Catalysis Pillared clays

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. 

These findings enrich our knowledge of pillared clays and have potential applications in tailor-design nanoporous materials for adsorption and catalysis. 

Abbreviations AD, asymmetric dihydroxylation BPY, 2,2 -bipyridine DMTACN, 1,4-dimethyl-l,4,7-triazacyclonane EBHP, ethylbenzene hydroperoxide ee, enantiomeric excess HAP, hydroxyapatite LDH, layered double hydroxide or hydrotalcite-type structure mCPBA, meta-chloroperbenzoic acid MTO, methyltrioxorhenium NMO, A-methylmorpholine-A-oxide OMS, octahedral molecular sieve Pc, phthalocyanine phen, 1,10-phenantroline PILC, pillared clay PBI, polybenzimidazole PI, polyimide Por, porphyrin PPNO, 4-phenylpyridine-A-oxide PS, polystyrene PVP, polyvinylpyridine SLPC, supported liquid-phase catalysis f-BuOOH, tertiary butylhydroperoxide TEMPO, 2,2,6,6-tetramethyl-l-piperdinyloxy TEOS, tetraethoxysilane TS-1, titanium silicalite 1 XPS, X-ray photoelectron spectroscopy. 

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... 

The role of catalysis in the petroleum industry has been equally revolutionary. Meta I-supported systems (e.g. of Topsoe and Shell) for catalytic reforming, hydrodesulfurization and hydrodenitrification, alkylation catalysts and shape selective systems (e.g. zeolites and pillared clays) for catalytic cracking (FCC) and production of gasoline from methanol (Mobil MTG) all represent significant technical and commercial achievements. 

Bradley, S.M. and Kydd, R.A., 1991. A Comparison of the Thermal Stabilities of Gaj3, GaAlj2 and AIj3 Pillared Clay Minerals. Catalysis Letters, 8 185. 

Figueras, F., 1988. Pillared Clays as Catalysts. Catalysis Reviews-Science and Engineering, 30(3) 457. 

Ming-Yuan, H., Zhonghui, L. and Enze, M., 1988. Acidic and Hydrocarbon Catalytic Properties of Pillared Clays. Catalysis Today, 2 321. 

Vaughan, D. E. W. 1988. Pillared clays—A historical perspective. Catalysis Today, 2 187-198. 

Recently, it has been shown that hydrotalcite-type clays interlayered by polyoxometalate anions lead to a new class of pillared materials for selective adsorption and catalysis. The heptamolybdate- and decavanade-pillared hydrotalcite-type clays were synthesized by Drezdzon (1988). An organic-anion-pillared clay precursor was prepared and subsequently exchanged with the appropriate isopolymetalate under mildly acidic conditions (pH = 4.T-4.9). These pillared intercalates were found difficult to obtain in highly crystalline form. This is ascribed to the fact that the Mg and Al hydroxide layers have a basic nature, whereas Mo7024 and anions are stable in acidic conditions. 

R. Burch (ed.) "Pillared Clays" Special Edition of Catalysis Today, Elsevier, Amsterdam, 1988. 

On September 25-30, 1988 in Los Angeles, California the first ACS Symposium on zeolite synthesis emphasized the importance that gel chemistiy, zeolite nucleation, crystal growth, crystallization kinetics, and structure-directing phenomena have in understanding zeolite (and molecular sieve) synthesis. The objectives of a similar ACS Symposium held in New York on August 25-30, 1990 where expanded to include papers on pillared clay synthesis and on the synthesis of other microporous materials that could be used in catalyst preparation. About 90% of all the chemical processes in the U.S. are based on catalysis and today catalysts have become indispensable to petroleum refining, an industry that in 1990 had sales of 140 billion (U.S. Dept, of Commerce U.S. Industrial Outlook, 1991). 

Six of the eleven chapters are devoted primarily to the intercalation chemistry of smectite clays, the most versatile among all lamellar compounds. Two of these chapters are devoted to the experimental and theoretical aspects of the clay structures and surface chemistry, including chemical catalysis. Organo clays and polymer-clay nanocomposites, the adsorption of nitroaromatic compounds of environmental significance onto clay surfaces, photochemical processes, and pillared clays and porous clay heterostructures are the subjects of the remaining four chapters. These six chapters provide detailed discussions of the factors that influence access to the intragallery surfaces of the clay host and the materials properties of the resulting intercalates. 

The content of this Handbook reflects the fact that the bulk of knowledge in this field concerns clays. In Part 1, which concentrates on clays, there is considerable focus on clay-organic interactions because of their relevance to catalysis. A chapter on nitroaromatic compound sorption is included because it provides an excellent example of clay-organic interactions. Other pertinent topics include molecular modeling of surface chemistry and photochemical processes, including photocatalysis. Pillared clays and porous clay heterostructures are the subject of an entire chapter. Chapters in Part 2 cover synthesis, characterization, host-guest pillaring, sorption, and catalysis for each class of layered material. 

Vaccari details other reactions as well, including the loading of elements such as Pt, Pd, Ru, Rh, Ni, and Cu to create hydrogenation catalysts (where the lamellar structure appears to add size and shape selectivity), Diels-Alder reactions, phenol nitration, and triphase catalysis (66). Pillaring clays has offered many new possibilities, especially with respect to shape selectivity, as is discussed in Chapter 6. 

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