Catalyst high selectivity catalysts

Description In the direct oxidation process, ethylene and oxygen are mixed with recycle gas and passed through a multi-tubular catalytic reactor (1) to selectively produce EO. A special silver catalyst (high-selectivity catalyst) is used it has been improved significantly over the years. Methane is used as ballast gas. Heat generated by... 

The same four operating steps are used with the complex batch reactor as with the simple batch reactor. The powerhil capabiUties of the complex batch reactor offset their relatively high capital cost. These reactors can operate at phenol to alkene mole ratios from 0.3 to 1 and up. This abiUty is achieved by designing for positive pressure operation, typically 200 to 2000 kPa (30 to 300 psig), and for the use of highly selective catalysts. Because these reactors can operate at low phenol to alkene mole ratios, they are ideal for production of di- and trialkylphenols. 

The main by-products ia the dehydrogenation reactor are toluene and benzene. The formation of toluene accounts for the biggest yield loss, ie, approximately 2% of the styrene produced when a high selectivity catalyst is used. Toluene is formed mostly from styrene by catalytic reactions such as the foUowiag ... 

The benzene—toluene fraction is further fractionated in a small column, not shown in Figure 5, to recover benzene for recycle to the alkylation unit and toluene for sale. This toluene can be converted to benzene by hydrodealkylation but the high selectivity catalyst has reduced the formation of toluene in the dehydrogenation reactor to the point where the cost of installing a hydrodealkylation unit is difficult to justify even in a large styrene plant. 

A significant breakthrough was achieved by Overman and Donde in 1999 they reported the first highly selective catalyst 41 for the aza-Claisen rearrangement of benzimidates 39 (Fig. 20) [58]. Enantioselectivities were in most cases good to very good. 

Interestingly, significant progress has been made for the hydroamination of more reactive substrates such as styrenes, alkynes, dienes, and allenes. Specifically, highly selective catalysts have been discovered for the synthesis of fine chemicals (pharmaceuticals, natural products, chemical intermediates). In this area however, the problem of catalyst stabiUty can also be questioned in several cases. 

Examples of creating highly selective catalysts by adjusting the pore diameter to accommodate certain-size reactants or products are (1) creating channels narrow enough that molecules move single file, so once products are... 

The reaction of organometallics with metal surfaces is a very promising aspect of surface organometallic chemistry related to fine chemicals. The precise understanding of the reactions between organometallics and metal surfaces is essential to obtain highly selective catalysts by this route.292,293... 

The limitations of homogeneous systems have been recognized, and this has stimulated the development of supported catalysts to the extent that a few of them now reach activity levels comparable to those of the homogeneous counterparts. Highly selective catalysts have been reported. although the selectivity patterns are often different to those of a homogeneous analog (see Section IV). Supported asymmetric catalysts... 

The oxazole-phosphinite complexes 14 (Fig. 30.14) proved to be highly selective catalysts, comparable to the best catalysts developed so far (see entries in Tables 30.9 and 30.11-30.13) [26]. 

H2 production technologies based on natural gas. Operating the reaction at relatively lower temperature, between 300 and 450 °C could minimize the CO formation because the equilibria for WGS and CO oxidation reactions are thermodynamically more favorable at lower temperatures. In order to achieve this goal, highly selective catalysts that are specific for reforming via acetaldehyde formation rather than ethanol decomposition to CH4 and/or ethylene are required. The success in the development of ethanol-based H2 production technology therefore relies on the development of a highly active, selective and stable catalyst. 

Styrene-divinylbenzene resins, 23 353 Styrene-DVB copolymers, 14 388 Styrene ionomers, 14 466, 481 properties of, 14 470-473 Styrene liquid, 23 347 Styrene-maleic anhydride (SMA) copolymers, 23 391 copolymer, 10 207 Styrene manufacture, 24 259 Styrene manufacturing, 23 326, 334-345 development of high selectivity catalyst for, 23 339... 

Unfortunately, none of these catalysts displayed practical levels of selectivity in the KR of aryl aUcyl yec-alcohols. Miller therefore embarked in the design of a third generation catalyst that could enable the KR of a larger number of substrates. In this context, he developed an elegant fluorescence-based activity assay which allowed rapid screening of a large number of structurally unique catalysts. This protocol based on proton-activated fluorescence led to the identification of octapeptide 52 as a highly selective catalyst for the KR of aryl alkyl. yec-alcohols but also alkyl yec-alcohols... 

For example, a wide range of a-(acyloxy)acrylates have been hydrogenated with excellent enantioselectivity using the Et-DuPhos-Rh catalyst. High selectivities are also obtained for the asymmetric hydrogenation of the B/Z-isomeric mixtures of yS-substituted derivatives (Eq. 12). Asymmetric hydrogenation of enol phosphates with either Du-Phos-Rh or BPE-Rh catalyst provides moderate to excellent enantioselectivity (Eq. 13)... 

The 3,3 -cross-linked polymeric binaphthol ligand 238 in combination with A1Mc3 is also a highly selective catalyst for the 1,3-dipolar cycloaddition reaction in Scheme 12.69 (345). The only observable diastereomer resulting from the reactions was exo-233, which was obtained with an enantioselectivity of up to 99% ee using the aluminium catalyst of 238 (20 mol%). One of the advances of using a polymeric catalyst is the easy removal and recovery of the ligand from the... 

Recently, Pfaltz and co-workers reported that iridium complexes with chiral P,N-ligands are highly selective catalysts for asymmetric hydrogenation of several... 

Enzymic (or enzymatic) Process A chemical reaction or series of reactions catalyzed by an enzyme or enzymes. An enzyme is a protein which acts as a highly selective catalyst permitting reactions to take place rapidly in living cells under physiological conditions. 

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