Clays clay-supported catalysts

Yadav, G. D., Asthana, N. S., and Kamble, V. S. 2003. Friedel-Craftsbenzoyla-tion of p-xylene over clay-supported catalysts novelty of cesium-substituted dodecatungstophosphoric acid on K-10 clay. Appl. Catal. A General 240 53-69. 

Homologation. The hydroesterification of alkenes using Pd(OAc)2, CO, Ph,P, and an alcohol under pressure also works when the clay-supported catalyst is used. ... 

Preparation of Polyolefin Nanocomposites by In Situ Polymerization Using Clay-Supported Catalysts... 

Powder x-ray diffraction of (a) 1-tetradecylammonium-modified fluorohectorite, (b) the organoclay after intercalation of catalyst VI, (c) after exposure of the clay-supported catalyst to ethylene for 135 min, and (d) after exposure to ethylene for 24 h. (Reproduced from Bergman, J.S. et al., Chem. Commun., 2179,1999. With permission from The Royal Society of Chemistry.)... 

The first report of bimodal PE from any supported metallocene involved a clay-supported catalyst. Sodium montmorillonite (Kunipia-F) was dried at 500°C, then... 

Scott, S. L., Peoples, B. C., Yung, C., Rojas, R. S., Khaima, V., Sano, H., Suzuki, T, and Shimizu, F. 2008. Highly dispersed clay-polyolefin nanocomposites free of compatibil-izers, via the in-situ polymerization of a-olefins by clay-supported catalysts. Chemical Communications 4186 188. 

As the polymerization proceeds, the initial catalyst support fragments and is dispersed within the growing polymer matrix. In the case of clay-supported catalysts, one needs to include another level of mass transfer to account for monomer diffusion and polymer formation between the clay platelets. A model to describe this process, called the multilayer model (MLM), is depicted in Figure 3.11. 

This concept is useful for the interpretation of particle break-up during in-situ polymerization with clay-supported catalysts. Maneshi et al. [69] used ethylene... 

In many pubhcations on the in-situ polymerization of olefins with clay-supported catalysts, Bronsted acid sites located on clay edges have been considered to be... 

As a catalyst support material, clays possess unique electronic and structural properties. They may be considered as solid acids, with electrostatic properties that can affect catalytic behavior and, possibly, the microstructure of polymers made with clay-supported catalysts. The layered structure of these aluminosilicates has also been reported to affect polymerization kinetics. Studies in this area have focused on three main effects polymerization activity and stability, polymer molecular weight, and polymer tacticity. 

G. Nagendrappa, Organic synthesis using clay and clay-supported catalysts, Appl. Clay Sci. 53 (2011) 106-138. 

Choi, W.J., Kim, H.-J., Yoon, K.H., Kwon, O.H., Hwang, C.I. Preparation and barrier property of poly(ethylene terephthalate)/clay nanocomposite using clay-supported catalyst. Journal of Applied Polymer Science 100 (6), pp. 4875-4879 (2006)... 

Because clays (rocks) usually contain more than one mineral and the various clay minerals differ in chemical and physical properties, the term clay may signify entirely different things to different clay users. Whereas the geologist views clay as a raw material for shale, the pedologist as a dynamic system to support plant life, and the ceramist as a body to be processed in preparation for vitrification, the chemist and technologist view clay as a catalyst, adsorbent, filler, coater, or source of aluminum or lithium compounds, etc. 

Another problem that required solving was the moderate yield obtained in the cyclopropanation reaction when only one equivalent of styrene was used. By increasing the amount of styrene up to its use as the reaction solvent, a noticeable effect on the selectivities was observed when laponite was used as the support [58]. The active role of the clay support was definitely estabhshed when the results in homogeneous and heterogeneous phases were compared (Table 9). These effects involved the reversal of the trans preference in solution to the cis preference with the laponite-supported catalyst in styrene, and also a reversal in the absolute configuration of the major cis enantiomer ob-... 

In the case of the reaction between N-acryloyloxazolidin-2-one and cy-clopentadiene, both catalysts showed activities and enantioselectivities similar to those observed in homogeneous phase. However, a reversal of the major endo enantiomer obtained with the immobilized 6a-Cu(OTf)2 catalyst, with regard to the homogeneous phase reaction, was noted. Although this support effect on the enantioselectivity remains unexplained, it resembles the surface effect on enantioselectivity of cyclopropanation reaction with clay supports [58]. 

Clay-supported heteropoly acids such as H3PW12O40 are more active and selective heterogeneous catalysts for the synthesis of MTBE from methanol and tert-butanol, etherification of phenethyl alcohols with alkanols, and alkylation of hydroquinone with MTBE and tert-butanoi (Yadav and Kirthivasan, 1995 Yadav and Bokade, 1996 Yadav and Doshi, 2000), and synthesis of bisphenol-A (Yadav and Kirthivasan, 1997). 

Other metal oxide catalysts studied for the SCR-NH3 reaction include iron, copper, chromium and manganese oxides supported on various oxides, introduced into zeolite cavities or added to pillared-type clays. Copper catalysts and copper-nickel catalysts, in particular, show some advantages when NO—N02 mixtures are present in the feed and S02 is absent [31b], such as in the case of nitric acid plant tail emissions. The mechanism of NO reduction over copper- and manganese-based catalysts is different from that over vanadia—titania based catalysts. Scheme 1.1 reports the proposed mechanism of SCR-NH3 over Cu-alumina catalysts [31b],... 

Glycals can be transformed into 1,6-anhydro sugar derivatives by intramolecular cyclization in the presence of Lewis and Brpnsted acids, a reaction that has been termed the intramolecular Ferrier glycosylation.168 Sharma el al.169 showed that a montmorillonite clay-supported silver reagent can be an efficient catalyst for this transformation. The 1,6-anhydro-2,3-dehydro sugars obtained were then selectively dihydroxylated to furnish 1,6-anhydro saccharides. 

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