Quasi-equilibrium desorption steps

By using the quasi-equilibrium procedure, Grillet et al. (1993) were able to detect the sub-step, AB, in the water isotherm at pjp° 0.15. The fact that the sub-step can be seen in both the adsorption and desorption isotherms (although at slightly... 

This scheme means that the adsorption and half-dehydrogenation are fast (in quasi-equilibrium) so that the left side of the equation represents one pool. The reversible but nonequilibrium step then leads to the second pool the adsorption-desorption of i-butene is also in quasi-equilibrium. Note that the reactants and products are both in the same physical well-mixed gas phase, and the surface species are on the same surface phase this will be taken into account in the balance equations that follow. 

When a prior discharge step producing the adsorbed intermediate, for example, H in the HER, can be considered in quasi-equilibrium when the desorption step is rate controlling (an experimentally encountered situation at a number of metals), 6 is expressed by an electrochemical Langmuir-type adsorption relation ... 

In the derivation of the rate equation, it is assumed that the surface reaction is irreversible and rate determining, whereas the adsorption steps of hydrogen and aldol are rapid enough for the quasi-equilibrium hypothesis to be applied. The desorption step of triol is assumed to be irreversible and very rapid (cr —>0). 

The reaction order in buta-1,3-diene is close to zero, indicating that the fraction of vacant sites is very low, and at the total consumption of buta-1,3-diene the mole fractions of butenes are not equal to zero. The assumption of equilibrium adsorption of the intermediate compound (but-l-ene) in the case of irreversible butadiene hydrogenation and but-l-ene isomerization and hydrogenation cannot explain the latter observation. Therefore, adsorption/desorption steps for buta-1,3-diene but-l-ene, but-2-ene are thought to be reversible and have an "adsorption-assisted desorption " nature. The desorption of butane step 15 is assumed to be irreversible and fast. For conformational isomerization (step 2) a quasi-equilibrium approximation will be used. 

The phase boundaries of the Pd-X (X = H,D,T) system were determined from pressure concentration temperature data because of the high risk of handling PdT samples outside our tritium loading equipment. Pd forms no stable oxide layers as is the case for or Nb that prevent the tritium to leave the sample. The boundaries between the miscibility gap and the 3-phase were obtained from the shape of the desorption isotherms. The values of concentration and temperature of the solvus line between the a- and the two phase regions a+3 were obtained by quasi isochoric measurements. A PdX sample with the concentration x slightly in the miscibility gap was heated in small temperature steps so that the concentration of the sample decreased and finally belonged to the pure a-phase. The change of slope in the equilibrium pressure as a function of the inverse temperature is interpreted as the intersection with the solvus line. 

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