Platinum Metals Review - Volume 11, Issue 2, 1967

Because of their extreme sensitivity, radiochemical methods are of great help in the study of catalytic processes. Changes at a surface at concentrations less than those required to yield monolayer coverage can readily be detected without interrupting the system for analysis. This article describes the application of such methods to the determination of metal areas and of catalytically active areas in supported metal catalysts and also reviews their usefulness in the study of electrocatalysis and in the unravelling of catalytic reaction mechanisms.

It is well known that the addition of about 0.2 per cent palladium to titanium significantly increases its resistance to corrosion in non-oxidising acids. It has usually been assumed that the palladium is present as elemental particles at the metal surface and that these function electrochemically to provide anodic passivation of the titanium matrix. It has, however, now been demonstrated that even in low concentration palladium additions to titanium form Ti2Pd, and that before onset of passivation the palladium dissolves in the corrodent and is then reprecipitated in elemental form from solution. This process is accompanied by the growth of a protective film of TiO2. In substantiation of this mechanism it can be shown that corrosion of unalloyed titanium in non-oxidising acids can be halted by the addition to the acid of a very small quantity of a soluble palladium salt.

New and unexpectedly stable compounds of rhodium with hydrogen directly co-ordinated to the metal have been prepared. They are soluble in water, and their cold aqueous solutions readily take up ethylene and acetylene with the formation of ethyl and vinyl derivatives in which the organic radical is co-ordinated directly to the metal. These hydrido-compounds have a potential usefulness as catalysts for the hydrogenation of unsaturated organic acids.

In the second part of this article, concluded from the January issue of Platinum Metals Review, the author deals principally with the problem of platinum losses from gauzes during operation, with the catalytic reduction of tail gases and with the production and handling of gauzes for use in ammonia converters.