Preparation, reduction, and CO chemisorption properties of cyanide-derived CuxFe/Al2O3 catalysts

A series of copper-iron catalysts with Cu-to-Fe proportions of 1.0, 1.5, and 2.0 has been prepared by the precipitation of three different copper-iron cyanide complexes, viz. Cu2Fe(CN)(6), Cu-3[Fe(CN)(6)](2) and CuFe(CN)(5)NO, onto a gamma-Al2O3 support. Oxidative decomposition of these stoichiometric heteronuclear cyanide complexes resulted in the formation of particles of uniform Cu-to-Fe ratio, made up of intimately mixed CuO and Fe2O3 crystallites. The reduction of the oxidic precursors was studied by means of magnetization measurements and Mossbauer spectroscopy. The presence of Cu facilitates the reduction of the iron oxide. The distribution of the Cu and Fe atoms in the bimetallic particles appeared to be strongly dependent on the applied reduction procedure. Slow reduction prevents excessive phase separation. Exposure of the reduced catalysts to carbon monoxide results in a rapid segregation of Fe to the particle surface. Infrared spectroscopy indicates the presence of several types of linearly and bridged-bonded CO species on the bimetallic surface. Reversibly adsorbed CO on Cu-like sites decreases the apparent intensity of the absorption band due to irreversibly adsorbed CO on Fe-like sites. Experiments with isotopically labeled (CO)-O-18 suggest that the CO on Fe-like sites is mobile and can be exchanged with CO bonded to adjacent Cu-Like sites. (C) 1998 Elsevier Science B.V. All rights reserved.