Catalysts acidity comparison between

The results obtained with this approach are quite impressive. Large rate accelerations (kcat/kuncat = 3 X 104) were observed with the best of the catalysts. A comparison between the best catalyst and a catalytic antibody system designed for phosphomonoester hydrolysis is reported. The combinatorial derived system gives an observed rate constant that is five times larger than that reported for the antibody system. In a control experiment, it was determined that polymers with just one type of carboxylic acid attached did not have catalytic activity. It... 

So far, no systematic work has been done on the use of recyclable, solid-phase catalysts in cross-coupling reactions. Most of the examples have been obtained for cross-couplings with either arylboronic acids or terminal acetylenes. It should be noted, however, that due care should be exercised when interpreting results on the cross-coupling of arylboronic acids with aryl iodides, as this extremely facile reaction can be catalyzed by practically any palladium-containing material, including trivial Pd black,481 e.g., as a sediment on the reaction vessel. Therefore, this reaction cannot serve as a reliable test for comparison between different catalytic systems. 

Recently, Falk and Seidel-Morgenstern [143] performed a detailed comparison between fixed-bed reactors and fixed-bed chromatographic reactors. The reaction studied was an equilibrium limited hydrolysis of methyl formate into formic acid and methanol using an ion-exchange resin as both the catalyst and the adsorbent. The analysis was based on a mathematical model, which was experimentally verified. The comparison was based on the following four assumptions ... 

A process performance study has been conducted by David et al. [47] taking the coupling of pervaporation with the esterification reactions of 1-propanol and 2-pro-panol with propionic acid as a model system. Toluene sulfonic acid was appHed as the homogeneous acid catalyst A PVA-based composite membrane from GFT was used. Fig. 13.5 shows the comparison between the esterification reaction with and without pervaporation. Without pervaporation, the conversion factor reaches a hm-it, which corresponds to the equihbrium of the esterification reaction. Coupling of the esterification to pervaporation allows the reaction to reach almost complete conversion. 

Figure 9. A comparison between the catalytic performance through 2,6-xylenol yield, and relative acidity (solid diamonds) obtained from the area of v8a and vl9b bands from pyridine adsorbed on catalyst surface at lOOOC and the relative basicity (solid circles) obtained from the area of the bands between 1700 and 1250 cm-1 from C02 adsorbed on Cul-xCoxFe204 catalysts at 250C.

The kinetic isotope effect observed for the FTT synthesis by Lancet and Anders71) on C02, CH4, C2 + (which means ethane and heavier hydrocarbons) and a wax fraction recovered from the catalyst, is not in disagreement with the experimental values (comparison between Fig. 2,1 and II A). The same group 1 have pointed out that in the case of FTT in the presence of NH3, the amino acid data (813C as high as +44%0) would not be inconsistent with the experimental values either (see Fig. 1). 

A comparison between pulsed flow and conventional pulsed static calorimetry techniques for characterizing surface acidity using base probe molecule adsorption has been performed by Brown and coworkers [20, 21]. In a flow experiment, both reversible and irreversible probe adsorption occurring for each dose can be measured, and the composition of the gas flow gas can be easily modified. The AHads versus coverage profiles obtained from the two techniques were found to be comparable. The results were interpreted in terms of the extent to which NH3 adsorption on the catalyst surface is under thermodynamic control in the two methods. 

As homogeneous acid catalysts, trifluoromethanesulfonic acid (CF3SO3H) and its silylated form, trimethylsilyl triflate (CF3S03SiMc3), were chosen for comparison of the acid catalysis between heterogeneous and homogeneous acids. The reaction of 14a with 15a or 15b proceeded smoothly even at low temperature in the presence of CF3S03SiMe3 as well as CF3SO3H (Table XIV, Entries 8, 10 Table XV, Entries 12, 13, 15). The catalytic behavior of... 

The importance of catalyst acidity is emphasised by comparisons between initial coke formation on cobalt molybdate based catalysts and on sodium molybdate based systems [24]. In the latter case, the acidity is low, the steady state specific activity is not too dissimilar from cobalt molybdate and the initial deactivation is very much less. 

Model 23 R-16 (NiMo) is a new HDS promoted catalyst developed by ICERP to be used in desulphurization units in order to reach the new diesel fuel specifications. The catalyst is based on a new type of alumina obtained by an original preparing method which offers a correct interaction degree between metal and its support. The acidic property and the pore size were improved by the addition of promoteurs such as silica and phosphorus (P2O5). Some of the properties of new 23 R-16 (NiMo) promoted catalyst in comparison with the standard hydrofining catalyst are listed in Table 2. 

Described in this paper is a model system - one in which well-characterized lanthanide complexes exhibit high catalyst activities for ethylene polymerization but where the corresponding oligomerization of propene is sufficiently slowed so that stepwise insertion of the olefin can be studied quantitatively and all important intermediates observed or isolated. Emphasized in this paper is the effect of added Lewis acids and bases on the rate of olefin insertions, and comparison between ethylene and propene reactions. The catalysts, of general structure M(ri -Cp )2CH3 L (M = Yb, Lu ... 

Figure 2a illustrates the comparison between the evolution of either the bismuth losses or the gluconic acid yields, with respect to the Bi/Pd molar ratio. The gluconic acid yield increases with the Bi/Pd molar ratio till Bi/Pd is equal to 1 and then slightly decreases. On the other hand, bismuth dissolution increases further with the Bi/Pd ratio, showing that for Bi-rich compositions, the excess of Bi is leached from the catalyst without affecting significantly the catalytic activity. 

Comparison between various acid solid catalysts. 

Hydroxylation of phenol by hydrogen peroxide over solid acids exhibits an autocatalysis that has never been described in earlier works. The induction period is dependent on the acidity and is reduced by initial addition of dihydroxybenzenes or other electron-transfer agents. A new mechanism, initiated by the slow formation of dihydroxybenzenes in the induction period, should be considered. Comparison of various catalysts shows that the reaction is also dependent on the structure of the solid. Zeolites with too small a porosity are not active, according to a large space demand of the reaction. Catalysis by titanium silicalites does not show such behaviour the reactivity is low but regular. Thus, our results show that valuable comparison between catalysts cannot be deduced from tests performed by stopping the reaction at a determined time, but that kinetic studies are essential. 

As Shown in Figure 4, catalyst deactivation is an important factor in the hydroxy-alkylation reactions. This makes quantitative comparison difficult, as each material has a balance between activity and deactivation. The main conclusion from the results is that materials having a low acidity, ALPO-5 (vide supra) and 7-alumina, give best results, because of their low rate of deactivation. Already when SAPO-5, having an acid strength between ALPO-5 and aluminosilicates, is used, a rapid deactivation was observed in the phenol/formaldehyde reaction. 

Cyclohexanone and related cyclic ketones generally gave poor results with L-proline catalyst. L-Azetidinone carboxyhc acid catalyst (4) showed improved enantioselectivities (88-90% ee. Table 11.2) for the a-amination of cyclohexanone with DEAD or dibenzyl azodicarboxylate (DEAD) [13]. The benzimidazole-pyrrolidine (EIP) catalyst 5 was comparable to L-proUne in terms of enantioselectivity with cyclohexanone and l-silacyclohexa-4-one as substrates [14]. In a comparison between the efficiencies of L-proUne and 4-silyloxyproline 6 in the a-amination of cyclohexanone and derivatives, catalyst 6 provided higher yields and enantioselectivities [15]. 

Activity tests for a 1.1mm particle size with total 5g of SAPO-34 which was divided into three beds where the top bed has 25 wt % SAPO-34, middle has 50 wt % and bottom has 75 wt % SAPO-34 was prepared. Another fixed bed reactor with total of 0.61 g SAPO-34 size of 1.1 (un powder catalyst and a-alumina was also prepared. The results are shown in Figures 5 and 6. A comparison between SAPO-34,1.1 mm catalyst and powder SAPO-34 ( 1.1 pm) was made. The results show that 1.1 pm powder catalyst produces more ethylene and propylene than dimethyl ether (DME) compared to the 1.1mm SAPO-34 bed. The most probable cause is that there is diffusion limitation to DME. The DME was not able to diffuse into the 1.1mm particle acid sites and form ethylene and propylene. 

There are several ways to reduce acid consumption (and hence acid costs) significantly. These costs frequently account for about one-third of total operating costs of an alkylation unit using sulfuric acid as the catalyst. First, the refinery s choice of the feed acid has a fairly large effect on acid consumption. As a comparison, feed acids of between 98% and 99.5% acidity values will be considered, and the acids will be reduced to acidity values of 90%. In the first case, the acidity is decreased by 8% but for the second acid by 9.5%. Assuming that the acidity decreases per pass in the reactor are equal, then approximately 18-19% more alkylate are produced with the more concentrated feed acid. Several refineries currently use 99.5% feed acids, but others employ 98.5% feed acids. 

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