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