本研究以具有氧空缺之CeO2觸媒進行CO2的氧脫除反應，並針對不同形貌與摻雜不同金屬之CeO2觸媒兩部分進行討論。在第一部分的研究中，主要利用水熱法合成不同形貌之CeO2觸媒，實驗結果顯示Tube觸媒經900 oC氫氣還原與CO2 pulse反應測試，仍能維持原來形貌，推測Tube相較於其他形貌之CeO2觸媒能維持較多氧空缺，並以pulse方式進行CO2氧脫除反應，探討起始反應速率、反應終止之O2吸附總量及對應OSC的影響。在CO2氧脫除反應中，起始反應速率隨著反應溫度增加而增加，而O2吸附總量則受CeO2觸媒結構變化影響，僅Tube形貌之CeO2觸媒在不同氫氣活化下仍可維持結構完整性，因此各觸媒之OSC皆可達到最高的O2吸附總量，由實驗結果推測CeO2觸媒中氧擴散行為為速率決定步驟。而第二部分的研究中則為不同金屬含量(Gd、Zr、In)修飾CeO2觸媒，除Zr0.5摻雜之CeO2觸媒外，其他金屬摻雜之CeO2觸媒之OSC皆可達到最高總氧吸附量，其中In摻雜的CeO2觸媒在CO2氧脫除反應過程中會生成In2O3幫助CO2脫氧，故在CO2氧脫除反應中較使用其他金屬摻雜的CeO2觸媒效果顯著。

CO2 utilization can be realized via oxygen stripping reaction to produce CO. This study examine how the oxygen vacancies of CeO2 can be applied for oxygen stripping of CO2 and the effects of particle shape and of metal doping are discussed. CeO2 with different shapes, namely, tube, rod, cube, and polyhedral, are synthesized by hydrothermal methods. Tubular CeO2 is the only one that can maintain the original morphology after hydrogen reduction at 900oC and CO2 pulse reaction while the others change and sinter to polyhedra. Oxygen vacancies generated by hydrogen reduction at 900oC can react with CO2 to produce CO, with an initial stable rate and a subsequent fast decay to zero conversion when the OSC (oxygen storage capacity, reversible oxygen vacancies) are saturated. CeO2 tubes have more OSC than the other shapes. The initial rate decreases when reaction temperature changes from 700 to 500 oC, with an estimated activation energy of 21 kJ/mol. The reactivity decreases significantly if the samples are pretreated by H2 at lower temperature, attributable to lower OSC. We also examine Zr-, Gd-, and In-doped CeO2. With the exception of Zr0.5-CeO2, all catalysts get the highest total amount of O2 adsorption. Among them, In0.05-CeO2 shows the highest OSC and similar initial rate for oxygen stripping from CO2. The results suggest that the oxygen diffusion in CeO2 is the rate-determining step.

1. 台灣經濟研究院, Conceptual Strategies of developing CCS technology roadmap and industry cluster in Taiwan. NSC 101-3113-P-301-008.
2. Kikkinides, E.S., R.T. Yang, and S.H. Cho, Concentration and recovery of carbon dioxide from flue gas by pressure swing adsorption. Industrial & Engineering Chemistry Research, 1993. 32(11): p. 2714-2720.
3. Siriwardane, R.V., et al., Adsorption of CO2 on Zeolites at Moderate Temperatures. Energy & Fuels, 2005. 19(3): p. 1153-1159.
4. Pandey, P. and R.S. Chauhan, Membranes for gas separation. Progress in Polymer Science, 2001. 26(6): p. 853-893.
5. Koros, W.J. and R. Mahajan, Pushing the limits on possibilities for large scale gas separation: which strategies? Journal of Membrane Science, 2000. 175(2): p. 181-196.
6. Smith, A.R. and J. Klosek, A review of air separation technologies and their integration with energy conversion processes. Fuel Processing Technology, 2001. 70(2): p. 115-134.
7. Baker, R.W., Future Directions of Membrane Gas Separation Technology. Industrial & Engineering Chemistry Research, 2002. 41(6): p. 1393-1411.
8. C.H., H., C.H. and Tan, C.S., A Review of CO2 Capture by Absorption and Adsorption. Aerosol and Air Quality Research, 2012. 12: p. 25.
9. Varghese, O.K., et al., High-Rate Solar Photocatalytic Conversion of CO2 and Water Vapor to Hydrocarbon Fuels. Nano Letters, 2009. 9(2): p. 731-737.
10. Yang, C.-C., et al., Artificial Photosynthesis over Crystalline TiO2-Based Catalysts: Fact or Fiction? Journal of the American Chemical Society, 2010. 132(24): p. 8398-8406.
11. Roy, S.C., et al., Toward Solar Fuels: Photocatalytic Conversion of Carbon Dioxide to Hydrocarbons. ACS Nano, 2010. 4(3): p. 1259-1278.
12. Song, C., Global challenges and strategies for control, conversion and utilization of CO2 for sustainable development involving energy, catalysis, adsorption and chemical processing. Catalysis Today, 2006. 115(1–4): p. 2-32.
13. Guo, X., et al., The influence of La doping on the catalytic behavior of Cu/ZrO2 for methanol synthesis from CO2 hydrogenation. Journal of Molecular Catalysis A: Chemical, 2011. 345(1–2): p. 60-68.
14. Sahibzada, M., D. Chadwick, and I.S. Metcalfe, Hydrogenation of carbon dioxide to methanol over palladium-promoted Cu/ZnO/A12O3 catalysts. Catalysis Today, 1996. 29(1–4): p. 367-372.
15. Goguet, A., et al., Study of the origin of the deactivation of a Pt/CeO2 catalyst during reverse water gas shift (RWGS) reaction. Journal of Catalysis, 2004. 226(2): p. 382-392.
16. Valderrama, G., A. Kiennemann, and M.R. Goldwasser, La-Sr-Ni-Co-O based perovskite-type solid solutions as catalyst precursors in the CO2 reforming of methane. Journal of Power Sources, 2010. 195(7): p. 1765-1771.
17. McKee, D.W., Catalytic effects of alkaline earth carbonates in the carbon-carbon dioxide reaction. Fuel, 1980. 59(5): p. 308-314.
18. Chen, Z., et al., Splitting CO2 into CO and O2 by a single catalyst. Proceedings of the National Academy of Sciences, 2012. 109(39): p. 15606-15611.
19. Z.F. Chen, T.J.M., Copper (II) catalysis of water oxidation. Angew. Chem. Int. , 2013. Ed.52.
20. Chueh, W.C., et al., High-Flux Solar-Driven Thermochemical Dissociation of CO2 and H2O Using Nonstoichiometric Ceria. Science, 2010. 330(6012): p. 1797-1801.
21. Pacchioni, G., Oxygen vacancy: the invisible agent on oxide surfaces. ChemPhysChem, 2003. 4(10): p. 7.
22. Song, H. and U.S. Ozkan, Ethanol steam reforming over Co-based catalysts: Role of oxygen mobility. Journal of Catalysis, 2009. 261(1): p. 66-74.
23. K. A. Gschneidner, J.a.L.R.E., Handbook on the Physics and Chemistry of Rare Earths. North-Holland, 1984. 32.
24. Wood, N.B.K.a.J.V., The effect of the calcination process on the crystallite shape of sol-gel cerium oxide used for glass polishing. Journal of Materials Science, 1995. 30(8): p. 5.
25. Taylor, K.C., Nitric Oxide Catalysis in Automotive Exhaust Systems. Catalysis Reviews: Science and Engineering, 1993. 35(4): p. 25.
26. X. L. Song, G.Z.Q.a.P.Q., Advances in Research on Applications and Synthesis Methods of CeO2 Nanoparticles. Rare Metal Mater. Eng., 2004. 33: p. 6.
27. Patsalas, P., et al., Structure-dependent electronic properties of nanocrystalline cerium oxide films. Physical Review B, 2003. 68(3): p. 035104.
28. Sugiura, M., Oxygen Storage Materials for Automotive Catalysts: Ceria-Zirconia Solid Solutions. Catalysis Surveys from Asia. 7(1): p. 77-87.
29. Campserveux, J. and P. Gerdanian, Etude thermodynamique de l'oxyde CeO2−x pour 1.5 <OCe < 2. Journal of Solid State Chemistry, 1978. 23(1): p. 73-92.
30. Staudt, T., et al., Ceria reoxidation by CO2: A model study. Journal of Catalysis, 2010. 275(1): p. 181-185.
31. Pan, Y.-x., et al., Effects of Hydration and Oxygen Vacancy on CO2 Adsorption and Activation on β-Ga2O3(100). Langmuir, 2010. 26(8): p. 5551-5558.
32. Funk, S. and U. Burghaus, Adsorption of CO2 on oxidized, defected, hydrogen and oxygen covered rutile (1 [times] 1)-TiO2(110). Physical Chemistry Chemical Physics, 2006. 8(41): p. 4805-4813.
33. Hammami, R., H. Batis, and C. Minot, Combined experimental and theoretical investigation of the CO2 adsorption on LaMnO3+y perovskite oxide. Surface Science, 2009. 603(20): p. 3057-3067.
34. Chueh, W.C. and S.M. Haile, Ceria as a Thermochemical Reaction Medium for Selectively Generating Syngas or Methane from H2O and CO2. ChemSusChem, 2009. 2(8): p. 735-739.
35. Tamaura, Y. and M. Tahata, Complete reduction of carbon dioxide to carbon using cation-excess magnetite. Nature, 1990. 346(6281): p. 255-256.
36. Nordhei, C., et al., Decomposition of Carbon Dioxide over the Putative Cubic Spinel Nanophase Cobalt, Nickel, and Zinc Ferrites. The Journal of Physical Chemistry C, 2008. 112(16): p. 6531-6537.
37. Yi, K.B., et al., Improvement of the cyclic stability of high temperature CO2 absorbent by the addition of oxygen vacancy possessing material. Catalysis Today, 2009. 146(1–2): p. 241-247.
38. Sayle, T.X.T., S.C. Parker, and D.C. Sayle, Oxidising CO to CO2 using ceria nanoparticles. Physical Chemistry Chemical Physics, 2005. 7(15): p. 2936-2941.
39. Martin, P., et al., Atomistic Modeling of Multilayered Ceria Nanotubes. Nano Letters, 2007. 7(3): p. 543-546.
40. Namai, Y., K.-i. Fukui, and Y. Iwasawa, Atom-Resolved Noncontact Atomic Force Microscopic Observations of CeO2(111) Surfaces with Different Oxidation States:  Surface Structure and Behavior of Surface Oxygen Atoms. The Journal of Physical Chemistry B, 2003. 107(42): p. 11666-11673.
41. Esch, F., et al., Electron Localization Determines Defect Formation on Ceria Substrates. Science, 2005. 309(5735): p. 752-755.
42. Yao, H.C. and Y.F.Y. Yao, Ceria in automotive exhaust catalysts. Journal of Catalysis, 1984. 86(2): p. 254-265.
43. Bera, P., et al., Ionic Dispersion of Pt and Pd on CeO2 by Combustion Method: Effect of Metal–Ceria Interaction on Catalytic Activities for NO Reduction and CO and Hydrocarbon Oxidation. Journal of Catalysis, 2000. 196(2): p. 293-301.
44. Descorme, C., et al., Oxygen storage capacity measurements of three-way catalysts under transient conditions. Applied Catalysis A: General, 2002. 223(1–2): p. 287-299.
45. Reddy, B.M., et al., Structural Characteristics and Catalytic Activity of Nanocrystalline Ceria−Praseodymia Solid Solutions. The Journal of Physical Chemistry C, 2009. 113(36): p. 15882-15890.
46. Desclaux, P., et al., Investigation of direct carbon conversion at the surface of a YSZ electrolyte in a SOFC. International Journal of Hydrogen Energy, 2011. 36(16): p. 10278-10281.
47. Balducci, G., et al., Reduction Process in CeO2−MO and CeO2−M2O3 Mixed Oxides:  A Computer Simulation Study. Chemistry of Materials, 2003. 15(20): p. 3781-3785.
48. Masui, T., et al., Preparation of ceria–zirconia sub-catalysts for automotive exhaust cleaning. Journal of Alloys and Compounds, 2000. 303–304: p. 49-55.
49. Otsuka, K., Y. Wang, and M. Nakamura, Direct conversion of methane to synthesis gas through gas–solid reaction using CeO2–ZrO2 solid solution at moderate temperature. Applied Catalysis A: General, 1999. 183(2): p. 317-324.
50. Jean, S.-T. and Y.-C. Her, Growth Mechanism and Photoluminescence Properties of In2O3 Nanotowers. Crystal Growth & Design, 2010. 10(5): p. 2104-2110.
51. Wu, X.C., et al., Fabrication and photoluminescence characteristics of single crystalline In2O3 nanowires. Chemical Physics Letters, 2003. 373(1–2): p. 28-32.
52. Wang, W., et al., Reverse water gas shift over In2O3–CeO2 catalysts. Catalysis Today, 2016. 259, Part 2: p. 402-408.
53. Si, R. and M. Flytzani-Stephanopoulos, Shape and Crystal-Plane Effects of Nanoscale Ceria on the Activity of Au-CeO2 Catalysts for the Water–Gas Shift Reaction. Angewandte Chemie International Edition, 2008. 47(15): p. 2884-2887.
54. Wan, C., et al., Fabrication of CeO2 nanotube supported Pt catalyst encapsulated with silica for high and stable performance. Chemical Communications, 2015. 51(48): p. 9785-9788.
55. Tang, C.C., et al., Cerium Oxide Nanotubes Prepared from Cerium Hydroxide Nanotubes. Advanced Materials, 2005. 17(24): p. 3005-3009.
56. Sutthisripok, W., S. Sattayanurak, and L. Sikong, Effect of specific surface area on oxygen storage capacity (OSC) and methane steam reforming reactivity of CeO2. Journal of Porous Materials, 2008. 15(5): p. 519-525.
57. Larese, C., et al., Effects of the CePO4 on the oxygen storage and release properties of CeO2 and Ce0.8Zr0.2O2 solid solution. Journal of Catalysis, 2004. 226(2): p. 443-456.
58. Tauc, J., Optical properties and electronic structure of amorphous Ge and Si. Materials Research Bulletin, 1968. 3(1): p. 37-46.
59. Meher, S.K. and G. Ranga Rao, Tuning, via Counter Anions, the Morphology and Catalytic Activity of CeO2 Prepared under Mild Conditions. Journal of Colloid and Interface Science, 2012. 373(1): p. 46-56.
60. Tauc, J., R. Grigorovici, and A. Vancu, Optical Properties and Electronic Structure of Amorphous Germanium. physica status solidi (b), 1966. 15(2): p. 627-637.
61. Guo, M., et al., UV and Visible Raman Studies of Oxygen Vacancies in Rare-Earth-Doped Ceria. Langmuir, 2011. 27(7): p. 3872-3877.
62. Bensalem, A., et al., Preparation and characterization of highly dispersed silica-supported ceria. Applied Catalysis A: General, 1995. 121(1): p. 81-93.
63. Mohanty, B.C., et al., Dopant induced variations in microstructure and optical properties of CeO2 nanoparticles. Materials Research Bulletin, 2011. 46(6): p. 875-883.
64. Phokha, S., et al., Synthesis, characterization, and magnetic properties of monodisperse CeO2 nanospheres prepared by PVP-assisted hydrothermal method. Nanoscale Research Letters, 2012. 7(1): p. 1-13.
65. Wang, W.-C., et al., Towards understanding the electronic structure of Fe-doped CeO2 nanoparticles with X-ray spectroscopy. Physical Chemistry Chemical Physics, 2013. 15(35): p. 14701-14707.
66. Bianconi, A., et al., Specific intermediate-valence state of insulating 4 \textit{f} compounds detected by ${L}_{3}$ x-ray absorption. Physical Review B, 1987. 35(2): p. 806-812.
67. Sham, T.K., R.A. Gordon, and S.M. Heald, Resonant inelastic x-ray scattering at the Ce L3 edge of CePO4 and CeO2 : Implications for the valence of CeO2 and related phenomena. Physical Review B, 2005. 72.
68. Soldatov, A.V., et al., Proceedings of the 8th International Conference on X-ray Absorption Fine StructureL3 edge X-ray absorption spectrum of CeO2: crystal structure effects. Physica B: Condensed Matter, 1995. 208: p. 53-55.
69. Lin, Y., et al., Enhancing grain boundary ionic conductivity in mixed ionic-electronic conductors. Nat Commun, 2015. 6.
70. Wang, J.A., et al., Spectroscopic study and catalytic evaluation of mesostructured Al-MCM-41 and Pt/H3PW12O40/Al-MCM-41 catalysts. Applied Catalysis A: General, 2009. 357(2): p. 223-235.
71. Nosaka, Y., Finite depth spherical well model for excited states of ultrasmall semiconductor particles: an application. The Journal of Physical Chemistry, 1991. 95(13): p. 5054-5058.
72. Mandapaka, R.K. and G. Madras, Microkinetic Modeling of CO Oxidation on Ionic Palladium-Substituted Ceria. Industrial & Engineering Chemistry Research, 2016. 55(8): p. 2309-2318.