Platinum Metals Review - Volume 28, Issue 3, 1984

Recent work at the Johnson Matthey Research Centre has thrown fresh light upon the electronic effects in hydrogenation catalysis that underlie the whole nature of the catalytic act and in particular many of the effects that may manifest themselves as support metal interactions. The results show that currently accepted models of the catalytic act are incomplete, that ionic intermediates are sometimes important and that both the relative acidity of the reaction system and the redox potential of products and intermediates must be considered.

Surface morphological and X-ray examinations have been carried out on catalyst gauzes exposed to the conditions encountered during the oxidation of ammonia. A model, based upon observations of platinum and rhodium-platinum single crystals is proposed to explain the structural changes that occur on rhodium-platinum alloys during industrial use.

A viable technique for the electrodeposition of palladium-silver alloys could find application during the manufacture of electrical contacts. Previously such a process has not been available but some alloys with useful physical properties can now be deposited from an ammoniacal system, while a better understanding of the mechanisms involved has been gained during the work reported here.