| Abstract |
High temperature oxidation-reduction studies were undertaken on binary intermetallic compounds LnCu(2) (Ln = La, Ce, Pr, Nd, Eu, Gd, Dy, Tm, Yb). A two steps cycle was optimized by O-2-TG and H-2-TG or H-2-TPR studies along the lanthanide series. The oxidation mass uptake occurs over a wide range of temperature (200-900 degrees C), leading to two bimetallic copper-lanthanide oxides families according to the lanthanide: 3CuO center dot Ln(2)CuO(4) (Ln = La, Pr, Nd, Eu, Gd) and 2CuO center dot Ln(2)Cu(2)O(5) (Ln = Dy, Tm, Yb), except for CeCu2 that gives 2CuO center dot CeO2, Under hydrogen, all systems exhibit two reduction steps accompanied by mass losses in the 150-600 degrees C temperature range. The first mass loss is linked to the reduction of CuO, whereas the second mass loss corresponds to copper reduction in the Ln(2)CuO(4) or Ln(2)Cu(2)O(5) phase with concomitant formation of Ln(2)O(3). The reduction products were characterized by XRD and different stoichiometries were obtained according to the lanthanide: 2Cu/CeO2, 3Cu/Ln(2)CuO(4) or 2Cu/Ln(2)Cu(2)O(5), after the first reduction step, and 4Cu/Ln(2)O(3) after the second reduction one. Therefore, the binary intermetallic compounds LnCu(2) decompose into a copper-rare earth oxide phase that after reduction leaves their surface highly enriched on the copper. The structure of the oxidized and reduced intermetallics can best be described as copper embedded in lanthanide oxides (Ln(2)O(3)) or type supported catalysts and exhibited activity for the 2-propanol oxidative dehydrogenation-dehydration reaction, which was also used to characterize their acid-base properties. (C) 2008 Elsevier B.V. All rights reserved. |
