Formic acid assisted synthesis of Cu-ZnO-Al₂O₃ catalyst and its performance in CO₂ hydrogenation to methanol

The Cu/Zn/Al precursor by coprecipitation was treated with formic acid and then calcined in N₂ to obtain Cu-ZnO-Al₂O₃ catalyst (CZA) for the CO₂ hydrogenation to methanol. XRD, BET, TG-DSC, SEM, H₂-TPR, N₂O titration, XPS-AES and CO₂-TPD characterization techniques were used to analyze the phase composition, structural properties of the catalyst, the Cu specific surface area, the dispersion and valence of the Cu species. The results showed that the formic acid treatment tuned the ratio of Cu⁺ and Cu⁰, increased the number of medium-strong base sites in the catalyst, and raised the selectivity of methanol. Under reaction conditions of W/F(H₂/CO₂=70/23)=10 g∙h/mol, t =200 ℃ and p =3 MPa, using Cu-ZnO-Al₂O₃ treated under HCOOH/Cu (molar ratio) =0.8, the CO₂ conversion and the methanol selectivity were 6.7% and 76.3%, respectively.