Catalyst limited

Oxidizing toluene to benzaldehyde is a catalyzed reaction in which a selective catalyst limits further oxidation to benzoic acid. In the first step, benzyl alcohol is formed and then oxidized to benzaldehyde. Further oxidation produces benzoic acid ... 

Hammett equation use, 17 92-96 of published data, 17 83-99 soUd catalysts limitations, 17 78-83 Taft equation use, 17 85-92 linear free energy relationships, 29 158-159 multiplet theory of, 19 1-195 of nature of catalyst, 19 159-176 metals, 19 159-161... 

L. G. Lee and G. M. Whitesides, Preparation of optically active 1,2-diols and a-hydroxy ketones using glycerol dehydrogenase as catalyst limits to enzyme-catalyzed synthesis due to noncompetitive and mixed inhibition by product, J. Org. Chem. 1986, 51, 25-36. 

Bayer in the middle of 1990s. The reaction was performed using Candia Antarctica lipase B (CAL-B) to afford the free amine (A)-123 in high enantiomeric excess (> 99.5% ee).99 However, the requirement of high concentration of the catalyst limits the exploitation of the process on industrial scale.100... 

This catalyst limits the addition to 1 mole of H2, which adds to the same face of the double bond. 

The application of Ti02-catalysts limits the use of solar energy, because the efficiency is below 5%, due to the large bandgap of this material. Therefore, various attempts have been made to find stable semiconductors of a lower gap. One example are mixed oxides of titanium and iron. The absorption edge shifts considerably with increasing iron content. The decomposition rate, however, passes a maximum for 2.5% Fe, as shown for the oxidation of dichloroacetate [221]. 

Enolate Amination. Amination likewise can be effected using Di-t-butyl Azodicarboxylate (DBAD). Despite the excellent yields and diastereoselectivity obtained using this methodology (eq 24), the harsh conditions required for further transformation of the resultant hy drazide adducts (Triftuoroacetic Acid and hydrogenation at 500 psi over Raney Nickel catalyst) limit its synthetic utility. 

However, palladium and nickel catalyzed versions promise, at the moment, an even wider range of possibilities. The need to maintain the catalytic cycle by continuous regeneration of the zerovalent metal catalyst limits, nevertheless, the functionalizability of the metallated center in the cyclized intermediate. For the same reason, the readily accessible starting materials may contain various functional groups which are compatible with the reaction conditions and which may be of value for the syntheses of complex heterocycles such as alkaloids. Carbon monoxide insertion reactions of the cyclized a-metal intermediates were shown to afford monocyclic methyl carboxylates and/or annulated cyclopentanones (cyclopentenones) with concomitant stereocontrolled formation of up to four carbon-carbm bonds. 

Site density and pellet size in FT synthesis catalysts may not be entirely within the control of the catalyst designer. Low site densities may be required in order to bring catalysts limited by CO transport into the optimum region of x values, a modification that unfortunately also lowers reactor productivity. Pellet size may be decreased instead in order to eliminate CO... 

Such an independent measure is the selectivity of bifunctionally catalyzed consecutive reactions, e.g., the isomerization followed by hydrocracking of n-decane. By model calculations one can show that for a bifunctional catalyst limited in the acid function, the selectivity for intermediate product is high and does not change upon variation of the activity of the metal function. Large changes in selectivity because of such variations are expected for catalysts where neither the metal function nor the acidic function is ratelimiting. If a bifunctional catalyst is really limited in the metal function, this limitation is accompanied by a very low selectivity for intermediate products. 

A system designed to manage NOx between 150 and 500 C in a lean bum environment has been explored as an alternative to current lean NOx catalyst limitations. 

These results confirm that the Fries rearrangement can be performed in the presence of specific transition metal triflates as homogeneous, highly active catalysts with low toxicity, moisture and air tolerance. However, the high cost of these catalysts limits their use to small-scale production. 

Poor molecular weights of polymer products is a major drawback of metaUo-cene-based polymerization catalysts, limiting them from being fully exploited for practical applications. However, technical breakthroughs have been achieved in that specially designed zirconocene catalysts (Spaleck et al., 1992) can produce polymers with molecular weights far above 100,000. 

Challenges within this approach lie in the deposition and material of the catalyst, limited temperature budget in combination with high quality requirements for the CNTs, which normally need temperatures above 600°C to get structurally and electrically adequate results. 

Reactions between components of a gas and a liquid, the kinetics of which were discussed in Chapter 6, are carried out in a variet> of equipment, often having confusing names. The variety stems from a number of conditions that have to be fulfilled simultaneously efficient contact between gas and liquid—and eventually a solid catalyst, limitation of pressure drop, ease of removal of heat, low cost of construction and operation. Depending on whether the main mass transfer resistance is located in the gas or in the liquid, multiphase reactors or absorbers are operated either with a distributed gas phase and continuous liquid phase or vice versa. Whether co- or countercurrent flow of gas and liquid is used depends on the availability of driving forces for mass and heat transfer and reaction. 

Finally vanadia catalysts are used extensively for oxidations of aromatic hydrocarbons. With bei zene, the mechanism for ring breakage is not well defined, and the desorption of maleic anhydride itself appears to be ratecontrolling. For the oxidation of o-xylene, the use of supported vanadia-titania catalysts limits ring cleavage. A well-defined major product sequence, o-xyltne o-tolualdehyde o-toluic acid phthalide phthalic anhydride... 

Lindlar s catalyst limits addition of hydrogen to an alkyne to 1 mole and produces a c/s alkene. 

For example, prior to the discovery of this new single-site catalyst type, commercial grades of polyethylene were primarily manufactured over the compositional range of 0-4 mol% of comonomer (1-butene, 1-hexene or 1 -octene) that provided ethylene copolymers over the density range of 0.915-0.970 g/cc. Commercial catalysts were primarily the Cr-based Phillips-type of catalyst or a Ti-based Ziegler catalyst with the xmderstand-ing that both types of catalyst consisted of many different types of active sites. Each type of active site produced a different composition of polyethylene (different molecular weight and branching content) which resulted in a final polyethylene material with a complex molecular structure. These multi-site catalysts limited the composition of the polyethylene that was commercially available due to both process and product constraints imposed by such catalysts. 

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