Gamallo P, Sayós R
Departament de Química Física and Institut de Recerca de Química Teórica i Computacional, Universitat de Barcelona, Spain.
Phys Chem Chem Phys. 2007 Oct 7;9(37):5112-20. doi: 10.1039/b705452a. Epub 2007 Jul 31.
The interaction of atomic oxygen and nitrogen on the (0001) surface of corundum (alpha-alumina) is investigated from first-principles by means of periodic density functional calculations within the generalized gradient approximation. A large Al(2)O(3) slab model (18 layers relaxing 10) ended with the most stable aluminium layer is used throughout the study. Geometries, adsorption energies and vibrational frequencies are calculated for several stationary points for two spin states at different sites over an 1 x 1 unit cell. Two stable adsorption minima over Al or in a bridge between Al and O surface atoms are found for oxygen and nitrogen, without activation energies. The oxygen adsorption (e.g., E(ad) = 2.30 eV) seems to be much more important than for nitrogen (e.g., E(ad) = 1.23 eV). Transition states for oxygen surface diffusion are characterized and present not very high-energy barriers. The computed geometries and adsorption energies are consistent with similar adsorption theoretical studies and related experimental data for O, N or alpha-alumina. The present results along with our previous results for beta-cristobalite do not support the assumption of an equal E(ad) for O and N over similar oxides, which is commonly used in some kinetic models to derive catalytic atomic recombination coefficients for atomic oxygen and nitrogen. The magnitude of O and N adsorption energies imply that Eley-Rideal and Langmuir-Hinshelwood reactions with these species will be exothermic, contrary to what happens for beta-cristobalite.
通过广义梯度近似下的周期性密度泛函计算，从第一性原理出发研究了原子氧和氮在刚玉（α - 氧化铝）(0001)表面的相互作用。在整个研究中使用了一个大型的Al₂O₃平板模型（18层，10层弛豫），其末端为最稳定的铝层。针对1×1晶胞上不同位置的两种自旋态的几个驻点，计算了几何结构、吸附能和振动频率。发现氧和氮在Al上或在Al与O表面原子之间的桥位存在两个稳定的吸附极小值，且无活化能。氧的吸附（例如，E(ad) = 2.30 eV）似乎比氮的吸附（例如，E(ad) = 1.23 eV）重要得多。表征了氧表面扩散的过渡态，其能垒不高。计算得到的几何结构和吸附能与关于O、N或α - 氧化铝的类似吸附理论研究及相关实验数据一致。目前的结果连同我们之前关于β - 方石英的结果并不支持在类似氧化物上O和N具有相等吸附能（E(ad)）的假设，而这一假设在一些动力学模型中常用于推导原子氧和氮的催化原子复合系数。O和N吸附能的大小意味着与这些物种发生的埃利 - 里德反应和朗缪尔 - 欣谢尔伍德反应将是放热的，这与β - 方石英的情况相反。
