Properties of Cu/ZnO/Al₂O₃ catalysts modified by titanium additives in synthesis of methanol from syngas using orthogonal experimental design

Ternary Cu/ZnO/Al₂O₃ catalysts, prepared by reverse co-precipitation, were modified with small amounts of titanium additives using orthogonal experimental design. Precipitating temperature, precipitating mode, additive and precipitating environment were chosen as the main parameters for investigation. Catalytic performance of the catalysts in synthesis of methanol was evaluated in a fixed-bed reactor at 5 MPa and 240 °C. After initial evaluation, the catalysts were used at 350 °C for 5 h and then cooled to 240 °C for re-evaluation. The structure and morphology of the catalysts were studied by differential thermal gravimetric analysis, X-ray diffraction, nitrogen adsorption isotherms, temperature-programmed reduction and transmission electron microscopy. It was found that high precipitating temperature promoted high mixing degrees, which increased initial catalytic yield in methanol synthesis. Combined with the synergistic effects between precursors and additives, a small amount of residual carbonate grains remaining after calcination due to the heat-resistance of rutile nanofibers and octa-potassium titanate whiskers proved beneficial to the catalytic activity.