Effect of Cobalt on the Surface Properties of Zn-Cr and Cu-Zn-Cr Methanol Synthesis Catalysts

The catalytic activity in the synthesis of methanol of cobalt-free and 2 atom % cobalt-containing Zn-Cr and Cu-Zn-Cr catalysts was investigated. The adsorption of hydrogen and CO was studied by FT-IR spectroscopy. It is suggested that small amounts of cobalt inhibit the catalytic activity of Zn-Cr catalysts through an inhibition of their ability to activate hydrogen dissociatively. In the case of copper-containing catalysts, cobalt ions do not modify apparently the properties of the surface copper species. Also in this case the synthesis of methanol is inhibited by cobalt, probably again through the inhibition of the hydrogen dissociation on the spinel phase, that would represent the first step in hydrogen activation. The results are interpreted as evidences of the role of the oxide phase even in copper-containing catalysts.