Rate of hydrogenation as a function

The rate of hydrogenation as a function of the concentration of PPh3 supports these assumptions. The rate was measured at a fixed complex concentration of 10 3M, and the results in Figure 2 indicate that Reaction 3 shifts from HRh(PPh3)2 toward the less active HRh(PPh3)3 when the concentration of PPh3 is increased. The rate then is expressed as... 

Figure 3.15 Initial rate data of benzene hydrogenation over Ni-kieselguhr. (a) rate of hydrogenation as a function of hydrogen concentration, P = 760 Torr (b) rate of hydrogenation as a function of benzene concentration, P = 760 torr (c) product inhibition effects at low conversions, P = 760 Torr, T = 124 °C. [After J.P.G. Kehoe and J.B. Butt, J. Appl. Chem. BiotechnoL, 23, with permission of the Society of Chemical Industry, (1972).]...

We also have used C fixation to measure equilibria and rates of dissociation as a function of temperature. The conclusions reached from these studies have been reported. The dependence of the dissociation equilibria on pH was consistent with dissociation reactions involving the addition to two protons per subunit, a pH-independent dissociation, and a dissociation upon the loss of one proton per subunit. The rate constants for dissociation were consistent with terms first order in hydrogen and hydroxide ions and a pH-independent path. The equilibrium constants in the range 3-35° at pH 7.2 exhibited no dependence on temperature the association reaction was entropy-driven with A5 = 68 cal moL The rate constants for the pH-independent dissociation followed A// = 6 kcal mol The order of effectiveness of concentrated salts in promoting dena-turation was correlated with their effect on the activity coefficient of ace-tyltetraglycine ethyl ester and suggested that peptide groups became more exposed upon dissociation. 

Thietane 1-oxides may be reduced to thietanes by iodide ion in acidic mediaby hydrogen sulfide, and by zinc-hydrochloric acid. Thietane 1-oxide is reduced by iodide about four times more rapidly than dimethyl sulfoxide the rate of reduction as a function of ring-size decreases as follows 5 > 4 > 6. The mechanism of reduction by iodide involves slow formation of an iodosulfonium salt 120. The thietane product is unstable in the aeidic medium and was not identified. 

In terms of coupling these observations of reactive intermediates to a definitive mechanistic framework, the paper of Halpern and Landis plays a central role [33]. Through careful kinetic measurements of hydrogenation as a function of temperature, pressure and catalyst concentration, the soundness of the enamide equilibration/hydrogenation model is established. Rate constants have been derived for the steps defined in Fig. 7 which give self-consistent results for hydro-... 

Figure 5 The rate of reaction as a function of hydrogen partial pressure. Reaction conditions 1 g 5% Ir/graphite, T= 85 C...

Figure 46 shows the dependence of the rate of surface reaction (24) and the rate of alkylation as a function of the amount of surface metallic copper atoms in the catalyst. " The rate of surface reaction (24) increases with the amount of metallic copper. This behavior can be expected as the reaction of tin tetraethyl with adsorbed hydrogen takes place only on metallic copper surface sites (Cu°surface)- ° Contrary to that, as emerges from Figure 46, the alkylation activity of the catalyst decreases with increasing the amount of zero valence surface copper atoms in the catalyst. 

For intermediate partial pressures of hydrogen, the full Langmuir expression would be needed to determine the surface concentration and the rate of diffusion as a function of hydrogen partial pressure. The exponent of the partial pressure of hydrogen would lie between 0 and 0.5. 

Figure 9. Relative rate of CO hydrogenation as a function of copper coverage on a Ru(OOOl) catalyst Reaction temperature 575K. Results for sulfur poisoning from Figure 7 have been replotted for comparison.

Figure 12. The relationship between the logarithm of the relative hydrogenation rate over CFP-supported rhodium nanoclusters, with respect to the polymer-stabilized nanostructured catalyst, for a number of a number of alkenes, as a function of their affinity to the support (expressed as the square difference of the solubility parameter of the support and of the substrate). (Reprinted from Ref [33], 1991, with permission from the American Chemical Society.)...

Copper-nickel alloy films similarly deposited at high substrate temperatures and annealed in either hydrogen or deuterium were used to study the hydrogenation of buta-1,3-diene (119) and the exchange of cyclopentane with deuterium (120). Rates of buta-1,3-diene hydrogenation as a function of alloy composition resemble the pattern for butene-1 hy-... 

As already shown by Wiese et al. [17] mass transport rates in biphasic catalysis can be dramatically influenced by hydrodynamics in a tube reactor with Sulzer packings. Above all, the volume rate of the catalyst phase in which the substrates are transported by diffusion plays a decisive role in accelerating the mass transport rate. This effect was also investigated for citral hydrogenation in the loop reactor. Overall reaction rates and conversions as a function of the catalyst volume rate can be seen in Fig. 15. 

Fig. 1 Conversion of glucose as a function of time in five successive hydrogenations for the different catalysts (a) RNi (b) RNiMo (c) RNiCr (d) RNiFe (e) RNilndl (f) RNilnd2. The initial rates rQ (mol h 1g ) are given for the first and fifth reactions. Tne lower curve in (e) corresponds to a catalyst after many industrial hydrogenations.

Results of the activity for heteroatom removal of nanoscale 8%Mo/ Fe203/S042, Mo2N Oy and Mo2CxOy are shown in Figure 27.6. They are expressed as the fraction of heteroatom removed (S, O, N), or the fraction of hydrogen consumed to obtain complete hydrogenation, as a function of reaction time. Table 27.3 summarizes the results for the activity of the nanoscale catalysts with the activity expressed as an areal rate (rate m-2), and also as a turnover rate for the oxycarbide and oxynitride. 

Although no one has succeeded in directly measuring the rate constant of this reaction, Kelly et al. (27) have reported some kinetic data which permit us to estimate an upper limit for the rate constant. These investigators followed the reaction of sodium with ethanol in liquid ammonia at —33.4° C. by measuring the evolved hydrogen as a function of time. 

For the same catalytically active material but with different catalyst carriers, different reaction rates and rate equations can be expected. Consider the hydrogenation of 2,4 DNT as discussed in Section 9.2 for 5% Pd on an active carbon catalyst with an average particle size of 30 (im [3]. These experiments were later repeated but with a Pd on an alumina catalyst [5]. This catalyst consisted of 4 x 4mm pellets, crushed to sizes of lower than 40/um in order to avoid pore diffusion limitations. In Figure 2.9 the measured conversion rates are given as a function of the averaged catalyst particle diameter, showing that above a diameter of 80/im the rate measured diminishes. For small particles they determined the rate equations under conditions where there were no pore diffusion lim-... 

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