneously and further exchange occurred only after ultrasonic treatment. From these observations, it is proposed that the role of ultrasonics in the present synthesis is the acceleration of diffusion of the intercalating aluminium pillaring species followed by an ion exchange process.
Journal of Porous Materials, 2016
Al pillared montmorillonites (Al-PILM) were synthesized by the reaction of Na ?-montmorillonite (Na ?-Mt) and hydroxy-Al cation after pre-intercalation with dodecylamine (DA) under different drying methods and calcination temperatures. The results showed that Al-PILM dried at room temperature was more crystalline and had larger c-axis spacing, d (001) , BET specific surface area (S BET) and microporous volume, compared to those by common air-blast drying or vacuum drying and the superiority in the above properties of the drying methods is as follows: air drying [ air-blast drying [ vacuum drying. This suggests that natural air drying at room temperature favored the formation of more ordered pillar formation. It was also found that the pre-intercalation of DA had important influence on the physicochemical properties of Al-PILM. When the amount of pre-intercalated DA was 1/2 CEC of Na ?-Mt, c-axis spacing, d (001) , S BET and microporous volume of Al-PILM were increased and larger than those prepared without pre-intercalation of DA and the former sample had a more regularly ordered pillar distribution due probably to the reduced pillar density in the montmorillonite interlayers. The DA pre-intercalated PILMs were stable at a larger range of temperatures. With the increase of calcination temperature, the interlayer spacing d (001) value decreased, and the S BET and microporous volume increased firstly and then decreased. During calcination, the pre-intercalated DA was removed and the hydroxyl-Al cation was converted into the rigid Al 2 O 3 pillars, which resulted in decreased pillar size between Mt layers followed by porosity improvement of Al-PILM.
Asian Journal of Chemistry
The preparation of aluminium pillared montmorillonite (Al-PILM) from Indonesian natural montmorillonite and its catalytic activity study in the bio-oil cracking has been investigated. The synthesis of Al-PILM catalyst was conducted through intercalation process of Al13 Keggin ion at the Al ratio of 5 mmol Al/g montmorillonite followed by dehydroxylation processing to get aluminium oxide pillar in montmorillonite interlayer. Catalyst characterization performed by XRD, surface area analyzer and surface acidity measurement and SEM. Activity test of material as catalyst in bio-oil cracking focused on the effect of Al-PILM utilization to the product distribution and liquid product composition. The result showed that Al-PILM has higher activity to produce lighter fraction of hydrocarbon than montmorillonite. The increase in liquid product and selectivity to produce smaller hydrocarbon compounds attributed to the improvement of catalyst performance after pillarization.
Journal of Catalysis, 1999
Zr- and Zr,Al-pillared smectites have been prepared and characterised by X-ray diffraction and nitrogen sorption measurements. The residual cation exchange capacities and the acid contents have been determined. Hydroconversion of heptane over Pt-impregnated samples was used to evaluate their catalytic properties. The results were compared with those obtained over Al-pillared forms of the same smectites. For the Zr-pillared clays, mixtures of pillared and unpillared fractions were obtained in proportions depending on the preparation conditions. The pillared fractions exhibited poorer thermal resistance than the corresponding Al-pillared forms. Mixed Al,Zr-pillared clays behaved much like Al-pillared clays. The conversion of heptane over the Zr-pillared montmorillonites was substantially enhanced with respect to the Al-pillared analogues, due to the enhanced hydrogenolysis on platinum. Isomerisation activity at the opposite drastically decreased. These changes were less pronounced in the case of the pillared saponites. Zr-pillared saponite with low tetrahedral charge showed an intermediate behaviour.
Synthesis and characterization of Al-pillared montmorillonite in presence of Mn(II)
Applied Clay Science, 2011
The possibility of substituting aluminum in the Keggin tridecamer [Al 13 O 4 (OH) 24 (H 2 O) 12 ] 7+ by Mn(II) has been investigated and then the obtained polycation has been used as pillars for smectite. Pillaring solutions are prepared by a slow and partial hydrolysis of Al(III)-Mn(II) aqueous solutions with different Mn/(Al + Mn) molar ratio (r = Mn/(Al + Mn) = 0, 1/13, 2/13 and 3/13) and examined by 27 Al NMR spectroscopy. Powder Xray diffraction (XRD), physisorption of N 2 , chemical analysis and scanning electron microscope analyses (SEM) are used to study the precipitated sulfate salts and/or pillared clay minerals. This study reveals the absence of MnAl 12 species in the pillaring solution. The crystal system of the obtained Al 13 -SO 4 salt is cubic (tetrahedral particles) in absence of Mn(II) and monoclinic (plate particles) in presence of Mn(II). When r is equal to 3/13, in addition to the monoclinic phase, an amorphous phase takes place. The intercalation process of montmorillonite is only disturbed, when r is equal to 3/13, because of the presence of a high polymeric aluminum phase.
Pillared clays with Al–Fe and Al–Ce–Fe in concentrated medium: Synthesis and catalytic activity
Applied Catalysis A-general, 2009
This paper proposes a new methodology for the modification of clays with the mixed Al-Fe and Al-Ce-Fe systems, which involves the synthesis of solid polymeric precursors and their use as pillaring agents in the modification of clays. The process of intercalation of clay with Al 13 , Al 13 + Fe and Al 13 + Ce + Fe nitrate was performed using ultrasound. The pillaring agents Al 13 , Al 13 + Fe and Al 13 + Ce + Fe were characterized by XRF, XRD, SEM and 27 Al NMR techniques, and pillared clays were characterized by XRF, XRD and N 2 adsorption to 77 K. The catalytic properties of pillared clays were evaluated using catalytic wet peroxide oxidation of phenol in dilute aqueous medium, demonstrating activity comparable to that of solids modified by the conventional method. ß
Solid State Ionics, 1993
The location, environment and availability of the interlamellar species in modified layered silicates have been investigated using two montmorillonites selected with different charge deficit distributions. A structural study has revealed release of protons and further migration to the lattice as thermal treatments are performed. The proton availability has been examined through a catalytic reaction, all the modified samples showing similar activities in this test. A possible explanation for this levelling effect has been suggested.