Next Article in Journal
Hydraulic Characterization of Variable-Speed Pump Turbine under Typical Pumping Modes
Next Article in Special Issue
The Influence of Metal–Support Interactions on the Performance of Ni-MoS2/Al2O3 Catalysts for Dibenzothiophene Hydrodesulfurization
Previous Article in Journal
Performance Evaluation and MOORA Based Optimization of Pulse Width Control on Leather Specimens in Diode Laser Beam Cutting Process
Previous Article in Special Issue
Enhanced Activation of Peroxymonosulfate via Sulfate Radicals and Singlet Oxygen by SrCoxMn1−xO3 Perovskites for the Degradation of Rhodamine B
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Processes
Volume 11
Issue 10
10.3390/pr11102902
processes-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

The Preparation of Mn-Modified CeO2 Nanosphere Catalysts and Their Catalytic Performance for Soot Combustion

by
Siyu Gao
1,
Di Yu
2,
Shengran Zhou
1,
Chunlei Zhang
1,
Lanyi Wang
2,
Xiaoqiang Fan
1,
Xuehua Yu
1,* and
Zhen Zhao
1,2,*
1
Institute of Catalysis for Energy and Environment, College of Chemistry and Chemical Engineering, Shenyang Normal University, 253# Huanghe North Street, Huanggu District, Shenyang 110034, China
2
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, 18#Fuxue Road, Chang Ping, Beijing 102249, China
*
Authors to whom correspondence should be addressed.
Processes 2023, 11(10), 2902; https://doi.org/10.3390/pr11102902
Submission received: 28 August 2023 / Revised: 25 September 2023 / Accepted: 28 September 2023 / Published: 2 October 2023
(This article belongs to the Special Issue Metal-Support Interactions in Heterogeneous Catalysis)
Browse Figures
Versions Notes

Abstract

:
With the increasing stringency of environmental protection regulations, reducing the severe pollution caused by soot particles from diesel vehicle exhaust has become a widespread concern. Catalytic purification technology is currently an efficient method for eliminating soot particles, which needs to develop high-activity catalysts. This work uses a two-step hydrothermal method to synthesize MnOx/CeO2 nanosphere catalysts, which have synergistic effects between manganese and cerium, and have high reactive oxygen species. Among them, the MnCe-1:4 catalyst represents the optimal catalytic activity, and the values of T10, T50, and T90 are 289, 340, and 373 °C, respectively. On account of their simple synthetic procedure and low cost, the prepared MnOx/CeO2 nanosphere catalysts have good prospects for practical applications.

1. Introduction

Diesel engines have durability and environmental friendliness [1,2]. However, the soot particles discharged by diesel engines are the main cause of hazy weather and lead to severe environmental pollution. Soot particles can also adsorb other harmful substances and cause serious harm to humans [3]. Therefore, reducing or eliminating the soot particles discharged by diesel engines is crucial. The use of diesel particulate filters (DPFs) for aftertreatment technology is an effective method for controlling soot emission, which requires the development of highly active catalysts to ensure the periodic regeneration of the DPF [4,5].
Noble metal catalysts display high activity for soot combustion and are extensively used as three-way catalysts [6,7]. However, the expensive price of noble metal catalysts has limited their broader application [8,9]. Researchers have developed various catalysts for catalytic soot combustion. Alkali metal catalysts feature a high surface fluidity, however, the low melting and boiling points of alkali metals can lead to their loss at high temperatures [10]. Transition metal catalysts have lower prices, but their catalytic activity is not ideal and is also prone to poisoning [11]. Rare-earth metal catalysts have a good poisoning resistance, high melting and boiling points, and a high economic value. CeO2 has shown an excellent catalytic performance because it has the capacity for converting between the +3 and +4 valence of cerium, which can produce more active oxygen species [12,13,14,15]. Huang et al. [16] prepared nano-CeO2 catalysts via a precipitation method and evaluated their catalytic activity. The ignition temperature of the soot oxidation reaction was 348 °C. Pure CeO2 exhibits high activity in soot combustion, but its thermal stability is poor. High-temperature calcination will cause the sintering of CeO2, reducing its catalytic activity. In this regard, introducing other metals into CeO2 can improve this shortcoming [17,18,19,20].
Manganese has an outstanding redox ability, and its incorporation into CeO2 can enhance the activity of catalysts [21,22,23]. Lin et al. [24]. synthesized a MnOx–CeO2 catalyst and concluded that entering manganese into CeO2 is beneficial for forming oxygen vacancies. Wang et al. [25] hydrothermally synthesized a MnxCe1−xO2 solid solution catalyst, which had a unique mesoporous nanosheet structure and abundant active oxygen species.
The contact of the catalyst and soot particle also affects its activity [26]. Zhang et al. [27] synthesized CeO2 with nanorod, nanoparticle, and nanosheet morphologies via hydrothermal and solvothermal methods. Among them, the CeO2 nanorods exhibited the lowest peak temperatures of soot combustion, at approximately 368 °C, under tight contact modes. Therefore, designing and synthesizing cerium-based oxide catalysts with preferred morphologies could improve their contact efficiency with soot particles, thereby reducing the soot combustion temperature and improving the catalytic performance [28,29,30].
In this work, we first synthesized a range of MnOx/CeO2 nanosphere catalysts, analyzed the physical and chemical properties of the MnOx/CeO2 nanosphere catalysts using various characterization techniques, and ultimately evaluated their activity for soot combustion.

2. Experimental Section

2.1. Catalyst Preparation

2.1.1. Preparation of CeO2 Nanospheres

Some improvements were made to the previously reported preparation methods of CeO2 nanospheres [31]. Ce(NO3)3·6H2O (2.5 g) and polyethylene pyrrolidone (1 g, K90) were added into a mixture solution of deionized water (10 mL) and ethylene glycol (70 mL), and the mixture was stirred until the solution became transparent. The solution was transferred to a 150 mL stainless steel autoclave and reacted at 160 °C for 24 h. After cooling, the product was centrifugally washed multiple times using anhydrous ethanol and deionized water until the upper solution was colorless. The products were dried at 80 °C for 12 h and then calcined at 500 °C for 3 h (2 °C/min).

2.1.2. Preparation of MnOx/CeO2 Nanosphere Catalysts

First, the CeO2 nanospheres (0.6 g) and a certain amount of Mn(NO3)2 (50% solution) in Mn/Ce molar ratios of 1:16, 1:8, 1:4, 1:2, and 1:1 were added to deionized water (55 mL) and ultrasonically treated for 15 min. Next, 1 mol/L of NaOH solution was dropwise added into the solution to adjust it to pH 10 under continuous stirring. The solution was transferred to a 100 mL stainless steel autoclave and reacted at 120 °C for 24 h after stirring for two hours. After cooling, the product was centrifugally washed multiple times. The products were dried at 80 °C for 12 h and calcined at 500 °C for 3 h (2 °C/min). The prepared MnOx/CeO2 nanosphere catalysts are referred to as MnCe-1:16, MnCe-1:8, MnCe-1:4, MnCe-1:2, and MnCe-1:1 based on their Mn/Ce ratio. As shown in Table 1, we selected the MnCe-1:8, MnCe-1:4, and MnCe-1:1 catalysts to determine the contents of cerium and manganese elements in the catalysts via ICP measurement. From the ICP results, it can be observed that the actual content of Mn element in the catalyst increased with increasing the Mn/Ce molar ratios, while the actual content of Ce element showed a downward trend. However, the content of Mn element did not match the actual feeding ratio, which may have been due to the fact that MnOx did not grow on the CeO2 support during the hydrothermal process and was lost after centrifugal washing.

2.1.3. Preparation of MnOx Catalysts

The MnOx catalyst was prepared via the following steps. Firstly, Mn(NO3)2 (50% solution, 2.06 g) was added into 55 mL of deionized water. The pH of the solution was adjusted to 10 by the dropwise addition of ammonia aqueous (25% solution) under constant stirring. The solution was transferred to a 100 mL stainless steel autoclave and reacted at 120 °C for 24 h after stirring for two hours, which was then allowed to cool. The product was washed multiple times via centrifugation. Finally, the products were dried at 80 °C for 12 h and calcined at 500 °C for 3 h (2 °C/min).

2.2. Catalyst Characterization

X-ray diffraction (XRD) with a scanning range of 10–90° and a speed of 10°/min using Cu Kα radiation was conducted on the Rigaku Ultima IV X-ray diffractometer.
N2 adsorption/desorption was conducted on the Micromeritics Tristar II 3020 specific surface analyzer. Before conducting the analysis, the catalyst was pretreated under vacuum and 300 °C conditions for 3 h.
Scanning electron microscopy (SEM) images were obtained using the Hitachi SU8010 system, and to improve the quality of the SEM images, 10 nm gold nanoparticles were coated on the catalyst surface prior to imaging. Transmission Electron Microscopy (TEM) was observed on a Thermo Scientific Talos F200x transmission electron microscope and an EDX analysis was performed on the same device. Before conducting the transmission electron microscopy observation, the catalyst was first ultrasonically treated in anhydrous ethanol for 15 min, and then the upper clear liquid was dropped onto a copper grid.
A H2 temperature-programmed reduction (H2-TPR) was obtained using the Micromeritics AutoChem II 2920 chemical adsorption system. First, 100 mg of catalyst was pretreated under conditions of N2 gas and 300 °C, and then cooled. The gas was replaced with a hydrogen/argon mixture, and the temperature was raised to 850 °C (10 °C/min). The hydrogen consumption was detected using a thermal conductivity detector. O2 temperature-programmed desorption (O2-TPD) was performed on the same instrument, which differed from the H2-TPR method in that the catalyst was pretreated in O2 gas, and then the gas was changed to He. The amount of O2 desorption was detected using the same thermal conductivity detector.
X-ray photoelectron spectroscopy (XPS) was performed on a Thermo ESCALAB 250Xi instrument. The carbon 1s peak was set to 284.8 eV.
Soot-TPR was conducted in 50 mL/min Ar gas. In total, 100 mg of catalyst was mixed with 10 mg of soot to achieve a loose-contact mode. The mixture was pretreated at 200 °C and under Ar gas conditions for 30 min, and then heated from 200 °C to 800 °C (4 °C/min). The outlet gas composition was detected using the Agilent 7890B gas chromatograph.
In situ DRIFTS spectra was obtained using a Vertex 80v spectrometer (Bruker) FT-IR spectrometer. Before starting adsorption, the catalyst was pretreated in Ar gas at 500 °C for 0.5 h. During the cooling process, the background spectrum was scanned every 50 °C. Then, the gas was changed to NH3 after adsorbing and saturating, then changed to Ar gas, and blown for 30 min. Finally, it was heated up to 500 °C and the infrared spectrum was recorded every 50 °C.
NO temperature-programmed oxidation (NO-TPO) was conducted on an optical flue gas analyzer FGA10. In total, 100 mg of catalyst was pretreated in Ar gas at 200 °C for 30 min, then heated from 100 °C to 500 °C (2 °C/min) under conditions of 10% O2, 800 ppm NOx, and Ar balance (100 mL/min).

2.3. Catalytic Activity Measurements

The catalytic performance of the catalysts was measured using the TPO method. Simulated soot was purchased from Frankfurt Degussa, Germany, and consisted of Printx-U particles with a diameter of 25 nm. Its elemental composition was 92.0% C, 3.5% O, 3.5% other elements, 0.7% H, 0.2% S, and 0.1% N. A total of 100 mg of catalyst with 10 mg of soot was mixed using a spatula to achieve a loose contact mode (or ground in an agate mortar for 10 min to achieve a tight contact mode). Under a total 50 mL/min flow of 10% O2, 2000 ppm NO, and Ar balance, the mixture was heated from 100 °C to 650 °C on a fixed-bed tubular quartz reactor (Φ = 8 mm, 2 °C/min). The composition of the outlet gas was analyzed using the Agilent 7890B gas chromatograph. At 380 °C, the Ni catalyst completely converted CO and CO2 into CH4. The temperatures T10, T50, and T90, corresponding to the soot conversion rates of 10%, 50%, and 90%, were used to evaluate the activity of the catalyst. The calculation formula for CO2 selectivity (SCO2) is SCO2 = CCO2/(CCO + CCO2). CCO2 and CCO represent the outlet concentrations of CO2 and CO, respectively, and the SCO2m is the CO2 selectivity when the combustion rate of soot was the fastest.

3. Result and Discussion

3.1. Structural Features of the Synthesized Catalysts

3.1.1. XRD Analysis

Figure 1 presents the XRD results. In Figure 1(a–f), four distinct peaks are located at 2θ values of 28.5° (111), 33.1° (200), 47.5° (220), and 56.3° (311), corresponding to the characteristic peaks of CeO2 (indicated with “★” in Figure 1, JCPDS Card No. 43-1002) [32,33]. The positions of the peaks for the MnOx/CeO2 nanosphere catalysts were consistent with those for the CeO2 support, demonstrating that the loading of MnOx would not affect the structure of CeO2. No diffraction peaks other than CeO2 are observed in Figure 1(a–f), which may be because of the high dispersion of MnOx. In addition, as seen in Figure 1(g), the XRD results exhibited that the prepared MnOx catalyst showed distinct peaks located at 2θ values of 23.1° (211), 32.9° (222), 38.2° (400), and 55.2° (044), corresponding to the characteristic peaks of bixbyite Mn2O3 (indicated with “◆” in Figure 1, JCPDS Card No. 41-1442) [34].

3.1.2. N2 Physisorption Analysis

Figure 2 shows the N2 physisorption results of the catalysts. According to the definition of IUPAC, the catalysts showed typical type IV adsorption/desorption isotherms [35]. In Figure 2, H2 hysteresis loops appear within the range of 0.9–1.0 relative pressure (P/P0), and the catalysts have a mesoporous structure in the range of 2–20 nm. From Figure 2B(a–f), it can be observed that the original CeO2 nanospheres had a rich pore structure with pore sizes of 20–60 nm. However, this pore structure disappeared with increasing manganese loading, which can be ascribed to the filling of the pores by the loaded manganese species. Table 2 shows a decreasing trend in the specific surface area of the catalyst, which may be relevant to the MnOx species filling the stacking pores between the nanospheres. The pore volume remained within the range of 0.067–0.119 cm3/g for all of the catalysts, while the pore size ranged from 4.7 to 7.2 nm.

3.1.3. Morphological Characterization of the Prepared Catalysts

Figure 3 shows the morphology of the prepared catalysts. The original CeO2 nanospheres exhibited a uniformly distributed nano-spherical structure (Figure 3A). As shown in Figure 3B–D, after the hydrothermal growth of the manganese species, when the Mn/Ce ratios were 1:16, 1:8, and 1:4, the catalyst morphology did not undergo significant changes. However, as shown in Figure 3E,F, further increasing the manganese loading to Mn/Ce ratios of 1:2 and 1:1 led to the destruction of the nano-spherical structure and adhesion between the MnOx/CeO2 nanospheres. The TEM image of the MnCe-1:4 catalyst is shown in Figure 3G, and the catalyst exhibits nano-spherical morphology. Based on the HAADF-STEM image (Figure 3H), elemental mapping images (Figure 3I–K), and the EDS spectrum (Figure 3L), the MnOx species had a good dispersibility in the MnCe-1:4 catalyst, with a Ce element content of 18.59% and a Mn element content of 6.07% (Mn:Ce = 1:3.06), which were approximated with the surface content of elements obtained from XPS (Mn:Ce = 1:3.38).

3.1.4. H2-TPR Analysis

The reduction performance of the MnOx/CeO2 nanosphere catalysts was investigated using H2-TPR. In Figure 4(a), the peak of the CeO2 nanospheres at 483 °C corresponds to the reduction in surface CeO2 to Ce2O3. The peak of 600–800 °C corresponds to the reduction in bulk-phase CeO2. After the manganese species loading, the positions and types of reduction peaks changed. In Figure 4(b–f), the three reduction peaks from low to high temperatures below 500 °C can be attributed to the reduction in the surface-adsorbed oxygen, Mn4+ to Mn3+, and Mn3+ to Mn2+ [34,36]. The reduction peak located above 600 °C belongs to the reduction in CeO2 [37]. In addition, a lower peak temperature indicated a more facile reduction and a larger peak area reflected a greater hydrogen consumption. In Figure 4, the reduction peaks increase in area and shift toward lower temperatures with increasing manganese loading.

3.1.5. O2-TPD Analysis

Figure 5 shows the O2-TPD results. The desorption peak of the oxygen physiosorbed on the catalyst surface (O2 or Osur, labeled α) is within the range of 50–250 °C. The chemically adsorbed (O2−/O−, named as β) desorption peak ranges from 250 to 450 °C. Finally, the desorption peak in the range of 450–850 °C corresponds to the lattice oxygen (O2−, named as γ) [38,39,40]. As can be observed from Figure 5, the MnCe-1:4 catalyst resulted in the largest peak area for the chemically adsorbed oxygen species in the β region; therefore, it had the most active oxygen species.

3.1.6. XPS Analysis

As shown in Figure 6 and Table 3, the CeO2, MnCe-1:16, MnCe-1:4, and MnCe-1:1 catalysts were selected as representative catalysts for the XPS characterization. Figure 6A shows the cerium 3d spectrum, which could be fitted by eight peaks based on four pairs of spin–orbit doublets [41,42,43]. When the manganese species were loaded onto a CeO2 support, Ce4+ would transform into Ce3+ and oxygen vacancies were generated. Table 3 shows the calculated ratios of the Ce3+ peak area to the total cerium peak area, which were used to estimate the relative Ce3+ contents on the catalyst surfaces. It can be concluded that, as the manganese content increased, the Ce3+ content first increased and then decreased. The MnCe-1:4 catalyst had the highest Ce3+ content at 18.59%, which meant it contained the most surface oxygen vacancies.
Figure 6B shows the manganese 2p spectrum. Due to the difficulty in distinguishing the valence state of the manganese solely based on the Mn 2p spectrum, the manganese 3 s spectra were also measured to confirm the valence states. The correlation between ΔE and the average valence state of the manganese can be expressed as follows: average valence state = 8.95 − 1.13 × ΔE [44,45]. From Figure 6C, it can be seen that the ΔE values for the MnCe-1:4 and MnCe-1:1 catalysts were 5.43 and 5.10 eV, indicating average valence states of 2.81 and 3.19, respectively. Previous studies have shown that high-valent Mn4+ cations in oxides are often reduced to Mn3+ with the formation of oxygen vacancies (Vo), as follows: 2Mn4+ + O2− → 2Mn3+ + Vo + 0.5O2(g) [46,47]. From Table 3, it can be seen that the MnCe-1:4 catalyst had the highest Mn3+ content among the catalysts, indicating that it had more oxygen vacancies.
Figure 6D shows the oxygen 1s spectrum, from which three types of oxygen species can be observed. The O-I species with binding energies of 531.94–532.70 ev corresponds to the surface-adsorbed oxygen (Osur), the O-II species with binding energies of 530.84–531.57 eV corresponds to the chemically adsorbed oxygen (Oads), and the O-III species with binding energies of 529.10–530.0 eV corresponds to the lattice oxygen (Olatt) [48]. Combined with the O2-TPD results, these three kinds of oxygen species are consistent with the XPS results. However, the contents of the three oxygen species obtained by O2-TPD are different from the XPS results. The reason for this phenomenon is as follows: XPS can directly detect the proportions of the three oxygen species in the catalyst, while the O2-TPD detects the released oxygen species from the catalyst. Similar to the O2-TPD results, with the increase in manganese loading, the proportion of O-II species first increased and then decreased. The MnCe-1:4 catalyst had the most O-II species.

3.1.7. Soot-TPR Analysis

Soot-TPR can reflect the situation of oxygen defect sites in the catalyst [46]. Therefore, we conducted Soot-TPR measurements on the CeO2 and MnCe-1:4 catalysts. As shown in Figure 7, the peaks at 200–480 °C belong to the surface-adsorbed oxygen, and the peaks at 480–800 °C belong to the lattice oxygen. Compared to the CeO2 catalyst, the amount of CO2 generated by the MnCe-1:4 catalyst significantly increased, indicating that the catalyst had more oxygen defect sites [49,50]. At the same time, the MnCe-1:4 catalyst had a lower temperature for the desorption of lattice oxygen, so the loading of Mn species could generate more active oxygen species and promote their migration, which suggests that the contents of oxygen vacancies were abundant when Mn species were loaded on the CeO2. Meanwhile, the variation tendency of oxygen vacancies is also consistent with the catalyst activities of catalysts.

3.1.8. NO-TPO Analysis

The conversion ability of NOx can affect the catalytic activities of catalysts for soot combustion. Therefore, we tested the NO2 concentration (Figure 8A) and NO concentration (Figure 8B) of the CeO2 and MnCe-1:4 catalysts under different temperatures. From Figure 8A, it can be seen that the NO2 concentration of the CeO2 and MnCe-1:4 catalysts first increased and then decreased. Among them, the CeO2 catalyst reached its maximum concentration of NO2 at about 403 °C. Compared to CeO2, the MnCe-1:4 catalyst generated a higher NO2 content and lower temperature (about 340 °C) for the maximum NO2 concentration, while the trend of NO concentration in Figure 8B is opposite to that of NO2. The results suggested that the MnOx species loading on CeO2 could improve the NO oxidation capacity.

3.1.9. In situ DRIFTS Analysis

The acid sites on the catalyst surface were investigated using NH3 adsorption/desorption in situ infrared spectroscopy. Figure 9A,B show the IR spectra of the CeO2 and MnCe-1:4 catalysts under the temperature range of 100–500 °C, respectively. As shown in Figure 9A, the surface components of the CeO2 catalyst were mainly Lewis acid-coordinated ammonia (1179 cm−1) and Brønsted acid-coordinated NH4+ (1448 cm−1) [51,52]. When the temperature rose to 400 °C, NH3 desorption occurred on the surface of CeO2, and the Lewis acid sites gradually decreased. After loading manganese species on the CeO2 support, the types of acid sites did not change, which were Lewis acid-coordinated ammonia (1227 cm−1) and Brønsted acid-coordinated NH4+ (1448 cm−1) (Figure 9B) [53]. From Figure 9, it can be concluded that, when Mn species were loaded onto the CeO2 support, the Lewis acid sites changed and the peak intensity increased due to the simultaneous adsorption of NH3 by Mn. Based on the above discussion, the improvement in catalytic activity may have been related to the increase in the number of acid sites.

3.2. Catalytic Performance in Soot Combustion

Table 4 shows the activities of the prepared catalysts and pure soot under loose contact mode. The catalytic activity of the pure CeO2 support was weak, but the catalytic activity was significantly improved after loading the manganese species; among them, the MnCe-1:4 catalyst had the highest activity, with T10, T50, and T90 values of 289, 340, and 373 °C, respectively. Due to the small difference in catalytic performance between the catalysts with different Mn loadings, three repeated activity tests were conducted on the MnCe-1:4 catalyst to test the repeatability and stability of the activity test method in this work. Table 5 shows the activity of the three repeated tests, and the relative errors (δ) of the repeated activity tests were calculated. As shown in Table 5, all the values of the relative errors were less than 2%. Therefore, it can be concluded that the activity test method had a high reliability. Therefore, the catalytic activity of the MnOx/CeO2 catalysts was meaningful. We also tested the catalytic performance of the MnCe-1:4 catalyst under tight contact mode. According to Table 4, the activity of the catalyst slightly increased. Therefore, the catalyst–soot contact mode had an impact on the catalyst activity. In addition, we tested the catalytic performance of the pure Mn2O3 and mechanical mixing of the Mn2O3 and CeO2 catalysts for soot combustion. As shown in Table 4, the catalytic activities of the pure Mn2O3 and the mechanical mixing of the CeO2 and Mn2O3 catalysts were lower than that of the MnOx/CeO2 catalysts. Therefore, the interaction between Mn and Ce was one of the reasons for the excellent catalytic activity of the MnOx/CeO2 catalysts. For further comparison, the catalytic performance of the MnCe-1:4 catalyst was compared with that of other cerium-based oxide catalysts (Table 6). Compared to CeO2 nanocubes without other active components, the MnCe-1:4 catalyst prepared in this study had lower T10, T50, and T90 values, indicating that the interaction between Mn and Ce is beneficial for enhancing the catalytic combustion of soot. In addition, the combustion temperature values of the MnCe-1:4 catalyst with a nano-sphere structure prepared in this study were lower than those of the CeO2@MnO2 catalyst with a core–shell structure, the catalysts with three-dimensionally ordered macropores (3DOM), such as (NiO-CeO2)-3DOM, 3DOM Co3O4-CeO2, and 3DOM Mn0.5Ce0.5Oδ, and the MnOx-CeO2-Al2O3 catalyst without a special morphology. This means that the nano-sphere structure of the MnCe-1:4 catalyst was beneficial for improving the contact efficiency between the soot and the catalyst, and had a superior soot combustion activity. The MnCe-1:4 catalyst prepared in this study had higher catalytic activity, indicating that the nano-spherical morphology of the catalyst, abundant active oxygen species, and the interaction between Mn and Ce species are beneficial for enhancing soot combustion.

4. Conclusions

A series of manganese-loaded CeO2 nanosphere catalysts were synthesized via a simple two-step hydrothermal method, and the prepared MnOx/CeO2 catalysts exhibited excellent catalytic activity for soot combustion. The characterization results confirmed that the catalysts possessed a nano-spherical structure and revealed that the manganese loading affected the specific surface area and improved their O2 adsorption and activation ability. Among the prepared catalysts, the MnCe-1:4 catalyst had the optimal catalytic performance, with T10, T50, and T90 values of 289, 340, and 373 °C, respectively, and a CO2 selectivity of 99.3%.

Author Contributions

Conceptualization, S.G. and X.Y.; methodology, S.G.; software, S.Z. and C.Z.; validation, D.Y., S.Z., C.Z. and L.W.; formal analysis, X.F.; investigation, S.G., D.Y. and S.Z.; resources, X.Y.; data curation, S.G.; Writing—Original draft preparation, S.G.; Writing—Review and editing, X.Y.; visualization, Z.Z.; supervision, X.Y.; project administration, Z.Z.; funding acquisition, X.F. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by National Key R&D Program of China (2022YFB3506200, 2022YFB3504100); National Natural Science Foundation of China (22372107, 22072095, U1908204); Excellent Youth Science Foundation of Liaoning Province (2022-YQ-20); Shenyang Science and Technology Planning Project (22-322-3-28); University Joint Education Project for China-Central and Eastern European Countries (2021097); Major/Key Project of Graduate Education and Teaching Reform of Shenyang Normal University (YJSJG120210008/YJSJG220210022).

Data Availability Statement

All the data during the study appeared in the submitted article.

Acknowledgments

The instruments and equipment used in this work are supported by Major Platform for Science and Technology of the Universities in Liaoning Province: The Engineering Technology Research Center of Catalysis for Energy and Environment and The Belt and Road International Joint Research Center of Catalysis for Energy and Environment.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Yu, X.; Wang, L.; Zhao, Z.; Fan, X.; Chen, M.; Wei, Y.; Liu, J. 3DOM SiO2-Supported Different Alkali Metals-Modified MnOx Catalysts: Preparation and Catalytic Performance for Soot combustion. ChemistrySelect 2017, 2, 10176–10185. [Google Scholar] [CrossRef]
  2. Frank, B.; Schuster, M.E.; Schlögl, R.; Su, D.S. Emission of Highly Activated Soot Particulate—The Other Side of the Coin with Modern Diesel Engines. Angew. Chem. Int. Ed. 2013, 52, 2673–2677. [Google Scholar] [CrossRef] [PubMed]
  3. Shao, J.; Lan, X.; Zhang, C.; Cao, C.; Yu, Y. Recent advances in soot combustion catalysts with designed micro-structures. Chin. Chem. Lett. 2022, 33, 1763–1771. [Google Scholar] [CrossRef]
  4. Liu, S.; Wu, X.; Weng, D.; Ran, R. Ceria-based catalysts for soot oxidation: A review. J. Rare Earths 2015, 33, 567–590. [Google Scholar] [CrossRef]
  5. Yeste, M.P.; Cauqui, M.Á.; Giménez-Mañogil, J.; Martínez-Munuera, J.C.; Muñoz, M.Á.; García-García, A. Catalytic activity of Cu and Co supported on ceria-yttria-zirconia oxides for the diesel soot combustion reaction in the presence of NOx. Chem. Eng. J. 2020, 380, 122370. [Google Scholar] [CrossRef]
  6. Bueno-López, A. Diesel soot combustion ceria catalysts. Appl. Catal. B 2014, 146, 1–11. [Google Scholar] [CrossRef]
  7. Lan, L.; Chen, S.; Li, H.; Wang, J.; Li, D.; Chen, Y. Optimized synthesis of highly thermal stable CeO2-ZrO2/Al2O3 composite for improved Pd-only three-way catalyst. Mater. Des. 2018, 147, 191–199. [Google Scholar] [CrossRef]
  8. Wei, Y.; Zhao, Z.; Liu, J.; Xu, C.; Jiang, G.; Duan, A. Design and Synthesis of 3D Ordered Macroporous CeO2-Supported Pt@CeO2-δ Core–Shell Nanoparticle Materials for Enhanced Catalytic Activity of Soot Oxidation. Small 2013, 9, 3957–3963. [Google Scholar] [CrossRef]
  9. Mukherjee, D.; Reddy, B.M. Noble metal-free CeO2-based mixed oxides for CO and soot oxidation. Catal. Today 2018, 309, 227–235. [Google Scholar] [CrossRef]
  10. Liu, T.; Li, Q.; Xin, Y.; Zhang, Z.; Tang, X.; Zheng, L.; Gao, P.-X. Quasi free K cations confined in hollandite-type tunnels for catalytic solid (catalyst)-solid (reactant) oxidation reactions. Appl. Catal. B 2018, 232, 108–116. [Google Scholar] [CrossRef]
  11. Neeft, J.P.A.; Makkee, M.; Moulijn, J.A. Metal oxides as catalysts for the oxidation of soot. Chem. Eng. J. Biochem. Eng. 1996, 64, 295–302. [Google Scholar] [CrossRef]
  12. Zhang, L.; Zhao, X.; Yuan, Z.; Wu, M.; Zhou, H. Oxygen defect-stabilized heterogeneous single atom catalysts: Preparation, properties and catalytic application. J. Mater. Chem. A 2021, 9, 3855–3879. [Google Scholar] [CrossRef]
  13. Ji, W.; Wang, N.; Li, Q.; Zhu, H.; Lin, K.; Deng, J.; Chen, J.; Zhang, H.; Xing, X. Oxygen vacancy distributions and electron localization in a CeO2(100) nanocube. Inorg. Chem. Front. 2022, 9, 275–283. [Google Scholar] [CrossRef]
  14. Xu, B.; Xia, L.; Zhou, F.; Zhao, R.; Chen, H.; Wang, T.; Zhou, Q.; Liu, Q.; Cui, G.; Xiong, X.; et al. Enhancing Electrocatalytic N2 Reduction to NH3 by CeO2 Nanorod with Oxygen Vacancies. ACS Sustain. Chem. Eng. 2019, 7, 2889–2893. [Google Scholar] [CrossRef]
  15. Machida, M.; Ueno, M.; Omura, T.; Kurusu, S.; Hinokuma, S.; Nanba, T.; Shinozaki, O.; Furutani, H. CeO2-Grafted Mn–Fe Oxide Composites as Alternative Oxygen-Storage Materials for Three-Way Catalysts: Laboratory and Chassis Dynamometer Tests. Ind. Eng. Chem. Res. 2017, 56, 3184–3193. [Google Scholar] [CrossRef]
  16. Huang, H.; Liu, J.; Sun, P.; Ye, S. Study on the simultaneous reduction of diesel engine soot and NO with nano-CeO2 catalysts. RSC Adv. 2016, 6, 102028–102034. [Google Scholar] [CrossRef]
  17. Lee, J.H.; Jo, D.Y.; Choung, J.W.; Kim, C.H.; Ham, H.C.; Lee, K.-Y. Roles of noble metals (M = Ag, Au, Pd, Pt and Rh) on CeO2 in enhancing activity toward soot oxidation: Active oxygen species and DFT calculations. J. Hazard. Mater. 2021, 403, 124085. [Google Scholar] [CrossRef]
  18. Wang, H.; Jin, B.; Wang, H.; Ma, N.; Liu, W.; Weng, D.; Wu, X.; Liu, S. Study of Ag promoted Fe2O3@CeO2 as superior soot oxidation catalysts: The role of Fe2O3 crystal plane and tandem oxygen delivery. Appl. Catal. B 2018, 237, 251–262. [Google Scholar] [CrossRef]
  19. Shan, W.; Yang, L.; Ma, N.; Yang, J. Catalytic Activity and Stability of K/CeO2 Catalysts for Diesel Soot Oxidation. Chin. J. Catal. 2012, 33, 970–976. [Google Scholar] [CrossRef]
  20. Małecka, M.A.; Kępiński, L.; Miśta, W. Structure evolution of nanocrystalline CeO2 and CeLnOx mixed oxides (Ln = Pr, Tb, Lu) in O2 and H2 atmosphere and their catalytic activity in soot combustion. Appl. Catal. B 2007, 74, 290–298. [Google Scholar] [CrossRef]
  21. Cheng, L.; Men, Y.; Wang, J.; Wang, H.; An, W.; Wang, Y.; Duan, Z.; Liu, J. Crystal facet-dependent reactivity of α-Mn2O3 microcrystalline catalyst for soot combustion. Appl. Catal. B 2017, 204, 374–384. [Google Scholar] [CrossRef]
  22. Xu, H.; Yan, N.; Qu, Z.; Liu, W.; Mei, J.; Huang, W.; Zhao, S. Gaseous Heterogeneous Catalytic Reactions over Mn-Based Oxides for Environmental Applications: A Critical Review. Environ. Sci. Technol. 2017, 51, 8879–8892. [Google Scholar] [CrossRef] [PubMed]
  23. Sun, M.; Yu, L.; Ye, F.; Diao, G.; Yu, Q.; Hao, Z.; Zheng, Y.; Yuan, L. Transition metal doped cryptomelane-type manganese oxide for low-temperature catalytic combustion of dimethyl ether. Chem. Eng. J. 2013, 220, 320–327. [Google Scholar] [CrossRef]
  24. Lin, X.; Li, S.; He, H.; Wu, Z.; Wu, J.; Chen, L.; Ye, D.; Fu, M. Evolution of oxygen vacancies in MnOx-CeO2 mixed oxides for soot oxidation. Appl. Catal. B 2018, 223, 91–102. [Google Scholar] [CrossRef]
  25. Wang, J.; Yang, S.; Sun, H.; Qiu, J.; Men, Y. Highly improved soot combustion performance over synergetic MnxCe1−xO2 solid solutions within mesoporous nanosheets. J. Colloid Interface Sci. 2020, 577, 355–367. [Google Scholar] [CrossRef] [PubMed]
  26. Zhang, C.; Yu, D.; Peng, C.; Wang, L.; Yu, X.; Wei, Y.; Liu, J.; Zhao, Z. Research progress on preparation of 3DOM-based oxide catalysts and their catalytic performances for the combustion of diesel soot particles. Appl. Catal. B 2022, 319, 121946. [Google Scholar] [CrossRef]
  27. Zhang, W.; Niu, X.; Chen, L.; Yuan, F.; Zhu, Y. Soot Combustion over Nanostructured Ceria with Different Morphologies. Sci. Rep. 2016, 6, 29062. [Google Scholar] [CrossRef]
  28. Yang, Q.; Gu, F.; Tang, Y.; Zhang, H.; Liu, Q.; Zhong, Z.; Su, F. A Co3O4–CeO2 functionalized SBA-15 monolith with a three-dimensional framework improves NOx-assisted soot combustion. RSC Adv. 2015, 5, 26815–26822. [Google Scholar] [CrossRef]
  29. Zhang, G.; Zhao, Z.; Liu, J.; Jiang, G.; Duan, A.; Zheng, J.; Chen, S.; Zhou, R. Three dimensionally ordered macroporous Ce1−xZrxO2 solid solutions for diesel soot combustion. ChemComm 2010, 46, 457–459. [Google Scholar] [CrossRef]
  30. Zhang, G.; Zhao, Z.; Xu, J.; Zheng, J.; Liu, J.; Jiang, G.; Duan, A.; He, H. Comparative study on the preparation, characterization and catalytic performances of 3DOM Ce-based materials for the combustion of diesel soot. Appl. Catal. B 2011, 107, 302–315. [Google Scholar] [CrossRef]
  31. Su, Z.; Yang, W.; Wang, C.; Xiong, S.; Cao, X.; Peng, Y.; Si, W.; Weng, Y.; Xue, M.; Li, J. Roles of Oxygen Vacancies in the Bulk and Surface of CeO2 for Toluene Catalytic Combustion. Environ. Sci. Technol. 2020, 54, 12684–12692. [Google Scholar] [CrossRef] [PubMed]
  32. Feng, N.; Zhu, Z.; Zhao, P.; Wang, L.; Wan, H.; Guan, G. Facile fabrication of trepang-like CeO2@MnO2 nanocomposite with high catalytic activity for soot removal. Appl. Surf. Sci. 2020, 515, 146013. [Google Scholar] [CrossRef]
  33. Qi, G.; Yang, R.T.; Chang, R. MnOx-CeO2 mixed oxides prepared by co-precipitation for selective catalytic reduction of NO with NH3 at low temperatures. Appl. Catal. B 2004, 51, 93–106. [Google Scholar] [CrossRef]
  34. Yu, X.; Wang, L.; Chen, M.; Fan, X.; Zhao, Z.; Cheng, K.; Chen, Y.; Sojka, Z.; Wei, Y.; Liu, J. Enhanced activity and sulfur resistance for soot combustion on three-dimensionally ordered macroporous-mesoporous MnxCe1-xOδ/SiO2 catalysts. Appl. Catal. B 2019, 254, 246–259. [Google Scholar] [CrossRef]
  35. Sing, K.S.W. Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984). Pure Appl. Chem. 1985, 57, 603–619. [Google Scholar] [CrossRef]
  36. Yu, D.; Ren, Y.; Yu, X.; Fan, X.; Wang, L.; Wang, R.; Zhao, Z.; Cheng, K.; Chen, Y.; Sojka, Z.; et al. Facile synthesis of birnessite-type K2Mn4O8 and cryptomelane-type K2-xMn8O16 catalysts and their excellent catalytic performance for soot combustion with high resistance to H2O and SO2. Appl. Catal. B 2021, 285, 119779. [Google Scholar] [CrossRef]
  37. Chen, D.; He, D.; Lu, J.; Zhong, L.; Liu, F.; Liu, J.; Yu, J.; Wan, G.; He, S.; Luo, Y. Investigation of the role of surface lattice oxygen and bulk lattice oxygen migration of cerium-based oxygen carriers: XPS and designed H2-TPR characterization. Appl. Catal. B 2017, 218, 249–259. [Google Scholar] [CrossRef]
  38. Yu, D.; Wang, L.; Zhang, C.; Peng, C.; Yu, X.; Fan, X.; Liu, B.; Li, K.; Li, Z.; Wei, Y.; et al. Alkali Metals and Cerium-Modified La–Co-Based Perovskite Catalysts: Facile Synthesis, Excellent Catalytic Performance, and Reaction Mechanisms for Soot Combustion. ACS Catal. 2022, 12, 15056–15075. [Google Scholar] [CrossRef]
  39. Yu, X.; Ren, Y.; Yu, D.; Chen, M.; Wang, L.; Wang, R.; Fan, X.; Zhao, Z.; Cheng, K.; Chen, Y.; et al. Hierarchical Porous K-OMS-2/3DOM-m Ti0.7Si0.3O2 Catalysts for Soot Combustion: Easy Preparation, High Catalytic Activity, and Good Resistance to H2O and SO2. ACS Catal. 2021, 11, 5554–5571. [Google Scholar] [CrossRef]
  40. Cui, B.; Zhou, L.; Li, K.; Liu, Y.-Q.; Wang, D.; Ye, Y.; Li, S. Holey Co-Ce oxide nanosheets as a highly efficient catalyst for diesel soot combustion. Appl. Catal. B 2020, 267, 118670. [Google Scholar] [CrossRef]
  41. Li, Y.; Sun, Q.; Kong, M.; Shi, W.; Huang, J.; Tang, J.; Zhao, X. Coupling Oxygen Ion Conduction to Photocatalysis in Mesoporous Nanorod-like Ceria Significantly Improves Photocatalytic Efficiency. J. Phys. Chem. C 2011, 115, 14050–14057. [Google Scholar] [CrossRef]
  42. Zhang, Y.; Zhang, L.; Deng, J.; Dai, H.; He, H. Controlled Synthesis, Characterization, and Morphology-Dependent Reducibility of Ceria−Zirconia−Yttria Solid Solutions with Nanorod-like, Microspherical, Microbowknot-like, and Micro-octahedral Shapes. Inorg. Chem. 2009, 48, 2181–2192. [Google Scholar] [CrossRef] [PubMed]
  43. Niu, F.; Zhang, D.; Shi, L.; He, X.; Li, H.; Mai, H.; Yan, T. Facile synthesis, characterization and low-temperature catalytic performance of Au/CeO2 nanorods. Mater. Lett. 2009, 63, 2132–2135. [Google Scholar] [CrossRef]
  44. Biesinger, M.C.; Payne, B.P.; Grosvenor, A.P.; Lau, L.W.M.; Gerson, A.R.; Smart, R.S.C. Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Cr, Mn, Fe, Co and Ni. Appl. Surf. Sci. 2011, 257, 2717–2730. [Google Scholar] [CrossRef]
  45. Galakhov, V.R.; Demeter, M.; Bartkowski, S.; Neumann, M.; Ovechkina, N.A.; Kurmaev, E.Z.; Lobachevskaya, N.I.; Mukovskii, Y.M.; Mitchell, J.; Ederer, D.L. Mn 3s exchange splitting in mixed-valence manganites. Phys. Rev. B 2002, 65, 113102. [Google Scholar] [CrossRef]
  46. Yu, D.; Yu, X.; Zhang, C.; Wang, L.; Fan, X.; Zhao, Z.; Wei, Y.; Liu, J.; Gryboś, J.; Leszczyński, B.; et al. Layered Na2Mn3O7 decorated by Cerium as the robust catalysts for efficient low temperature soot combustion. Appl. Catal. B 2023, 338, 123022. [Google Scholar] [CrossRef]
  47. Hou, J.; Li, Y.; Mao, M.; Ren, L.; Zhao, X. Tremendous Effect of the Morphology of Birnessite-Type Manganese Oxide Nanostructures on Catalytic Activity. ACS Appl. Mater. Interfaces 2014, 6, 14981–14987. [Google Scholar] [CrossRef]
  48. Chen, H.; Sayari, A.; Adnot, A.; Larachi, F.ç. Composition–activity effects of Mn–Ce–O composites on phenol catalytic wet oxidation. Appl. Catal. B 2001, 32, 195–204. [Google Scholar] [CrossRef]
  49. Cao, C.; Xing, L.; Yang, Y.; Tian, Y.; Ding, T.; Zhang, J.; Hu, T.; Zheng, L.; Li, X. Diesel soot elimination over potassium-promoted Co3O4 nanowires monolithic catalysts under gravitation contact mode. Appl. Catal. B 2017, 218, 32–45. [Google Scholar] [CrossRef]
  50. Yang, Y.; Zhao, D.; Gao, Z.; Tian, Y.; Ding, T.; Zhang, J.; Jiang, Z.; Li, X. Interface interaction induced oxygen activation of cactus-like Co3O4/OMS-2 nanorod catalysts in situ grown on monolithic cordierite for diesel soot combustion. Appl. Catal. B 2021, 286, 119932. [Google Scholar] [CrossRef]
  51. Weiman, L.; Haidi, L.; Yunfa, C. Mesoporous MnOx–CeO2 composites for NH3-SCR: The effect of preparation methods and a third dopant. RSC Adv. 2019, 9, 11912–11921. [Google Scholar] [CrossRef] [PubMed]
  52. Wang, B.; Wang, M.; Han, L.; Hou, Y.; Bao, W.; Zhang, C.; Feng, G.; Chang, L.; Huang, Z.; Wang, J. Improved Activity and SO2 Resistance by Sm-Modulated Redox of MnCeSmTiOx Mesoporous Amorphous Oxides for Low-Temperature NH3-SCR of NO. ACS Catal. 2020, 10, 9034–9045. [Google Scholar] [CrossRef]
  53. Wang, L.; Ren, Y.; Yu, X.; Yu, D.; Peng, C.; Zhou, Q.; Hou, J.; Zhong, C.; Yin, C.; Fan, X.; et al. Facile preparation, catalytic performance and reaction mechanism of MnxCo1−xOδ/3DOM-m Ti0.7Si0.2W0.1Oy catalysts for the simultaneous removal of soot and NOx. Catal. Sci. Technol. 2022, 12, 1950–1967. [Google Scholar] [CrossRef]
  54. Sellers-Antón, B.; Bailón-García, E.; Cardenas-Arenas, A.; Davó-Quiñonero, A.; Lozano-Castelló, D.; Bueno-López, A. Enhancement of the Generation and Transfer of Active Oxygen in Ni/CeO2 Catalysts for Soot Combustion by Controlling the Ni–Ceria Contact and the Three-Dimensional Structure. Environ. Sci. Technol. 2020, 54, 2439–2447. [Google Scholar] [CrossRef] [PubMed]
  55. Jian, S.; Yang, Y.; Ren, W.; Xing, L.; Zhao, D.; Tian, Y.; Ding, T.; Li, X. Kinetic analysis of morphologies and crystal planes of nanostructured CeO2 catalysts on soot oxidation. Chem. Eng. Sci. 2020, 226, 115891. [Google Scholar] [CrossRef]
  56. Zhai, G.; Wang, J.; Chen, Z.; Yang, S.; Men, Y. Highly enhanced soot oxidation activity over 3DOM Co3O4-CeO2 catalysts by synergistic promoting effect. J. Hazard. Mater. 2019, 363, 214–226. [Google Scholar] [CrossRef]
  57. Wu, X.; Liu, S.; Weng, D.; Lin, F.; Ran, R. MnOx–CeO2–Al2O3 mixed oxides for soot oxidation: Activity and thermal stability. J. Hazard. Mater. 2011, 187, 283–290. [Google Scholar] [CrossRef]
  58. Yu, X.; Li, J.; Wei, Y.; Zhao, Z.; Liu, J.; Jin, B.; Duan, A.; Jiang, G. Three-Dimensionally Ordered Macroporous MnxCe1–xOδ and Pt/Mn0.5Ce0.5Oδ Catalysts: Synthesis and Catalytic Performance for Soot Oxidation. Ind. Eng. Chem. Res. 2014, 53, 9653–9664. [Google Scholar] [CrossRef]
Processes 11 02902 g001
Figure 1. XRD results (a: CeO2; b: MnCe-1:16; c: MnCe-1:8; d: MnCe-1:4; e: MnCe-1:2; f: MnCe-1:1; and g: Mn2O3).
Figure 1. XRD results (a: CeO2; b: MnCe-1:16; c: MnCe-1:8; d: MnCe-1:4; e: MnCe-1:2; f: MnCe-1:1; and g: Mn2O3).
Processes 11 02902 g001
Processes 11 02902 g002
Figure 2. Nitrogen adsorption–desorption isotherms (A) and pore size distributions (B) of prepared catalysts (a: CeO2; b: MnCe-1:16; c: MnCe-1:8; d: MnCe-1:4; e: MnCe-1:2; and f: MnCe-1:1).
Figure 2. Nitrogen adsorption–desorption isotherms (A) and pore size distributions (B) of prepared catalysts (a: CeO2; b: MnCe-1:16; c: MnCe-1:8; d: MnCe-1:4; e: MnCe-1:2; and f: MnCe-1:1).
Processes 11 02902 g002
Processes 11 02902 g003
Figure 3. SEM (A–F) images of prepared catalysts ((A): CeO2; (B): MnCe-1:16; (C): MnCe-1:8; (D): MnCe-1:4; (E): MnCe-1:2; and (F): MnCe-1:1), TEM (G), HAADF-STEM (H), elemental mapping images (I–K), and EDS spectrum (L) of MnCe-1:4 catalyst.
Figure 3. SEM (A–F) images of prepared catalysts ((A): CeO2; (B): MnCe-1:16; (C): MnCe-1:8; (D): MnCe-1:4; (E): MnCe-1:2; and (F): MnCe-1:1), TEM (G), HAADF-STEM (H), elemental mapping images (I–K), and EDS spectrum (L) of MnCe-1:4 catalyst.
Processes 11 02902 g003
Processes 11 02902 g004
Figure 4. H2-TPR results (a: CeO2; b: MnCe-1:16; c: MnCe-1:8; d: MnCe-1:4; e: MnCe-1:2; and f: MnCe-1:1).
Figure 4. H2-TPR results (a: CeO2; b: MnCe-1:16; c: MnCe-1:8; d: MnCe-1:4; e: MnCe-1:2; and f: MnCe-1:1).
Processes 11 02902 g004
Processes 11 02902 g005
Figure 5. O2-TPD results (a: CeO2; b: MnCe-1:16; c: MnCe-1:8; d: MnCe-1:4; e: MnCe-1:2; and f: MnCe-1:1).
Figure 5. O2-TPD results (a: CeO2; b: MnCe-1:16; c: MnCe-1:8; d: MnCe-1:4; e: MnCe-1:2; and f: MnCe-1:1).
Processes 11 02902 g005
Processes 11 02902 g006
Figure 6. XPS spectra (A: CeO2; B: MnCe-1:16; C: MnCe-1:4; and D: MnCe-1:1).
Figure 6. XPS spectra (A: CeO2; B: MnCe-1:16; C: MnCe-1:4; and D: MnCe-1:1).
Processes 11 02902 g006
Processes 11 02902 g007
Figure 7. Soot-TPR curves of CeO2 and MnCe-1:4 catalysts.
Figure 7. Soot-TPR curves of CeO2 and MnCe-1:4 catalysts.
Processes 11 02902 g007
Processes 11 02902 g008
Figure 8. NO2 concentration (A) and NO concentration profiles (B) over CeO2 and MnCe-1:4 catalysts.
Figure 8. NO2 concentration (A) and NO concentration profiles (B) over CeO2 and MnCe-1:4 catalysts.
Processes 11 02902 g008
Processes 11 02902 g009
Figure 9. In situ DRIFTS spectra of CeO2 (A) and MnCe-1:4 catalysts (B).
Figure 9. In situ DRIFTS spectra of CeO2 (A) and MnCe-1:4 catalysts (B).
Processes 11 02902 g009
Table 1. The actual contents of cerium and manganese elements in the catalysts.
Table 1. The actual contents of cerium and manganese elements in the catalysts.
CatalystsCeMn
MnCe-1:876.0%3.8%
MnCe-1:472.1%6.8%
MnCe-1:153.5%21.4%
Table 2. Textural properties of prepared catalysts.
Table 2. Textural properties of prepared catalysts.
CatalystsSurface Area (m2/g) aTotal Pore Volume (cm3/g) bPore Size (nm) c
CeO2110.90.1195.9
MnCe-1:1695.50.0834.7
MnCe-1:870.70.1035.6
MnCe-1:438.40.0706.9
MnCe-1:246.90.0745.9
MnCe-1:143.20.0677.2
a Calculated by BET method; b Calculated by BJH desorption cumulative volume of pores between 1.7 nm and 300 nm diameter; and c Calculated by BJH desorption average pore diameter.
Table 3. Composition and oxidation state of manganese, cerium, and oxygen on the surface of prepared catalyst.
Table 3. Composition and oxidation state of manganese, cerium, and oxygen on the surface of prepared catalyst.
SampleMolar Fraction
ManganeseCeriumOxygen
Mn4+Mn3+Mn2+Ce4+Ce3+OlattOadsOsur
CeO2 85.11%14.89%68.16%11.71%20.13%
MnCe-1:1617.34%26.21%56.45%81.94%18.06%69.94%14.15%15.91%
MnCe-1:416.78%47.04%36.18%81.41%18.59%74.04%14.70%11.26%
MnCe-1:143.95%30.56%25.48%92.19%7.81%74.07%9.97%15.96%
Table 4. Catalytic performance of prepared catalysts for soot combustion.
Table 4. Catalytic performance of prepared catalysts for soot combustion.
CatalystsT10/°CT50/°CT90/°CSCO2m/%
Soot46155259438.5%
CeO231836340296.5%
Mn2O329435739599.6%
Mn2O3 + CeO2
(mechanical mixing)		29435038499.5%
MnCe-1:1629435038499.5%
MnCe-1:829234437599.3%
MnCe-1:428934037399.3%
MnCe-1:4
(under tight contact mode)		27832735399.6%
MnCe-1:228634738299.5%
MnCe-1:128634638399.5%
Table 5. The catalytic activity of the MnCe-1:4 catalyst was repeatedly tested for soot combustion three times in loose contact mode, and the relative error was calculated.
Table 5. The catalytic activity of the MnCe-1:4 catalyst was repeatedly tested for soot combustion three times in loose contact mode, and the relative error was calculated.
Catalysts aT10/°Cδ bT50/°CδT90/°CδSCO2m/%δ
MnCe-1:4-12910.69%3400%3791.6%99.5%0.20%
MnCe-1:4-22921.04%3420.59%3740.27%99.6%0.30%
MnCe-1:4-32900.35%3370.88%3730%99.6%0.30%
a: Three repeated activity tests were performed on MnCe-1:4 catalyst; b: Calculation formula for relative error: δ = (x − μ)/μ × 100%, x represents the T10/T50/T90/SCO2m of the catalysts for repeated activity testing, and μ represents the value of T10/T50/T90/SCO2m corresponding to MnCe-1:4 catalyst.
Table 6. Catalytic activities of as-prepared catalysts and reported catalysts for soot combustion under loose contact conditions.
Table 6. Catalytic activities of as-prepared catalysts and reported catalysts for soot combustion under loose contact conditions.
CatalystsReaction ConditionsSoot/
Catalysts		T10/Ti
(°C)		T50/Tm
(°C)		T90/Tf
(°C)		References
CeO2@MnO2500 ppm NO + 5% O2 + N2 balance1:9312373423[32]
(NiO-CeO2)-3DOM500 ppm NO + 5% O2 + N2 balance1:4 530 [54]
CeO2 nanocube10 vol.% O2 + N2 balance1:10 459554[55]
3DOM Co3O4-CeO20.25% NO + 5% O2 + N2 balance1:10 406 [56]
MnOx-CeO2-Al2O31000 ppm NO + 10% O2 + N2 balance1:10 455 [57]
3DOM Mn0.5Ce0.5Oδ0.2% NO + 10% O2 + Ar balance1:10297358396[58]
MnCe-1:42000 ppm NO + 10% O2 + Ar balance1:10289340373This work
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Gao, S.; Yu, D.; Zhou, S.; Zhang, C.; Wang, L.; Fan, X.; Yu, X.; Zhao, Z. The Preparation of Mn-Modified CeO2 Nanosphere Catalysts and Their Catalytic Performance for Soot Combustion. Processes 2023, 11, 2902. https://doi.org/10.3390/pr11102902

AMA Style

Gao S, Yu D, Zhou S, Zhang C, Wang L, Fan X, Yu X, Zhao Z. The Preparation of Mn-Modified CeO2 Nanosphere Catalysts and Their Catalytic Performance for Soot Combustion. Processes. 2023; 11(10):2902. https://doi.org/10.3390/pr11102902

Chicago/Turabian Style

Gao, Siyu, Di Yu, Shengran Zhou, Chunlei Zhang, Lanyi Wang, Xiaoqiang Fan, Xuehua Yu, and Zhen Zhao. 2023. "The Preparation of Mn-Modified CeO2 Nanosphere Catalysts and Their Catalytic Performance for Soot Combustion" Processes 11, no. 10: 2902. https://doi.org/10.3390/pr11102902

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop