Efficiency of Catalysts

Catalyst circulation coke is a hydrogen-rich coke from the reactor-stripper. Efficiency of catalyst stripping and catalyst pore size distribution affect the amount of hydrocarbons carried over into the regenerator. 

Relative efficiency of catalysts and the kinetic order in catalyst concentration... 

Table 2. Formation of tri- and tetrasubstituted alkenes by RCM comparison of the efficiency of catalysts 1 and 24 (E=COOMe)a [19]...

The efficiency of catalysts 86-89 for the asymmetric aldol reaction of a series of nucleophiles toward benzyloxyacetaldehyde was studied. For example, compound 89c was found to be an excellent catalyst for the asymmetric aldol reaction of silylketene acetal derivatives of t-butyl thioacetate, ethyl thioacetate, and ethyl acetate with benzyloxyacetaldehyde. In the presence of 0.5 mol% of the catalyst, the asymmetric aldol reaction took place at —78°C in CH2C12, affording the respective /i-hydroxy esters with excellent enantioselectivity (Scheme 3-32). 

Efficiency of catalysts is affected by the presence of some compounds. Even small amounts of alien admixtures, especially with noble metal catalysts, can increase or decrease the rate of hydrogenation and, in some cases, even inhibit the hydrogenation completely. Moreover some compounds can even influence the selectivity of a catalyst. 

The Surface Properties of the Praseodymium Compound. Although the efficiency of catalysts in methane conversion has been ascribed to a variety of properties, a number of researchers have demonstrated the importance of basicity of the catalysts employed in this process (14-16). Thus estimates of basicity, such as may be obtained from the adsorption of carbon dioxide, are of some value in characterizing the catalysts. It is obvious that the surface state of a working catalyst at 750°C is different from that at room temperature. However, measurements of the adsorption of carbon dioxide at the latter temperature provide semiquantitative information on sites capable of donating electrons. 

The catalysts for oxygen reduction and oxygen oxidation are materials based on substances like Co, Ni, Fe, Mn [16, 19]. One of new applications of oxygen reduction catalysts is air-metal hydride accumulator. Electrodes based on La0.1Cao.4Co03, La0. Cao.,jMn03 [18] are used in this battery. The electrodes of similar composition could be used in SOFC. An insertion of the oxides in their composition (CuO for example) leads to increasing the conductivity of system and efficiency of catalyst [30]. 

Table XII shows that CBI varies directly with Pe, being low for mixed flow (low Pe) and high for plug flow (high Pe). Commercial FFB regenerators operate between the extremes of complete mixing and plug flow, while the conventional turbulent bed operates essentially with complete mixing. This explains the high efficiency of catalyst regeneration in FFB.

Although the Pt/Rh catalyst generally retains good efficiency for hydrocarbon control, it is desirable to enhance the efficiency of catalysts for hydrocarbon removal in the light of the severe future U.S. hydrocarbon standards. Developments in palladium catalyst technology have resulted in a significant improvement in hydrocarbon control. These catalysts will see application in close-coupled converter systems, either as a single palladium catalyst or as a palladium catalyst in combination with rhodium [9] and in some... 

Catalyst utilization Several factors limit the efficiency of catalyst utilization ... 

The results are shown in Table 17.9 the epichlorohydrin yield was stable at about 84%, and the recovery efficiency of catalyst remained 100% after five cycles. 

Increase the conversion efficiency of catalysts at their working temperature. 

Sulphur is not a catalyst poison like lead but strongly competes against pollutants for space on the active catalyst surface. This limits the efficiency of catalyst systems to convert pollutants at any sulphur concentration. The effect of sulphur as a competitor on the catalyst surface may be reversible but it can cause irreversible changes to the washcoat and some of the base metal components. Sulphur resistant catalysts are not an option because that necessitates trading off catalyst performance for the removal of other pollutants. In addition when particulate removal is required the conversion of sulphur to sulphate limits the total particulate reduction and can cause net increases in particulate. 

Separation of soluble catalysts from the reaction products and recycling them to the reactor are usually expensive. Most of the catalysts (e.g., Rh, Pd) are expensive, and the efficiency of catalyst recovery must be high. 

ATO and AFO type structures. At present the industrial process of lube oil dewaxing (ChevronTexaco) is realized on bifunctional catalyst with acidic SAPO-11 (AEL) component. Few examples in the literature devoted to comparative study of AEL-, ATO- and AFO-SAPO materials in hydroisomerization reaction are based on a single specimen of each catalyst, sometimes not phase-pure and often prepared by exotic or undefined method. Recently the authors found a new method for selective and reproducible synthesis of SAPO-31 (ATO type structure) materials in the presence of di-n-pentylamine and showed hydroisomerization efficiency of catalysts based on these systems [3,4]. 

Hartikka and Arvidsson demonstrated the high catalytic efficiency of catalyst 5a for the direct aldol reaction of acetone with various aldehydes. In the organocatalysed direct asymmetric aldol reaction, acetone reacted with aromatic and aliphatic aldehydes, resulting in formation of p-hydro) ketones with good yields and moderate to high enantiomeric excesses (Scheme 9.9). ... 

There are some substances that do not act as catalysts but enhance the efficiency of catalysts and prolong their lives. Such substances are called catalyst promoters. The promoter may react with the catalyst and form several active sites to enhance catalyst activity. For example, the catalytic activity of V2O5 in the oxidation of sulphur dioxide is enhanced appreciably when sulphates of alkali metals are added in small amounts. It prevents reduction in surface area during catalyst use and increases activity over a period of time. 

On the basis of the experimental results, the methoxy group on C2 has proven to be critical for the high efficiency of catalyst 87 in the reduction of the imines. A hexacoordinate silicon transition structure was proposed to justify the experimental observations. In a more extended mechanistic study iV-funtionalized pipecoli-namides 88 were proposed as an example of efficient catalyst after several variations in the C2 and the A-protected group ([185], for more recent L-pipecolinic basic organocatalysts for hydrosilylation of imines, see [186, 187]). 

It is known that the efficiency of catalysts is not only a function of the kind of active site, but also dependent on the constimtion of the carbon support, that will influence the overall electronic properties of the catalyst material [96, 107-109]. For platinum-based catalysts, it was shown that by nitrogen doping of the carbon support, the platinum particles are stronger linked to the support material compared to the not-modified carbon. The resultant smaller particles with a more homogeneous distribution enabled higher ORR activity and an improved long-term stability [107, 110]. 

Fig. 26. Comparison of the efficiency of catalysts in oxidation of SO2 at different gas volume...

Thus it can be seen that under certain working conditions, (H2/N2)m for the maximum reaction rate is directly proportional to the efficiency of catalysts and any factor which lowers the catalyst efficiency (activity) will lower the best H2/N2. The various factors that affect the best H2/N2 ratio are shown in Table 8.9. 

Therefore, how to enhance the catalytic efficiency of catalyst in water solution and prevent catalyst from poison are important factors in increasing the cmrent efficiency and stability of electrode in the electrochemical ammonia synthesis. The use of solid electrol de is one of ways to solve these problems. 

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