No decomposition catalysts prepared from amorphous Ni-Ta-Pd alloys

The effects of hydrofluoric acid (HF) treatment and bulk structure of precursor alloys on the catalytic decomposition of nitrogen monoxide have been investigated. Alloy catalysts were prepared from Ni-40 valve metal (Ta, Nb, Ti and Zr)-1Pd alloys by the HF treatment and subsequent pre-oxidation at 750 °C. The tantalum-containing catalyst without previous HF treatment shows the highest activity among the catalysts examined, while the preparation of the active catalysts from other amorphous alloys requires HF treatment for surface roughening and for surface enrichment of palladium prior to the pre-oxidation treatment. The catalyst prepared from the amorphous Ni-40Ta-1Pd alloy is superior to the conventionally prepared Pd/Al₂O₃ catalyst, in spite of the fact that the BET surface area of the latter catalyst is two orders of magnitude higher than that of the Ni-Ta-Pd catalyst. The catalyst prepared from the amorphous Ni-40Ta-Pd alloy shows a better performance for the NO decomposition in comparison with the catalyst prepared from the crystalline counterpart, because the amorphous precursor becomes a more irregular and more microporous catalyst.