The reduction of copper in porous matrices


Tkachenko O., Klementiev K., Koc N., Yu X., Bandyopadhyay M., Grabowski S., ...Daha Fazla

RECENT ADVANCES IN THE SCIENCE AND TECHNOLOGY OF ZEOLITES AND RELATED MATERIALS, PTS A - C, cilt.154, ss.1670-1678, 2004 (SCI İndekslerine Giren Dergi) identifier

  • Cilt numarası: 154
  • Basım Tarihi: 2004
  • Dergi Adı: RECENT ADVANCES IN THE SCIENCE AND TECHNOLOGY OF ZEOLITES AND RELATED MATERIALS, PTS A - C
  • Sayfa Sayıları: ss.1670-1678

Özet

The reduction of copper oxide species dispersed in microporous and mesoporous matrices has been studied by TPR, XPS/XAES, and XAFS. While the reduction of bulk CuO and of Cu(II) in mesoporous MCM-48 (5.6 wt-%) proceeded in one step without intermediate Cu(I) being detectable under the experimental conditions, Cu(II) in microporous matrices was reduced ill two steps. The two-step scheme cannot be identified with the reduction steps Cu(II) -> Cu(I) and CL(I) -> CU(0). Instead, highly disperse Cu(0) may be present already after the first reduction step. In siliceous matrices, coexistence of Cu(0), and Cu ions was observed over a wide temperature range, obviously due to the absence of ail autocatalytic reduction process. The latter occurred in Cu-ZSM-5, apparently involving simultaneous segregation of Cu metal from the matrix. This suggests that very small (oligorneric) Cu metal Clusters are unable to activate hydrogen. The reduction behaviour of Cu in Y zeolite depends critically on the thermal history of the sample due to the population of hidden sites by copper upon calcination. Highly disperse Cu particles are stable in MCM-48 up to 500 degrees C.