Having calculated equilibrium constant Keq and total
adsorption sites Gtot and considering Eq. (14), the only independent variable in Eq. (44) remains kf (or kr) This
parameter can be obtained by fitting of experimental data in
Fig. 3 and this values are reported in Table 2.
Fig. 5a reports the logarithms of reaction rate coefficients
(e.g. Ln(kf) and Ln(kr)) versus reciprocal of absolute temperature
which provides the apparent activation energies. Fig. 5b
shows a schematic view of the controlling step of the process
with values of forward and backward apparent activation
energies.
The experimental data shown in Fig. 3 let us to introduce
the waiting time t0 which is the time needed to transfer
reactant to the reactive site. This characteristic time in principle
relies on the diffusion coefficient and concentration
gradient and also the distance from adsorption site to reactive
site. The dependencies of t0 on the temperature and pressure
by the same reaction system are reported in Fig. 6. An exponential
dependency of this parameter on the reciprocal of
temperature is displayed in Fig. 6a and almost linear dependency
on the pressure is seen in Fig. 6b.
The linear dependency of t0 on H2 pressure also enables us
to predict ideal pressure at which point the reaction starts
immediately. For example, the intercepts (dash lines in Fig. 6b)
extended from fitting experimental data at horizontal coordinate
show that 33, 39, 71 and 116 bars of H2 pressure are able
to facilitate the immediate reaction at 634, 611, 584 and 558 C,
respectively.
Having calculated equilibrium constant Keq and totaladsorption sites Gtot and considering Eq. (14), the only independent variable in Eq. (44) remains kf (or kr) Thisparameter can be obtained by fitting of experimental data inFig. 3 and this values are reported in Table 2.Fig. 5a reports the logarithms of reaction rate coefficients(e.g. Ln(kf) and Ln(kr)) versus reciprocal of absolute temperaturewhich provides the apparent activation energies. Fig. 5bshows a schematic view of the controlling step of the processwith values of forward and backward apparent activationenergies.The experimental data shown in Fig. 3 let us to introducethe waiting time t0 which is the time needed to transferreactant to the reactive site. This characteristic time in principlerelies on the diffusion coefficient and concentrationgradient and also the distance from adsorption site to reactivesite. The dependencies of t0 on the temperature and pressureby the same reaction system are reported in Fig. 6. An exponentialdependency of this parameter on the reciprocal oftemperature is displayed in Fig. 6a and almost linear dependencyon the pressure is seen in Fig. 6b.The linear dependency of t0 on H2 pressure also enables usto predict ideal pressure at which point the reaction startsimmediately. For example, the intercepts (dash lines in Fig. 6b)extended from fitting experimental data at horizontal coordinateshow that 33, 39, 71 and 116 bars of H2 pressure are ableto facilitate the immediate reaction at 634, 611, 584 and 558 C,respectively.
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