Abstract:

The interaction of Cu2+, Ni2+ and Al3+ ions during the impregnation step of K/γ-Al2O3 support was studied. Cu-Ni catalyst precursors ("just impregnated solids"), just reduced precursors (H2, 300°C), and calcined precursors in the range of 400-800°C were characterised by X-ray diffraction (XRD), temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) measurements. In addition, the catalytic behaviour of reduced precursors and calcined catalysts was analysed in the ethanol steam reforming reaction at 300°C and atmospheric pressure. XRD results of different precursors indicated that, after the impregnation step, copper is present in two different phases: a copper basic nitrate and a CuAl and/or CuNiAl hydrotalcite-type compound (HT). In the sample containing only nickel, this metal is present as a NiAl-HT compound. At constant copper content of 6 wt.%, the ratio between the copper phases depends on the nickel content. Adding nickel favours the formation of HT compounds. While calcination of Cu-Ni precursors in the range of 400-800°C produces a CuO segregated phase and/or a phase of copper called "surface spinel", nickel is always found as a nickel aluminate after the calcination treatment. The catalytic behaviour of the samples strongly depends on the conditions of the thermal treatments. Thus, the increase in the calcination temperature of the precursors produces a strong interaction between nickel and aluminium, decreasing nickel reducibility and selectivity to C1 compounds. On the other hand, the just reduced precursors showed to have the best catalytic performance for the ethanol steam reforming reaction at 300°C. © 2002 Elsevier Science B.V. All rights reserved.