Effect of CuO/ZnO catalyst preparation condition on alcohol-assisted methanol synthesis from carbon dioxide and hydrogen

CuO/ZnO catalysts are synthesized using a co-precipitation method with different precipitation temperatures (298–353 K) and pH values (5–9). A conventional precipitation is compared to an ultrasonic-assisted precipitation at each precipitating temperature. Methanol is directly synthesized from CO₂ and H₂ (1:3 mol ratio) through an alcohol-assisted reaction (423 K, 5 MPa, 24 h) by using different alcohols (ethanol, propanol and butanol) as a medium. There are two parts for the challenge of this research, including the preparation of CuO/ZnO catalysts using an ultrasonic-assisted precipitation and, methanol synthesis through an alcohol-assisted method. It is found that the precipitation temperature and pH value significantly affect the catalyst properties and the reaction activity. An ultrasonic irradiation helps facilitate the crystalline phase formation and decrease precipitation temperature. The highest yield of methanol is obtained when CuO/ZnO is precipitated at 333 K from the conventional precipitation (31%) while it is at 313 K from the ultrasonic-assisted precipitation (32%). In addition, the different type of alcohol strongly affects methanol yield and CO₂ conversion. The use of larger alcohol molecules offers higher CO₂ conversion but lower methanol yield.