Chemisorption equilibrium constants

The overall quality of the model is excellent, with a coefficient of determination of 0.987 and a relative standard deviation of the error of 14.5 percent. Nonetheless, the values for K, K2, and K3 are jointly confounded with one another and thus represent only one of many families of values for the parameters that would fit the data virtually equally well. This means that inferences that these parameters really represent chemisorption equilibrium constants are unwarranted, but the model is nonetheless useful for its intended purpose. If it had been desirable to do so, additional experiments could have been run to narrow the joint confidence intervals of these parameters. 

Broadly speaking then, chemisorption equilibrium constants are expected to cluster around the trend line shown in Figure 9.1 and to be limited on the enthalpy side by the strength of the weakest bond in the adsorbing species. Release of more energy than that is likely to lead to bond breakage. 

Kj = chemisorption equilibrium constant for component j C = concentration of active sites in the catalyst... 

To understand the chemisorptive property of lr/ln/H-ZSM-5 in a comparison with that of ln/H-ZSM-5, the chemisorption data were analyzed in detail. The data shown in Fig. 3 are relatively well fitted to the Langmuir isotherm, as shown in Fig. 5. From these relations, the equilibrium constant (K) and the amount of NO2 adsorbed at saturation (Vo) were determined according to the following equations ... 

It is interesting to note that, although the intrinsic rate of desorption is slower than that of adsorption, both rates were found to be sufficiently fast under our experimental conditions so that the adsorption-desorption process on the Pt surface can be assumed to rapidly equilibrate at all times that is, even a ten-fold increase in both the adsorption and desorption rate constants (while keeping their ratio constant) did not significantly change the predicted step responses. With the assumption of chemisorption equilibrium, Equations (1) and (4) can be combined into the form (35)... 

Poisoning is caused by chemisorption of compounds in the process stream these compounds block or modify active sites on the catalyst. The poison may cause changes in the surface morphology of the catalyst, either by surface reconstruction or surface relaxation, or may modify the bond between the metal catalyst and the support. The toxicity of a poison (P) depends upon the enthalpy of adsorption for the poison, and the free energy for the adsorption process, which controls the equilibrium constant for chemisorption of the poison (KP). The fraction of sites blocked by a reversibly adsorbed poison (0P) can be calculated using a Langmuir isotherm (equation 8.4-23a) ... 

The duality of cracking mechanisms is summarized in Fig. 5, where RH paraffin feed, R -C=C = olefinic product, Kq = equilibrium constant of olefin chemisorption. Free Bronsted acid sites HZ interact directly with the paraffin feed by protonation, producing monomolecular cracking. When the acid sites are covered with adsorbed olefins to form... 

The variations in pHn> of hematite in DDA-HC1 solutions are attributed to the chemisorption of RNH2 on MeO- sites, and the logarithm of the equilibrium constant of the chemisorption reaction is 12.71 0.14. The proposed method qualitatively accounts for the variation of pHjP of hematite in NaOl. The change in the pH1P occurs because of the chemisorption of RCOOH on MeO" sites and RCOO on MeOH sites. The chemisorption of RCOO" on MOH2 sites probably occurs as well, but it does not affect the pHIP. 

However, whereas this analysis of competition effects in anisole acetylation is very attractive, the following oversimplification which was made also has to be considered indeed, the competitive adsorption of the very polar acetic acid product, which inhibits arene acetylation[52,53] and the adsorption equilibrium constants were related to adsorption within the zeolite micropores only, without taking into consideration chemisorption over the protonic active sites. 

To determine whether a change in dispersion or in the type of catalytic sites is responsible for these different effects of phosphate, Jian and Prins (59, 75) investigated the kinetics of these hydrogenation and elimination reactions. Unfortunately, no simple chemisorption method has proved capable of determining the dispersion of supported metal sulfides (6). Therefore, an indirect method, involving the determination of rate and adsorption equilibrium constants (the first proportional to the number of sites and the second dependent only on the type of site) had to be used. 

This suggested mechanism is consistent with a number of observations made here and with previous work reported in the literature. For example it was found that recarbonation rates were relatively insensitive to temperature. This would indicate non-activated chemisorption and, as Fischbeck and Snaidt report (10), mineral recarbonation is often independent of temperature when the temperature dependencies of the decarbonation rate conr-stant and the equilibrium constant are similar. This is exactly what is observed in western oil shales (Ref (9), Equations (6) and (7)). Previous work has also pointed to the role of chemisorption phenomena in mineral decomposition reactions. Spencer and Topley (11) have suggested that finely grained oxides can chemisorb HoO as well as H2 and Soni and Thomson (12) observed higher recarbonation rates when CO2 was produced on the surface during oil shale char combustion. 

Now an anion. A", is introduced into the system. For simplicity, we will assume that only the monodentate surface bonding reaction (4.30) is important. The equilibrium constant for chemisorption of this anion is then... 

However, experiments10 have shown no significant influence of the H20/H2 ratio. This result may appear surprising in view of the high heat of chemisorption of oxygen on nickel10 (ca.430 kJ/mol 0-). But this value is less than the heat of chemisorption for sulfur, (ca. 520 kJ/mol 2, Table 1). These values correspond to an equilibrium constant "TO13 for the reaction,... 

As discussed previously (2), the contribution to 0 from hydrogen chemisorption must be negligible. By means of Equations (2) and (6), values for the equilibrium constant, Ki, have been determined for palladium black and palladium-silver alloys of different compositions at various temperatures and are collected in Fig. 2. For every sample, data were obtained at two different water-vapor pressures. The lines drawn through the experimental points were taken as straight lines, whose slopes were used to com-... 

Electroanalytical chemistry encompasses a group of qualitative and quantitative analytical methods based on the electrical properties of a solution of the anahie when it is made part of an electrochemical cell. Electroan-alytical techniques are capable of producing loir detection limits and a wealth of characterization information describing electrochcmically accessible systems. Such information includes the stoichiometry and rate of interfacial charge transfer the rate of mass transfer, the e.ite.nt of adsorption or chemisorption, and the rates and equilibrium constants for chemical reactions. 

Consequently, measuring Pa va data pairs and correlating pa/va vs. Pa in linear fashion allows one to determine ua, monolayer via the slope, which can be verified experimentally at the chemisorption/physisorption crossover. The adsorp-tion/desorption equilibrium constant for gas A is calculated as follows ... 

J. V. Sinisterra, J. M. Marinas, and A. Llobura [Can. J. Chem., 61, 230 (1983)] employed an extended form of the Hammett equation to correlate data for esterification of ethanol with substituted benzoic acids in the gas phase over a solid AIPO4 catalyst. The focus of their efforts was correlation of values of the adsorption equilibrium constants and apparent rate constants. Use the information tabulated below to prepare a Hammett plot of experimental absorption equilibrium constants versus the corresponding values of the a parameters for the substituted benzoic acids indicated. Employ the a values in Table 7.2 of the text. In principle the intercept of the best straight line through these data should correspond to the adsorption equilibrium constant for benzoic acid. By how much does this value differ from the experimental value below What value of the parameter p characterizes the chemisorption of substituted benzoic acids ... 

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