Catalyst Comparisons

For practical appHcation in mixtures of water—organic solvent, only ammonium and phosphonium salts containing 15 or more C atoms are sufficiently lipophilic. In empirical catalyst comparisons crown ethers (hexaoxacyclooctodecanes) (1)—(3) were often as effective as the best onium salts. 

Anchored Wilkinson s Catalyst Comparison with the Homogeneous Catalyst and Supported Rhodium with Respect to Reaction Selectivity... 

Koebel, M. and Elsener, M. (1998) Selective Catalytic Reduction of NO over Commercial DeNOx-Catalysts Comparison of the Measured and Calculated Performance, Ind. Eng. Chem. Res., 37, 327. 

The silica-supported chromate can be activated directly to a very efficient ethylene polymerization catalyst by ethylene itself or by reduction under CO, to yield active Cr(ll) bisiloxy species, ](=SiO)2Cr] [8]. While the silsesquioxane Cr derivative on its own does not lead to an active polymerization catalyst under ethylene (albeit only low ethylene pressure were tested), the silsesquioxane chromate ester can yield an active polymerization catalyst by addition of methyl-aluminoxane as co-catalyst. Comparison between the two catalytic systems is therefore possible but suffers from the lack of molecular definition of the active homogeneous species obtained after activation with the alkylating agent (Scheme 14.11). 

Table IV. Isomerization of n-Hexane Over Pd-H-Zeolite Catalysts Comparison of Mordenite and Zeolite Y...

Gartek and Goldman relate the expansion of the concentration limit in upward propagation in lean hydrogen mixtures to the fact that due to the large coefficient of diffusion in the mixture, high temperatures may be achieved on the surfaces of particles of the catalyst. Comparison of hydrogen and deuterium confirms this point of view. In addition, a number of facts show that it is not the absolute value of the diffusion coefficient, but its... 

Differences in product yields can be amplified when low conversions are screened because the initial kinetics are monitored rather than integral productivities at high conversions. This can strategically be used to facilitate catalyst comparisons. 

A valuable indirect method of probing the Horiuti-Polanyi mechanism is the study and comparison of competitive rates of hydrogenation of olefins using both homogeneous and heterogeneous catalysts. Comparisons of individual rates... 

The relative number of active sites as deduced from thiophene HDS (of spent catalysts) is also shown in Figure 4 for the Mo/Si02 catalysts. Fully in line with the XPS results, independent of the coke level the number drops to about 25% of that of the fresh catalyst. Comparison of the coverage of 50% and the remaining number of active sites (25%) suggests that the coke is not randomly distributed over the catalyst but is to some extent primarily deposited onto the active phase. The latter conclusion can also be deduced from the results of the XPS study [7J. 

Catalyst Screening. The autoclave was modified to allow preheating and tar injection under pressure for the catalyst comparison runs. A high-pressure bomb made of stainless steel was used as an injection vessel. The bomb was equipped with a temperature-controlled heater to keep the tar at 150°C. A pressure head higher than the autoclave-system pressure is maintained on the tar so that die tar can be injected into the preheated autoclave after the isolation valve between the bomb and autoclave was open. 

The study of catalytic reactions using a batch autoclave reactor has been criticized for long heat-up times and nonsteady-state catalyst activity. This catalyst-comparison study was carried out by injecting coal tar into a preheated autoclave containing precoked catalyst and hydrogen in order to eliminate long heat-up times. Nevertheless, the inherent differences in results between an autoclave and a trickle-bed reactor, which is widely used for hydrorefining of heavy liquids, exist still (5). 

Wang, H-F, Kaden, WE, Dowler, R, Sterrer, M, and Freund, H-J. Model oxide-supported metal catalysts - comparison of ultrahigh vacuum and solution based preparation of Pd nanoparticles on a single-crystalline oxide substrate. Phys Chem Chem Phys. 2012 14 11525-11533. 

In comparing catalyst activities, alternative 2 gives a measurable, quantitative result without the need to know the function f. This is not the same for alternatives 3 and 4. If the catalyst comparisons are done at fixed weight hourly space velocity (WHSV), and if the temperature is varied to achieve the desired conversion, applying alternative 3 and Equation 1 gives (Equation 3) ... 

For catalyst comparison, the same monomer was polymerized with [Mo] and [Ru], affording polymers of equal branch content and M values of 72.0 and... 

G. Manos, I. Y. Yusof, N. Papayannakos, and N. H. Gangas, Catalytic cracking of polyethylene over clay catalysts. Comparison with an ultrastable Y zeolite, Ind. Eng. Chem. Res. 40, 2220 (2001). 

Figure 24 describes schematically the three recent modes of preparation of membrane/electrode assemblies based on commercially available dispersed platinum catalysts. Comparison of catalyst utilization obtained with the different PEFC catalyzation techniques is given in Fig. 25. The advantage in catalyst utilization of the thin-layer approach is clearly seen, increasing at the higher cell currents (lower cell voltage) thanks to minimized mass-transport limitations in the thin catalyst layer.

Catalysts comparison using a simpie first order kinetic model... 

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