RARE EARTH AND ACTINIDE INTERMETALLICS AS HYDROGENATION CATALYSTS

Abstract

Rare earth intermetallics (e.g., RNi5) and certain actinide internetallics (e.g., ThNi5) have been found to be catalytically active for the formation of methane from CO and H2. The rare earth intermetallics have also been found to be active as synthetic ammonia catalysts. Specific activities exceed those of good commercial catalysts by an order of magnitude or more. Examinations of the used catalyst have been made by surface area determinations, x-ray diffraction, scanning electron microscopy (SEM), energy dispersive analysis by x-rays (EDAX) and Auger Electron Spectroscopy (AES). These studies indicate that the original intermetallic has been transformed during reaction into a substrate of rare earth or actinide oxides supporting nodules of the transition element, the nodules being ~ 0.5 micrometer in diameter. These nodules are probably the active catalyst. However, the rare earth (or actinide) plays a role since the observed activation energies vary substantially, depending upon the nature of the specific rare earth involved. AES results indicate that the variation in activity is ascribable to the extent of carbon buildup on the surface of the nodules. This buildup is absent for ThNi5 which is an excellent methanation catalyst, and ia extensive for ZrNi5, which'is a poor methanation catalyst. The hydrogenation of C2H4 with LaNi5H2.4, studied by Soga et al. in Tokyo, is found to be diffusion controlled with an activation energy of 5.7 kcal/mole.