X-RAY-EMISSION SPECTROMETRY OF PHASE-SEPARATION IN PT-RH NANOPARTICLES FOR NITRIC-OXIDE REDUCTION

Composition determinations of individual sub-10 nm metal particles in Pt-Rh/alumina by analytical electron microscopy are consistent with a low-temperature miscibility gap below about 750 degrees C in this syst em. Pt-rich alloy particles are more active than pure Pt for the reduc tion of nitric oxide with hydrogen at temperatures less than or equal to 300 degrees C. Rh-rich particles appear to have low activity for th is reaction. Catalysts which contain a bimodal distribution of Pt-rich and Rh-rich particles are not as active as pure Pt. Composition versu s size plots of small metal particles appear to comprise a new charact erization method for supported metal catalysts.