CO2 Hydrogenation to Methanol over a Highly Active Cu–Ni/CeO2–Nanotube Catalyst

A series of Cu–Ni/CeO2-nanotube catalysts is prepared by an impregnation method for CO2 hydrogenation to CH3OH. Regular CeO2 nanotubes are perfectly formed with a tube diameter of about 30–50 nm and Cu–Ni alloy is well dispersed on CeO2 nanotube without nanotube morphology change. There is a synergistic effect between Ni and Cu, promoting the bimetallic Cu–Ni dispersion, reducibility, CO adsorption and hydrogenation. Additionally, a strong interaction is observed between Cu–Ni alloy and CeO2, and it contributes to partial reduction of Ce4+ to Ce3+ and formation of oxygen vacancies which adsorb and activate CO2. It is shown that both CO2 conversion and CH3OH space-time yield increase at first, reach their maximum values at a Ni/(Cu+Ni) ratio of 2/3, and then decrease with increasing the Ni/(Cu+Ni) ratio. The CeO2-nanotube supported CuNi2 catalyst gives CO2 conversion of 17.8% and CH3OH space-time yield of 18.1 mmol/(gcat·h) after preliminary optimization. Furthermore, it exhibits an excellent catalytic performance within a wide range of space velocity.