Abstract Silica-supported Cu I sites used as models of copper-based methanol synthesis catalysts are prepared either by selective reduction of Cu II precursors or by direct exchange by Cu I(NH 3) 2 ions. The oxidized species which are selectively reduced to Cu I by carbon monoxide or hydrogen at 100°C are (Cu II O Cu II) 2+ pairs, characterized by electron spin resonance, electron spectroscopy and magnetic measurements. The percentage of (Cu II O Cu II) 2+ pairs depends on the degree of exchange; at a copper loading higher than 2%, hyperdispersed CuO is formed, which is directly reduced to Cu O by simple outgassing. Below a Cu content of 1% part of the precursors exists as isolated Cu II ions which are directly reduced to Cu O above 300°C. Supported Cu I species were characterized by IR, X-ray photoelectron and Auger electron spectroscopy. The stability of the Cu Ispecies depends on their coordination with the support: the Cu I ions prepared by direct exchange are reduced to Cu O under vacuum from 200°C, whereas the Cu I ions stemming from the reduction of the cupric pairs are stable up to 800°C under vacuum and are reduced by carbon monoxide only above 350°C.