Platinum Metals Review - Volume 42, Issue 4, 1998

Biphasic catalysis is becoming an area of environmentally responsible catalysis, but its development and use have until recently been somewhat neglected. Here, the basic principles and the design of features going into such systems are explained, and a general overview is presented with the intention of encouraging greater interest in this under utilised technique. Some well-established aqueous-organic regimes are described and there is a discussion of some possible future directions involving ionic-liquid/organic systems.

Nanoscale changes in surface structure that accompany the low temperature exposure of palladium to hydrogen are reported. Field Emission Microscopy, a method for rapid in situ imaging of surface processes, has been used to examine palladium tips of radius ∼ 200 nm, produced by a novel technique. Images are presented of the initial stages of the uptake of hydrogen. Subsurface hydrides were initially formed when palladium tips were exposed to hydrogen gas at low temperatures, starting at highly open surfaces present on the tip. Extruding PdH particles were also formed on top of the palladium tip and their growth was observed to proceed in a ‘staccato’-like manner. Palladium crystallites remained on the surface after most of the hydrogen had been removed from the palladium sample by heating in vacuum. On heating the crystallites remained quite stable up to a temperature of ∼ 700 K, but then melted back into the tip.

The synthesis and reaction chemistry of high nuclearity transilion metal carbonyl clusters is briefly reviewed, and new synthetic strategies leading to the “rational” synthesis of bimetallic clusters containing metal cores of over 1 nm in dimension are described. The solid state structures of a number of osmium/mercury, osmium/gold and ruthenium/copper bimetallic clusters are discussed with regard to the nature of their formation, and of their bonding and redox properties. Suggestions are made as to how the synthetic strategies can be adapted to prepare bimetallic clusters of industrially useful combinations of metals. Recent work showing that bimetallic nanoparticles prepared from clusters are catalytically active when anchored inside mesoporous silica is also discussed.

The ability of fuel cells to use hydrocarbon fuels efficiently is important if they are to compete with battery power. Solid oxide fuel cells, particularly zirconia fuel cell devices, are generally well suited to utilise a variety of fuels. They are commercially attractive, especially in remote locations where battery supply and maintenance costs are prohibitive but where fuel, particularly butane, is readily available. Butane can be safely stored at high energy density and is thus a useful fuel for zirconia fuel cells in remote areas. Partial oxidation would be the preferred route to reform butane, but this requires a suitable catalyst. Ruthenium is an excellent partial oxidation catalyst, giving nearly total reformation of butane and producing high levels of hydrogen. However, problems such as carbon deposition and catalyst optimisation need to be addressed. Here, work with a zirconia fuel cell successfully fuelled by butane and using a ruthenium catalyst under controlled reaction conditions is discussed.

At this time, the second anniversary of Geoffrey Wilkinson’s death on 26th September 1996, his work and influence on the development of inorganic chemistry and the chemistry of the platinum group metals are recalled by two of his former students and colleagues. Geoffrey Wilkinson’s early life and career, important areas of his platinum metals research and work leading to the award in 1973 of the Nobel Prize are surveyed. He is remembered by his relationship with Johnson Matthey, his work at Imperial College and by affectionate anecdotes from the laboratory.