Multiphase catalysts

Metal Nanoparticles in Ionic Liquids Recyclable Multiphase Catalyst-Systems 13... 

Kobayashi, S. J0rgensen, K. A. (Eds.) Cycloaddition Reactions in Organic Synthesis, Wiley-VCH, Weinheim, Germany, 2002 Carmichael, A. J., Earle, M. J., Holbrey, J. D. et al. The Heck reaction in ionic liquids a multiphasic catalyst system, Org. Lett., 1999, 1, 997-1000 Forsyth, S. A., Gunaratne, H. Q. N. Hardacre, C. et al. Utilisation of ionic liquid solvents for the synthesis of Lily-of-the-Valley fragrance beta-Lilial (R), 3-(4-t-butylphenyl)- 2-methylpropanal, J. Mol. Catal. A-Chem., 2005, 231(1-2), 61-66. 

Support. In multiphase catalysts, the active catalytic material is often present as the minor component dispersed upon a support sometimes called a carrier. The support may be catalyticaliy inert but it may contribute to the overall catalytic activity. Certain bifunctional catalysts ( 1.2.8) constitute an extreme example of this. In naming such a catalyst, the active component should be listed first, the support second and the two words or phrases should be separated by a solidus, for example, platinum/silica or platinum/silica-alumina. The solidus is sometimes replaced by the word on, for example, platinum on alumina. 

In two instances are the electronic spectra of the bulk of the catalyst particles of interest in catalysis research first, when chemisorption gives rise to electron exchange that extends to large distances into the solid and second, when various components of a multiphase catalyst Interact so as to dope one phase with the chemical elements of another, resulting in new, enhanced, or reduced activity of the catalyst. 

Cini P. and Harold M.P., Experimental study of the tubular multiphase catalyst, AIChE J. 37 991 (1991). 

Our recent work on the bismuth-cerium molybdate catalyst system has shown that it can serve as a tractable model for the study of the solid state mechanism of selective olefin oxidation by multicomponent molybdate catalysts. Although compositionally and structurally quite simple compared to other multiphase molybdate catalyst systems, bismuth-cerium molybdate catalysts are extremely effective for the selective ammoxidation of propylene to acrylonitrile (16). In particular, we have found that the addition of cerium to bismuth molybdate significantly enhances its catalytic activity for the selective ammoxidation of propylene to acrylonitrile. Maximum catalytic activity was observed for specific compositions in the single phase and two phase regions of the phase diagram (17). These characteristics of this catalyst system afford the opportunity to understand the physical basis for synergies in multiphase catalysts. In addition to this previously published work, we also include some of our most recent results on the bismuth-cerium molybdate system. As such, the present account represents a summary of our interpretations of the data on this system. 

Increased propylene ammoxidation activity of each phase upon alterion doping is due to the juxtaposition of all necessary elements for oxidation catalysis in a single phase. The requirements of a good oxidation catalyst are a) activation of the substrate molecule, b) oxidation activity (oxygen inserting) and c) facile redox capabilities to ease electron conduction and site reconstruction. For reasons discussed extensively in the literature (7 ), we assign these roles to Bi, Mo, and Ce ion sites respectively in the catalysts described here. The solid solution formation observed in these materials enables all of these functions to be represented in one phase and on one surface of the catalyst. Analysis of the Multiphase Catalyst... 

Ru(0) NPs dispersed in simple ILs are efficient multiphase catalysts for the partial hydrogenation of benzene under mild reaction conditions (4 atm, 75 °C). The ternary diagram (benzene/cyclohexene/BMI.PFs) indicated a maximum of 1% cyclohexene concentration in BMI.PFb, which is attained at 4% benzene concentration in the ionic phase. This solubihty difference in the IL was used for the extraction of cyclohexene during benzene hydrogenation by Ru catalysts suspended in BMI.PFb. Selectivity up to 39% in cyclohexene can be attained at very low benzene conversion (Scheme 6.7). Although the maximum yield of 2% in cyclohexene is too low for technical appUcations, it represents a rare example of partial hydrogenation of benzene by soluble transition metal NPs [80]. 

It is obvious that this is commercially impossible for the industrial production of bulk chemicals such as butanal or a-alkenes, since additional manufacturing costs of cents (or even fractions of cents) per kilogram are prohibitive. The maximum permissible burden for fine chemicals might be higher, and may render this equipment possible for realization of new ideas about the recycling of multiphase catalysts. 

Carmichael AJ, Earle MJ, Holbrey JD, McCormac PB, Seddon KR (1999) The Heck reaction in ionic liquids a multiphasic catalyst system. Oig Lett 1 997-1000... 

Yin YG. Research Methods on Multiphase Catalysts, Beijing Chemical Industry Press, 1988. 

Some trends in the study of carbon monoxide and carbon dioxide hydrogenations over metal oxides and metal-metal oxide systems were examined in this chapter. These reactions usually take place over multicomponent and often multiphase catalyst systems with bifunctional sites, and produce HC and alcohols. The selectivity in these reactions is basically determined by the nature of the catalytic function, which determines largely the interaction of carbon oxides and hydrogen on the catalyst surface. CO binds to coordinatively unsaturated Zn + sites and acts as a... 

Frydman A, Campbell CT, Castner D, Schmal M. A method for accurate quantitative XPS analysis of multimetallic tu multiphase catalysts on supprut particles. J Catal. 1995 157 133. ... 

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