Of the 143 communications presented at this Congress, some sixty dealt with the ad-sorptive and catalytic properties of metals, the remainder dealing with metal oxides, acidic catalysts, and some aspects of homogeneous catalysis. Of these sixty, about one-third referred specifically to metals of the platinum group; it is clear that for many fundamental and applied studies, nickel is still the favoured metal, while a few papers dealt with the catalytic properties of iron, cobalt, copper and zinc.

The chemisorption of hydrogen and oxygen on platinum black was studied by Aston and his associates at 0°C and below (1): their technique of “thermal titration”, which has recently been described in J. Amer. Chem. Soc. (23), involves the addition of hydrogen to a surface covered by oxygen, and vice versa, and the measurement of the subsequent heat changes. The adsorption of benzene on alumina-supported platinum reforming catalysts was studied by determining the response of the effluent composition to transient changes in the benzene-nitrogen or benzene-hydrogen feed gas; gas-liquid chromatography was used for this purpose (2).

Several papers were devoted to catalytic hydrogenation and related problems. One of the simplest conceivable systems, the exchange of one hydrogen isotope adsorbed on a metal with another in the gas phase, was studied by Boreskov and Vassilevitch (3) using platinum films at low temperatures. By observing the relative rates of hydrogenation of pairs of the xylenes over platinum in acetic acid, it was concluded that the order of the adsorption of the three isomers is: ortho>meta>para (4). The hydrogenation of derivatives of furan has been studied using platinum, osmium, iridium, ruthenium and rhodium, all supported on charcoal and using skeletal palladium and platinum (5).

Remarkable synergistic (co-operative) phenomena were observed when mixed palladium-ruthenium catalysts were employed for liquid-phase hydrogenation (6). Thus, for example, while neither 5 per cent platinum or ruthenium on charcoal is active for the hydrogenation of nitropropane, a catalyst consisting of 2.5 per cent of each metal was satisfactorily active. Similar results were obtained with nitriles and with pyridine. This synergistic effect was said to be due to the ability of one metal to hydrogenate an intermediate which would strongly adsorb on, and hence poison, the other.

In the hydrogenation of acetylene and its derivatives (7, 8), highly selective formation of olefins was achieved in the initial stages using alumina-supported palladium, and the reduction could be caused to stop entirely at the olefin stage by selective poisoning by dimethylsulphide (7) or mercury vapour (9).

The state of platinum in supported catalysts was the subject of several papers, which should be compared with those recently summarised in Platinum Metals Review (24). In a typical alumina-supported reforming catalyst, the platinum was shown to be very highly dispersed (10), and evidence was adduced to show that the dehydrocyclisation activity of a related catalyst was associated with an irreducible platinum complex formed from chloroplatinic acid and the support (11). The corresponding palladium complex was rapidly reduced. The possibility of using silica-alumina molecular sieves, e.g. de-cationised Linde type Y, as supports for reforming catalysts was demonstrated (12). The kinetics of reforming processes were discussed (13), and the reactions of poly-methylcyclopentanes over alumina-supported platinum were reported (14).

Gray and his associates (15) described the isomerisation of n-pentane over alloys of the platinum metals supported on eta-alumina; the combinations used were Pt-Rh, Pd-Rh, Pt-Ir, Pt-Ru, Os-Pt and Pt-Re. In most cases, an alloy of a certain composition showed an activity greater than that of either of the components separately; this composition corresponded to that having exactly one d-band vacancy per atom. The phenomenon, which was especially marked in the Pt-Ru system, is reminiscent of that described in reference (6), but the two are probably unrelated.

Three papers were devoted to catalytic oxidation. The rearrangement of surface atoms during the oxidation of methane by air over incandescent platinum, 10 per cent Rh-Pt and 25 per cent Ir-Pt was demonstrated, and the suggestion made that the catalyst initiates some homegeneous reaction (16). Radioactive rare gas ions introduced into platinum by ion bombardment are released when the hydrogen-oxygen reaction is performed, again showing the rearrangement of surface atoms (17). The oxidation of carbon monoxide in the presence of palladium-gold alloys has been investigated (18); the activation energy is about 2 Kcal/ mole ¹ for 100 to 60 per cent gold, and about 30 Kcal/mole^-1 for 60 to 0 per cent gold.

The activity sequence for some of the platinum metals in formic acid decomposition is (19):

This reaction has also been observed by infra-red spectroscopy to occur over supported platinum at — 60°C (20).

Finally, attention should be drawn to two theoretical papers, one (21) emphasising the role of surface geometry, and the other (22) the importance of the latent heat of sublimation of the catalytic metal. It is very doubtful whether either approach by itself will materially assist the progress of the science of catalysis.