Effect of Chloride on Oxygen Adsorption

This interpretation conflicts with that of Kilty et al. Using a silver powder, they showed that pre-adsorption of chlorine suppressed the non-activated adsorption of oxygen on a one-to-one basis. When the chlorine coverage was greater than about 0.25, this adsorption was completely suppressed and further addition of chloride began to suppress the activated associative adsorption of 

Kamenski, N. V. Kul kova, and D. Bonchev, React. Kinet. Catalysis Letters, 1977, 7, 481. 

Rovida, F. Pratesi, M. Maglietta, and E. Ferroni, Proc. 2nd Internal. Conf. on Solid Surfaces, 1974, Japan,/. Appl. Phys. (Suppl. 2, Pt. 2), 1974, 117. 

One way in which the adsorption of a chlorine atom could affect more than one adsorption site is if the chlorine is incorporated into the subsurface oxide layer. No direct evidence of chloride accumulation in the catalyst subsurface has been published. However, there is at 373 K an apparent competition between chlorine and oxygen for adsorption sites which, we have argued above, correspond to the formation of the first monolayer of the oxide film. In view of this it would be surprising if chloride accumulation in the subsurface did not occur under practical epoxidation conditions. The net result would be to modify the electronic properties of this semi-conducting layer and hence the adsorptive properties of the surface. The chloride catalysed reorganization of surface silver atoms is perhaps indirect evidence of such an affect.  

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