A Beeck-type calorimeter has been used to measure the integral heat of adsorption of oxygen on evaporated films of titanium, chromium, manganese, iron, cobalt, nickel, niobium, molybdenum, rhodium, palladium, tantalum, tungsten, platinum and aluminium. The variation of the heat with the extent of the adsorption has also been determined, except with palladium, platinum and aluminium, for which the amounts of oxygen adsorption were too small to allow this to be done. The heats of adsorption reported are based on a careful determination of the heat capacity of the calorimeter and the overall error is not more than ± 5 kcal/mole. Some investigations of calorimetric behaviour have been made. The surface areas of the films have been measured before and after an adsorption by the B.E.T. method; krypton isotherms at — 196 °C were used for this purpose. From these data, it has been possible to estimate the number of atoms of oxygen adsorbed per surface metal atom. In most cases, this quantity, together with the heat of adsorption, can be related to the oxygen/metal ratios and the heats of formation of certain oxides; this observation is remarkable in view of the limited extent of the adsorption. In the cases of rhodium, palladium and platinum the adsorption stops short of a monolayer and is probably true chemisorption rather than oxide formation. For those metals on which oxide formation occurs, the decrease in heat of adsorption with increasing coverage has been interpreted, in general, in terms of an increase in the oxidation number of surface metal ions by electron transfer within the adsorbed layer. Some theoretical correlations between the heat of adsorption and the atomic and the bulk properties of the species concerned have been examined and found of little value; an empirical relation with the metallic radius is given.

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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.

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