THE REDUCTION OF COPPER IN POROUS MATRICES
O. P. Tkachenkoa, c), K. V. Klementieva, d), N. Koca,
e), X. Yua, M. Bandyopadhyay b),
S. Grabowskib, H. Gies b), W. Grünert
a)
a) Lehrstuhl für Technische Chemie, Ruhr-Universität
Bochum, D-44780 Bochum, Germany (w.gruenert@techem.rub.de), b) Lehrstuhl für Kristallographie,
Ruhr-Universität Bochum, D-44780 Bochum, Germany, c) N. D. Zelinsky Institute
of Organic Chemistry, Russian Academy of Sciences, Moscow, Russia, d) Hasylab, Hamburg, Germany, e Department
of Chemical Engineering, Istanbul University, 34850 Istanbul, Turkey
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 in two
steps. The two-step scheme cannot be identified with the reduction steps
Cu(II) ®
Cu(I) and Cu(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 an 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 (oligomeric) 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 °C.
Proceedings: 14th International Zeolite Conference, 25-30 April
2004-05-13
Editors: E. van Steen et al
ISBN: 0-958-46636-X
Cape Town, South Africa
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