In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to study the reaction mechanism of a new methanol synthesis method on Cu/ZnO at low temperatures from syngas (CO/CO2/H-2) using ethanol promoter. The adsorbed formate species were formed by exposing Cu/ZnO catalysts to syngas (CO/CO2/H-2), and it reacted easily with ethanol in the gas phase to form ethyl formate in two states of species, gas phase and physisorbed, at low temperatures. Ethyl formate was the reactive intermediate, and it was reduced easily by hydrogen atoms on Cu to form gas-phase methanol. The reaction temperature was significantly decreased due to the catalytic action of ethanol and a new reaction route. In order to accelerate this reaction, a large amount of ethanol must be introduced into the reaction system. When there was no ethanol or little ethanol in the reaction system, this reaction was difficult to complete at a temperature as low as 443 K. (C) 2004 Elsevier Inc. All rights reserved.