Copper-zinc oxide catalysts. Part IV. Thermal treatment in air, argon and hydrogen and XRD study of new bimetallic precursors - Direct formation of alloys

Article abstract of DOI:10.1016/0040-6031(96)02869-9

Four new Cu-Zn bimetallic precursors of model catalysts for methanolization of syngas, Zn(NH₃)₂Cu(CN)₃ (ZCA), [Zn(en)₃]₆[Cu₅(CN)₁₇]·nH ₂O (n = 8.4) (ZCE3), [Zn(en)] [Cu(CN)₃] (ZCE1) and [Zn_1-xCu_x(en)] [Cu(CN)₃] (ZCCE1), were thermally treated in air, hydrogen and argon atmosphere between 200 and 900°C. The calcinations in air yield firstly a mixture of cyano-ligand-containing compounds which transform at temperatures above 300°C to CuO and ZnO; the crystallite size of both oxides increases with temperature. The reduction in hydrogen at 300°C gives zinc cyanide and metallic copper which are converted at 450°C mainly to β′-brass including some α-and γ-alloys. The thermal treatment in argon displays the very high thermal stability of zinc cyanide to 900°C and formation of copper or α-CuZn alloy. Only the hydrogen treatment avoids the segregation of both metallic elements. The results are discussed on the basis of thermodynamic data.