Alcohol-assisted low temperature methanol synthesis from syngas over Cu/ZnO catalysts: Effect of pH value in the co-precipitation step

• Cu/ZnO catalysts were successfully prepared by a co-precipitation method.
• Alcohol-assisted low temperature methanol synthesis from syngas was conducted.
• Co-precipitation pH value had a strong influence on the catalytic activity of Cu/ZnO.
• Cu crystallite size and strong acidity of the catalyst played key roles in this reaction.

Alcohol-assisted low temperature methanol synthesis from syngas was conducted in a batch type reactor using ethanol as both a solvent and a reaction intermediate. Cu/ZnO_X catalysts were prepared by a co-precipitation method with different co-precipitation pH values (X = 6–10), with an aim of investigating the effect of pH value on the catalytic activity of Cu/ZnO_X catalysts in this reaction. The co-precipitation pH value had a strong influence on the Cu crystallite size, the surface morphology, and the surface acidity, leading to the different activities of Cu/ZnO_X catalysts depending on the pH value (X). Catalyst characterization and reaction mechanism clearly revealed that Cu crystallite size and strong acidity of Cu/ZnO_X catalysts played key roles in determining their catalytic activity in this reaction. Yield for methanol showed a tendency to increase with decreasing Cu crystallite size and with increasing strong acidity of Cu/ZnO_X catalysts. Among Cu/ZnO_X catalysts, Cu/ZnO_8 catalyst prepared at pH 8 showed the best catalytic performance due to the finely dispersed Cu particles and the high strong acidity. In addition, the catalytic activity of Cu/ZnO_8 catalyst maintained at the same level even after a 60 h-catalytic reaction, leading to the high feasibility of application of Cu/ZnO_8 catalyst to the continuous reaction system along with the batch reaction system for methanol production from syngas.

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