Carbon dioxide hydrogenation to methanol over Cu/ZrO2/CNTs: effect of carbon surface chemistry

Methanol synthesis from CO2 hydrogenation in a fixed-bed plug flow reactor was investigated over Cu-ZrO2 catalysts supported on CNTs bearing various functional groups. The highest methanol activity (turnover frequency 1.61 x 10(-2) s(-1), space time yield 84.0 mg g(cat)(-1) h(-1)) was obtained over the Cu/ZrO2/CNTs catalyst (CZ/CNT-3) with CNTs functionalized by nitrogen-containing groups and Cu loading only about 10.3 wt% under the reaction conditions of 260 degrees C, 3.0 MPa, V(H-2) : V(CO2) : V(N-2) = 69 : 23 : 8 and GHSV of 3600 h(-1). The catalysts were fully characterized by N-2 physisorption, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), H-2-temperature-programmed reduction (H-2-TPR) and temperature-programmed desorption of H-2 (H-2-TPD) techniques. The excellent performance of CZ/CNT-3 is attributed to the presence of nitrogen-containing groups on the CNTs surface, which increase the dispersion of copper oxides, promote their reduction, decreases the crystal size of Cu, and enhances H-2 and CO2 adsorption capability, thus leading to good catalytic performance towards methanol synthesis.