Thermochimica Acta, Vol.279, 65-76, 1996
Copper-Zinc Oxide Catalysts .4. Thermal-Treatment in Air, Argon and Hydrogen and XRD Study of New Bimetallic Precursors-Direct Formation of Alloys
Four new Cu-Zn bimetallic precursors of model catalysts for methanolization of syngas, Zn(NH3)(2)Cu(CN)(3) (ZCA), [Zn(en)(3)](6)[Cu-5(CN)(17)]. nH(2)O (n = 8.4) (ZCE3), [Zn(en)] [CCu(CN)(3)] (ZCE1) and [Zn1-xCux(en)] [CCu(CN)(3)] (ZCCE1), were thermally treated in air, hydrogen and argon atmosphere between 200 and 900 degrees C. The calcinations in air yield firstly a mixture of cyano-ligand-containing compounds which transform at temperatures above 300 degrees C to CuO and ZnO; the crystallite size of both oxides increases with temperature. The reduction in hydrogen at 300 degrees C gives zinc cyanide and metallic copper which are converted at 450 degrees C mainly to beta’-brass including some alpha- and gamma-alloys. The thermal treatment in argon displays the very high thermal stability of zinc cyanide to 900 degrees C and formation of copper or alpha-CuZn alloy. Only the hydrogen treatment avoids the segregation of both metallic elements. The results are discussed on the basis of thermodynamic data.
Keywords:POWDER DIFFRACTION PATTERNS