The catalytic action of copper. Part VI.—An explanation of the reproducibility of the catalyst, and of the period change in its activity, together with some experiments on the activation of the catalyst by alternate oxidation and reduction

The experiments of Parts I, II, III, IV, and V, have shown that the catalyst activity of supported copper films can be made reproducible throughout successive oxidations and reductions. Particularly was this the case during comparison of the velocities of dehydrogenation of various alcoholic substance in Part V. The catalyst which had been reduced at 420°C. showed a fall activity for several reductions at 225°C., after which the activity remain constant for almost twenty reductions. The maximum variation was about 10 per cent. In view of the random variation which is often observed in activity of surfaces, it is interesting to attempt to discover why this film catalyst is stable under standard conditions of oxidation and reduction. The films were activated by successive oxidation and reduction. It thought that a study of the reaction velocity temperature curves for dehydrogenation of ethyl alcohol during the activation might throw light on the structure of the film. The behaviour of copper films supported on copper foil has been studied by Hinshelwood, and though there is still some doubt whether interference or diffraction is the cause of the colour, there seems to little doubt that the structure is granular. He suggested that these active films have a structure “which is fine grained compared with the wave-length of light, but coarse grained compared with molecular magnitudes.” The fil were made active by successive oxidation and reduction. “During the activation process . . . the copper atoms are able, under the influence of surface tension, to aggregate themselves more and more completely into small discre units (Beilby’s open formation), and the film assumes a granular structure free permeable to gases. . . . Each small unit of copper is oxidised independent I the extent to which it is converted to oxide determined the colour of the fracted light. It is suggested that, while in oxidation each existing granule gradually converted into oxide, reduction necessitates the growth of fresh granules, which grow about nuclei of copper, so that the film is an assemblage of wing granules of copper and diminishing granules of oxide.”