The activities of evaporated metal films in gas chemisorption

Abstract

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 degrees 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.