Platinum Metals Review - Volume 18, Issue 4, 1974

Continuous observations by controlled atmosphere microscopy of the effects of heating platinum and rhodium-platinum alloy wires in ammonia-air mixtures indicated that attack on the wire surfaces predominates at the grain boundaries. The alloy wires, including used commercial catalyst gauzes, exhibited the formation of mobile promontories preceding the formation of angular crystalline platelets, whereas pure platinum wires did not show so much promontory growth, even at higher temperatures.

The basic particles of palladium blacks have been observed to cluster into macroscopic aggregates. Hydrogen treatment increases remarkably both the extent and degree of ordering of these aggregates. This may result in a substantial percentage of their surface areas being unavailable for adsorption. A theoretical model is proposed to account for the effects of this phenomenon in these and other unsupported and supported catalysts. Its predictions can be used to optimise their surface area and activity.