Decomposition of nitrogen monoxide over NiTa₂O₆-supported palladium catalysts prepared from amorphous alloy precursors

Active catalysts for the direct decomposition of nitrogen monoxide were prepared from amorphous Ni-40Ta-Pd alloys by HF-treatment and subsequent pre- oxidation. The pre-oxidized catalyst consists of NiO, Ta₂O₅ and PdO, and PdO is decomposed to fcc Pd by heating at temperatures higher than 600°C. At further higher temperatures NiO and Ta₂O₅ are transformed to a very fine grained double oxide NiTa₂O₆. The catalysts thus formed consist of three layers and show high catalytic activity for the decomposition of nitrogen monoxide in a wide temperature range from 550 to 850°C. The catalytic behavior is affected by the structural change in the catalyst. With the transformation from NiO and Ta₂O⁵ to NiTa²O⁶, the catalytic activity and the nitrogen formation selectivity increase significantly. TEM observation of ultramicrotomed cross-sections revealed that finely dispersed palladium supported on very fine grained NiTa₂O₆ is formed in the interface between the outer and intermediate layers. High catalytic activities and high nitrogen formation selectivities of the Ni-40Ta-Pd alloys are attributable to the formation of the NiTa₂O₆-supported palladium catalyst.