Platinum Metals Review - Volume 43, Issue 2, 1999

Nickel metal hydride (NiMH) rechargeable battery technology is currently the major competitor to well-established nickel cadmium (NiCad) technology. Due to new legislation in the European Union and elsewhere, NiCad cells are gradually being replaced to reduce the use of toxic cadmium, and NiMH cells are predicted to be a reliable alternative. NiMH batteries provide a higher energy density and are environmentally more acceptable than NiCad cells. In addition they have a low memory effect, allowing easy charging and discharging. However, current NiMH technology has limitations, particularly when cells are rapidly charged/discharged, and the lifetime of a cell is ~ 500 cycles, compared to ~ 1000 cycles for NiCad. Here, we report advances enabling rapid charging/discharging to be achieved by the modification of the surface of the metal hydride alloy with platinum group metals. This enhances the rates of sorption of hydrogen within the alloy, and the alloy is shown to be stable in air. An overview of NiMH battery technology is presented and developments resulting in high performance cells are described.

The loss of platinum from the catalyst gauzes used for the oxidation of ammonia in the manufacture of nitric acid has been studied for many years by catalyst producers and by users. In this paper, platinum losses from binary platinum-rhodium and ternary platinum-palladium-rhodium alloys, as well as from catalyst gauzes made of these materials, have been studied under laboratory and industrial conditions in atmospheric and medium pressure units, which are commonly found in P. R. China, and the rates of platinum loss and weight losses have been established. Adding a palladium component to the platinum-rhodium alloys or increasing the palladium content in platinum-palladium-rhodium alloys is clearly shown to decrease the rate of weight loss and the amount of platinum lost. This is attributed to the passive action of the palladium which accumulates on the surface and enriches the surface layer of the alloys, affecting both the platinum oxidation and platinum oxide reduction.

The production of the fatty base for edible margarines by the hydrogénation of vegetable oils is carried out at high temperatures and has serious disadvantages, among them the toxicity of the nickel catalysts and a fire-hazardous filtration stage. Here, a novel reactor and a new, active and selective, low-loaded palladium catalyst are described which allow vegetable oil hydrogénation to take place at lower temperatures producing high quality, pure hydrogenated fat, free of catalyst. Under these milder conditions, the thermal decomposition of oils and fats does not form secondary products, and heavy metals from the catalyst do not enter the final product. In addition, even lower hydrogénation températures can be used with the palladium catalyst, resulting in fat with a low trans-isomer content. The catalyst has been tested successfully in full-scale production. Using an inertial separator in a new reactor, catalyst loss has been eliminated.