Copper catalysts concentration

The rate of the uncatalysed reaction in all four solvents is rather slow. (The half-life at [2.5] = 1.00 mM is at least 28 hours). However, upon complexation of Cu ion to 2.4a-g the rate of the Diels-Alder reaction between these compounds and 2.5 increases dramatically. Figure 2.2 shows the apparent rate of the Diels-Alder reaction of 2.4a with 2.5 in water as a lunction of the concentration of copper(II)nitrate. At higher catalyst concentrations the rate of the reaction clearly levels off, most likely due to complete binding of the dienophile to the catalyst. Note that in the kinetic experiments... 

The equilibrium constants obtained using the metal-ion induced shift in the UV-vis absorption spectrum are in excellent agreement with the results of the Lineweaver-Burke analysis of the rate constants at different catalyst concentrations. For the copper(II)ion catalysed reaction of 2.4a with 2.5 the latter method gives a value for of 432 versus 425 using the spectroscopic method. 

Maximum conversion occurs by equilibration at the lowest possible temperature so the reaction is carried out sequentially on two beds of catalyst (a) iron oxide (400°C) which reduces the CO concentration from 11% to 3% (b) a copper catalyst (200°) which reduces the CO content to 0.3%. Removal of CO2 ( 18%) is effected in a scrubber containing either a concentrated alkaline solution of K2CO3 or an amine such as ethanolamine ... 

Recently, other authors when studying the activation of hydrogen by nickel and nickel-copper catalysts in the hydrogen-deuterium exchange reaction concentrated for example only on the role of nickel in these alloys (56) or on a correlation between the true nickel concentration in the surface layer of an alloy, as stated by the Auger electron spectroscopy, and the catalytic activity (57). 

Westerterp et al. reported the first-order reaction rate constant with respect to oxygen concentration in a solution at 30°C containing 100 g of sodium sulfite per liter. The catalyst concentration was 0.001 g-mole/liter. They found that k is 37,000 sec 1 for the CoS04 catalyst and 9800 sec"1 for CuS04 catalyst. For the same sodium sulfite concentration but with copper sulfate concentration greater than 0.005 g-mole/liter, the reaction rate constant as a function of temperature is approximated by ... 

Since ruthenium and rhodium are neighboring elements in the periodic table, a closer comparison of the properties of ruthenium-copper and rhodium-copper clusters is of interest (17). When we compare EXAFS results on rhodium-copper and ruthenium-copper catalysts in which the Cu/Rh and Cu/Ru atomic ratios are both equal to one, we find some differences which can be related to the differences in miscibility of copper with ruthenium and rhodium. The extent of concentration of copper at the surface appears to be lower for the rhodium-copper clusters than for the ruthenium-copper clusters, as evidenced by the fact that rhodium exhibits a greater tendency than ruthenium to be coordinated to copper atoms in such clusters. The rhodium-copper clusters presumably contain some of the copper atoms in the interior of the clusters. 

The oxidative dehydrogenation of ethanolamine to sodium glycinate in 6.2 M NaOH was investigated using unpromoted and chromia promoted skeletal copper catalysts at 433 K and 0.9 MPa. The reaction was first order in ethanolamine concentration and was independent of caustic concentration, stirrer speed and particle size. Unpromoted skeletal copper lost surface area and activity with repeated cycles but a small amount of chromia (ca. 0.4 wt%) resulted in enhanced activity and stability. 

Recently, a novel process for the preparation of chromia promoted skeletal copper catalysts was reported by Ma and Wainwright (8), in which Al was selectively leached from CuA12 alloy particles using 6.1 M NaOH solutions containing different concentrations of sodium chromate. The catalysts had very high surface areas and were very stable in highly concentrated NaOH solutions at temperatures up to 400 K (8, 9). They thus have potential for use in the liquid phase dehydrogenation of aminoalcohols to aminocarboxylic acid salts. 

The effect of reactant concentrations on reaction rate was studied using unpromoted skeletal copper catalysts initially leached at 278 K and then... 

The oxidative dehydrogenation of ethanolamine over skeletal copper catalysts at temperatures, pressures and catalyst concentrations that are used in industrial processes has been shown to be independent of the agitation rate and catalyst particle size over a range of conditions. A small content of chromia (ca. 0.7 wt %) provided some improvement to catalyst activity and whereas larger amounts provided stability at the expense of activity. 

It has been pointed out earlier that the anti/syn ratio of ethyl bicyclo[4.1,0]heptane-7-carboxylate, which arises from cyclohexene and ethyl diazoacetate, in the presence of Cul P(OMe)3 depends on the concentration of the catalyst57). Doyle reported, however, that for most combinations of alkene and catalyst (see Tables 2 and 7) neither concentration of the catalyst (G.5-4.0 mol- %) nor the rate of addition of the diazo ester nor the molar ratio of olefin to diazo ester affected the stereoselectivity. Thus, cyclopropanation of cyclohexene in the presence of copper catalysts seems to be a particular case, and it has been stated that the most appreciable variations of the anti/syn ratio occur in the presence of air, when allylic oxidation of cyclohexene becomes a competing process S9). As the yields for cyclohexene cyclopropanation with copper catalysts [except Cu(OTf)2] are low (Table 2), such variations in stereoselectivity are not very significant in terms of absolute yields anyway. 

The EfZ ratio of stilbenes obtained in the Rh2(OAc)4-catalyzed reaction was independent of catalyst concentration in the range given in Table 22 357). This fact differs from the copper-catalyzed decomposition of ethyl diazoacetate, where the ratio diethyl fumarate diethyl maleate was found to depend on the concentration of the catalyst, requiring two competing mechanistic pathways to be taken into account 365), The preference for the Z-stilbene upon C ClO -or rhodium-catalyzed decomposition of aryldiazomethanes may be explained by the mechanism given in Scheme 39. Nucleophilic attack of the diazoalkane at the presumed metal carbene leads to two epimeric diazonium intermediates 385, the sterically less encumbered of which yields the Z-stilbene after C/C rotation 357,358). Thus, steric effects, favoring 385a over 385 b, ultimately cause the preferred formation of the thermodynamically less stable cis-stilbene. 

A somewhat unusual copper catalyst, namely a zeolite in which at least 25% of its rhodium ions had been exchanged by Cu(II), was active in decomposition of ethyl diazoacetate at room temperature 372). In the absence of appropriate reaction partners, diethyl maleate and diethyl fumarate were the major products. The selectivity was a function of the zeolite activation temperature, but the maleate prevailed in all cases. Contrary to the copper salt-catalyzed carbene dimer formation 365), the maleate fumarate ratio was found to be relatively constant at various catalyst concentrations. When Cu(II) was reduced to Cu(I), an improved catalytic activity was observed. 

It can be obtained from cyclohexane. Cyclohexane is air oxidised to yield a mixture of cyclohexanol and cyclohexanone. Cyclohexanol is dehydrogenated to cyclohexanone over copper catalyst. Cyclohexanone when treated with hydroxylamine sulphate at 20°-95°C gives an oxime. The oxime when treated with concentrated sulphuric acid undergoes Beckmann rearrangement to yield caprolactam. 

Given that the number of a and d protons are the same, an identical set of equations with Ad in place of Aa can also be used. Here we have used an average of Aa and Ad with the areas assessed after Lorentzian deconvolution in order to provide better separation of the 2.99 and 3.02 ppm lines. Mole fractions derived using this NMR method for reaction over the unpromoted copper catalyst are shown as a function of time in Figure 5. Clearly IDA is formed largely via HEG as intermediate since the concentration of the latter passes through a well-defined maximum. 

The formulation was intensively mixed for 15 s in a cylindrical vessel of 9.5 cm diameter and 10 cm height. A copper-constantan thermocouple was centered, and the signal continuously monitored. Figure 5.16 shows adiabatic temperature rise curves for different catalyst concentrations. The adiabatic temperature rise was estimated as 155°C. 

A typical process (Fig. 2) consists of two continuous steps. I n the first step the oxidation of toluene to benzoic acid is achieved with air and cobalt salt catalyst at a temperature between 121 and 177°C (206 kPa gauge), and the catalyst concentration is between 0.1 and 0.3%. The reactor effluent is distilled, and the purified benzoic acid is collected. In the second processing step, the benzoic acid is oxidized to phenyl benzoate in the presence of air and a catalyst mixture of copper and magnesium salts (234°C, 147 kPa gauge). The phenyl benzoate is then hydrolyzed with steam in the second reactor to yield phenol and carbon dioxide (200°C and atmospheric pressure). 

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