Conditioning of catalysts

C02 solubility. For example, the desired branched aldehyde formed upon hydroformylation of vinylnaphthalene is considerably more soluble in scC02 than its linear isomer. Therefore, the ratio of the branched to linear product increases from approximately 90 10 in the condensed phase to up to 98 2 in the C02 phase in a single extraction step under the low density conditions of catalyst separation. 

D. Farcasiu and J. Q. Li, Preparation of sulfated zirconia catalysts with improved control of sulfur content, 111 effect of conditions of catalyst synthesis on physical properties and catalytic activity,... 

These multi-phase approaches, however, suffer from the drawback that some of the reaction media must be separated from the catalyst or the reaction products. Therefore, the conditions of catalyst separation may be very different from those of the reaction such that catalyst decomposition may still occur. Furthermore, most approaches have two or three phases during the reaction, which may cause problems in controlling the phase equilibria and in controlling the distribution of the reacting components and the catalytically active component between the phases. Most effective agitation of the reaction mixture is often required. 

As the surface condition of catalyst reflects the EDA of MRNi as already mentioned, the EDA is a very sensitive parameter from which to get information on the surface character of the catalyst. For example, when MAA is used for the substrate, a 1 x 10 3 (%) change of the surface condition is observable, because the optical rotation of optically pure MHB is 22.95°... 

The extent to which the various reactions occur is a function of operating conditions, feed stock, and condition of catalyst. 

A study of the completion of reaction vs. time was also made on the direct esterification of a typical olefin with a primary alkyl acid 0-phthalate. By titration of the reaction mass with 0.5N sodium hydroxide, we determined the rate of reaction using standard conditions of catalyst level, reaction temperature and olefin excess as previously described. The acid value reached a minimum and longer time cycles did not reduce this to any great extent. 

The influence of additives was investigated after changing the conditions of catalyst activation especially after modifying the calcination temperature. It can be seen in Table 3 that the selectivity varies very much with this activation step and also that the final result depends on the nature of the additive ... 

Condition of Catalyst Fresh Aged Fresh Aged... 

The HBEA catalyst can be reused after regeneration simply by heating in air for 8 h at 773 K (i.e. under the conditions of catalyst activation). 

Conditions of Catalyst Preparation by Galvanostatic Pulse Electrodeposition and... 

Many ruthenium complexes have been tested in the silylative coupling reaction. In the synthetic procedure the absence of by-products of the homocoupling of vinylsilanes is required so an excess of the olefin has usually been used. However, the screening tests performed at the 1 1 ratio of styrene and phenyldimethylvinylsilane with a variety of ruthenium catalysts have shown that pentacoordinated monocarbonyl bisphosphine complexes appear to be the most active and selective catalysts of which RuHCl(CO)(PCy3)2 has shown high catalytic activity under conditions of catalyst loadings as low as 0.05 mol % [55]. Cuprous salts (chloride, bromide) have recently been reported to be very successful co-catalysts of ruthenium phosphine complexes, markedly increasing the rate and selectivities of all ruthenium phosphine complexes [54]. 

Studies of the Fischer-Tropsch synthesis on nitrided catalysts at the Bureau of Mines have been described (4,5,23). These experiments were made in laboratory-scale, fixed-bed testing units (24). In reference 5, the catalyst activity was expressed as cubic centimeters of synthesis gas converted per gram of iron per hour at 240°C. and at a constant conversion of 65%. Actually, the experiments were not conducted at 240°C., but the activity was corrected to this temperature by the use of an empirical rate equation (25). Conditions of catalyst pretreatment for one precipitated and two fused catalysts are given in Table IV. 

Several catalyst regeneration experiments were conducted with pyridine as the solvent using different extraction conditions and the catalyst activities were measured. The conditions of catalyst extractions are listed in Table II and the stabilized activities of the catalysts after 5-6 h of activity tests are shown in Figures 2 and 3. The catalyst characteristics were examined only in one run, which are shown in Table III. 

The reaction rate per unit volume of catalyst as well as its selectivity depend on both the specific catalytic activity and the surface area of the active component per unit catalyst volume, as well as on its pore structure. These characteristics are determined by the conditions of catalyst preparation. Therefore, when developing a new catalyst, it is extremely important to be able to determine in advance the required internal surface area and the most suitable pore structure of the catalyst for the given reaction. 

Similar reactions have been reported for a mixture of 2,6-dimethoxyi-odobenzene, copper(I) oxide, and 1,3,5-trinitrobenzene in pyridine 21). Di- and triarylation can be effected under suitable conditions of catalyst, solvent, and temperature. No simple hypothesis can explain the experimental facts for the copper(I) oxide reactions. 

The performance of a solid catalyst typically depends on structural properties of the active sites and/or the support. These properties are frequently determined by the conditions of catalyst synthesis and/or the activation procedure. Knowing how properties of final catalysts are influenced by peculiarities of synthesis and conditioning procedures is of interest because, on the basis of such knowledge, synthesis procedures might be optimized to produce desired catalyst properties. The following two examples illustrate the versatility of EPR spectroscopy for monitoring catalyst syntheses in both gas-solid and liquid-solid systems. 

It has been shown for both the selective oxidation of butane (43) and the ammoxidation of methyl-substituted aromatics (55) that the strength of spin-spin exchange in -containing bulk catalysts is related to the catalytic performance. Moreover, results discussed in this section illustrate that the spin-spin exchange properties are already determined by the conditions of catalyst formation and can be assessed in a unique way by EPR spectroscopy. Thus, this technique provides local structural information even for amorphous constituents or disordered phases—information that is hardly accessible by other methods such as XRD. This point is significant because active sites in real catalysts are frequently not located in well-crystallized phases but instead in disordered or even amorphous phases. 

A typical catalyst containing 2.5% of chromium in n-hexane (20 mg 1" ) activated by aluminium diethyl ethoxide (0.3 mg 1" ) gave a yield of 140 g polymer per h at 88—91°C and a monomer pressure of 300 p.s.i.g. The chromocene based catalysts are also of high activity, this being dependent on the conditions of catalyst preparation. Dehydration at 670°C gave the highest yield of polymer. Detailed kinetics were not carried out, but yields of 130—1670 g polymer per mmole Cr per 100 p.s.i. ethylene per h at 60°C were reported. 

Most kinetic studies on copolymerizations using coordination catalysts have been restricted to the determination of monomer reactivity ratios. There are problems both experimentally and in interpretation since the major simplification assumed to hold for most free radical initiated systems, namely that monomer incorporation is determined only by the monomer concentrations and the four rate coefficients, cannot be taken for granted. Further, catalyst activity and selectivity are influenced by the conditions of catalyst preparation including the manner and order of... 

Halopyridines are typically poor substrates for Heck reactions due to the possibility of pyridyl-bridged palladium dimers preventing additional reactions. Improved reaction conditions, of catalyst and the use of DMA as cosolvent, have allowed greater functional group tolerance [136], This was reduced to practice in the transformation of 388 into 389. 

A typical example of reaction was the following (catalyst) = 5.185 X 15 M (substrate) = 3.085 x 10 M pH = 9.1 Trls 0.02M y 0.02 T 26 C ratio [catalyst]/[substrate] = 16.8. Absorb-ance versus time curves were obtained. A blank on each kinetic run was prepared and the blank value was subtracted from the catalytic value. All data obtained under conditions of [catalyst] [substrate] were, unless otherwise noted, treated as pseudo first-order kinetics by plotting iln(A -A. ) versus time. A j x used instead of A. The slope of the straight line was taken as kobs the case of accelerative behavior the slope at 75% of... 

Fig. 1.12 Reduction by a train of hydrogen pulses of previously C>2-oxidised Pt catalysts. For pre-treatment conditions of catalysts Ml and M2, see text above.

In order to assess the importance of Pt-Re interactions Bertalocini112 compared the performance of adjoining beds of Pt-alumina and Re-alumina with that of co-impregnated Pt-Re catalysts, and concluded that they were equally effective no migration of Re onto the Pt catalyst was observed. However, it is not clear in this reference whether the catalysts were optimally sulphided, or indeed approximated to the condition of catalysts in Ultraformer88operations. In contrast, Sachtler78 found that physical mixtures are less stable than co-impregnated catalysts. 

The second step in the analysis is to classify the different conditions of catalyst operation and determine the distribution of emissions between the different types of operating conditions. This step in the analysis allows one to identify the most significant conditions of operation where catalyst performance can be improved. In catalyst aging tests, one can identify conditions of operation where catalyst performance has deteriorated most and, thus, were stability should be improved. 

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