纳米团簇Au_(19)Pd和Au_(19)Pt催化解离N_2O（英文）

Nitrous Oxide Decomposition Catalyzed by Au_(19)Pd and Au_(19)Pt Clusters

采用密度泛函理论研究Au-Pd和Au-Pt纳米团簇催化解离N2O.首先根据计算得到Au19Pd和Au19Pt团簇的最优构型(杂原子均位于团簇的表面).以Au19Pd催化解离N2O为例研究催化解离的反应机理.对此主要考虑两个反应机理,分别是Eley-Rideal(ER)和Langmuir-Hinshelwood(LH).第一个机理中N2O解离的能垒是1.118 e V,并且放热0.371 e V.N2分子脱附后,表面剩余的氧原子沿着ER路径消除需要克服的能垒是1.920e V,这比反应沿着LH路径的能垒高0.251 e V.此外根据LH机理,氧原子在表面的吸附能是-3.203 e V,而氧原子在表面转移所需的能垒是0.113 e V,这表明氧原子十分容易在团簇表面转移,从而促进氧气分子的生成.因此,LH为最优反应路径.为了比较Au19Pd和Au19Pt对N2O解离的活性,根据最优的反应路径来研究Au19Pt催化解离N2O,得到作为铂族元素的铂和钯对N2O的解离有催化活性,尤其是钯.同时,将团簇与文献中的Au-Pd合金相比较,得到这两种团簇对N2O解离有较高的活性,尤其是Au19Pd团簇.再者,O2的脱附不再是影响反应的主要原因,这可以进一步提高团簇解离N2O的活性.

The catalytic decomposition of N2 O using Au19 Pd and Au19 Pt clusters as catalysts with optimized geometries was studied using density functional theory（DFT）. The optimized geometries of the Au19 Pd and Au19 Pt clusters were obtained as a function of structural and thermodynamic analyses, in which the heteroatoms are on the surfaces of the clusters. We selected the Au19 Pd cluster as a model cluster to investigate the reaction mechanism of N2 O decomposition. There are two reaction pathways to be considered： Eley-Rideal（ER） and Langmuir-Hinshelwood（LH）. We found that the first N2 O decomposition needs to surmount an energy barrier of 1.118 e V, and is exothermic by 0.371 e V. The elimination of the residual oxygen atom on the surface has an energy barrier of 1.920 e V along the ER pathway after N2 desorption, which is higher than that along the LH channel（1.669 e V）. The adsorption energy of the oxygen atom on the surface is-3.203 e V, and the oxygen atom diffusion on the surface needs to surmount an energy barrier of 0.113 e V along the LH pathway. This indicates that the oxygen atom is prone to transfer on the cluster to promote the generation of the O2 molecule,and therefore the LH is the optimized reaction pathway. We investigated the catalytic activity of Au19 Pt for N2 O decomposition along the LH pathway in comparison with the Au19 Pd cluster. Both platinum and palladium have catalytic activities for N2 O decomposition, especially the palladium in this study. Comparison between this work and the theoretical study on periodic systems shows that these two clusters can be used as better catalysts for N2 O decomposition, especially the Au19 Pd cluster. Furthermore, the O2 desorption is no longer the main barrier to the reaction, which further enhances the catalytic activities of these two clusters for N2 O decomposition.