Coadsorption electron donor

Thus, it may again be concluded, as in the case of alkali coadsorption with H, that chemisorbed H exhibits amphoteric, i.e. both electron donor and electron acceptor characteristics. 

The coadsorption of oxygen as well as of other electronegative additives on metal surfaces favors in general the 7t-bonded molecular state of ethylene, as the latter exhibits, compared to the di-o bonded state, a more pronounced electron donor character and a negligible backdonation of electron density from the metal surface. 

The example given above is not an isolated phenomenon. Table 2.9 (p. 269) gives examples of several systems where the coadsorption of an electron donor and an acceptor leads to the formation of ordered structures, while the coadsorption of two electron donors or two electron acceptors yields disordered surface monolayers. Thus, in these systems at least, it is clear that the attractive forces arising from donor-acceptor interaction are crucially important in determining the stability and structure of the coadsorption system. With the coadsorption of benzene with CO on Rh(l 11), there is little change in the decomposition/desorption temperatures of either the CO or benzene. By contrast, the coadsorption of CO with alkali metals can have... 

Repulsive interaction is also observed with the coadsorption of potassium and ammonia. Both species are electron donors to transition metals. On iron, a 4-kcal /mole (17-kJ /mole) decrease in the heat of chemisorption of NHj is observed due to coadsorbed potassium. 

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