potential user’s site in container drums. The salts during the methanol drying technique, results from the trial, which should last for at then fast economic pay-back times can be anti- least 1000 hours of continuous operation, will cipated and a remarkably cheap hydrogen allow the viability of the process to be proven source deployed. J.E.P. at small cost, before a full size plant is commis- References sioned. I J. E. Philpott, Platinum Metals Rev., 1976, to, Where a trial is successful and when the (4), I 10; and references therein operating variables are established, including, 2 M. J. C(ole), Platinum Metals Rev., 1981,25, (I), I2 for example, the regularity of water rinsing 3 J. E. Philpott, Platinum Metals Rev., 1985, 29, necessary to prevent the build up of ammonium (I), 12; and references therein Improved Catalyst System for the Wacker Process The Wacker process for the palladium plete oxidation of ethylene to carbon dioxide catalysed conversion of ethylene to and water is avoided. acetaldehyde is one of the oldest industrial The authors have combined a number of con- homogeneous catalyst systems. The original cepts which have been available for some time, process was plagued by problems of corrosion and appear to have developed a system which within the reactor system, and has been replac- avoids most of the pitfalls associated with other ed by a heterogeneous catalyst system which catalyst systems for the Wacker process. If it suffers, however, from the problem of poor can be established that the catalyst maintains its catalyst utilisation. activities for substantially greater than one Acetaldehyde used to be a major source of week, does not cause corrosion, and if catalyst acetic acid and while this route has largely been attrition is not a problem, then the system may superseded by rhodium catalysed carbonyla- have considerable commercial significance. tion, the Wacker process remains a major route However, the relative simplicity and high to acetaldehyde. The problems outlined above stability of the catalyst components in the that are associated with the Wacker catalyst Wacker catalyst system may mean that it is dif- have been, to a large extent, circumvented by a ficult to apply this technology in a more general new catalyst system developed by workers in fashion. M.J.H.R. the Department of Chemical and Materials Engineering at the University of Iowa (V. Rao Hydrogen Storage Material and R. Datta, J. Cutul., 1988, 114, (2), Although iron-titanium is an excellent 377-3871. material for hydrogen storage, it becomes deac- The supported liquid melt catalyst which tivated after repeated charge-discharge cycles. they have used consists of a spherical silica sup- The mechanism of this phenomenon has been port which contains a palladium chloride- determined by J. H. Sanders and B. J. Tatar- copper(I1) chloride catalyst in a eutectic melt of chuk of Auburn University, Alabama, U.S.A., copper(1) chloride-potassium chloride. The who have also investigated the use of thin location of the homogeneous catalyst within the palladium films to protect the alloy from deac- pores of the support avoids the problems both tivation (Thin Solid Films, 1988,166, 225-233; of corrosion of the plant and also pro- 3. Phys. F: Met, Phys., 1988, 18, (II), ductlcatalyst separation, which are associated L267-L270). with the conventional homogeneous system. Deactivation is triggered by oxygen im- However, the system remains in essence a solu- purities in the hydrogen charging gas reacting ble catalyst and retains the benefits of the rates with titanium in the surface layer of the iron- and conversions achieved with the titanium matrix, forming titania and metallic homogeneous catalyst. It shows a better utilisa- iron crystallites which are inert to reversible tion of metal than the conventional supported hydrogen storage. However under the condi- liquid phase catalysts. In addition the use of a tions of interest a thin gnm layer of palladium melt media avoids the rapid deactivation provides an effective barrier to oxygen, preven- associated with supported liquid phase catalysis ting deactivation and so increasing the useful containing aqueous catalyst solutions. The use life of the alloy. The integrity of the coating has of a copper(1) chloride-potassium chloride with been verified by conversion electron MGssbauer a melting point of 423K means that the com- spectroscopy.

Platinum Metals Rev., 1989, 33, (2) 60