Effect of the aging time of the precipitate on the activity of Cu/ZnO catalysts for alcohol-assisted low temperature methanol synthesis

Abstract Cu/ZnO_X catalysts were prepared by a co-precipitation method with various aging times of the precipitate (X = 10 min–10 h). All prepared catalysts were evaluated in alcohol-assisted methanol synthesis through a low temperature liquid phase reaction using a batch type reactor under a reaction pressure of 50 bar at a temperature of 150 °C. Unlike the conventional low temperature methanol synthesis, ethanol was adopted as both the solvent and the reaction intermediate in this study. Variation of the aging time of the precipitate led to numerous changes in the surface properties of catalysts, resulting in the different catalytic activity in this reaction. This means that aging time of the precipitate should be precisely controlled for obtaining an efficient Cu/ZnO catalyst by a co-precipitation method. The results of catalytic activities and catalyst characterizations clearly demonstrated that the copper particle size, the morphology, and the strong acidity of the Cu/ZnO catalysts played key roles in this reaction. Small copper particle size, plate-like morphology, and high strong acidity of the catalysts were favorable for efficiently producing methanol in this reaction. Among the Cu/ZnO_X catalysts, the Cu/ZnO_5 h catalyst showed the best catalytic activity. According to the proposed reaction pathway, not only the intrinsic activity of metallic copper but also the acid properties of catalysts were important factors to determine the activity of Cu/ZnO catalysts in this reaction.