钡原子对Ru(0001)表面氮分子吸附和解离过程的影响

Effects of Barium Atoms on Adsorption and Dissociation of Nitrogen Molecules on Ru(0001) Surface

采用密度泛函理论方法研究了钡原子对Ru(0001)表面氮分子解离过程的影响.计算结果表明:在Ru(0001)表面,钡原子失去电子后形成Ba(1+δ)+阳离子.表面转移电荷增强了衬底钌原子d轨道和氮分子π轨道间的杂化作用以及氮分子内的库仑排斥作用,减弱了氮分子键.在钡原子的作用下,γ态氮分子键键长从0.113 nm增加到0.123 nm,分子拉伸振动频率从2221 cm-1减小到1745 cm-1.α态氮分子键键长从0.120 nm增加到0.133 nm,而分子拉伸振动频率则从1486减小到1052 cm-1.钡原子的作用使氮分子的解离反应势垒从Ru(0001)表面的2.06 eV降低到Ru(0001)-Ba表面的1.17 eV,提高了500 K下Ru(0001)表面平台的反应活性约9个数量级.研究结果说明,在Ru(0001)表面金属钡原子具有电子型助催剂的特征.

First principles calculations had been performed to present the effects of barium atom on disso-ciation of nitrogen molecule on Ru（0001） surface.Barium atoms became cations on Ru（0001） surface by lose electrons.Charge transfer enhanced the hybridization between d orbitals of substrate and π orbitals of nitrogen molecule.Bond strength of nitrogen molecule was weakened by effects of barium atom.Bond length of γ state nitrogen molecule was increased from 0.113 nm on Ru（0001） surface to 0.123 nm on Ru（0001）-Ba surface,and stretch vibration frequency was decreased from 2221 to 1745 cm-1.Bond length of α state nitrogen molecule was increased from 0.120 nm on Ru（0001） surface to 0.133 nm on Ru（0001）-Ba surface,and vibration frequency was decreased from 1486 to 1052 cm-1.The barrier energy of nitrogen mo-lecular dissociation on Ru（0001） surface was reduced from 2.06 to 1.17 eV by effects of barium atom,and activities of Ru（0001） terrace surface was magnified about 9 orders at 500 K.It was indicated that barium atom had some characters to be an electronic promoter on the process of activating nitrogen molecules on Ru（0001） surface.