Pt原子在γ-Al2O3(001)表面的吸附及迁移

采用密度泛函理论(DFT)中广义梯度近似(GGA)方法, 对Pt原子与γ-Al₂O₃(001)面的相互作用及迁移性能进行了研究. 分析了各种可能吸附位及吸附构型的松弛和变形现象, 吸附能和迁移能垒的计算结果表明: Pt团簇能够稳定吸附在该表面. Pt原子在表面O位的吸附能明显较高, 这主要是由Pt向基底O原子转移了电子所致. 电荷布居分析表明, Pt原子显电正性, Pt和Al原子之间存在排斥作用, 导致与Al原子产生较弱相互作用. 计算的平均吸附能大小依赖于Pt团簇的大小和形状, 总体趋势是随着Pt原子数增多, 吸附能降低. Pt原子在γ-Al₂O₃(001)表面迁移过程所需克服的迁移能垒最高值为0.51 eV. 随着吸附的Pt原子数增多,更倾向于形成Pt团簇. 因此, Pt原子在γ-Al₂O₃(001)表面的吸附演变不可能形成光滑、均匀平铺的吸附构型, 而在一定条件下容易出现团聚.

Adsorption and Migration of Pt Atoms on γ-Al2O3(001) Surface

We present a systematic study using density functional theory (DFT) with the generalized gradient approximation (GGA) method to understand the adsorption and migration of Pt atoms on the γ-Al₂O₃(001) surface. Energetically the most favorable adsorption sites were identified and all these adsorption configurations were found to show substantial structural relaxation. Our calculated adsorption and energy barrier of migration results indicate that the Pt clusters can be stably anchored onto the surface. A significantly higher adsorption energy at the O site is largely attributed to the fact that charge transfer from Pt to O atoms results in positively charged Pt atoms. The repulsion between Pt and Al atoms leads to much weaker bonds. The calculated average adsorption energies were found to be size and shape dependent and in general decrease as the number of Pt atoms increases. The highest energy barrier for Pt atom migration on the γ-Al₂O₃(001) surface is about 0.51 eV. The formation of a metal cluster would be strongly preferred upon high Pt atom loading. Consequently, the evolution of Pt atoms on the γ-Al₂O₃(001) surface is unlikely to be smooth and agglomeration can occur under certain conditions.