Inverse ZrO2/Cu as a highly efficient methanol synthesis catalyst from CO2 hydrogenation

Abstract

Enhancing the intrinsic activity and space time yield of Cu based heterogeneous methanol synthesis catalysts through CO₂ hydrogenation is one of the major topics in CO₂ conversion into value-added liquid fuels and chemicals. Here we report inverse ZrO₂/Cu catalysts with a tunable Zr/Cu ratio have been prepared via an oxalate co-precipitation method, showing excellent performance for CO₂ hydrogenation to methanol. Under optimal condition, the catalyst composed by 10% of ZrO₂ supported over 90% of Cu exhibits the highest mass-specific methanol formation rate of 524 g_MeOHkg_cat^-1h^-1 at 220 °C, 3.3 times higher than the activity of traditional Cu/ZrO₂ catalysts (159 g_MeOHkg_cat^-1h^-1). In situ XRD-PDF, XAFS and AP-XPS structural studies reveal that the inverse ZrO₂/Cu catalysts are composed of islands of partially reduced 1-2 nm amorphous ZrO₂ supported over metallic Cu particles. The ZrO₂ islands are highly active for the CO₂ activation. Meanwhile, an intermediate of formate adsorbed on the Cu at 1350 cm^-1 is discovered by the in situ DRIFTS. This formate intermediate exhibits fast hydrogenation conversion to methoxy. The activation of CO₂ and hydrogenation of all the surface oxygenate intermediates are significantly accelerated over the inverse ZrO₂/Cu configuration, accounting for the excellent methanol formation activity observed.