Catalysts clay catalysis

First, the question of where nucleotide monomers may have come from is critical. Given that the formose reaction is the most likely candidate for the synthesis of prebiotic ribose, but yields very little pure material, the role of stereoselective catalysts (clays, amino acids, or lipid aggregates) in directing the reaction should be fully explored. In this respect, Wachters-hauser16 has advanced a scheme for nucleotide synthesis based on pyrite catalysis than can be readily tested. 

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... 

Other THF polymerization processes that have been disclosed in papers and patents, but which do not appear to be in commercial use in the 1990s, include catalysis by boron trifluoride complexes in combination with other cocatalysts (241—245), modified montmorrillonite clay (246—248) or modified metal oxide composites (249), rare-earth catalysts (250), triflate salts (164), and sulfuric acid or Aiming sulfuric acid with cocatalysts (237,251—255). 

Some work has also been achieved with heterogeneous catalysis. These catalysts include Amberlyst-15, Nafion-H, montmorillonite KSF clay, ferrihydrite silica gel aerogels containing 11-13% iron, silica sulfuric acid, and zeolites. ... 

Traditionally, the production of LABs has been practiced commercially using either Lewis acid catalysts, or liquid hydrofluoric acid (HF).2 The HF catalysis typically gives 2-phenylalkane selectivities of only 17-18%. More recently, UOP/CEPSA have announced the DetalR process for LAB production that is reported to employ a solid acid catalyst.3 Within the same time frame, a number of papers and patents have been published describing LAB synthesis using a range of solid acid (sterically constrained) catalysts, including acidic clays,4 sulfated oxides,5 plus a variety of acidic zeolite structures.6"9 Many of these solid acids provide improved 2-phenylalkane selectivities. 

Montmorillonite is a laminar and expandable clay with wet binding properties and widely available throughout the world. The layers have permanent negative charges due to isomorphic substitutions. The scientific interest of montmorillonite lies in its physical and chemical properties as well as its low price. Consequently, the industrial application of montmorillonite is an attractive process [1]. On the other hand, among numerous reports published so far, crystallization of zeolite Beta draws much attention because of its unique characteristics, in particular, acidity and acid catalysis. It is reasonable to conceive that a catalyst system based on Beta/montmorillonite composite with suitable composition should provide a good catalytic capacity. 

In this chapter, we demonstrate the potential of such agents as catalysts/promoters in key steps for the derivatization of sugars. The most significant catalytic approaches in carbohydrate chemistry that use aluminosilicate porous materials, namely zeolites and montmorillonite clays, are reviewed and discussed. Silica gel is a porous solid silicate that has also been used for heterogeneous catalysis of organic reactions in general. We include here its usefulness as promoter and reagent support for the reactions under consideration. 

Z- Configuration is typical of the majority of a-aryl(hetaryl)-/V-alkylaldo-nitrones. The isolation of -isomers in the condensation of aromatic aldehydes with iV-j3-]ihenyletli Tliydroxylamine has been described (155). The synthesis of a, N -diary lnitrones gives best results if acidic catalysis is employed (156), or when clay is used as a catalyst (157). Significant reduction of reaction time and increase in the yields of nitrones can be achieved if microwave irradiation is used (158, 159). On the basis of polymeric arylaldehydes, the synthesis of polymeric a,-diarylnitrones has been described (160). 

A heterogeneous natural system such as the subsurface contains a variety of solid surfaces and dissolved constituents that can catalyze transformation reactions of contaminants. In addition to catalytically induced oxidation of synthetic organic pollutants, which are enhanced mainly by the presence of clay minerals, transformation of metals and metalloids occurs with the presence of catalysts such as Mn-oxides and Fe-containing minerals. These species can alter transformation pathways and rates through phase partitioning and acid-base and metal catalysis. 

There has been an enormous technological interest in tertfa/j-butanol (tBA) dehydration during the past thirty years, first as a primary route to methyl te/f-butyl ether (MTBE) (1) and more recently for the production of isooctane and polyisobutylene (2). A number of commercializable processes have been developed for isobutylene manufacture (eq 1) in both the USA and Japan (3,4). These processes typically involve either vapor-phase tBA dehydration over a silica-alumina catalyst at 260-370°C, or liquid-phase processing utilizing either homogenous (sulfonic acid), or solid acid catalysis (e.g. acidic cationic resins). More recently, tBA dehydration has been examined using silica-supported heteropoly acids (5), montmorillonite clays (6), titanosilicates (7), as well as the use of compressed liquid water (8). 

These examples illustrate that biomolecules may act as catalysts in soils to alter the structure of organic contaminants. The exact nature of the reaction may be modified by interaction of the biocatalyst with soil colloids. It is also possible that the catalytic reaction requires a specific mineral-biomolecule combination. Mortland (1984) demonstrated that py ridoxal-5 -phosphate (PLP) catalyzes glutamic acid deamination at 20 °C in the presence of copper-substituted smectite. The proposed pathway for deamination involved formation ofa Schiff base between PLP and glutamic acid, followed by complexation with Cu2+ on the clay surface. Substituted Cu2+ stabilized the Schiff base by chelation of the carboxylate, imine nitrogen, and the phenolic oxygen. In this case, catalysis required combination of the biomolecule with a specific metal-substituted clay. 

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. 

In the early history of acid catalysis, clays had a significant utility. The acid leaching of natural smectite clays produced amorphous silica-alumina [Si-Al] materials with large surface areas and active acid sites, which were used as acid catalysts [31],... 

Obviously, it is very desirable to substitute these modes of benzylic ether preparation by an heterogeneous catalysis process. Clays (50) and resins (51, 52) which were the first solid acid catalysts used have given low or moderate yields. The first experiments with zeolites were carried out by Rhodia (53, 54) on the etherification of vanillic alcohol (A) in a batch reactor over a HBEA zeolite with a Si/Al ratio of 12.5 ... 

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