ELSEV IER Applied Catalysis B: Environmental 11 (1997) 243-255 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJ 8: zyxwvutsrqponmlkjihgfedcbaZYX ENVIRCNMENTAL NO decomposition catalysts prepared from amorphous Ni-Ta-Pd alloys M. Komori, E. Akiyama, H. Habazaki, A. Kawashima, K. Asami, K. Hashimoto * Institute for Materials zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFE Research, Tohoku University, Sendai 980-77, Japan Received 4 September 1995; revised 23 February 1996; accepted 23 April 1996 zyxwvutsrqponmlkjihgfedcbaZYX Abstract 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-40valve 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 treat- ment 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/Al,O, 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-4OTa-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. Keywords: Amorphous alloy precursor; NO decomposition; Pd/AI,O,; Ni-Ta-Pd alloy 1. Introduction Nitrogen oxides contained in exhaust gases contribute to the greenhouse effect and serious environmental disruption, such as the destruction of ozone layer, urban smog and acid rain. Nitrogen oxides are formed at temperatures higher than lOOOT, as a result of combustion of fossil fuels, but are thermody- namically unstable at lower temperatures. Accordingly, their catalytic decompo- sition into nitrogen and oxygen is feasible and expected to be one of the most * Corresponding author. 0926-3373/97/$17.00 Copyright 0 1997 Elsevier Science B.V. All rights reserved. PII SO926-3373(97)00049-5