Infrared and EXAFS Study of Compositional Effects in Nanoscale Colloidal Palladium−Copper Alloys

The reaction between colloidal palladium and cupric acetate in 2-ethoxyethanol leads sequentially to the reduction of Cu(II) to Cu(0) at the surface of the palladium particle and dissolution of the deposited copper in the palladium matrix. The reaction was monitored by infrared spectroscopy using carbon monoxide adsorbed on samples of the colloid during the reaction and by X-ray absorption spectroscopy (NEXAFS and EXAFS) on the colloidal metal after completion was reached. The Cu K near-edge X-ray absorption spectrum shows reduction of Cu(II) to Cu(0). After deposition on the palladium surface the copper is zerovalent, and subsequently it migrates into the palladium particle but only to within a few atomic layers of the surface.