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Article

Carbon Monoxide and Propylene Catalytic Oxidation Activity of Noble Metals (M = Pt, Pd, Ag, and Au) Loaded on the Surface of Ce0.875Zr0.125O2 (110)

by
Chenxi Zhang
1,2,
Xuesong Cao
2,
Lili Guo
1,
Zhihao Fang
1,
Di Feng
1,* and
Xiaomin Sun
2
1
Shandong Provincial University Laborator for Protected Horticulture, Weifang University of Science and Technology, Weifang 262700, China
2
Environment Research Institute, Shandong University, Qingdao 266200, China
*
Author to whom correspondence should be addressed.
Catalysts 2023, 13(12), 1505; https://doi.org/10.3390/catal13121505
Submission received: 4 November 2023 / Revised: 29 November 2023 / Accepted: 4 December 2023 / Published: 11 December 2023
(This article belongs to the Section Computational Catalysis)
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Versions Notes

Abstract

:
With the advances in engine technology, the exhaust gas temperature of automobiles has further reduced, which in turn leads to an increase in the emissions of carbon monoxide (CO) and hydrocarbons (HCs). In order to understand the influence of CeO2-based catalysts loaded with different noble metals on the catalytic oxidation activity of CO and HCs, this study constructed catalyst models of Ce0.875Zr0.125O2 (100) surfaces loaded with Pt, Pd, Ag, and Au. The electronic density and state density structures of the catalysts were analyzed, and the reaction energy barriers for CO oxidation and C3H6 dehydrogenation oxidation on the catalyst surfaces were also calculated. Furthermore, the activity sequences of the catalysts were explored. The results revealed that after loading Pt, Pd, Ag, and Au atoms onto the catalyst surfaces, these noble metal atoms exhibited strong interactions with the catalyst surfaces, and electron transfer occurred between the noble metal atoms and the catalyst surfaces. Loading with noble metals can enhance the catalytic activity of CO oxidation, but it has little effect on the dehydrogenation oxidation of C3H6. Of the different noble metals, loading with Pd exhibits the best catalytic activity for both CO and C3H6 oxidation. This study elucidated the influence of noble metal doping on the catalytic activity of catalysts at the molecular level, providing theoretical guidance for the design of a new generation of green and efficient catalysts.

Graphical Abstract

1. Introduction

In recent years, with the increasingly stringent automotive exhaust emission standards worldwide, higher requirements have been put forward for improving fuel efficiency and reducing exhaust emissions [1,2]. In order to improve fuel efficiency, low-temperature combustion (LTC) and cold start technologies have been adopted, which reduce the emissions of NOx and particulate matter (PM) due to the decrease in exhaust temperature, but increase the emissions of CO and hydrocarbons (HCs) [3,4]. Therefore, finding appropriate catalysts and improving the efficiency of CO and HC elimination is an important task.
Cerium oxide (CeO2) has been widely used in the oxidation reactions of CO and HC due to its unique redox properties [5,6]. The state of Ce can easily shuttle between Ce3+ and Ce4+, which gives CeO2 excellent oxygen-storage capacity (OSC) and a large number of surface oxygen vacancies [7,8]. To improve the thermal stability and low-temperature redox performance of CeO2, it is often doped with zirconium dioxide (ZrO2) to form a Ce-Zr mixed oxide, namely a CexZr1−xO2 solid solution [9,10,11]. Compared with pure CeO2 catalysts, the thermal stability and oxygen-storage performance of CexZr1−xO2 solid solutions have been greatly improved.
Studies have shown that the addition of noble metals can improve the activities of CeO2 and CexZr1−xO2 solid solutions in oxidation reactions [12]. Ag can enhance the OSC of CeO2, which supports the oxidation ability of CeO2 [13]. Dou et al. prepared a series of Ag/CeO2 catalysts using incipient wetness impregnation for C3H6 oxidation experiments [14]. Their results show that the participation of Ag-CeO2 reduces the ignition temperature of C3H6 by more than 50 °C and increases the conversion rate by 36.1%. A single Au atom on the CeO2 (110) surface promotes the oxidation of CO by the surface O atoms of CeO2 [15]. Pt/CeO2 can enhance the catalytic activity and stability of particulate matter oxidation [16]. Li et al. successfully synthesized a Pt@CeO2x/ZrO2 catalyst, which exhibited excellent catalytic activity for soot combustion [17]. Pd-CeO2 catalyst is a good cold start catalyst, showing lower ignition temperatures during CO and light HC ignition [18,19]. Shen et al. prepared Pd/CeO2 catalysts with different Pd loading ratios and found that the oxidation performance of CO and C3H6 improved with increasing Pd loading [2]. Yoo et al. examined the effects of the Pd precursor on the activities and properties of Pd/CeO2 catalysts, concluding that highly dispersed Pd can promote the CO oxidation reaction [20]. However, the relationship between catalytic oxidation activity and different noble metals is still unclear, and there are no reports in the literature on the activity sequences of various noble metals loaded onto CeO2.
In recent years, using theoretical calculation methods to study the properties of catalysts and to explain experimental phenomena has become a popular technical means [21,22,23,24,25]. Although experiments have used advanced instruments, such as scanning transmission electron microscopy (STEM), X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), and Fourier transform infrared (FTIR) spectroscopy, they still have not been able to clearly explain the electronic structure of catalysts [26]. By applying density functional theory (DFT) calculations, the precise structure of noble metal single atoms anchored on the surfaces of CeO2-based catalysts can be obtained. By calculating the potential barriers of catalytic oxidation reactions, the activity sequences of catalysts can be obtained more intuitively.
The aim of the present study is to understand the CO and HC catalytic oxidation activity of different noble metals (M = Pt, Pd, Ag, and Au) on CeO2-based catalysts for oxidation reactions. For this purpose, surface models of Pt, Pd, Ag, and Au supported by Ce0.875Zr0.125O2, which showed the most promising surface lattice oxygen release activity of all CexZr1−xO2 solid solutions, were constructed [27]. Then, the electron density and density of states (DOS) structures of the catalysts were analyzed to understand the electronic structure characteristics of the noble-metal-doped catalysts. The reaction energy barriers for the catalytic oxidation of CO and C3H6, a typical HC in gasoline vehicle exhaust, were calculated to explore the activity sequences of the catalysts. This elucidated the influence of the structural characteristics of the catalysts on their catalytic activity at the molecular level, which has theoretical guiding significance for the design of a new generation of green and efficient catalysts.

2. Results and Discussion

For CeO2-supported catalysts, the (110) surface is catalytically more active than the (111) and (100) surfaces and it is often chosen to study the reaction mechanism [27,28]. Thus, the Ce0.875Zr0.125O2 (110) surface was selected to further investigate the catalytic activity of catalysts loaded with noble metals (M = Pt, Pd, Ag, and Au).
The surfaces of Ce0.875Zr0.125O2 (110) loaded with Pt, Pd, Ag, and Au atom catalysts are shown in Figure 1. The Pt, Pd, Ag, and Au single atoms are adsorbed onto the double O-bridge sites of the Ce0.875Zr0.125O2 (110) surface, which has been proven to have the lowest adsorption energy [28,29]. The surface models of Pt1/Ce0.875Zr0.125O2 (110), Pd1/Ce0.875Zr0.125O2 (110), Ag1/Ce0.875Zr0.125O2 (110), and Au1/Ce0.875Zr0.125O2 (110) all consist of four atomic layers, with the bottom two layers of atoms fixed and the top two layers of atoms and the adsorbed Pt, Pd, Ag, and Au single atoms unfixed. The thickness of the vacuum layer in the models is 15 Å, to eliminate the interactions between the lattice and the lattice in the z direction.

2.1. Structural Characteristics of the Catalysts

The structures and binding energies of the (Pt, Pd, Ag, and Au)1/Ce0.875Zr0.125O2 catalysts were analyzed. As shown in Figure 1, on the Pt1/Ce0.875Zr0.125O2 surface, the distances between the Pt atom and the surface O, Ce, and Zr atoms are 2.12, 2.89, and 3.01 Å, respectively. The Pt atom is anchored at the quadruple O vacancies on the Ce0.875Zr0.125O2 (110) surface. Figure 2a,b show the electron density of the Pt1/Ce0.875Zr0.125O2 surface. The electron orbitals of Pt overlap with those of the Ce0.875Zr0.125O2 (110) surface, indicating that the Pt atoms are tightly bound to the Ce0.875Zr0.125O2 (110) surface through chemical adsorption. The large binding energies of the Pt atoms on the Ce0.875Zr0.125O2 (110) surface (−4.16 eV) also indicate that Pt can be stably adsorbed on the (110) surface of Ce0.875Zr0.125O2. In addition, as shown in Table 1, the Mulliken charge of the Pt atom on the surface of Pt1/Ce0.875Zr0.125O2 is 0.14 e, indicating a transfer of 0.14 e from the Pt atom to the surface. The same method was used to analyze the surface of Pd1/Ce0.875Zr0.125O2 (Figure 1 and Figure 2c,d). The bond length between Pd and the surface O is 2.13 Å, while the Pd–Ce and Pd–Zr distances are 2.91 and 2.98 Å, respectively, which are similar to the structure of Pt1/Ce0.875Zr0.125O2. The binding energy between Pd and the surface is −3.07 eV, and the electron densities of the Pd and surface atoms also overlap with each other, with 0.21 e of the Mulliken charge of Pd transferred to the surface. The binding energy between Ag atoms and the Ce0.875Zr0.125O2 (110) surface is −1.77 eV, which is lower than the adsorption energies of Pt and Pd atoms. Additionally, the distances between the Ag and surface O, Ce, and Zr atoms are relatively large: 2.52, 3.09, and 3.05 Å, respectively. The electron density map of the Ag1/Ce0.875Zr0.125O2 (110) surface indicates that orbital overlap is still present between the Ag atoms and the surface, with the Ag atoms transferring a large number of electrons (0.25 e) to the surface. The geometric model of the Au1/Ce0.875Zr0.125O2 (110) surface is shown in Figure 1. The adsorption of Au leads to the lifting of the O atoms connected to the Ce and Zr atoms. The distances between the Au and surface O, Ce, and Zr atoms are 2.10, 3.12, and 3.12 Å, respectively, and the binding energy between Au and the surface is also low (−1.99 eV). Orbital overlap is also found between the electron density of Au atoms and the electron density of the surface, as the binding energy is approximately −2.00 eV, indicating strong chemical adsorption, although this value is lower than those of Pt and Pd.
In general, the results indicate that the Pt, Pd, Ag, and Au atoms all have strong interactions with the surface, and electron transfer takes place between them and the surface. The binding energies of Pt and Pd atoms are higher than those of Ag and Au atoms. Further calculations were conducted of the density of states of the M (Pt, Pd, Ag, and Au)1/Ce0.875Zr0.125O2 (110) surfaces, and the results are shown in Figure 3. As shown in Figure 3, no apparent change occurs after the adsorption of all the orbitals, indicating that the Ce0.875Zr0.125O2 (110) surface can remain stable after noble metal adsorption. In addition, compared with the Ce0.875Zr0.125O2 (110) surface, all the orbitals of the M/Ce0.875Zr0.125O2 (110) surfaces shift toward lower energy levels after noble metal loading, indicating the formation of a more stable configuration. Among them, orbital movement after Pd adsorption is the most significant.
The Pd1/Ce0.875Zr0.125O2, Ag1/Ce0.875Zr0.125O2, and Au1/Ce0.875Zr0.125O2 surfaces exhibit the same trend.

2.2. Oxidation of C3H6 Catalyzed by M/Ce0.875Zr0.125O2 Catalysts

As a common hydrocarbon (HC) in automotive exhaust emissions, propylene (C3H6) is often used as a typical gas molecule to investigate the activity of three-way catalysts and is also a gas that needs to be eliminated from automotive exhaust emissions. The exploration of the oxidation reaction of C3H6 on the M (Pt, Pd, Ag, and Au)1/Ce0.875Zr0.125O2 (100) surfaces can elucidate the C3H6 oxidation activity of CeO2-supported catalysts and identify the most suitable catalyst for eliminating HCs.
The complete catalytic oxidation of C3H6 proceeds via a complex reaction process. The first C–H bond activation step always initiates the entire process and is generally thought of as a crucial step in C3H6 oxidation [30]. Two different C–H bonds, namely the Csp3–H bond and Csp2–H bond, are considered as active sites for oxidation reactions. Among them, the activation of the Csp3–H bond has been proven to be a favorable pathway [30]. This is also consistent with the study of Yang et al., who found that propene is adsorbed onto Pt (111) with the C atoms sp3-hybridized [31]. Therefore, this study utilized the Csp3–H bond cleavage of C3H6 molecules on the M/Ce0.875Zr0.125O2 surface catalyst as a probe reaction to investigate the effect of noble metal doping on the oxidation activity of C3H6 at the molecular level. Figure 4 illustrates the reaction mechanism of the oxidation of C3H6 by Pt1/Ce0.875Zr0.125O2. Firstly, C3H6 tends to adsorb onto surface lattice O atoms with higher Eads values [30]. There are two types of surface lattice O atoms on the (110) surface of Pt1/Ce0.875Zr0.125O2: lattice O (OA) connected to two Ce atoms, and lattice O (OB) connected to one Ce and one Zr atom. The activities of OA and OB in the oxidation of C3H6 are different. The adsorption energy of the H atoms of the C3H6 methyl group at OA sites is −0.77 eV, and the H–OA bond length is 2.82 Å. Subsequently, the Csp3–H bonds of C3H6 break, and the H atoms move toward OA. In TS-1, the H–OA bond length is 1.30 Å, and the Csp3–H bond length increases from the original 1.11 Å to 1.54 Å. Finally, CH2=CHCH2* and a surface hydroxyl group (–OAH) are formed. The energy barrier and enthalpy of the reaction are 1.19 and 0.94 eV, respectively. It is worth noting that the ΔE of C3H6 dehydrogenation oxidation is positive and the process requires additional energy, which is not favorable in terms of thermodynamics. The oxidation reaction of C3H6 follows the same steps at the OB sites, where the adsorption energy of C3H6 is −0.78 eV, slightly lower than that at the OA sites. In addition, Valcárcel et al. studied the adsorption of propene on Pt (111) surfaces using both slab and cluster models and density functional theory methods; the predicted binding energy of C3H6 on Pt (111) ranges from −0.9 to −0.10 eV [32]. This indicates that it becomes easier to adsorb C3H6 after Pt loading of the Ce0.875Zr0.125O2 (110) surface. The Ea and ΔE of the reaction are 0.81 and 0.68 eV, respectively. The energy barrier is lower than that at the OA sites, indicating that the oxidation of C3H6 is more likely to occur at the OB sites of the Pt1/Ce0.875Zr0.125O2 (110) surface.
The reaction path of C3H6 oxidation on the Pd1/Ce0.875Zr0.125O2 (110) surface is similar to that on the Pt1/Ce0.875Zr0.125O2 (110) surface. As shown in Figure S1, the adsorption energies of C3H6 at the OA (C3H6 ads-3) and OB (C3H6 ads-4) sites on the Pd1/Ce0.875Zr0.125O2 (110) surface are −0.76 and −0.58 eV, respectively. The H–OA and H–OB bond lengths are 2.68 and 2.93 Å, respectively. The energy barriers that need to be overcome in the dehydrogenation oxidation reaction are 1.03 eV (TS-3) and 0.49 eV (TS-4), and the reaction energies are 0.87 and 0.44 eV, respectively. The reaction energy barrier for extracting H from the OB sites is significantly lower than that from the OA sites.
The mechanisms of the oxidation reaction of C3H6 molecules on the Ag1/Ce0.875Zr0.125O2 (110) and Au1/Ce0.875Zr0.125O2 (110) surfaces were also calculated and are shown in Figures S2 and S3, respectively. The reaction energy barriers for the OA and OB oxidation of C3H6 on the (110) surface of Ag1/Ce0.875Zr0.125O2 are 1.19 eV (TS-5) and 0.87 eV (TS-6), respectively. The reaction energy barriers for the OA and OB oxidation of C3H6 on the (110) surface of Au1/Ce0.875Zr0.125O2 are 1.50 eV (TS-7) and 0.89 eV (TS-8), respectively. A comparison of these values shows that, on the same catalyst surface, the reaction energy barrier at OB sites is lower than that at OA sites, indicating that the catalytic activity of OB sites in the oxidative dehydrogenation of C3H6 is higher than that of OA sites. The energy barrier for the oxidation of C3H6 at the OB sites of the Pd1/Ce0.875Zr0.125O2 (110) surface is the lowest (0.49 eV), indicating the highest catalytic activity for the oxidation of C3H6, which makes it the optimal catalyst surface. The activity of (Pt, Pd, Ag, and Au)1/Ce0.875Zr0.125O2 in the oxidation of C3H6 decreases in the order Pd > Ag > Au > Pt.
However, compared with the calculated energy barrier (0.45 eV) for C3H6 oxidation on the Ce0.875Zr0.125O2 (110) surface discussed in the previous section, the addition of noble metals does not reduce the energy barrier for the C3H6 dehydrogenation oxidation reaction [30]. This indicates that the addition of Pt, Pd, Ag, and Au single atoms does not enhance the activity of Ce0.875Zr0.125O2 in the oxidation of C3H6.

2.3. CO Oxidation Catalyzed by M/Ce0.875Zr0.125O2 Catalysts

There is a general consensus on the detailed mechanism of CO oxidation on the surface of CeO2, termed the Mars–van Krevelen (MvK) mechanism [5,33]. CO extracts a surface lattice O from the CeO2 surface to form CO2, which results in the creation of oxygen vacancies (OV), which is then supplemented with gas-phase O2 to complete the catalytic cycle.
This study employed the reaction of CO-capturing surface lattice OA, which has been proven to be the optimal site, as a probe reaction to investigate the catalytic activity of different noble metals on Ce0.875Zr0.125O2 catalysts for CO oxidation [27]. Figure 5 and Figure S4 show the energy barrier diagrams and structural models of the corresponding reactants, transition states, and products for the oxidation of CO on the surfaces of Pt1/Ce0.875Zr0.125O2, Pd1/Ce0.875Zr0.125O2, Ag1/Ce0.875Zr0.125O2, and Au1/Ce0.875Zr0.125O2. CO is adsorbed at the OA sites of the Pt1/Ce0.875Zr0.125O2 (110) surface, with a CO–OA distance of 2.83 Å and an adsorption energy of −0.44 eV. Subsequently, CO migrates toward OA, resulting in the CO−OA distance of TS-9 being shortened to 1.49 Å, with a C–O–OA angle of 120°. Finally, CO extracts the surface lattice oxygen according to the MvK mechanism, generating CO2 and surface OV. The activation energy barrier of the pathway is 0.71 eV and the reaction enthalpy is −0.37 eV.
The adsorption energy of CO at the OA sites of the Pd1/Ce0.875Zr0.125O2 (110) surface is −0.44 eV, and the distance between the O atom of the CO group and the surface OA lattice atoms is 2.93 Å. Subsequently, CO extracts the OA atom, and the O–OA distance is shortened to 1.24 Å (TS-10); the Pd–OA distance increases from 2.12 to 2.60 Å (TS-10), ultimately generating a Pd1/Ce0.875Zr0.125O2 defective surface containing an oxygen vacancy and CO2. The activation energy barrier that needs to be overcome in this process is 0.49 eV and the reaction enthalpy is −0.50 eV. The adsorption energy of CO on the Ag1/Ce0.875Zr0.125O2 surface is −0.40 eV; the reaction has an energy barrier of 1.05 eV (TS-11) and releases 0.63 eV of heat. The adsorption energy of CO on the surface of Au1/Ce0.875Zr0.125O2 is −0.43 eV; the reaction energy barrier and enthalpy are 0.64 eV (TS-12) and −0.50 eV, respectively.
The comparison of the reaction energy barriers for CO oxidation on the M/Ce0.875Zr0.125O2 (100) surfaces shows that the surface of Pd1/Ce0.875Zr0.125O2 (100) has the lowest energy barrier for activating CO (0.49 eV), which is considerably lower than the experimental (1.8–2.1 eV) and theoretical values (1.7–1.8 eV) for CO oxidation on CeO2 surface [34,35]. It is also lower than the reaction energy barrier (0.90 eV) for CO oxidation on the Ce0.875Zr0.125O2 (110) surface and CO oxidation on the Pd1/CeO2 (110) surface (0.95 eV) [27,36]. Therefore, the addition of Pt, Pd, Ag, and Au single atoms leads to an increase in catalytic activity for CO oxidation, with the Pd1/Ce0.875Zr0.125O2 surface having the highest level of activity.

3. Computational Methods and Parameter Settings

The DMol3 module of the Materials Studio software package was used to optimize the structure of all single-atom models [37,38]. The GGA–PBE exchange-correlation functional and the DND basis set were adopted in the calculations [39]. Ce (4f1, 5s2, 5p6, 5d1, and 6s2) and Zr (4s2, 4p6, 4d2, and 5s2) electrons were treated as valence electrons using the effective core potential (ECP) method, while O, C, and N atoms were treated using the all-electron method to increase the calculation speed [40]. SCF and Fermi smoothing were set to 1 × 10−5 and 0.005 Ha, respectively, to accelerate the convergence. The orbital cutoff radius and k-point precision were set to 5.0 Å and (1 × 2 × 1), respectively. The convergence thresholds for the energy, maximum force, and maximum displacement were 2 × 10−5 Ha, 0.004 Ha/Å, and 0.005 Å, respectively.
To properly account for the band structure of CeO2, Hubbard U corrections were applied to f electrons in some calculations [41,42]; however, previous research studies have indicated that plain DFT calculations could provide reasonable predictions of reduction energies, even better than those using DFT + U [35,43]. To ascertain the importance of the U parameter, we calculated the oxygen vacancy formation energies on the Ce0.875Zr0.125O2 (110) surface when U = 5 eV and without incorporating U. The results show that the vacancy formation energy without incorporating U (10.88 kcal mol−1) is within 1% of that when U = 5 eV (10.98 kcal mol−1). Hence, the DFT + U method is not considered in this work.
The calculation formula for the adsorption energy (Eads) of the catalyst surfaces is as follows:
Eads = Esubstrate+adsorbate − Esubstrate − Eadsorbate
where Esubstrate+adsorbate is the total energy of the molecule or atom adsorbed on the catalyst surface; Esubstrate is the energy of the catalyst surface; and Eadsorbate is the optimized energy of the molecule or atom. A more negative value of Eads indicates a stronger binding between the noble metal atom and the catalyst surface. The transition state (TS) of the reaction is found using the LST/QST method, and the rationality of the TS is verified by calculating the imaginary frequency of the structure [44].
The calculation formulas for reaction heat (ΔE) and reaction barrier (Ea) are as follows:
ΔE = EFS − EIS
Ea = ETS − EIS
where EIS is the total energy of the reactant (IS); ETS is the energy of the transition state (TS); and EFS is the total energy of the product (FS).

4. Conclusions

Based on DFT calculations, this work developed a structural model of the (110) surfaces of M/Ce0.875Zr0.125O2 catalysts and systematically determined the structural characteristics of the (Pt, Pd, Ag, and Au)1/Ce0.875Zr0.125O2 (110) surfaces as well as their catalytic activities for C3H6 oxidation and CO oxidation. This study provides a better understanding of the CO and C3H6 catalytic activity of different noble metals loaded onto CeO2-based catalysts for the purification of automotive exhaust emissions. Based on the results of the DFT calculations, the following conclusions can be drawn:
  • Pt, Pd, Ag, and Au atoms can stably bind to the (110) surface of Ce0.875Zr0.125O2. Electron density overlaps and electron-transfer effects are observed between single atoms and the surface, indicating a strong degree of interaction;
  • The activity of (Pt, Pd, Ag, and Au)1/Ce0.875Zr0.125O2 in the oxidation of C3H6 decreases in the order Pd > Ag > Au > Pt. Moreover, the activity of surface OB sites in the oxidative dehydrogenation of C3H6 is higher than that of OA sites. Compared with the energy barrier for the oxidation of C3H6 on the (110) surface of Ce0.875Zr0.125O2 (0.45 eV), the addition of noble metals does not reduce the reaction energy barrier for C3H6 dehydrogenation oxidation;
  • The catalytic activity of (Pt, Pd, Ag, and Au)1/Ce0.875Zr0.125O2 in the oxidation of CO decreases in the order Pd > Au > Pt > Ag. The (110) surface of Pd1/Ce0.875Zr0.125O2 has the lowest energy barrier (0.49 eV) in the activation of CO, and the loading of single-atom Pt, Pd, Ag, and Au can increase the activity of Ce0.875Zr0.125O2 during CO oxidation.

Supplementary Materials

The following are available online at: https://www.mdpi.com/article/10.3390/catal13121505/s1, Figure S1: Calculated energy profile and corresponding optimized configurations of reactants, transition states, and products of the activation of the Csp3–H bond of C3H6 on the Pt1/Ce0.875Zr0.125O2 (110) surface; Figure S2: calculated energy profile and corresponding optimized configurations of reactants, transition states, and products of the activation of the Csp3–H bond of C3H6 on theAg1/Ce0.875Zr0.125O2 (110) surface; Figure S3: calculated energy profile and corresponding optimized configurations of reactants, transition states, and products of the activation of the Csp3–H bond of C3H6 on the Au1/Ce0.875Zr0.125O2 (110) surface; Figure S4: the reactants, transition states, and products of the CO oxidation reaction on the Pt1/Ce0.875Zr0.125O2, Pd1/Ce0.875Zr0.125O2, Ag1/Ce0.875Zr0.125O2, and Au1/Ce0.875Zr0.125O2 (110) surfaces.

Author Contributions

Conceptualization, C.Z. and D.F.; data curation, X.C.; formal analysis, L.G.; funding acquisition, C.Z.; investigation, C.Z.; software, X.C. and Z.F.; supervision, D.F.; validation, C.Z. and X.S.; visualization, C.Z. and X.C.; writing—original draft, C.Z. and X.C.; writing—review and editing, D.F. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China, grant number 21607011, and the Key Research and Development Project of Shandong Province, grant number 2019GSF109021. The APC was funded by the Fundamental Research Funds of Weifang University of Science and Technology, grant number KJRC2022013.

Data Availability Statement

Data are contained within the article and supplementary materials.

Conflicts of Interest

The authors declare no conflict of interest.

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Catalysts 13 01505 g001
Figure 1. Optimized structure models of Pt1/Ce0.875Zr0.125O2, Pd1/Ce0.875Zr0.125O2, Ag1/Ce0.875Zr0.125O2, and Au1/Ce0.875Zr0.125O2 (110) surfaces.
Figure 1. Optimized structure models of Pt1/Ce0.875Zr0.125O2, Pd1/Ce0.875Zr0.125O2, Ag1/Ce0.875Zr0.125O2, and Au1/Ce0.875Zr0.125O2 (110) surfaces.
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Figure 2. (a) Three-dimensional view of deformation electron density and (b) two-dimensional view of deformation electron density of the Pt1/Ce0.875Zr0.125O2 (110) surface. (c) Three-dimensional view of deformation electron density and (d) two-dimensional view of deformation electron density of the Pd1/Ce0.875Zr0.125O2 (110) surface. (e) Three-dimensional view of deformation electron density and (f) two-dimensional view of deformation electron density of the Ag1/Ce0.875Zr0.125O2 (110) surface. (g) Three-dimensional view of deformation electron density and (h) two-dimensional view of deformation electron density of the Au1/Ce0.875Zr0.125O2 (110) surface.
Figure 2. (a) Three-dimensional view of deformation electron density and (b) two-dimensional view of deformation electron density of the Pt1/Ce0.875Zr0.125O2 (110) surface. (c) Three-dimensional view of deformation electron density and (d) two-dimensional view of deformation electron density of the Pd1/Ce0.875Zr0.125O2 (110) surface. (e) Three-dimensional view of deformation electron density and (f) two-dimensional view of deformation electron density of the Ag1/Ce0.875Zr0.125O2 (110) surface. (g) Three-dimensional view of deformation electron density and (h) two-dimensional view of deformation electron density of the Au1/Ce0.875Zr0.125O2 (110) surface.
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Catalysts 13 01505 g003
Figure 3. Total density of states and partial density of states of (a) Pt1/Ce0.875Zr0.125O2, (b) Pd1/Ce0.875Zr0.125O2, (c) Ag1/Ce0.875Zr0.125O2, and (d) Au1/Ce0.875Zr0.125O2 (110) surfaces compared with that of the clean (110) surfaces and the electron states of the free metal atoms.
Figure 3. Total density of states and partial density of states of (a) Pt1/Ce0.875Zr0.125O2, (b) Pd1/Ce0.875Zr0.125O2, (c) Ag1/Ce0.875Zr0.125O2, and (d) Au1/Ce0.875Zr0.125O2 (110) surfaces compared with that of the clean (110) surfaces and the electron states of the free metal atoms.
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Figure 4. Calculated energy profile and corresponding optimized configurations of reactants, transition states (TS), and products (FS) of the activation of the Csp3–H bond of C3H6 on the Pt1/Ce0.875Zr0.125O2 (110) surface.
Figure 4. Calculated energy profile and corresponding optimized configurations of reactants, transition states (TS), and products (FS) of the activation of the Csp3–H bond of C3H6 on the Pt1/Ce0.875Zr0.125O2 (110) surface.
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Catalysts 13 01505 g005
Figure 5. Calculated energy profiles of the CO oxidation reaction on the Pt1/Ce0.875Zr0.125O2, Pd1/Ce0.875Zr0.125O2, Ag1/Ce0.875Zr0.125O2, and Au1/Ce0.875Zr0.125O2 (110) surfaces.
Figure 5. Calculated energy profiles of the CO oxidation reaction on the Pt1/Ce0.875Zr0.125O2, Pd1/Ce0.875Zr0.125O2, Ag1/Ce0.875Zr0.125O2, and Au1/Ce0.875Zr0.125O2 (110) surfaces.
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Table 1. Binding energy and Mulliken charge of M (Pt, Pd, Ag, and Au) on the Ce0.875Zr0.125O2 (110) surface.
Table 1. Binding energy and Mulliken charge of M (Pt, Pd, Ag, and Au) on the Ce0.875Zr0.125O2 (110) surface.
Noble MetalEads (eV)Mulliken (e)
Pt−4.160.14
Pd−3.070.21
Ag−1.770.25
Au−1.990.02
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Zhang, C.; Cao, X.; Guo, L.; Fang, Z.; Feng, D.; Sun, X. Carbon Monoxide and Propylene Catalytic Oxidation Activity of Noble Metals (M = Pt, Pd, Ag, and Au) Loaded on the Surface of Ce0.875Zr0.125O2 (110). Catalysts 2023, 13, 1505. https://doi.org/10.3390/catal13121505

AMA Style

Zhang C, Cao X, Guo L, Fang Z, Feng D, Sun X. Carbon Monoxide and Propylene Catalytic Oxidation Activity of Noble Metals (M = Pt, Pd, Ag, and Au) Loaded on the Surface of Ce0.875Zr0.125O2 (110). Catalysts. 2023; 13(12):1505. https://doi.org/10.3390/catal13121505

Chicago/Turabian Style

Zhang, Chenxi, Xuesong Cao, Lili Guo, Zhihao Fang, Di Feng, and Xiaomin Sun. 2023. "Carbon Monoxide and Propylene Catalytic Oxidation Activity of Noble Metals (M = Pt, Pd, Ag, and Au) Loaded on the Surface of Ce0.875Zr0.125O2 (110)" Catalysts 13, no. 12: 1505. https://doi.org/10.3390/catal13121505

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