The activities of evaporated metal films in gas chemisorption

The interaction of N 2 , H 2 , CO, C 2 H 4 , C 2 H 2 and O 2 with clean evaporated films of some twenty metals has been investigated between 0 and – 183° C. The results are expressed as gas chemisorbed or gas not chemisorbed. O 2 chemisorption is universal among all the metals studied, with the single exception of Au. Chemisorption of N 2 and H 2 is limited to transition metals and alkaline earth metals, and chemisorption of CO, C 2 H 4 and C 2 H 2 to these and to Al, Cu and Au. O 2 chemisorption is believed to take place with formation of O 2- ions at the surface, with electron donation from the s and p bands of the metals. The inactivity of Au towards O 2 is, however, only partly understandable in terms of this mechanism . The remaining five gases are believed to form covalent bonds with the metal d bands in chemisorption; with Cu and Au it is suggested that d – s promotion takes place in the act of chemisorption to allow such covalence. Al is exceptional, and with the light metals, s and p band electrons may be active in chemisorption: a further exception is the interaction of K with C 2 H 2 . Some applications of these results to catalytic systems are discussed.