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采用密度泛函理论研究了Ru(0001) /BaO表面的原子层结构和氮分子的吸附性质. 研究结果表明, 在低覆盖度下氧化钡倾向于以相同的构型形成Ru(0001) 表面原子层. 在此构型中, 氧原子位于表面p(1 1) 结构的hcp谷位, 而钡原子则位于同一p(1 1) 结构的顶位附近. 钌氧键键长等于0.209 nm, 比EXAFS的实验值大0.018 nm. 在Ru(0001) /BaO表面氮分子倾向吸附于钡原子附近. 相应位置的氮分子吸附能位于0.70到0.87 eV之间, 大于氧原子附近的氮分子吸附能. 钡原子附近的钌原子对氮分子具有更强的活化性能. 相应位置的氮分子拉伸振动频率等于1946 cm- 1, 比氧原子附近的最大分子振动频率小约130 cm-1. Ru(0001) /BaO表面氮分子键强度介于清洁Ru(0001) 和Ru(0001) /Ba表面之间. Ru(0001)/BaO表面不同位置的氮分子吸附性质差异是由钡和氧原子化学性质不同造成的. 表面钡原子的作用能够减少吸附氮分子的*轨道电子密度, 增加*轨道电子密度, 从而增强氮分子和钌原子间的轨道杂化作用, 弱化氮分子键.
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关键词:
- 氨合成催化剂 /
- Ru(0001)/BaO表面 /
- 表面形成能 /
- 分子振动
First principles calculations are performed to study the geometric structures and the nitrogen adsorption properties of BaO adlayer on Ru(0001) surface. It is suggested that BaO adlayer is more stable on Ru(0001) surface at low coverage. A configuration is observed in surface phase at low coverage. In this structure oxygen is adsorbed on the hcp site of one p(1 1) cell, and barium is adsorbed close to the top site of the same p(1 1) cell. Bond length of oxygen and ruthenium is calculated to be 0.209 nm, longer than the EXAFS experimental value about 0.018 nm. Nitrogen prefers to be adsorbed on the sites close to barium. Nitrogen adsorption energies at those sites are calculated to be in a range from 0.70 to 0.87 eV, which are bigger than those at the sites close to oxygen. Adsorption sites near barium atoms have more activities to weaken nitrogen. The lowest N-N stretching vibrational frequency on the sites is about 1946 cm-1, less than the highest frequency on sites around oxygen (about 130 cm- 1). Bond strengths of nitrogen on Ru(0001) /BaO surface are between those on clean Ru(0001) and Ru(0001) /Ba surface. The adsorption properties of sites around BaO layer are determined by chemical characteristic of barium and oxygen. Electron transfer from barium to ruthenium enhances the hybridization between ruthenium and nitrogen by reducing and increasing the occupation of * and * orbitals respectively.-
Keywords:
- ammonia synthesis catalyst /
- Ru(0001)/BaO /
- surface formation energy /
- molecular vibration
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[63] -
[1] Kowalczyk Z, Krukowski M, Rarog-Pilecka W, Szmigiel D, Zielinski J 2003 Appl. Catal. a-Gen. 248 67
[2] Rossetti I, Pernicone N, Forni L 2001 Appl. Catal. a-Gen. 208 271
[3] [4] [5] Rarog-Pilecka W, Miskiewicz E, Szmigiel D, Kowalczyk Z 2005 J. Catal. 231 11
[6] [7] Zhong Z, HAika K 1998 Inorg. Chim. Acta 280 183
[8] Zeng H S, Inazu K, Aika K 2002 J. Catal. 211 33
[9] [10] [11] Truszkiewicz E, Rarog-Pilecka W, Schmidt-Szatowski K, Jodzis S, Wilczkowska E, Lomot D, Kaszkur Z, Karpinski Z, Kowalczyk Z 2009 J. Catal. 265 181
[12] [13] Hansen T W, Wagner J B, Hansen P L, Dahl S, Topsoe H, Jacobsen C J H 2001 Science 294 1508
[14] [15] Hansen T W, Hansen P L, Dahl S, Jacobsen C J H 2002 Catal. Lett. 84 7
[16] Bielawa H, Hinrichsen O, Birkner A, Muhler M 2001 Ang. Chem. Inter. Ed. 40 1061
[17] [18] [19] Guraya M, Sprenger S, Rarog-Pilecka W, Szmigiel D, Kowalczyk Z, Muhler M 2004 Appl. Surf. Sci. 238 77
[20] McClaine B C, Siporin S E, Davis R J 2001 J. Phys. Chem. B 105 7525
[21] [22] [23] Dahl S, Logadottir A, Egeberg R C, Larsen J H, Chorkendorff I, Tornqvist E, Norskov J K 1999 Phys. Rev. Lett. 83 1814
[24] [25] Zhao X X, Tao X M, Chen W B, Cai J Q, Tan M Q 2005 Acta Phys. Sin. 54 5849 (in Chinese) [赵新新, 陶向明, 陈文斌, 蔡建秋, 谭明秋 2005 54 5849]
[26] [27] Zhao X X, Tao X M, Mi Y M, Chen S, Tan M Q 2009 Acta Phys. Chim. Sin. 25 2305 (in Chinese) [赵新新, 陶向明, 宓一鸣, 陈戍, 谭明秋 2009 物理化学学报 25 2305]
[28] Zhao X X, Tao X M, Mi Y M, Wu J B, Wang L L, Tan M Q 2011 Acta Chim. Sin. 69 2201 (in Chinese) [赵新新, 陶向明, 宓一鸣, 吴建宝, 汪丽莉, 谭明秋 2011 化学学报 69 2201]
[29] [30] [31] Kim Y K, Morgan G A, Yates J T 2005 Surf. Sci. 598 14
[32] [33] Zambelli T, Trost J, Wintterlin J, Ertl G 1996 Phys. Rev. Lett. 76 795
[34] [35] Kresse G, Furthmuller J 1996 Comp. Mater. Sci. 6 15
[36] Kresse G, Furthmuller J 1996 Phys. Rev. B 54 11169
[37] [38] Blhl P E 1994 Phys. Rev. B 50 17953
[39] [40] Perdew J P, Burke K, Ernzerhof M 1996 Phys. Rev. Lett. 77 3865
[41] [42] [43] Monkhorst H J, Pack J D 1976 Phys. Rev. B 13 5188
[44] Kittel C 1976 Introduction to Solid State Physics (7th Ed.) (New York: John Wiley and Sons) pp23-57
[45] [46] [47] Methfessel M, Hennig D, Scheffler M 1992 Phys. Rev. B 46 4816
[48] Feibelman P J, Houston J E, Davis H L, Oneill D G 1994 Surf. Sci. 302 81
[49] [50] Mannstadt W 2003 Surf. Sci. 525 119
[51] [52] [53] Kim Y D, Seitsonen A P, Over H 2000 Surf. Sci. 465 1
[54] Honkala K, Hellman A, Remediakis I N, Logadottir A, Carlsson A, Dahl S, Christensen C H, Norskov J K 2005 Science 307 555
[55] [56] Hellman A, Honkala K, Remediakis I N, Logadottir A, Carlsson A, Dahl S, Christensen C H, Norskov J K 2009 Surf. Sci. 603 1731
[57] [58] Cheng L, Ge Q F 2007 Surf. Sci. 601 L65
[59] [60] [61] Bader R F W 1990 Atoms in Molecules-A Quantum Theory (Oxford: Oxford University Press) p116
[62] Mortensen J J, Hammer B, Noskov J K 1998 Surf. Sci. 414 315
[63]
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