Recoverable catalysts

Even with proper operation of the reactor and regenerator cyclones, catalyst particles smaller than 20 microns still escape from both of these vessels. The catalyst fines from the reactor collect in the fractionator bottoms slurry product storage tank. The recoverable catalyst fines exiting the regenerator are removed by the electrostatic precipitator or lost to the environment. Catalyst losses are related to ... 

Gladysz JA (ed) (2002) Chem Rev 102 issue 10, special issue recoverable catalysts and reagents... 

It seems reasonable to believe that this problem could be overcome by studying more coordinating ligands with the same structural features. Very recently, it has been demonstrated [56] that the use of iminobis(oxazolines) (Fig. 18) leads to better enantioselectivities and recoverable catalysts, both with laponite and nalion-silica supports (Table 8). Theoretical calculations are consistent with the stronger coordinating ability of iminobis(oxazolines) being the origin of these results [57]. 

Gladysz, J.A. (2001) Recoverable Catalysts. Ultimate Goals, Criteria of Evaluation, and the Green Chemistry Interface. Pure and Applied Chemistry, 73, 1319-1324. 

While cobaloximes are the most active CCT catalysts known, they are sensitive to air and moisture, so the more robust porphyrins were considered a better choice for a recoverable catalyst. To better understand how to design an optimal thermomorphic catalyst we initiated an investigation to learn how polyethylene length, number, and the covalent linker influence the catalyst activity and the final color of the methaciylate resin. A series of polyethylene-supported CCT catalysts were thus prepared for study (Scheme 36.2). 

Baruwati, B., Gum, D. and Manorama, S.V. (2007) Pd on surface-modified NiFe204 nanopartides a magnetically recoverable catalyst for Suzuki and Heck reactions. Organic Letters, 9 (26), 5377—5380. 

Jacinto, M.J., Santos, O., Landers, R., Kiyohara, P.K. and Rossi, L.M. (2009) On the catalytic hydrogenation of polycyclic aromatic hydrocarbons into less toxic compounds by a facile recoverable catalyst. Applied Catalysis B Environmental, 90 (3-4), 688-692. 

The development of highly efficient and easily recoverable catalyst systems. Today, the high cost of hydrogenated polymers is due mainly to the cost of the metal catalyst and its recovery operation. 

Pincer complexes catalyze a variety of other organic reactions [49-51]. Hence, this work is currently being extended to other metals, and other more readily accessible PCP systems. For example, as shown in Scheme 3, lO-Rfs can be converted to the iridium hydride chloride complex 15-Rfs. Closely related dihydride complexes catalyze dehydrogenations of alkanes at high temperatures [52], However, no efforts to develop recoverable catalysts have been reported to date. 

C. A. McNamara, M. J. Dixon, M. Bradley, Recoverable Catalysts and Reagents Using Recyclable Polystyrene-based Supports, Chem. Rev. 102 (2002) 3275-3300. 

For a special issue on recoverable catalysts and reagents, see Gladysz, ).E. 

Heuze et al. (34) synthesized three generations of bis(tert-butylphosphine)- and bis(cyclohexylphosphine)-functionalized Pd(II) DAB dendritic complexes that serve as copper-free recoverable catalysts for the Sonogashira coupling between aryl halides and alkynes (Scheme 9). 

Friedel-Crafts (FC) alkylation, acylation, and sulfonylation reactions are important C-C or C-S bond forming reactions in organic chemistry [60-64], Since the seminal works of Charles Friedel and James Mason Crafts published in 1877 in which they report the use of A1C13 for alkylation reactions [65], the search for more active catalysts, especially for acylation reactions, continues. Due to increasing environmental concerns, the need for green catalysts and processes for the FC reaction has gained significant importance. Bi(III) salts have shown to be efficient and recoverable catalysts with applicability in this area [13]. 

Recoverable catalysts also offer a promising way to economize the cost of liquefaction catalysts (74, 75). Dow designed a process that utilized fine powders of MoS2 that were reported to be recoverable by hydroclone however, specific details have not been published (76). 

The difficulty in the recovery of catalysts from unreacted coal and minerals and the poor regenerability of used catalysts forces one to use disposable catalysts, especially in the primary stage. This increases the cost of coal liquefaction considerably. This section reviews the mechanism of catalyst deactivation, design of recoverable catalysts in the primary stage, and catalyst deactivation in the secondary stage. 

BINAM - the diamino analogue of BEMOL - has been converted to its C2-symmetric bis(prolinamide).116 The latter acts as a recoverable catalyst of direct aldols in DMF-H2O at 0 °C, giving high des and ees. Butan-2-one showed significant regioselectivity, giving predominantly the iso product. 

Thematic Issue Recoverable Catalysts and Reagents, J. A. Gladysz (ed.), Chem. Rev. 

Gladyz, J.A. (Ed.), Thematic Issue on Recoverable Catalysts and Reagents, Chemical Reviews, 102, 3215-3892 (2002). 

Janda KD, Dickerson TJ, Reed NN (2002) Soluble polymers as scaffolds for recoverable catalysts and reagents. Chem Rev 102 3325-3244... 

Ge J, Huynh T, Hu Y, Yin Y (2008) Hierarchical magnetite/silica nanoassemblies as magnetically recoverable catalyst support. Nano Lett 8 931-934... 

An easy recovery of a catalyst from a mixture of reagents/products as well as its simple handling and recycling are important problems in chemical synthesis. Consequently, new recoverable catalysts attract increasing attention and the use of polymeric supports became a common practice. Polystyrene [1] is one of the most popular polymer supports due to its availability, facile functionalization and chemical inertness. However, such organic polymers usually show a solvent swelling dependent performance, which impacts the catalytic activity of the supported species. Polysiloxanes, due to unusually high flexibility of the polymer chain and low barrier... 

McNamara CA, Dixon MJ, Bradley M (2002) Recoverable catalysts and reagents using recyclable polystyrene-based supports. Chem Rev 102 3275-3300... 

Table 14 Comparison of recoverable catalyst (290) with well-defined complex (97a)...

S)-Proline-modified functionalized chiral ionic liquid is useful as a recoverable catalyst for direct asymmetric reactions [95] ... 

Recoverable catalysts for asymmetric hetero Diels-Alder reactions 02CRV3385. 

Recoverable catalysts for asymmetric epoxidation reactions 02CRV3385. 

A series of supported chiral VO(salen) complexes anchored on silica, single-wall carbon nanotube, achvated carbon or ionic liquids have been prepared through the simple methods based on the addition of mercapto groups to terminal C=C double bonds (Scheme 7.17) [58]. The four recoverable catalysts and the standard VO(salen) complex 37 were tested for the enantioselechve cyanosilylation of benzaldehyde using trimethylsilyl cyanide (Table 7.9). It should be noted that the ionic liquid-supported IL-VO(salen) showed the highest catalyhc achvity, though the ee-value was considerably reduced compared to the soluble 37 in [bmim][PF6] (entries 4 and 5). 

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