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

Abstract

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 × 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 °C, 3.0 MPa, V(H₂) : V(CO₂) : V(N₂) = 69 : 23 : 8 and GHSV of 3600 h⁻¹. The catalysts were fully characterized by N₂ physisorption, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), H₂-temperature-programmed reduction (H₂-TPR) and temperature-programmed desorption of H₂ (H₂-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 H₂ and CO₂ adsorption capability, thus leading to good catalytic performance towards methanol synthesis.