Journal of Electron Spectroscopy and Related Phenomena 144–147 (2005) 373–376 In situ EXAFS studies of copper on ZrO 2 during catalytic hydrogenation of CO 2 S.-H. Liu a , H. Paul Wang a, ∗ , H.-C. Wang b , Y.W. Yang c a DepartmentofEnvironmentalEngineering,NationalChengKungUniversity,TainanCity,Taiwan b DepartmentofMedicine,VeteransGeneralHospital-Kaoshiung,Kaoshiung,Taiwan c NationalSynchrotronRadiationResearchCenter,Hsinchu,Taiwan Available online 11 March 2005 Abstract Speciation of copper on ZrO 2 during the catalytic hydrogenation of CO 2 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 Cu O bond distance of 1.95 ˚ A in the calcined Cu/ZrO 2 catalyst. Reduction of the catalyst in hydrogen at 573 K led to a formation of Cu Cu (2.56 ˚ A) bonds with a coordination number (CN) of 5.6. Mainly CO and CH 3 OH were generated in the hydrogenation of CO 2 catalyzed by the reduced Cu/ZrO 2 catalyst at 673 K. About 76% of the Cu(0) species was oxidized to Cu(I) (27%) and Cu(II) (49%) on ZrO 2 during the catalytic hydrogenation process. © 2005 Elsevier B.V. All rights reserved. Keywords: CO 2 ; Hydrogenation; ZrO 2 ; XANES; EXAFS 1. Introduction Hydrogenation of CO 2 to generate valuable chemicals has been widely investigated from the viewpoint of reducing the global warming effect caused by the CO 2 emission. It is also of great interest from the aspect of use of carbon source from CO 2 for the synthesis of oxygenates and hydrocarbons [1]. In the near future, due to the rapid decline of petroleum reserves, the use of CO 2 as C 1 building blocks in the organic synthesis would be environmentally and economically attractive. The amount of CO 2 to be fixed that way is very small compared to the huge amount of CO 2 produced by burning fossil fuels. However, the industrial use of CO 2 as a feedstock has so far been limited by its inherent thermodynamic stability. In the past decade, considerable researches have been investigated to develop methods of activating CO 2 for subsequent chemical transformation [2]. Processes for synthesis of methanol from syngas catalyzed by Cu/ZnO/Al 2 O 3 have been well established in an industrial ∗ Corresponding author. Tel.: +886 6 276 3608; fax: +886 6 275 2790. E-mailaddress: wanghp@mail.ncku.edu.tw (H.P. Wang). process [3]. However, they have been suffered a very poor activity for the hydrogenation of CO 2 [4]. Generally, catalyst preparation procedures such as im- pregnation, ion exchange, deposition precipitation and co- precipitation may influence the catalytic behavior [3]. Var- ious metal oxides have been used as support materials for hydrogenation of CO 2 . ZrO 2 is of great interest in catalysis because of its mechanical and thermal stability, high specific surface area, and semiconductor properties. ZrO 2 has been found to maintain a good long-term stability in catalytic hy- drogenation of CO 2 [5]. ZrO 2 -supported copper catalysts are very active with a high selectivity for methanol synthesis [6]. However, nature of the catalyst in the CO 2 hydrogenation process has not been extensively studied. X-ray absorption near edge structural (XANES) and ex- tended X-ray absorption fine structural (EXAFS) spectro- scopies are very useful in identification of elements with a different environment, degree of aggregation, or location [7]. By EXAFS, we found that copper oxides (in ZSM-5 or ZSM- 48) involved in the catalytic decomposition of NO [8] and oxidation of chlorophenols in supercritical water [9]. These speciation data was very useful in revealing the structure of 0368-2048/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.elspec.2005.01.281