Hydrogen kinetic curves

Two kinetic experiments with different CD concentrations were used for kinetic modeling. In this simulation all of the rate constants not involved in the hydrogenation step were not altered. The calculated and simulated kinetic curves and optical yield-conversion dependencies are shown in Figure 9a and 9b. The results of kinetic modeling indicates that the whole kinetic curve and the optical yield - conversion dependencies can be well described by a kinetic model derived from the shielding effect model. 

Assuming zero order kinetics, the reaction rate constants can be calculated from the slope of the hydrogen uptake curve. Table 1 shows that the first three catalysts have similar rate constants on catalyst weight basis, from 5.6xl0"3 to... 

NMR spectroscopy provides analogue results. Inspection of hydrogen consumption curves following the hydrogenation of X- or E-methyl 3-acetamidobu-tenoate with [Rh(Et-DuPHOS)(MeOH)2]BF4 (Et-DuPHOS = l,2-bis(2,5-diethyl-phospholanyl)benzene)) showed the reaction to exhibit first-order kinetics (Fig. 10.19). 

These induction periods, which have also been described qualitatively by others [14], considerably complicate a comparison of the activity of various catalysts and a kinetic analysis of the hydrogen consumption curve. 

The process was controlled by determination of active hydrogen in Si-H groups for several times [2, 6], The influence of the structure of dihydride monomers on the reaction rate, yield and properties of obtained polymers has been studied (table 1, figure 1). Based on kinetic curves (figure 1) of Si-H groups conversion, the reaction rate constants have been determined (table 1). The total reaction order equals to 2. 

Absorption test starts with purging process as well as evacuation and then system is thermally stabilized under vacuum. Subsequently, hydrogen at desired absorption pressure is admitted into the system and by observing the pressure decreasing as a function of time, the kinetic curve is registered. 

Consequently, the powder which absorbed at 250°C went through four full cycles as described above. Figure 2.4a shows typical kinetic curves of absorption at various temperatures. The absorption cnrves shown in Fig. 2.4a are quite similar to the ones reported by Vigeholm et al. [12] under the same 1.2 MPa hydrogen pressure as the one used in our work. In onr case, abont 4.5 wt.%H2 is absorbed at 325°C in 4,500 s vis-a-vis about 4.5 at 312°C absorbed in 4,000 s as... 

Fig. 2.6 (a) Desorption kinetic curves at various temperatures under initial hydrogen pressure of 0.1 MPa of the as-received, nonactivated, commercial MgH powder Tego Magnan and (b) the Arrhenius plot of the desorption rate for the estimate of the apparent activation energy, fi, using kinetics data for four temperatures 350, 375, 400, and 420°C (fi -120 kJ/mol). Coefficient of fit = 0.996... 

Fig. 2.53 Desorption kinetic curves at various temperatures obtained in a Sieverts-type apparatus under 0.1 MPa of hydrogen pressure of (a) ABCR MgH + n-Ni (SSA = 14.5 mVg) baU-miUed for 15 min and (b) Tego Magnan MgH + m-Ni ball-milled for 20 h...

DSC tests show a substantial reduction of the hydrogen desorption onset (red circles) (T J and peak (T ) temperatures due to the catalytic effects of n-Ni as compared to the hydrogen desorption from pure MgH also milled for 15 min. (Fig. 2.57). It is interesting to note that there is no measurable difference between spherical (Fig. 2.57a) and fdamentary (Fig. 2.57b) n-Ni, although there seems to be some effect of SSA. We also conducted desorption tests in a Sieverts apparatus for each SSA and obtained kinetic curves (Fig. 2.58), from which the rate constant, k, in the JMAK equation was calculated. The enhancement of desorption rate by n-Ni is clearly seen. At the temperature of 275°C, which is close to the equilibrium at atmospheric pressure (0.1 MPa), all samples desorb from 4 to 5.5 wt.% within 2,000 s. 

MgH constituent. Althongh, in the strict sense, the desorption cnrves in Fig. 3.34 are not kinetic curves, since they are registered dnring continnons heating to a constant temperature of 300°C, it seems that the rate of hydrogen desorption is rather fast. The 30, 50 and 70 wt%LiAlFl composite desorbs the corresponding maximnm amonnt of Fl within 1,200 s. 

This kinetic equation is applied to the observed kinetic curves obtained in cyclohexene hydrogenation (model reaction) following the molecular hydrogen consumption. Of note, the present kinetic equation provides the value of fe2obs and not kj. However, the real value of the rate constant k2 can be obtained easily using the relationship k2 = k2obs x S/C, where S/C is the substrate/catalyst molar ratio (the catalyst is given as the number of metaUic moles employed). 

Kinetic curves displaying the influence of contact time (r) on methane hydroxylation with hydrogen peroxide are shown in Figure 7.27. 

Figure 2.6a shows typical kinetic curves of first desorption carried out in a Sieverts-type apparatus at the initial hydrogen pressure of 0.1 MPa (atmospheric pressure of 1 bar) for the as-received, nonmilled, and nonactivated Tego Magnan powder. For each temperature, a fresh load of sample was desorbed. At each temperature in Fig. 2.6a, the desorption process is complete with 100% of MgH2 des-... 

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