COPPER-ZINC OXIDE CATALYSTS .4. THERMAL-TREATMENT IN AIR, ARGON AND HYDROGEN AND XRD STUDY OF NEW BIMETALLIC PRECURSORS-DIRECT FORMATION OFALLOYS

Four new Cu-Zn bimetallic precursors of model catalysts for methanoliz ation 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-xCu x(en)] [CCu(CN)(3)] (ZCCE1), were thermally treated in air, hydrogen a nd argon atmosphere between 200 and 900 degrees C. The calcinations in air yield firstly a mixture of cyano-ligand-containing compounds whic h transform at temperatures above 300 degrees C to CuO and ZnO; the cr ystallite size of both oxides increases with temperature. The reductio n in hydrogen at 300 degrees C gives zinc cyanide and metallic copper which are converted at 450 degrees C mainly to beta'-brass including s ome alpha- and gamma-alloys. The thermal treatment in argon displays t he very high thermal stability of zinc cyanide to 900 degrees C and fo rmation of copper or alpha-CuZn alloy. Only the hydrogen treatment avo ids the segregation of both metallic elements. The results are discuss ed on the basis of thermodynamic data.