The First-princilpes Study On The Catalytic Properties Of The Ceria Namoparticle

Due to its enormous oxygen storage capacity, CeO₂is used as one of the important components of thethree-way catalyst （TWC） and has attracted popular attention worldwide. Though there are a lot of paperspublished on the catalytic properties of CeO₂bulk or surfaces, the catalytic ablity of the CeO₂cluster at thenanometer scale is still dimness, and the corresponding studies is fewer. In this paper, we will study thecatalytic properties of the CeO₂nanocluster by the Vienna Ab-initio Simulation Package （VASP） based onthe Density Functional Theory （DFT）. The periodic boundary condition is ensured by the three-dimensionalsupercell. The on-site strong correlation interaction of the Ce4f state is corrected by the LDA+U method.This work mainly includes the following three parts:（1） A representative cluster （Ce₄O₈） is chosen as the research model. The corresponding atomic andelectronic structures of the cluster with and without one oxygen vacancy （Ov） are studied. The formationenergy of an oxygen vacancy is calculated, and the calculated results show that: the oxygen vacancyformation on the Ce₄O₈cluster is easier than that on the CeO₂bulk or surfaces. The formation energy of anOvis reduced a lot, which is mainly attributed to the nano-effects and structural flexibility of the clusters.Compared with the bulk or surface, the cluster has more space to accommodate the larger Ce³⁺ion, whichcan explain the reason for the decrease of the formation energy of oxygen vacancies.（2） The adsorption and oxidation properties of CO on the Ce₄O₈cluster are studied. After the structuralrelaxation for the CO adsorption on different adsorption sites, three typical adsorption configurations arereached. By the atomic and electronic structure analysis, we found that the CO can be oxidized to CO₃species, or can be directly oxidized to CO₂gas molecules, which can detach from the cluster easily. Thislatter result has not been found on the CeO₂bulk or surfaces. In a word, the calculation results show that:the Ce₄O₈nanocluster has much improved catalytic properties as compared with the CeO₂bulk or surfaces,and may be used as an ideal catalyst.（3） The adsorption of a noble metal Pt atom on the Ce₄O₈cluster is further studied in order tounderstand the cooperative catalytic mechanism of noble metal with the nanoclusters. By a systemicconfiguration optimization, the final adsorption structures can be divided into three categories: single bond, double bond and multi-bond by the number of bonds formed between the Pt adatom and the Ce₄O₈clusterand the adsorption energy. It is found that i) only the configuration on the Ce atoms top, which correspondsto a single bond class, has a net total magnetic moment. All the other adsorption configurations arenonmagnetic; ii) the multi-bond class configurations are the most stable adsorption configurations, and thecorresponding adsorption energy of the Pt atom is bigger than that on CeO₂（111） surface, which meansthat there is stronger interaction between the Pt atom and the Ce₄O₈cluster. In this structure, the adsorptionof the Pt adatom alters the electronic structures of the Ce₄O₈cluster a lot. The Pt adatom lost an electronwhich is transfered to the Ce₄O₈cluster, resulting in one of the Ce ions in the cluster reduced from Ce4+toCe³⁺. Correspondingly, a new gap state is induced, which makes the cluster more active with strongerability to gain and lose electrons.These calculation results will help to further understand the characteristics of the CeO₂clusters in thenano-scale. The catalytic activity of ceria will be improved by cutting to the nanometer level or adsorbingnoble metal atoms on the nanoclusters. These results give an idea and provide a theoretical guidance forgetting better catalysts in practical application.