Hallac B F, Asscher M
Department of Physical Chemistry and the Farkas Center for Light Induced Processes, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
Langmuir. 2007 Aug 14;23(17):8891-8. doi: 10.1021/la700895r. Epub 2007 Jul 18.
The interaction and reactivity of trimethylamine (TMA) has been studied over clean and oxygen-covered Ru(001) under UHV conditions, as a model for the chemistry of high-density hydrocarbons on a catalytic surface. The molecule adsorbs intact at surface temperature below 100 K with the nitrogen end directed toward the surface, as indicated from work function change measurements. At coverage less than 0.05 ML (relative to the Ru substrate atoms), TMA fully dissociates upon surface heating, with hydrogen as the only evolving molecule following temperature-programmed reaction/desorption (TPR/TPD). At higher coverage, the parent molecule desorbs, and its desorption peak shifts down from 270 K to 115 K upon completion of the first monolayer, indicating a strong repulsion among neighbor molecules. The dipole moment of an adsorbed TMA molecule has been estimated from work function study to be 1.4 D. Oxygen precoverage on the ruthenium surface has shown efficient reactivity with TMA. It shifts the surface chemistry toward the production of various oxygen-containing stable molecules such as H2CO, CO2, and CO that desorb between 200 and 600 K, respectively. TMA at a coverage of 0.5 ML practically cleans off the surface from its oxygen atoms as a result of TPR up to 1650 K, in contrast to CO oxidation on the O/Ru(001) surface. The overall reactivity of TMA on the oxidized ruthenium surface has been described as a multistep reaction mechanism.
在超高真空条件下，研究了三甲胺（TMA）在清洁的和被氧覆盖的Ru(001)表面上的相互作用和反应活性，以此作为催化表面上高密度烃类化学反应的模型。根据功函数变化测量结果表明，该分子在表面温度低于100 K时完整吸附，氮端朝向表面。在覆盖度小于0.05 ML（相对于Ru衬底原子）时，TMA在表面加热时完全解离，程序升温反应/脱附（TPR/TPD）后仅产生氢气这一逸出分子。在较高覆盖度下，母体分子脱附，并且在完成第一个单分子层后其脱附峰从270 K下移至115 K，这表明相邻分子之间存在强烈排斥作用。通过功函数研究估计吸附的TMA分子的偶极矩为1.4 D。钌表面上的预覆盖氧已显示出与TMA的高效反应活性。它使表面化学朝着生成各种含氧化合物稳定分子的方向转变，例如分别在200至600 K之间脱附的H2CO、CO2和CO。与O/Ru(001)表面上的CO氧化相反，覆盖度为0.5 ML的TMA通过高达1650 K的TPR实际上将表面上的氧原子清除掉了。TMA在氧化钌表面上的整体反应活性已被描述为一种多步反应机理。
