Selective shape catalysis

Weisz P B 1981 Molecular shape selective catalysis Proc. 7th Int. Congr. on Catalysis (Tokyo) 1 1... 

Ti, B, Ni, Cr, Fe, Co, Mn) has been described, as was the synthesis of nonsiliceous materials such as oxides of W, Fe, Pb, Mo, and Sb [18]. Although these materials do not represent tme zeolites, they are highly interesting materials which are commonly covered in the zeolite literature with great potential for shape-selective catalysis of bulky molecules. 

Anotlier important modification metliod is tire passivation of tire external crystallite surface, which may improve perfonnance in shape selective catalysis (see C2.12.7). Treatment of zeolites witli alkoxysilanes, SiCl or silane, and subsequent hydrolysis or poisoning witli bulky bases, organophosphoms compounds and arylsilanes have been used for tliis purjDose [39]. In some cases, tire improved perfonnance was, however, not related to tire masking of unselective active sites on tire outer surface but ratlier to a narrowing of tire pore diameters due to silica deposits. 

Only a very few selected examples have been discussed. The number of processes based on shape-selective catalysis by zeolites is ever increasing, particularly in the field of speciality and fine chemicals and quite a few have been... 

Csicsery S M 1976 Shape-selective catalysis Zeoiite Chemistry and Cataiysis ACS Monograph vol 171, ed J A Rabo (Washington, DC American Chemical Society) pp 680-713... 

Weitkamp J, Ernst S and Puppe L 1999 Shape-selective catalysis in zeolites Cataiysis and Zeoiites, Fundamentais and Appiications ed J Weitkamp and L Puppe (Berlin Springer) pp 327-76... 

Shape anisotropy Shape control Shape factors Shape-memory alloys Shape-selective catalysis Shape selectivity Sharpless catalyst Shaving cream Shaving creams... 

N. Y. Chen, W. E. Garwood, and F. G. Dwyer, Shape Selective Catalysis in Industrial Applications, Marcel Dekker, Inc., New York, 1989. 

In shape-selective catalysis, the pore size of the zeoHte is important. For example, the ZSM-5 framework contains 10-membered rings with 0.6-nm pore size. This material is used in xylene isomerization, ethylbenzene synthesis, dewaxing of lubricatius oils and light fuel oil, ie, diesel and jet fuel, and the conversion of methanol to Hquid hydrocarbon fuels (21). 

Shape selective catalysis as typically demonstrated by zeolites is of great interest from scientific as well as industrial viewpoint [17], However, the application of zeolites to organic reactions in a liquid-solid system is very limited, because of insufficient acid strength and slow diffusion of reactant molecules in small pores. We reported preliminarily that the microporous Cs salts of H3PW12O40 exhibit shape selectivity in a liquid-solid system [18]. Here we studied in more detail the acidity, micropore structure and catal3rtic activity of the Cs salts and wish to report that the acidic Cs salts exhibit efficient shape selective catalysis toward decomposition of esters, dehydration of alcohol, and alkylation of aromatic compound in liquid-solid system. The results were discussed in relation to the shape selective adsorption and the acidic properties. 

The shape selective catalysis was examined by choosing five kinds of the reactions, Eqs. (1) - (5), that is, dehydration of 2-hexanol, decompositions of three kinds of esters and alkylation of 1,3,5-trimethylbenzene with cyclohexene. 

As was stated above, the very strong acidity (and probably together with the organophilicity of the pore wall) makes these salts very active catalysts in liquid-solid organic reaction systems. We wish to emphasize that this is the first example for the shape selective catalysis of heteropolyacids at least to our knowledge. 

Reverse Osmosis Technology Applications for High-Purity-Water Production, edited by Bipin S. Parekh Shape Selective Catalysis in Industrial Applications,... 

Zeolites possess the remarkable property of exhibiting shape-selective catalysis even when they are X-ray amorphous. Clearly, even though there is no long range order, there is still a degree of structural organization in the aluminosilicate adequate to exert shape-selectivity in the "noncrystalline" regions of the samples. Thanks to HREM we can now understand how this state of affairs arises (17). 

Csicsery, S.M. (1984). Shape-selective catalysis in zeolites. Zeolites 4, 202-213... 

HZSM-5, 5 241 72 192 nitration using, 5 333 shape-selective catalysis, 5 243-244 HZSM5 zeolite. See Zeolite HZSM5 HZSM-11, nitration using, 5 333... 

See also Cross-sectional shape Shape-selective catalysis, 5 242-244 Shaping... 

Derouane, E.G., New aspects of molecular shape-selectivity catalysis by zeolite ZSM-5 Imelik, B. Naccache, C. ... 

Figure 4.20 MTG/MTO reaction path and aromatics distribution with different zeolites as catalysts. (Reprinted from C.D. Chang, W.H. Lang, W.K. Bell, Catalysis in Organic Reactions, Molecular Shape-Selective Catalysis in Zeolites, pp. 93-94. Copyright 1981. With permission from Marcel Dekker.)...

Weitkamp, J., Ernst, S., and Puppe, L. (1999) Shape-selective catalysis in zeolites, in Catalysis and Zeolites, vol. 

Xie, Y., Zhao, B., Long, X., and Tang, Y. (2000) Dispersion of oxides on H-ZSM-5 and tlireshold effect on shape selective methylation of toluene. ACS Symp. Sen, 738 (Shape Selective Catalysis), 188-200. 

The unique catalytic properties of supported metal complexes, compared with different from metal and metal oxides, have been devoted to various chemical processes, including selective oxidation catalysis, shape selective catalysis and... 

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