Aluminum-pillared clays

G. Manos, Y. I. Yusof, N. H. Gangas, and N. Papayannakos, Tertiary Recycling of Polyethylene to Hydrocarbon Fuel by Catalytic Cracking over Aluminum Pillared Clays, Energy Fuels, 16, 485-489 (2002). 

The original pillared clays were made by (/) mixing smectite with a polymeric cationic hydroxy metal complex such as aluminum chlorhydrol (2) allowing a minimal amount of time for the cationic hydroxy metal complex to exchange with the interlayer cations and (7) calcining the resulting material to decompose the hydroxy metal complex (110). A number of newer methods have been developed to make pillared clays (111—117). 

In this section we first describe the results of measurements made on fresh and aged solutions. Potentlometric, pH, measurements, which Indicate the extent of hydrolysis of the aluminum Ions, were made on all solutions during the aging process. Next, we report surface areas of pillared clays made from the aged solutions. Finally, we will discuss the cracking activities of some selected pillared clay samples. 

Fig. 5 (a) shows the nitrogen adsorption isotherms of aluminum hydroxy pillared clays after heat-treatment at 300-500°C. These are of the typical Langmuir type isotherm for microporous crystals. Fig, 5 (b) shows the water adsorption isotherms on the same Al-hydroxy pillared clays [27]. Unlike the water adsorption isotherms for hydrophilic zeolites, such as zeolites X and A, apparently these isotherms cannot be explained by Langmuir nor BET adsorption equations the water adsorption in the early stages is greatly suppressed, and shows hydrophobicity. Water adsorption isotherms for several microporous crystals [20] are compared with that of the alumina pillared clay in Fig. 6. Zeolites NaX and 4A have very steep Langmuir type adsorption isotherms, while new microporous crystals such as silicalite and AlPO -S having no cations in the...

Iron impurities in clays have been thought responsible for these type of catalysts low carbon selectivity (4,5). The purpose of this paper is to investigate and report the influence that the location, chemical state and environment of iron impurities have on the cracking properties of pillared clays prepared by reacting several smectites with aluminum chlorhydroxide solutions. 

Here we report the synthesis and catalytic application of a new porous clay heterostructure material derived from synthetic saponite as the layered host. Saponite is a tetrahedrally charged smectite clay wherein the aluminum substitutes for silicon in the tetrahedral sheet of the 2 1 layer lattice structure. In alumina - pillared form saponite is an effective solid acid catalyst [8-10], but its catalytic utility is limited in part by a pore structure in the micropore domain. The PCH form of saponite should be much more accessible for large molecule catalysis. Accordingly, Friedel-Crafts alkylation of bulky 2, 4-di-tert-butylphenol (DBP) (molecular size (A) 9.5x6.1x4.4) with cinnamyl alcohol to produce 6,8-di-tert-butyl-2, 3-dihydro[4H] benzopyran (molecular size (A) 13.5x7.9x 4.9) was used as a probe reaction for SAP-PCH. This large substrate reaction also was selected in part because only mesoporous molecular sieves are known to provide the accessible acid sites for catalysis [11]. Conventional zeolites and pillared clays are poor catalysts for this reaction because the reagents cannot readily access the small micropores. 

Cheng J, Yu SM, Zuo P (2006) Horseradish peroxidase immobilized on aluminum-pillared interlayered clay for the catalytic oxidation of phenolic wastewater. Water Res 40 283-290... 

Recent advances in this technology include the use of 2 1 clays converted to hydrophobic forms through the introduction of surfactants in the interlayer. For example, Boyd et al. (1991) introduced cationic chain surfactants into 2 1 clay minerals. Such clays were demonstrated to have high affinity for hydrophobic organic chemicals. Additionally, polyethylene oxides (PEOs) have been intercalated into aluminum-pillared montmorillonite (Montarges et al., 1995). Because PEOs have a... 

Many cation-exchanged clays are suitable for the production of metal-oxide-pillared clays. The hydrolysis of the cation helps the pillaring step, so, at first, the aluminum ion was applied as a pillaring agent. Later, other elements were also used, for example, zirconia chromium iron transition metal elements and some lantanoids, organometallic complexes, surfactants, and polymers. 

The acidity of pillared clays has been characterized by both microcalorimetric measurements of the adsorphon of aromatic molecules and pyridine and the catalytic ethylbenzene test reaction [111]. The aromatic probe molecules used were a reactant and a product of the catalytic reaction ethylbenzene and m-diethylben-zene, respectively. In this way, only the strongest of the accessible acid sites were htrated. The heats of adsorphon of these molecules indicate that a zirconium oxide pillared clay had stronger acidity than an aluminum oxide pillared clay, whereas the pyridine results were equal for both samples. 

The most well-known examples are aluminum oxide pillared clays, which are stable in both oxidizing and reducing atmospheres. AI2O3 pillared clays are... 

The smectite clays exhibit catalytic activity related to the presence of add sites contained at the surface of the clay layer. The role the pillar plays in the catalytic activity of these materials has not been successfiiUy elucidated due to the overriding activity found in the clay itself. The aluminum pillar, for example, produces both Bronsted and Lewis acidity upon thermal treatment ... 

Parker WO Jr, Millitri R, Kiricsi I (1995) Aluminum complexes in partially hydrolyzed aqueous AICI3 solutions used to prepare pillared clay catalysts. Appl Catalysis A General 121 L7-L 11 Persson P, Karlsson M., Ohman L-O. (1998) Coordination of acetate to Al(III) in aqueous solution and at the water-aluminum hydroxide interface a potentiometric and attenuated total reflectance FTIR study. Geochim Cosmochim Acta 62 3657-3668... 

Selectivity in the dehydration of olefins is improved with pillared clays. Clays with aluminum oxide or mixed aluminum and iron oxide pillars converted isopropyl alcohol to propylene with more than 90% selectivity.256 A small amount of isopropyl ether was formed. When zeolite Y is used, the two products are formed in roughly equal amounts. A tantalum-pillared montmorillonite converted 1-butanol to butenes at 500°C with 100% selectivity at 41% conversion.257 The product contained a 17 20 16 mixture of 1 -butene/c/s-2-butene/fra/ s-2-butene. No butyraldehyde or butyl ether was formed. A pillared clay has been used for the alkylation of benzene with 1-dodecene without formation of dialkylated products.258 The carbonylation of styrene proceeded in 100% yield (6.50).259... 

Finally, between the TOT layers of a smectite, large cationic species that are polymeric or oligomeric hydroxyl metal cations formed by the hydrolysis of metal salts of aluminum, gallium, chromium(III), silicon, titanium(IV), iron(III), and mixtures of them can be inserted by cation exchange, giving the so-called pillared clays... 

Protons are released upon heating which in part balance the negative charge of the host clay layers. A number of review articles have recently appeared which summarize the synthesis and physical properties of metal oxide pillared days derived fix>m the intercalation of polyoxocations of aluminum, zirconium, chromium and many other metals [10-12]. The Lewis acid sites provided by coordinatively unsaturated metal ion sites on the pillar and the Bronsted addity formed upon thermolysis imparts novel chemical catalytic properties [13,14]. Since the pores between pillars often are larger than those foimd in conventional zeolites, there is considerable interest in the use of metal oxide pillared clays for the processing of large organic molecules, espedally petroleum [14-17]. 

Pillared clays have shown a diversity of behaviors indicating that they may find applications as catalysts. The theoretical pore sizes for aluminum Keggin ion- pillared clays are calculated and compared with literature data. Layered phosphates and titanates have much higher charges, which should produce smaller cavities. Methods of achieving a range of pore sizes are described and compared to preliminary experimental results on the pillaring of these classes of layered compounds. 

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