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

Abstract

Four new CuZn bimetallic precursors of model catalysts for methanolization of syngas, Zn(NH 3) 2Cu(CN) 3 (ZCA), [Zn(en) 3] 6[Cu 5(CN) 17]· nH 2O ( n = 8.4) (ZCE3), [Zn( en)] [Cu(CN) 3] (ZCE1) and [Zn 1− x Cu 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.