Effect of Temperature on a and b Values

Normally, with increase of temperature, a increases and b decreases (13) in some systems, e.g., Hg on Ni, Ru, Ir, Pd, Ph ZnO-CraOg, WS2, more precise relationships have been obtained, e.g., both b and In a being proportional to the reciprocal of the temperature (5). The presence of discontinuities in the Elovich plots, however, often obscure such dependences. Nevertheless, even in their absence, complex changes are often evident, e.g., a temperature increase may cause b to pass through maximum or minimum values as for H2 on ZnO, ZnO-MoOa O2 on ZnO, or the variation of a with T may be changed by altering the ambient pressure. 

In general, therefore, despite the usefulness of the Elovich equation as a method of representing data on rates of adsorption, not only the variation of the two important parameters a, and b with pressure and temperature, but also the presence of discontinuities, require that any acceptable theoretical model should, at least qualitatively, explain these results. Therefore, we first discuss the various theoretical interpretations of this equation. 

---