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Chemisorption activation energies

Activation Energy - Chemisorption can be an activated process therefore, only those molecules possessing the required activation energy can be chemisorbed. However, many, if not most, chemisorption processes on clean metal surfaces are nonactivated at temperatures near or above 300 K, especially for nondissodative adsorption. [Pg.88]

It was noted in Section XVII-1 that chemisorption may become slow at low temperatures so that even though it is favored thermodynamically, the only process actually observed may be that of physical adsorption. Such slowness implies an activation energy for chemisorption, and the nature of this effect has been much discussed. [Pg.703]

Fig. XVIII-13. Activation energies of adsorption and desorption and heat of chemisorption for nitrogen on a single promoted, intensively reduced iron catalyst Q is calculated from Q = Edes - ads- (From Ref. 130.)... Fig. XVIII-13. Activation energies of adsorption and desorption and heat of chemisorption for nitrogen on a single promoted, intensively reduced iron catalyst Q is calculated from Q = Edes - ads- (From Ref. 130.)...
When gaseous or liquid molecules adhere to thesurface of the adsorbent by means of a chemical reaction and the formation of chemical bonds, the phenomenon is called chemical adsorption or chemisorption. Heat releases of 10 to 100 kcal/g-mol are typical for chemisorption, which are much higher than the heat release for physisorption. With chemical adsorption, regeneration is often either difficult or impossible. Chemisorption usually occurs only at temperatures greater than 200 C when the activation energy is available to make or break chemical bonds. [Pg.276]

Regardless of the exact extent (shorter or longer range) of the interaction of each alkali adatom on a metal surface, there is one important feature of Fig 2.6 which has not attracted attention in the past. This feature is depicted in Fig. 2.6c, obtained by crossploting the data in ref. 26 which shows that the activation energy of desorption, Ed, of the alkali atoms decreases linearly with decreasing work function . For non-activated adsorption this implies a linear decrease in the heat of chemisorption of the alkali atoms AHad (=Ed) with decreasing > ... [Pg.30]

This linear variation in catalytic activation energy with potential and work function is quite noteworthy and, as we will see in the next sections and in Chapters 5 and 6, is intimately linked to the corresponding linear variation of heats of chemisorption with potential and work function. More specifically we will see that the linear decrease in the activation energies of ethylene and methane oxidation is due to the concomitant linear decrease in the heat of chemisorption of oxygen with increasing catalyst potential and work function. [Pg.164]

This is an important result and shows that the dramatic decrease in catalytic activation energy, EA, upon increasing is due to the decrease in Ed and concomitant weakening of the Pt=0 chemisorptive bond upon increasing UWr and O. [Pg.174]

One of the most striking results is that of C2H4 oxidation on Pt5 where (xads,o ctact = -1, i.e. the decreases in reaction activation energy and in the chemisorptive bond strength of oxygen induced by increasing work function ethylene epoxidation and deep oxidation on Ag.5... [Pg.268]

The interaction of hydrogen (deuterium) molecules with a transition metal surface c an be conveniently described in terms of a Lennard--Jones potential energy diagram (Pig. 1). It cxxislsts of a shallcw molecular precursor well followed by a deep atomic chemisorption potential. Depending on their relative depths and positions the wells m or may not be separated by an activation energy barrier E as schematically Indicated by the dotted cur e in Fig. 1. [Pg.224]

In our view the final verification was given to this conclusion in paper [66] in which simultaneous O2 adsorption on partially reduced ZnO and resultant change in electric conductivity was studied. It was established in this paper that the energies of activation of chemisorption and that of the change of electric conductivity fully coincide. The latter is plausible only in case when localization of free electron on SS is not linked with penetration through the surface energy barrier which is inherent to the model of the surface-adjacent depleted layer. [Pg.123]

Works [40, 91] surveyed y versus temperature for deactivation of 02( Aj ) on quartz at 350- 900 K. The obtained temperature dependencies were in the Arrhenius form with the activation energy of 18.5kJ/mole. A conclusion was drawn up about the chemisorption mechanism of singlet oxygen deactivation on quartz surface. A similar inference was arrived at by the authors of work [92] relative to 02( A ) deactivation (on a surface of oxygen-annealed gold). [Pg.302]


See other pages where Chemisorption activation energies is mentioned: [Pg.9]    [Pg.37]    [Pg.1353]    [Pg.9]    [Pg.37]    [Pg.1353]    [Pg.14]    [Pg.601]    [Pg.703]    [Pg.703]    [Pg.707]    [Pg.712]    [Pg.1188]    [Pg.285]    [Pg.27]    [Pg.172]    [Pg.174]    [Pg.267]    [Pg.367]    [Pg.380]    [Pg.382]    [Pg.397]    [Pg.442]    [Pg.266]    [Pg.137]    [Pg.14]    [Pg.46]    [Pg.46]    [Pg.86]    [Pg.88]    [Pg.233]    [Pg.236]    [Pg.241]    [Pg.242]    [Pg.270]    [Pg.276]    [Pg.311]    [Pg.314]    [Pg.389]    [Pg.394]   
See also in sourсe #XX -- [ Pg.128 ]

See also in sourсe #XX -- [ Pg.15 ]




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