In situ EXAFS studies of copper on ZrO₂ during catalytic hydrogenation of CO₂

Speciation of copper on ZrO₂ during the catalytic hydrogenation of CO₂ has been studied by in situ extended X-ray absorption fine structural (EXAFS) spectroscopy in the present work. The EXAFS data indicated that about 3.1 nearest oxygen atoms surrounded the Cu atoms with a CuO bond distance of 1.95 Å in the calcined Cu/ZrO₂ catalyst. Reduction of the catalyst in hydrogen at 573 K led to a formation of CuCu (2.56 Å) bonds with a coordination number (CN) of 5.6. Mainly CO and CH₃OH were generated in the hydrogenation of CO₂ catalyzed by the reduced Cu/ZrO₂ catalyst at 673 K. About 76% of the Cu(0) species was oxidized to Cu(I) (27%) and Cu(II) (49%) on ZrO₂ during the catalytic hydrogenation process.