1. A First-Principles Study into the Properties and Activities of Rare-earth and Tranisition Metal
Materials in Envorimental Catalysis-Medical Journal
Automotive exhaust emission serves as one of the preliminary sources in air pollution. The
modern three-way catalyst can simultaneously convert the three primary pollutants CO,
hydrocarbons(HCs) and NOx into CO2, N2 and H2O. The catalyst generally contains the support,
washcoat and the active precious-metal component, in which washcoat is composed of ceria-based
oxygen storage material and alumina, while the used metals are usually the precious metal such as
Pt, Pd and Rh et al. Owing to the more stringent emission standards and demand for low-cost
catalyst, there are three key problems in the current catalyst:(i) identification of
composition-structure-activity relationship in ceria-based oxygen storage materials and design of
higher-performance oxygen storage material; (ii) removal of NOx under lean conditions; (iii) low
activity of the current catalyst in cold-start process. Aiming at these three problems, in this thesis
we carried out density functional theory to study the following issues at the atomic level. They are
(a) mechanism of function regulation in ceria-based oxides and transition metal-based catalyst
materials; (b) shedding light on the principles related to the catalyst screening for NO oxidation
which is the key reaction in NOX removal technique; (c) identification of structure-activity
relationship in low-temperature CO and HCs oxidation by some kinds of typical catalyst such as
gold and CO3O4 catalyst.Formation, Structures and diffusion mechanism of surface oxygen
vacancy in CeO2-based materials:(i) By carrying out density functional theory calculations, we
systematically studied single surface oxygen vacancy on CeO2(111). It is found surprisingly that
multiple configurations with the two excess electrons localized at different positions can exist. We
show that the origin of the multi-configurations of 4f electrons is a result of geometric relaxation
on the surface and strong localization characteristic of 4f electrons in ceria. (ii) As for the diffusion
of surface oxygen on CeO2(110) surface, we reported a new surface diffusion mechanism, i.e. the
two step exchange one, which gives a kinetic elucidation into excellent OSC of ceria. It was found
that the hopping mechanism, the most intuitive surface O vacancy diffusion mechanism, possesses
a high barrier (1.60 eV), while the diffusion barrier of the two step exchange mechanism is much
lower (0.61 eV) and expected to be favored. Based on this mechanism, we propose some doping
rules to further reduce the diffusion barrier of lattice oxygen in CeO2-based materials, (iii) The
interaction of NH3 with the CeGeO4(101) surface was studied, and it is found that under the
experimental temperature, the surface oxygen of CeGeO4(101) can oxidize NH3 to form NOx and
H2O accomplished by the formation of surface oxygen vacancies. Electronic analysis shows that
in the formation of surface oxygen vacancy, Ce3+and Ge2+ will be formed by receiving two left
electrons, and Ge4+shows more powerful capacity to receive electrons. When the temperature
achieves the boiling point of GeO, the formed Ge2+may be gasified in the form of GeO and give
rise to the further decomposition of GeGeO4 into CeO2 foam.Oxygen Storage/Release Capacity
of Ce1-xZrxO2:(i) The O vacancy formation energies of CexZr1-xO2 solid solutions with a series
of Ce/Zr ratios were calculated and analyzed. A model was proposed to understand the O vacancy
formation energies; it consists of electrostatic and structural relaxation terms. It is found that the
structural relaxation plays a vital role in affecting the O vacancy formation energies. (ii) Different
arrangement of Ce/Zr cations in CexZr1-xO2 with the same composition may give different OSC.
To pin down the key properties underlying the outstanding OSC ofκ-Ce2Zr2O8 at the atomic
level, first principles calculations were carried out, and it is found that inκ-Ce2Zr2O8 the

2. structural relaxation plays a key role in determining the O vacancy formation energy and it is
largely localized, forming an independent local relaxation unit consisting of the six nearest
neighbor OⅢions with a OⅡvacancy. To maximize both the local relaxation and the number of
local relaxation units plays a crucial role for the superb OSC ofκ-Ce2Zr2O8.NO oxidation
catalyzed by precious metals ans their oxides:(i) By combining DFT data and microkinetic
analysis, we studied activity trend of NO oxidation on the surfaces of metal Ru, Rh, Pd, Os, Ir and
Pt. Under typical experimental condition, the activity trend varies with the metal species as a
volcano curve, and the optimum catalyst in terms of oxygen chemisorption energy is located
between the Pt and Ir. Analysis shows that, first, the activity trend is in general determined by the
competition between the reaction barrier and the coverage of surface free sites (θ). Second, since
the dissociation of many important molecules, such as N2, O2 and CO, follows the same BEP
relationship,θis thus usually a decisive term that affects the overall activity. Third, an equation
was derived forθand its implications were discussed. (ii) Under realistic oxygen-excess condition,
metal could be oxidized to form oxides. We investigated NO oxidation on the platinum group
metal oxides (PtO2, IrO2, OSO2), aiming at shedding light on the activities of metal oxides and
exploring the activity variation of metal oxides compared to their corresponding metals. A
microkinetic model, taking into account the possible low diffusion of surface species on metal
oxide surfaces, is proposed for NO oxidation. The resultant turnover frequencies of NO oxidation
show that under the typical experimental condition:(a) IrO2(110) exhibits higher activity than
PtO2(110) and OsO2(110); and (b) compared to the corresponding metallic Pt, Ir and Os, the
activity of PtO2 to catalyze NO oxidation is lower, but interestingly IrO2 and OsO2 exhibits
higher activities. The reasons for these activity differences are addressed in the
thesis.Low-temperatue CO oxidation by thin Au-film and Co3O4:Gold and Co3O4 catalyst are
two currently best catalysts for low-temperature CO oxidation. With respect to gold catalyst, we
used density functional theory calculations to study structures and their activities of Au thin films
supported at anatase TiO2(101) and Au substrate. The results show that O2 can hardly adsorb at
flat and stepped Au thin films, even supported by fully-reduced TiO2(101) that can highly disperse
Au atoms and offer strong electronic promotion. Interestingly, in both oxide supported and pure
Au systems, wire-structured Au can adsorb both CO and O2 rather strongly, and kinetic analysis
suggests its high catalytic activity for low-temperature CO oxidation. A generalized structural
model based on the wire-structured film is proposed for active Au, and possible support effects are
discussed:Selected oxide surfaces can disperse Au atoms and stabilize the formation of film-like
structure; they may also serve as template for the preferential arrangement of Au atoms in wire
structure under low Au coverage.As for Co3O4 catalyst, through analyses of elementary reactions
of CO oxidation on its commonly exposed surfaces, i.e. (110)-A, (110)-B, (111) and (100), we
found the following regarding the relation between the activity and structure:(i) the active site
contains Co3+and surface lattice O3C coordinated with three Co3+; (ii) (110)-A is more active
compared to the three other surfaces; (ii) To understand the oxides in general, we extend the
investigation to other common oxides, i.e. MnO2(110), Fe3O4(110), CuO(110) and Cu(111), and
proposed three properties that largely determine actitvity; CO adsorption strength, the barrier of
CO reacting with lattice O and the redox capacity of oxide; (iv) H2O-induced formation of surface
OH and bicarbonate are two key contributors in deactivation. Finally, as an interesting issue,
namely that, contrary with the case of Co3O4, H2O is generally a promoter on late metal surfaces
for CO oxidation, we identified that the significant difference of potential energy surfaces between

3. OH on metal and metal oxides is identified to be the origin.Co3O4(110) is able to catalyze
ethylene combustion at 0℃. Toward this surprising result, based on the conclusion of the
low-termperatuer CO oxidation, we studied the inherent reaction mechanism and possible C-C
bond cleavage pathway. It was found that the common C-C bond cleavage pathways can not work
on Co3O4(110) at low temperature. Interestingly, C-C bond breakage could proceed by the
CHOCO species as a result of iterative dehydrogenation and oxidation processes. With respect to
the related principles, we made a brief elucidation in terms of the isolated Co3+coordination
configuration and bond saturation of C atom in the intermediates. Finally, the catalytic activity of
Co3O4(110) toward low temperature ethylene combustion could be rationalized in terms of its
binding ability toward CH2CH2 molecule, high reactivity and reasonable basicity of surface
lattice oxygen. This C-C bond cleavage strategy may enlighten the design of low-temperature
catalyst for hydrocarbons oxidation.
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