CO2 hydrogenation to methanol over Cu/ZrO2 catalysts: Effects of zirconia phases

Structure–activity relationships of amorphous (a-), tetragonal (t-), monoclinic (m-) ZrO2 phase supported copper catalysts for methanol synthesis from CO2 hydrogenation were investigated with X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), N2O chemisorption, H2-temperature programmed reduction (H2-TPR), X-ray absorption spectroscopy (XAS), H2 and CO2 temperature-programmed desorption (H2- and CO2-TPD). The order of copper surface area is found to be as follows: Cu/a-ZrO2 > Cu/t-ZrO2 > Cu/m-ZrO2. The increased yield of methanol is correlated to the increase of copper surface area. However, normalization of the copper site specific activity (TOFmethanol) of Cu/t-ZrO2 is about 1.10–1.50 times and 1.62–3.59 times higher than Cu/a-ZrO2 and Cu/m-ZrO2, respectively. The high TOFmethanol is caused by a strong Cu–ZrO2 interaction and a high surface concentration of atomic hydrogen to CO2.