The adsorbate (and temperature-) dependent thermal behaviors of the metal-metal (M-M) bonds in Pd nanoclusters supported on alumina are described. XAS studies revealed that these materials possess: a dramatically nonbulklike nature. Under an ambient atmosphere, the clusters exhibit relaxations of the M-M bond distances, negative thermal expanswri (NTE), and large bond length disorder. Whereas under ambient hydrogen atmosphere, bond distance is markedly increased at lower temperature due to hydrogen induced expansion of lattice while the contraction occurs at high temperature by desorption of hydrogen. The temperature-dependent behaviors may illustrate the excellent catalytic properties for Pd catalyst occurs at low temperatures.
展开▼
