X-ray emission spectrometry of phase separation in PtRh nanoparticles for nitric oxide reduction

Composition determinations of individual sub-10 nm metal particles in PtRh/alumina by analytical electron microscopy are consistent with a low-temperature miscibility gap below about 750°C in this system. Pt-rich alloy particles are more active than pure Pt for the reduction of nitric oxide with hydrogen at temperatures ≤ 300°C. Rh-rich particles appear to have low activity for this reaction. Catalysts which contain a bimodal distribution of Pt-rich and Rh-rich particles are not as active as pure Pt. Composition versus size plots of small metal particles appear to comprise a new characterization method for supported metal catalysts.