Next Article in Journal
Wear Resistance Prediction of AlCoCrFeNi-X (Ti, Cu) High-Entropy Alloy Coatings Based on Machine Learning
Previous Article in Journal
Microstructure, Mechanical and Wear Properties of W-Si-C Composites Consolidated by Spark Plasma Sintering
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Metals
Volume 13
Issue 5
10.3390/met13050938
metals-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

Mn-Ce Catalysts/LDPC Modified by Mo for Improving NH3-SCR Performance and SO2 Resistance at Low Temperature

by
Tao Zhou
,
Jiang Jin
* and
Hua Zhang
*
College of Materials Science and Engineering, Nanjing Tech University, Nanjing 211816, China
*
Authors to whom correspondence should be addressed.
Metals 2023, 13(5), 938; https://doi.org/10.3390/met13050938
Submission received: 13 April 2023 / Revised: 6 May 2023 / Accepted: 10 May 2023 / Published: 11 May 2023
(This article belongs to the Special Issue Application and Properties of Metal and Metal Oxides in Catalysts)
Browse Figures
Review Reports Versions Notes

Abstract

:
Mn-Ce catalysts modified by Mo were loaded on low-density porous ceramics (LDPC) for simultaneous denitrification and dust removal. The Mn-Ce-Mo catalyst on LDPC had nearly 99% NOx conversion efficiency from 120 °C to 200 °C and still maintained more than 90% NOx conversion efficiency when the filtration velocity reached to 4 m/min. Mn-Ce-Mo catalysts/LDPC not only exhibited excellent catalytic performance at low temperature, they also exhibited good resistance to H2O and SO2. The NOx conversion efficiency remained above 89% at 160 °C when the flue gas contained 100 ppm SO2 and 7 vol.% H2O. The analysis of NH3-TPD and XPS confirmed that Mn2Ce1Ox catalysts modified with Mo had the stronger surface acidity and more adsorbed oxygen, leading to higher NH3-SCR activity and better resistance to SO2 and H2O.

1. Introduction

The Industrial revolution brought prosperity, but it also brought nitrogen oxides (NOx), harming the biological environment. Nitrogen oxides not only caused acid rain and smog, they also had serious effects on human life and health. There are several emerging technologies to control NOx emissions, such as the electron beam process (EBP) [1], low temperature adsorption (LTA) [2], or wet oxidative scrubbing (WOS) [3]. The emerging technologies mentioned above allow for very high performance, often even higher than traditional denitrification technologies. There are still challenges to the widespread application of the mentioned emerging technologies, such as high energy consumption and the high disposal costs of the generated waste.
The most widely used technologies for flue gas denitrification are selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) [4]. The application of SNCR was limited because of low denitrification efficiency and high activity temperature [5,6]. The selective catalytic reduction of ammonia (NH3-SCR) as a mature denitrification technology has been widely used in the power generation industry. Although vanadium-based catalysts have been widely used, especially V2O5-WO3/TiO2, they have high activity only in the temperature range of 300–400 °C [7,8,9]. The flue gas from the iron and steel industry was less than 300 °C and included H2O and SO2, which are harmful to catalytic performance [10,11,12,13]. Therefore, many efforts have been made to develop SCR catalysts without vanadium element that have low-temperature catalytic activity and tolerance to H2O and SO2 [14,15,16]. The Mn-based catalysts showed good redox and high oxygen-atom migration ability in the field of flue gas denitrification below 300 °C [17]. However, the temperature window of these catalysts was too narrow, and they were also susceptible to the influence of SO2 in the flue gas [18,19,20,21,22]. Therefore, manganese-containing composite oxide catalysts were developed to improve the overall performance of catalyst. Li et al. [23] added Ni into MnOx catalyst and found that the catalyst had good catalytic activity in the middle and low temperature range. Lin et al. [24] found that loading Mn and Ce oxides onto zeolites could improve the generation of Mn-Ce acid sites by inhibiting grain growth and accelerating the SCR catalytic reaction. In addition, WO3 and MoO3 were commonly used to improve catalytic performance of catalysts [19,21]. Because of its excellent catalytic performance, Mo has been studied in recent years for use in low-temperature denitrification catalysts. Xiao et al. [25] prepared a series of Mo-modified Mox-MnOx catalysts using the co-precipitation method and found that the addition of Mo can increase the content of acidity sites, thus improving catalyst activity and H2O resistance performance. Chen et al. [26] reported that the addition of Mo significantly inhibited the deposition of ammonium bisulfate and improved the SO2 resistance performance of the catalyst.
Preparation method and catalyst carrier are of great interest in current research regarding catalytic denitrification. TiO2 and Al2O3 were favored in catalyst carriers [15,27,28]. In the flue gas purification process, the SCR reactor was installed in the back end of the desulfurization device and electrostatic precipitator. The dust removal and denitrification processes caused a series of issues such as occupying a large area, having a high cost, and being difficult to maintain [29,30,31]. The integrated purification process of flue gas has become a new trend because of its shorter process flow, lower investment and operating costs for equipment, and small footprint [32].
Ceramic filters have been widely used in gas purification because of their excellent performance in terms of mechanical strength, thermal shock resistance, heat resistance, and chemical resistance [33,34,35]. Low-density porous ceramics (LDPC) made of ceramic fibers could remove more than 99% of the dust in the flue gas. The porous ceramic loaded with catalyst could be used for simultaneous dust removal and denitrification. Li et al. [36] reported that MnCeOx/TiO2-Al2O3 catalyst exhibited 99% NOx conversion at 150 °C. The NOx conversion decreased to 93% when 10 vol.% H2O was introduced, and the NOx conversion decreased to 60% when 50 ppm SO2 was introduced. Zhou et al. [37] produced Mn-Fe-Ce catalysts by oxidative loading of Mn and Fe on the surface of CeO2 catalysts. The NOx conversion was 90% at the range of 190–240 °C. When 100 ppm SO2 was introduced in feed gas, the NOx conversion decreased to 30%. Therefore, the H2O and SO2 in the flue gas would adversely affect the catalytic activity. The high filtration velocity of the flue gas would prevent the catalyst from working to its full potential. Zhang et al. [38] prepared Ce(1.0)Mn/TiO2 catalyst and found that the increase of GHSV (gaseous hourly space velocity) led to a decrease in NOx conversion, from 98% to 80%, when the GHSV was 45,000 h−1.
In this study, Mn-Ce catalysts were loaded on LDPC using the impregnation method to achieve simultaneous dust removal and denitrification. Mo was used to modify Mn-Ce catalysts to improve the performance of Mn-Ce catalysts. The effect of adding Mo to Mn-Ce catalysts on NH3-SCR catalytic activity and SO2 and H2O resistance at low temperature was studied. In order to improve the operation efficiency of the equipment, the effect of filtration velocity on catalytic performance and filtration performance was also discussed.

2. Materials and Methods

2.1. Preparation of Catalysts

The specific description of LDPC preparation can be found in our previous articles [39,40]. Firstly, the alumina fiber, glass powder, binder, and water were mixed in a certain mass ratio. The mixture was then aged at room temperature for 24 h and pressed into a cylindrical body (φ 22 × 10 mm). Finally, the cylindrical body was sintered at 1150 °C for 1 h. The Mn-Ce catalysts (Mn/Ce = 1, 2, 3) were loaded on the LDPC matrix by impregnation. First, manganese nitrate and cerium nitrate hexahydrate were dissolved in distilled water in the designated proportion to form a precursor solution. The impregnation was operated at the pressure condition of −0.09 MPa for 15 min to ensure the penetration of precursor solution into LDPC. Finally, the catalyst-loaded LDPC was dried at 50 °C for 6 h and calcined at 400 °C for 3 h. The designated proportion of ammonium molybdate tetrahydrate was also added to the precursor solution to prepare Mo-modified Mn-Ce/LDPC. The rest of the steps were the same as previously described.

2.2. Catalytic-Activity Test

The performance of the catalysts for NOx reduction was measured in a tubular furnace reactor. The reactor consisted of a programmable temperature control furnace and two glass tubes (inner diameter, 38 mm and 22 mm). The cylindrical catalytic filter (diameter was 22 mm) was fixed at the end of the glass tube (diameter was 22 mm) (Figure 1). The gases used in the experiment were calibrated. The mass flow controllers were used to control the flow of various gases. The different components content of the gas after reaction were analyzed on-line using a flue gas analyzer. The feed gas consisted of 500 ppm NH3, 500 ppm NOx, 6 vol.%O2, 100 ppm SO2 (when used), and 7 vol.% H2O (when used), and was balanced with N2. The filtration velocity was controlled as 1 m/min, 2 m/min, and 4 m/min (GHSV = 75,000 h−1, 150,000 h−1, 300,000 h−1). At 2 h after the tube furnace reached the setting temperature, the NOx conversion was collected. Then, the temperature was elevated to the next setting point, and the NOx conversion at the next setting temperature was tested. The NOx concentration was detected by the ECOM-D flue gas analyzer (Ecom GmbH, Nordrhein-Westfalen, Germany) and was calculated according to Equation (1). NOin means the NOx concentration before the reaction, and NOout means the NOx concentration after the reaction. The resistance of the catalytic LDPC was measured according to the Chinese standard (GB/T 6165–2008). The filter resistance was obtained by calculating the static pressure difference of the filter under different air volume conditions.
NO X   conversion = NO in − NO out NO in × 100 %
The dust removal efficiency of the sample was studied through a simulation experiments, and the filter resistance was used to judge the dust removal efficiency of the sample. The dust concentration of gas was tested by laser dust analyzer. First, the LDPC and the catalyst-supported LDPC were covered with cement ash at 2–3 mm thickness, followed by pulse blowback. The process was repeated several times, and both the repeating times and the resistance of sample was recorded.
In order to show the results clearly, all data presented are the average of all replicate experiments.

2.3. Characterization of Catalysts

The phase of the catalyst was determined by X-ray diffraction (XRD) using the Rigaku Smartlab diffractometer equipped with the Cu Kα monochromator, and 2θ was collected from 10° to 90° in 0.02° steps at a scan rate of 10°/min. The microstructure and morphology of the sample was observed by scanning electron microscopy (SEM, JSM-6510). The distribution of catalysts was obtained by vantage DS X-ray energy spectrometer. X-ray photoelectron spectroscopy (XPS) was implemented on the KRATOS AXIS SUPRATM surface analysis system, using Al Kα radiation (1486.6 eV, 150 W) to analyze surface atomic concentrations and the chemical state of the elements. XPS spectroscopy was calibrated based on the binding energy of C1s (BE = 284.6 eV).
H2-temperature programmed reduction (H2-TPR) experiments were carried out on a chemisorption analyzer (Autochem II 2920, Micromeritics). Before the test, all samples were purged with Ar (50 mL/min) at 400 °C for 30 min, then cooled to 50 °C. H2-TPR was carried out in a mixed gas (50 mL/min) with 5% H2 and 95% Ar from 100 to 700 °C with a heating rate of 10°C/min.
NH3-temperature programmed desorption experiments (NH3-TPD) were performed on a chemisorption analyzer (Autochem II 2920, Micromeritics). The experiments included following steps: (1) samples were pretreated with He (50 mL/min) at 400 °C for 30 min. (2) Samples were kept in NH3 atmosphere at 50 °C for 1 h. (3) Samples were treated with He (50 mL/min) at 100 °C for 1 h to eliminate physically absorbed NH3. (4) Samples were heated from 100 to 700 °C at 10 °C/min in an He atmosphere (50 mL/min), and NH3-TPD data were recorded in the meantime.

3. Results and Discussion

3.1. Catalytic Performance

The ratio of Mn/Ce was an important factor in catalytic performance. NH3-SCR activity in the temperature range of 80–240 °C for different Mn/Ce ratio catalysts was shown in Figure 2a. It can be seen that Mn2Ce1Ox/LDPC and Mn1Ce1Ox/LDPC exhibited higher NOx conversion (more than 92%) at filtration speed of 1 m/min (GHSV = 75,000 h−1). Mn2Ce1Ox/LDPC exhibited a wider temperature window than Mn1Ce1Ox/LDPC. When the ratio of Mn/Ce was 2:1, the Mn-Ce catalysts/LDPC exhibited the best catalytic performance. The NOx conversion was improved after Mn-Ce catalysts/LDPC were modified by Mo. NOx conversion of Mn2Ce1Mo0.2Ox/LDPC always stayed at 99.6% from 120°C to 200 °C. When the temperature was too high, the adsorption of NOx and NH3 on the catalyst surface was inhibited. Therefore, the NOx conversion decreased at temperatures above 200 °C. The Mn2Ce1Mo0.2Ox/LDPC has best catalytic performance compared with other Mn-Ce catalysts/LDPC.
The catalyst loading was another important factor in catalytic performance. Overall, the catalytic performance increased as the catalyst loading increased. As shown in Figure 2b, the NOx conversion for the samples with the catalyst loading of 8 wt.% was highest, and the NOx conversion on Mn2Ce1Ox/LDPC with a catalyst load of 8 wt.% over a temperature range of 100 to 220 °C was above 95%.
On the other hand, the filtration resistance of the catalytic LDPC was influenced by the catalyst loading. The filter resistance increased slowly with the increase of catalyst loading. When catalyst loading reached 8 wt.%, the filter resistance of the catalytic LDPC increased by 40 Pa compared to LDPC without catalyst (90 Pa), which was an acceptable increment. There was a sharp increase in filtration resistance for the sample with 10 wt.% catalyst loading (Figure 2c). However, the catalytic efficiency of the sample with 10 wt.% catalyst loading did not increase significantly and showed a slight decrease. Therefore, LDPC with 8 wt.% catalyst loading had a high catalytic performance and relatively low filtration resistance.

3.2. Effects of H2O and SO2 to Catalytic Performance

The exhaust gas generally contains a certain amount of SO2 and H2O, resulting in the poisoning of the SCR catalyst and the gradual loss of catalyst activity. Therefore, the tolerance to SO2 and H2O poisoning for the catalysts must be evaluated. Figure 3 showed the results of H2O and SO2 resistance tests for Mn2Ce1Ox/LDPC, Mn2Ce1Mo0.1Ox/LDPC and Mn2Ce1Mo0.2Ox/LDPC. As can be seen from Figure 3a, the introduction of 7 vol% H2O in the feed gas has little effect on the activity of Mn2Ce1Ox/LDPC, Mn2Ce1Mo0.1Ox/LDPC and Mn2Ce1Mo0.2Ox/LDPC at 160 °C. The NOx conversion only decreased by less than 4% for all the samples. In addition, about an hour after stopping the introduction of H2O, The NOx conversion can be fully recovered. In general, the deactivation of the catalyst for the NH3-SCR reaction with H2O was caused by the competitive adsorption of H2O with NH3. The recovery of NOx conversion after stopping the water introduction also confirmed that the effect of H2O was reversible.
The effect of SO2 on the activity of Mn2Ce1Ox/LDPC, Mn2Ce1Mo0.1Ox/LDPC and Mn2Ce1Mo0.2Ox/LDPC were shown in Figure 3b. It can be observed that the introduction of 100 ppm SO2 into the feed gas resulted in a decrease in the NOx conversion. Specifically, after 4 h of reaction, NOx conversion over the Mn2Ce1Ox/LDPC decreased continuously from 96% to 70%. The NOx conversion over the Mn2Ce1Mo0.2Ox/LDPC only decreased from 99% to 94% under the same conditions. It clearly indicated that Mo was beneficial to improve the SO2 resistance of Mn2Ce1Ox/LDPC. In addition, after stopping SO2 introduction, the activity of these Mn-Ce catalysts/LDPC were only slightly restored (5–15%), indicating that the poisoning of SO2 on these Mn-Ce catalysts/LDPC were irreversible.
It was necessary to investigate the stability of samples under the condition of containing SO2 and H2O at low temperatures. When SO2 and H2O were introduced in the reaction gas, NOx conversion was decreased (Figure 3c). NOx conversion over the Mn2Ce1Ox/LDPC decreased from 96.4% to 57.6% after 4 h, and NOx conversion over the Mn2Ce1Mo0.2Ox/LDPC only decreased from 99% to 88% after 4 h. These phenomena clearly showed that the incorporation of an appropriate amount of Mo was beneficial to improve the SO2 and H2O resistance of Mn2Ce1Ox/LDPC. Table 1 provides a comparison of the catalytic performance in the presence of SO2 and H2O for Mn-Ce-Mo/LDPC with other catalysts reported in the literature.

3.3. Effects of High Filtration Velocity to Catalytic Performance

The NH3-SCR performance of Mn2Ce1Ox/LDPC, Mn2Ce1Mo0.1Ox/LDPC and Mn2Ce1Mo0.2Ox/LDPC at different filtration velocities (1 m/min, 2 m/min, and 4 m/min) were also tested (Figure 4). The NOx conversion for all Mn-Ce catalysts/LDPC decreased to different levels when the filtration velocity increased. It can be seen that the NOx conversion over Mn2Ce1Ox/LDPC was heavily influenced by the filtration velocity. NOx conversion decreased to 90% when the filtration velocity reached 4 m/min. Meanwhile, the NOx conversion over Mn2Ce1Mo0.2Ox/LDPC was scarcely influenced by the filtration velocity. When the filtration velocity rose to 4 m/min, the NOx conversion still stayed at 97% from 120 °C to 220 °C. This phenomenon indicated that the addition of Mo to Mn2Ce1Ox/LDPC was beneficial to maintain high denitrification performance at high filtration velocity.

3.4. Dust Removal Efficiency and Filtration Resistance

The dust removal efficiency and filtration resistance were both important elements of filtration performance for Mn-Ce catalysts/LDPC. The filtration performance of the Mn2Ce1Mo0.2Ox/LDPC was tested using dusty gas with dust concentration of 5 g/m3. After filtration, the dust concentration decreased to 0.5 mg/m3. The dust removal efficiency of Mn2Ce1Mo0.2Ox/LDPC was therefore calculated to be 99.99%.
Pulse blowback is often used to collect dust and reduce filter resistance in industry production. The effect of fly ash layer and pulse blowback on Mn2Ce1Mo0.2Ox/LDPC filtration resistance and catalytic performance has been reflected in Figure 5. As the times of pulse blowback increases, resistance of Mn2Ce1Mo0.2Ox/LDPC gradually stabilized to about 213 Pa. Compared to the initial resistance of Mn2Ce1Mo0.2Ox/LDPC (about 110 Pa), the resistance only increased by 100 Pa. A small change in the filtration resistance indicated that the filtration performance was excellent. The increase of filtration resistance would not affect the catalytic performance of Mn2Ce1Mo0.2Ox/LDPC. After 240 times pulse blowback and cleaning, the NOx conversion over Mn2Ce1Mo0.2Ox/LDPC did not significantly decrease.

3.5. Characterization

3.5.1. Crystal Phase Analysis

The XRD pattern of Mn-Ce catalysts in 2θ range from 10° to 90° were shown in Figure 6. The XRD pattern at 2θ of 28.55°, 33.58°, 47.79°, 56.47°, and 58.72° corresponded to the (1 1 1), (2 0 0), (2 2 0), (3 1 1), and (2 2 2) planes of CeO2’s fluorite cubic phase (PDF#34-0394), respectively. With the increase of Mn/Ce, the diffraction peaks became wider and weaker, which indicated the poor crystallization of CeO2 and MnO2. Poor crystallization would enhance catalytic performance [30]. The diffraction peak at 28.55° slightly shifted towards higher angle with the increase of Mn/Ce. This phenomenon implied that a part of Mn4+ incorporated into the lattice of CeO2 because the ion radius of Ce4+ (0.097 nm) was much bigger than ion radius of Mn4+ (0.053 nm). The incorporation of Mn into CeO2 would cause the structure to distort, which was beneficial to improving catalytic performance [43]. Those were consistent with our catalytic performance experiment.
It was also observed that there was a peak at 2θ of 37.33°, which was attributed to MnO2. It may be that the excessive Mn ions were not incorporated into the cerium oxide lattice. Compared to the XRD pattern of Mn2Ce1Ox, the peak at 2θ of 37.33° for Mn2Ce1Mo0.2Ox was not significant. This indicated that the addition of Mo inhibited the crystallization of MnO2. Combined with the results of catalytic performance, the poor crystallization of MnO2 was beneficial to the improvement of catalytic performance. It can be observed that the diffraction peak at 28.55° for Mn2Ce1Mo0.2Ox slightly shifted towards higher angle, which implied the contraction of the lattice. The incorporation of Mo6+ into the lattice induced a decrease in the lattice parameters because the ion radius of Mo6+ (0.059 nm) was less than the ion radius of Ce4+ (0.097 nm).

3.5.2. Microstructure and Morphology of Mn-Ce Catalytic LDPC

The microstructure and morphology of Mn-Ce catalytic LDPC was observed by SEM. Figure 7a,b showed the porous structure of Mn-Ce catalytic LDPC and LDPC matrix. Ceramic fibers built up 3D interconnected porous structure and formed gas channels, which allowed effective filtration for flue gas. The 3D interconnected porous structure ensured that the dust in the gas did not come into direct contact with catalysts. For Mn-Ce catalytic LDPC with catalyst loading of 8 wt.%, the channels were not blocked by catalyst. Meanwhile, for the sample with catalyst loading of 12 wt.%, the channels were blocked by catalyst. It is noticeable that the right amount of catalyst was an important factor to filtration resistance. An excess of catalyst will block the channels of the ceramic substrate and increase the filtration resistance, which was consistent with the resistance test results in this study.
Figure 8 showed the EDS mapping images of catalysts distribution for Mn-Ce catalysts/LDPC. The distribution of aluminum and silicon elements overlapped and showed the fiber matrix. Mn and Ce uniformly distributed around the fiber, which indicated that the catalyst was supported on the fibers.

3.5.3. Atomic Species and Valence Analysis

The XPS measurement revealed the various atomic species on the surface of Mn-Ce catalyst. Figure 9a–c showed the XPS spectra of Mn2p, Ce3d and O1s, respectively, and Table 2 showed binding energies and relative atomic percentages. As shown in Figure 9a, all catalysts had two peaks in the spectra that corresponded to Mn3+ (641.2 eV and 652.7 eV) and Mn4+ (642.3 eV and 653.8 eV), respectively. It was reported that the SCR activity of different manganese oxides followed the order MnO2 > Mn2O3 > Mn3O4, and Mn4+ presented the best NH3-SCR activity [15]. It can be seen that Mn4+ and Mn3+ were the dominant Mn species in the catalysts, and their proportions were 53% and 47% in Mn2Ce1Ox, 53.5% and 46.5% in Mn2Ce1Mo0.1Ox and 55.3% and 44.7% in Mn2Ce1Mo0.2Ox, respectively. The content of Mn4+ increased with the addition of Mo. Under redox conditions, more Mn4+ could produce more oxygen vacancy (Vo), which was helpful for the catalytic process, as shown in Equation (2). The gas phase oxygen could replenish oxygen vacancies and create active oxygen species to accelerate the catalytic reaction [44]. The results were consistent with our catalytic performance experiment.
2 Mn4+ + O2−(ads) → 2 Mn3+ + e− + VO + 1/2 O2(g)
In Figure 9b, the O1s spectrum was fitted into three peaks: chemical-adsorbed oxygen (Oβ) at 531.0 eV, surface chemisorbed water (Oγ) at 532.2 eV, lattice oxygen (Oα) at 529.4 eV [45]. In general, more chemical-adsorbed oxygen resulted in better SCR activity [46,47]. According to the calculations, the content of chemical-adsorbed oxygen (Oβ) increased slightly with the addition of Mo. According to Equation (2), more chemical-adsorbed oxygen (Oβ) could produce more oxygen vacancy (VO) and free electron (e−). More free electron (e−) could facilitate the process of redox reaction. These results suggest that the introduction of Mo increased the content of oxygen vacancy (VO) which improved the catalytic performance. The results were consistent with our catalytic performance experiment.
As shown in Figure 9c, the Ce3d spectrum can be divided into eight peaks. The v, v2, v3, u, u2, and u3 were considered to be Ce4+ species, while the v1 and u1 were considered to be Ce3+ species [45]. The percentage of Ce4+ were also calculated (87.1% for Mn2Ce1Ox, 85.5% for Mn2Ce1Mo0.1Ox, and 86.9% for Mn2Ce1Mo0.2Ox), and the order of Ce4+ ratios was Mn2Ce1Ox > Mn2Ce1Mo0.2Ox > Mn2Ce1Mo0.1Ox. Although Ce4+ was a key factor for SCR reaction, a slight change did not influence the catalytic activity decisively.

3.5.4. Reducibility and Acidity

The redox ability of catalyst was considered to be one of the most important factors in the NH3-SCR reaction [48]. In order to observe the effect of Mo on Mn2Ce1Ox, the redox ability of the sample was characterized by H2-TPR, as shown in Figure 10. Two reduction peaks were visible in the range of 200–400 °C. The peak in region I was attributed to the reduction of MnO2 → Mn2O3, and peak in region II was attributed to the reduction of Mn2O3 → Mn3O4. It is worth noting that the reduction peaks for the Mn2Ce1Mo0.2Ox catalyst shifted towards higher temperature compared to the Mn2Ce1Ox catalyst, and the relative area of the peak increased. This suggests that Mo can modulate the redox properties of the catalyst to ensure the activation of ammonia rather than the formation of nitrate species caused by excessive oxidation during the reaction. The addition of Mo resulted in a significant increase in H2 consumption, indicating that the incorporation of Mo increased the number of surface reducible species. The relative area of the peak was proportional to the redox ability, and strong redox ability creates better catalytic performance. The results were consistent with our experiment, indicating that the catalytic performance of the Mn2Ce1Mo0.2Ox catalyst was better than the Mn2Ce1Ox catalyst.
NH3-TPD tests were conducted to explore the relationship between catalytic performance and the surface acidity of the catalyst (as shown in Figure 10). It is well known that the surface acidity of the catalyst played an essential role in the NH3-SCR reaction, the overall area of the desorption peaks represents the numbers of acid sites, and the temperature of desorption peak is related to the acid strength [38]. It can be seen that the NH3-TPD profiles of Mn2Ce1Ox and Mn2Ce1Mo0.2Ox catalysts exhibited three desorption peaks (labeled as I, II, and III), which were ascribed to NH3 desorption from weak, medium, and strong acid sites, respectively. The low-temperature desorption peak (peak I) can be attributed to NH3 coordinated on Brønsted acid sites, while the high-temperature (peak II and III) desorption peak was related to the Lewis acid sites [49]. The relative area of all the desorption peaks increased with the addition of Mo, which represented the increase of acid sites on the catalyst surface. More acid sites were conducive to the improvement of catalytic performance. The peak III shifted to low temperature after the addition of Mo, which meant that the acidity of strong acid decreased to medium acid. More medium acid sites were beneficial to the capture and release of NH3 in SCR process. Combining the results of NH3-TPD, H2-TPR, and catalytic performance tests, it can be concluded that the introduction of Mo not only improved the acidity of Mn-Ce catalyst, but also facilitated the capturing and releasing of NH3 in the SCR reaction.

4. Conclusions

Mn-Ce catalysts/LDPC modified with Mo was synthesized by the simple impregnation method. The addition of Mo to Mn-Ce catalysts/LDPC enhanced the catalytic performance. Mn2Ce1Mo0.2Ox/LDPC showed the best denitrification activity with more than 95% NOx conversion in a wide temperature range (100–220 °C) and significant H2O and SO2 resistance. The NOx conversion remained above 89% after 100 ppm SO2 and 7 vol.% H2O were introduced to feed gas. The NOx conversion over Mn2Ce1Mo0.2Ox/LDPC stayed at 97% from 120 °C to 220 °C when the filtration velocity reached to 4 m/min. It indicated that Mn2Ce1Mo0.2Ox/LDPC could filter more flue gas with high NOx conversion efficiency in the same amount of time. The crystallinity of catalyst decreased and more oxygen vacancies and active oxygens were generated after adding Mo to Mn-Ce catalysts, which enhanced NOx conversion and SO2 resistance property. The Mn2Ce1Mo0.2Ox/LDPC had low filtration resistance and good dust removal performance and the NOx conversion was less affected by fly ash. The results exhibit that Mn2Ce1Mo0.2Ox/LDPC has good potential for simultaneous denitrification and dust removal.

Author Contributions

Conceptualization, J.J. and H.Z.; Experimental preparation and operation, writing—original draft, and employing software, T.Z.; writing—review and editing, H.Z.; supervision, J.J. and H.Z.; project administration, J.J. and H.Z.; funding acquisition, J.J. and H.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This work has received financial support from the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).

Data Availability Statement

All data that support the findings of this study are included within the article.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Chmielewski, A.G.; Sun, Y.; Zimek, Z.; Bułka, S.; Licki, J. Mechanism of NOx removal by electron beam process in the presence of scavengers. Radiat. Phys. Chem. 2002, 65, 397–403. [Google Scholar] [CrossRef]
  2. Wang, S.; Xu, S.; Gao, S.; Xiao, P.; Jiang, M.; Zhao, H.; Huang, B.; Liu, L.; Niu, H.; Wang, J.; et al. Simultaneous removal of SO2 and NOx from flue gas by low-temperature adsorption over activated carbon. Sci. Rep. 2021, 11, 11003. [Google Scholar] [CrossRef] [PubMed]
  3. Flagiello, D.; Erto, A.; Lancia, A.; Di Natale, F. Advanced Flue-Gas cleaning by wet oxidative scrubbing (WOS) using NaClO2 aqueous solutions. Chem. Eng. J. 2022, 447, 137585. [Google Scholar] [CrossRef]
  4. Muzio, L.J.; Quartucy, G.C.; Cichanowiczy, J.E. Overview and status of post-combustion NOx control: SNCR, SCR and hybrid technologies. Int. J. Environ. Pollut. 2002, 17, 4–30. [Google Scholar] [CrossRef]
  5. Fu, S.-l.; Song, Q.; Yao, Q. Study on the catalysis of CaCO3 in the SNCR deNOx process for cement kilns. Chem. Eng. J. 2015, 262, 9–17. [Google Scholar] [CrossRef]
  6. Guo, Y.; Luo, L.; Zheng, Y.; Wang, J.; Zhu, T. Low-medium temperature application of selective catalytic reduction denitration in cement flue gas through a pilot plant. Chemosphere 2021, 276, 130182. [Google Scholar] [CrossRef]
  7. Kong, M.; Liu, Q.; Zhou, J.; Jiang, L.; Tian, Y.; Yang, J.; Ren, S.; Li, J. Effect of different potassium species on the deactivation of V2O5-WO3/TiO2 SCR catalyst: Comparison of K2SO4, KCl and K2O. Chem. Eng. J. 2018, 348, 637–643. [Google Scholar] [CrossRef]
  8. Zheng, Z.; Du, X.; Wang, X.; Liu, Y.; Chen, K.; Lu, P.; Rac, V.; Rakic, V. Experimental investigation on the decomposition of NH4HSO4 over V2O5-WO3/TiO2 catalyst by NH4NO3 at low temperature. Fuel 2023, 333, 126443. [Google Scholar] [CrossRef]
  9. Kong, M.; Liu, Q.; Jiang, L.; Tong, W.; Yang, J.; Ren, S.; Li, J.; Tian, Y. K+ deactivation of V2O5-WO3/TiO2 catalyst during selective catalytic reduction of NO with NH3: Effect of vanadium content. Chem. Eng. J. 2019, 370, 518–526. [Google Scholar] [CrossRef]
  10. Ali, S.; Li, Y.; Zhang, T.; Bakhtiar, S.u.H.; Leng, X.; Li, Z.; Yuan, F.; Niu, X.; Zhu, Y. Promotional effects of Nb on selective catalytic reduction of NO with NH3 over Fe-Nb0.5--Ce0.5 (x = 0.45, 0.4, 0.35) oxides catalysts. Mol. Catal. 2018, 461, 97–107. [Google Scholar] [CrossRef]
  11. Tang, X.; Shi, Y.; Gao, F.; Zhao, S.; Yi, H.; Xie, Z. Promotional role of Mo on Ce0.3FeOx catalyst towards enhanced NH3-SCR catalytic performance and SO2 resistance. Chem. Eng. J. 2020, 398, 125619. [Google Scholar] [CrossRef]
  12. Kwon, D.W.; Nam, K.B.; Hong, S.C. The role of ceria on the activity and SO2 resistance of catalysts for the selective catalytic reduction of NOx by NH3. Appl. Catal. B Environ. 2015, 166–167, 37–44. [Google Scholar] [CrossRef]
  13. Sazama, P.; Wichterlová, B.; Tábor, E.; Šťastný, P.; Sathu, N.K.; Sobalík, Z.; Dědeček, J.; Sklenák, Š.; Klein, P.; Vondrová, A. Tailoring of the structure of Fe-cationic species in Fe-ZSM-5 by distribution of Al atoms in the framework for N2O decomposition and NH3-SCR-NOx. J. Catal. 2014, 312, 123–138. [Google Scholar] [CrossRef]
  14. Qi, G.; Yang, R.T. Low-temperature selective catalytic reduction of NO with NH3 over iron and manganese oxides supported on titania. Appl. Catal. B Environ. 2003, 44, 217–225. [Google Scholar] [CrossRef]
  15. Jin, R.; Liu, Y.; Wu, Z.; Wang, H.; Gu, T. Low-temperature selective catalytic reduction of NO with NH3 over Mn-Ce oxides supported on TiO2 and Al2O3: A comparative study. Chemosphere 2010, 78, 1160–1166. [Google Scholar] [CrossRef]
  16. Yang, N.-z.; Guo, R.-t.; Pan, W.-g.; Chen, Q.-l.; Wang, Q.-s.; Lu, C.-z. The promotion effect of Sb on the Na resistance of Mn/TiO2 catalyst for selective catalytic reduction of NO with NH3. Fuel 2016, 169, 87–92. [Google Scholar] [CrossRef]
  17. Chen, L.; Ren, S.; Liu, L.; Su, B.; Yang, J.; Chen, Z.; Wang, M.; Liu, Q. Catalytic performance over Mn-Ce catalysts for NH3-SCR of NO at low temperature: Different zeolite supports. J. Environ. Chem. Eng. 2022, 10, 107167. [Google Scholar] [CrossRef]
  18. Kong, M.; Zhang, H.; Wang, Y.; Liu, Q.; Liu, W.; Wu, H. Efficient MnO -CeO2/Ti-bearing blast furnace slag catalyst for NH3-SCR of NO at low temperature: Study of support treating and Mn/Ce ratio. J. Environ. Chem. Eng. 2022, 10, 108238. [Google Scholar] [CrossRef]
  19. Hu, X.; Huang, L.; Zhang, J.; Li, H.; Zha, K.; Shi, L.; Zhang, D. Facile and template-free fabrication of mesoporous 3D nanosphere-like MnxCo3−xO4 as highly effective catalysts for low temperature SCR of NOx with NH3. J. Mater. Chem. A 2018, 6, 2952–2963. [Google Scholar] [CrossRef]
  20. Geng, Y.; Chen, X.; Yang, S.; Liu, F.; Shan, W. Promotional Effects of Ti on a CeO2-MoO3 Catalyst for the Selective Catalytic Reduction of NOx with NH3. ACS Appl. Mater. Interfaces 2017, 9, 16951–16958. [Google Scholar] [CrossRef]
  21. Li, C.; Tang, X.; Yi, H.; Wang, L.; Cui, X.; Chu, C.; Li, J.; Zhang, R.; Yu, Q. Rational design of template-free MnOx-CeO2 hollow nanotube as de-NOx catalyst at low temperature. Appl. Surf. Sci. 2018, 428, 924–932. [Google Scholar] [CrossRef]
  22. Jiang, L.; Liu, Q.; Ran, G.; Kong, M.; Ren, S.; Yang, J.; Li, J. V2O5-modified Mn-Ce/AC catalyst with high SO2 tolerance for low-temperature NH3-SCR of NO. Chem. Eng. J. 2019, 370, 810–821. [Google Scholar] [CrossRef]
  23. Li, G.; Zhu, B.; Sun, Y.; Yin, S.; Zi, Z.; Fang, Q.; Ge, T.; Li, J. Study of the alkali metal poisoning resistance of a Co-modified Mn/Ni foam catalyst in low-temperature flue gas SCR DeNOx. J. Mater. Sci. 2018, 53, 9674–9689. [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 Environ. 2018, 223, 91–102. [Google Scholar] [CrossRef]
  25. Hu, X.; Shi, Q.; Zhang, H.; Wang, P.; Zhan, S.; Li, Y. NH 3 -SCR performance improvement over Mo modified Mox-MnOx nanorods at low temperatures. Catal. Today 2017, 297, 17–26. [Google Scholar] [CrossRef]
  26. Chen, Y.; Li, C.; Chen, J.; Tang, X. Self-Prevention of Well-Defined-Facet Fe2O3/MoO3 against Deposition of Ammonium Bisulfate in Low-Temperature NH3-SCR. Environ. Sci. Technol. 2018, 52, 11796–11802. [Google Scholar] [CrossRef]
  27. Ma, Y.; Lai, J.; Wu, J.; Zhang, H.; Yan, J.; Li, X.; Lin, X. Efficient synergistic catalysis of chlorinated aromatic hydrocarbons and NOx over novel low-temperature catalysts: Nano-TiO2 modification and interaction mechanism. Chemosphere 2023, 315, 137640. [Google Scholar] [CrossRef]
  28. Jin, R.; Liu, Y.; Wang, Y.; Cen, W.; Wu, Z.; Wang, H.; Weng, X. The role of cerium in the improved SO2 tolerance for NO reduction with NH3 over Mn-Ce/TiO2 catalyst at low temperature. Appl. Catal. B Environ. 2014, 148–149, 582–588. [Google Scholar] [CrossRef]
  29. Li, C.; Huangfu, L.; Li, J.; Gao, S.; Xu, G.; Yu, J. Recent advances in catalytic filters for integrated removal of dust and NO from flue gas: Fundamentals and applications. Resour. Chem. Mater. 2022, 1, 275–289. [Google Scholar] [CrossRef]
  30. Pan, B.; Chen, J.; Zhang, F.; Zhang, B.; Li, D.; Zhong, Z.; Xing, W. Porous TiO2 aerogel-modified SiC ceramic membrane supported MnOx catalyst for simultaneous removal of NO and dust. J. Membr. Sci. 2020, 611, 118366. [Google Scholar] [CrossRef]
  31. Shan, L.; Yin, R.; Xiao, J.; Wang, H.; Ma, L.; Li, J.; Chen, J. Simultaneous removal of NOx and dust with integrated catalytic filter: Interactions between NH3-SCR and filtration processes. Chem. Eng. J. 2023, 458, 141466. [Google Scholar] [CrossRef]
  32. Chen, Y.-S.; Hsiau, S.-S.; Smid, J.; Wu, J.-F.; Ma, S.-M. Removal of dust particles from fuel gas using a moving granular bed filter. Fuel 2016, 182, 174–187. [Google Scholar] [CrossRef]
  33. Ryś-Matejczuk, M.; Müller, M. Corrosion behaviour of ceramic filter candle materials for hot gas filtration under biomass gasification conditions at 850 °C. Adv. Appl. Ceram. 2014, 112, 466–470. [Google Scholar] [CrossRef]
  34. Heidenreich, S.; Haag, W.; Salinger, M. Next generation of ceramic hot gas filter with safety fuses integrated in venturi ejectors. Fuel 2013, 108, 19–23. [Google Scholar] [CrossRef]
  35. Zhong, Z.; Xing, W.; Li, X.; Zhang, F. Removal of Organic Aerosols from Furnace Flue Gas by Ceramic Filters. Ind. Eng. Chem. Res. 2013, 52, 5455–5461. [Google Scholar] [CrossRef]
  36. Li, G.; Mao, D.; Chao, M.; Li, G.; Yu, J.; Guo, X. Low-temperature NH3-SCR of NO over MnCeO/TiO2 catalyst: Enhanced activity and SO2 tolerance by modifying TiO2 with Al2O3. J. Rare Earths 2021, 39, 805–816. [Google Scholar] [CrossRef]
  37. Zhou, Y.; Ren, S.; Wang, M.; Yang, J.; Chen, Z.; Chen, L. Mn and Fe oxides co-effect on nanopolyhedron CeO2 catalyst for NH3-SCR of NO. J. Energy Inst. 2021, 99, 97–104. [Google Scholar] [CrossRef]
  38. Zhang, X.; Zhang, X.; Yang, X.; Chen, Y.; Hu, X.; Wu, X. CeMn/TiO2 catalysts prepared by different methods for enhanced low-temperature NH3-SCR catalytic performance. Chem. Eng. Sci. 2021, 238, 116588. [Google Scholar] [CrossRef]
  39. Song, X.; Jian, B.; Jin, J. Preparation of porous ceramic membrane for gas-solid separation. Ceram. Int. 2018, 44, 20361–20366. [Google Scholar] [CrossRef]
  40. Li, K.; Zhou, T.; Xu, X.; Han, C.; Zhang, H.; Jin, J. PTFE-Modified Mn-Co-Based Catalytic Ceramic Filters with H2O Resistance for Low-Temperature NH3-SCR. Sustainability 2022, 14, 5353. [Google Scholar] [CrossRef]
  41. Han, Q.; Jin, S.; Wang, J.; Wang, J.; Sun, P.; Zhou, Y.; Wang, X.; Zhang, R.; Qiao, W.; Ling, L.; et al. Insights to sulfur-resistant mechanisms of reduced graphene oxide supported MnOx-CeOy catalysts for low-temperature NH3-SCR. J. Phys. Chem. Solids 2022, 167, 110782. [Google Scholar] [CrossRef]
  42. Chang, H.; Li, J.; Chen, X.; Ma, L.; Yang, S.; Schwank, J.W.; Hao, J. Effect of Sn on MnO–CeO2 catalyst for SCR of NO by ammonia: Enhancement of activity and remarkable resistance to SO2. Catal. Commun. 2012, 27, 54–57. [Google Scholar] [CrossRef]
  43. Venkataswamy, P.; Rao, K.N.; Jampaiah, D.; Reddy, B.M. Nanostructured manganese doped ceria solid solutions for CO oxidation at lower temperatures. Appl. Catal. B Environ. 2015, 162, 122–132. [Google Scholar] [CrossRef]
  44. Li, D.; Li, K.; Xu, R.; Wang, H.; Tian, D.; Wei, Y.; Zhu, X.; Zeng, C.; Zeng, L. Ce1-xFexO2-δ catalysts for catalytic methane combustion: Role of oxygen vacancy and structural dependence. Catal. Today 2018, 318, 73–85. [Google Scholar] [CrossRef]
  45. Yang, J.; Ren, S.; Zhang, T.; Su, Z.; Long, H.; Kong, M.; Yao, L. Iron doped effects on active sites formation over activated carbon supported Mn-Ce oxide catalysts for low-temperature SCR of NO. Chem. Eng. J. 2020, 379, 122398. [Google Scholar] [CrossRef]
  46. Xu, H.; Wang, Y.; Cao, Y.; Fang, Z.; Lin, T.; Gong, M.; Chen, Y. Catalytic performance of acidic zirconium-based composite oxides monolithic catalyst on selective catalytic reduction of NOx with NH3. Chem. Eng. J. 2014, 240, 62–73. [Google Scholar] [CrossRef]
  47. Zhou, L.; Li, C.; Zhao, L.; Zeng, G.; Gao, L.; Wang, Y.; Yu, M.E. The poisoning effect of PbO on Mn-Ce/TiO2 catalyst for selective catalytic reduction of NO with NH3 at low temperature. Appl. Surf. Sci. 2016, 389, 532–539. [Google Scholar] [CrossRef]
  48. Lu, S.; Song, L.; Zhou, C.; Su, Z.; Shu, G.; Ma, K.; Yue, H. Ultra-high hydrothermal stability of Ce-based NH3-SCR catalyst for diesel engines: A substitute for Cu zeolites. Fuel 2023, 338, 127263. [Google Scholar] [CrossRef]
  49. Xiong, Z.; Liu, J.; Guo, F.; Du, Y.; Zhou, F.; Yang, Q.; Lu, W.; Shi, H. Influence of nonmetallic elements doping on the NH3-SCR activity and properties of Ce20W10Ti100O catalyst via melamine modification. J. Solid State Chem. 2023, 321, 123879. [Google Scholar] [CrossRef]
Metals 13 00938 g001 550
Figure 1. Catalytic activity test system: (1) mass flow controller; (2) mixing valve; (3) tube furnace; (4) catalytic ceramic filter; (5) water vapor generator; (6) flue gas analyzer.
Figure 1. Catalytic activity test system: (1) mass flow controller; (2) mixing valve; (3) tube furnace; (4) catalytic ceramic filter; (5) water vapor generator; (6) flue gas analyzer.
Metals 13 00938 g001
Metals 13 00938 g002 550
Figure 2. (a) NOx conversion of Mn-Ce catalysts (Filtration velocity = 1 m/min); (b) Nox conversion of Mn2Ce1Mo0.2Ox/LDPC with the catalyst loading of 4–12%; (c) The filtration resistance of Mn2Ce1Mo0.2Ox/LDPC with catalyst loading of 0–10% (Filtration velocity = 1 m/min).
Figure 2. (a) NOx conversion of Mn-Ce catalysts (Filtration velocity = 1 m/min); (b) Nox conversion of Mn2Ce1Mo0.2Ox/LDPC with the catalyst loading of 4–12%; (c) The filtration resistance of Mn2Ce1Mo0.2Ox/LDPC with catalyst loading of 0–10% (Filtration velocity = 1 m/min).
Metals 13 00938 g002
Metals 13 00938 g003 550
Figure 3. The NOx conversion of Mn2Ce1Ox/LDPC, Mn2Ce1Mo0.1Ox/LDPC and Mn2Ce1Mo0.2Ox/LDPC at 2 m/min filtration velocity, 160 °C. (a) added 7 vol% H2O, (b) added 100 ppm SO2, (c) added 100 ppm SO2 and 7 vol% H2O.
Figure 3. The NOx conversion of Mn2Ce1Ox/LDPC, Mn2Ce1Mo0.1Ox/LDPC and Mn2Ce1Mo0.2Ox/LDPC at 2 m/min filtration velocity, 160 °C. (a) added 7 vol% H2O, (b) added 100 ppm SO2, (c) added 100 ppm SO2 and 7 vol% H2O.
Metals 13 00938 g003
Metals 13 00938 g004a 550Metals 13 00938 g004b 550
Figure 4. NOx conversion of Mn2Ce1MocOx/LDPC with different filtration velocities: (a) Sample: Mn2Ce1Ox/LDPC; (b) Sample: Mn2Ce1Mo0.1Ox/LDPC; (c) Sample: Mn2Ce1Mo0.2Ox/LDPC; (d) Test temperature: 160 °C.
Figure 4. NOx conversion of Mn2Ce1MocOx/LDPC with different filtration velocities: (a) Sample: Mn2Ce1Ox/LDPC; (b) Sample: Mn2Ce1Mo0.1Ox/LDPC; (c) Sample: Mn2Ce1Mo0.2Ox/LDPC; (d) Test temperature: 160 °C.
Metals 13 00938 g004aMetals 13 00938 g004b
Metals 13 00938 g005 550
Figure 5. Filtration performance of Mn2Ce1Mo0.2/LDPC. (a) resistance after pulse blowback; (b) NOx conversion after pulse blowback.
Figure 5. Filtration performance of Mn2Ce1Mo0.2/LDPC. (a) resistance after pulse blowback; (b) NOx conversion after pulse blowback.
Metals 13 00938 g005
Metals 13 00938 g006 550
Figure 6. XRD patterns of (a) MnaCebMocOx catalyst, (b) Mn2Ce1Ox and Mn2Ce1Mo0.2Ox.
Figure 6. XRD patterns of (a) MnaCebMocOx catalyst, (b) Mn2Ce1Ox and Mn2Ce1Mo0.2Ox.
Metals 13 00938 g006
Metals 13 00938 g007 550
Figure 7. SEM images of different catalytic filters: (a,b) empty LDPC, (c) Mn2Ce1Mo0.2Ox/LDPC with the catalyst loading of 8 wt.%, (d) Mn2Ce1Mo0.2Ox/LDPC with the catalyst loading of 12 wt.%.
Figure 7. SEM images of different catalytic filters: (a,b) empty LDPC, (c) Mn2Ce1Mo0.2Ox/LDPC with the catalyst loading of 8 wt.%, (d) Mn2Ce1Mo0.2Ox/LDPC with the catalyst loading of 12 wt.%.
Metals 13 00938 g007
Metals 13 00938 g008 550
Figure 8. EDS mapping images of Mn-Ce catalyst/LDPC.
Figure 8. EDS mapping images of Mn-Ce catalyst/LDPC.
Metals 13 00938 g008
Metals 13 00938 g009 550
Figure 9. XPS spectra of Mn2Ce1Ox, Mn2Ce1Mo0.1Ox and Mn2Ce1Mo0.2Ox. (a) Mn2p, (b) O1s, (c) Ce3d.
Figure 9. XPS spectra of Mn2Ce1Ox, Mn2Ce1Mo0.1Ox and Mn2Ce1Mo0.2Ox. (a) Mn2p, (b) O1s, (c) Ce3d.
Metals 13 00938 g009
Metals 13 00938 g010 550
Figure 10. (a) H2-TPR profiles, (b) NH3-TPD profiles.
Figure 10. (a) H2-TPR profiles, (b) NH3-TPD profiles.
Metals 13 00938 g010
Table
Table 1. Comparison of NOx conversion.
Table 1. Comparison of NOx conversion.
CatalystsEvaluation ConditionsGHSVTemperature/°CNOx ConversionReferences
Mn2CeMo0.1/LDPC[NO]=[NH3] = 500 ppm, [O2] = 6% [H2O] = 7%, [SO2] = 100 ppm150,00016090%This study
Mn2CeMo0.2/LDPC[NO]=[NH3] = 500 ppm, [O2] = 6% [H2O] = 7%, [SO2] = 100 ppm150,00016085%This study
MnCeOx/TiO2-Al2O3[NO]=[NH3] = 500 ppm, [O2] =5% [H2O] = 10%, [SO2] = 50 ppm80,00017560%[36]
MnOxCeOy/rGO(0.1)[NO]=[NH3] = 500 ppm, [O2] = 5%, [H2O] = 5%, [SO2] = 100 ppm60,00016060%[41]
Sn(0.1)Mn(0.4)CeOx[NO]=[NH3] = 1000 ppm [O2] = 6% [H2O] = 12%, [SO2] = 100 ppm35,00011065%[42]
Table
Table 2. XPS results of MnaCebMocOx catalysts.
Table 2. XPS results of MnaCebMocOx catalysts.
CatalystO Species
Mn SpeciesCe SpeciesAbsorbed OxygenLattice Oxygen
Mn3+Mn4+Mn4+/Mn3+Ce4+Ce3+Ce4+/Ce3+OβOγOαOγ + Oβ/Oα
Mn2Ce147.053.01.1387.112.96.7413.116.870.10.42
Mn2Ce1Mo0.146.553.51.1585.514.55.8816.613.270.20.42
Mn2Ce1Mo0.244.755.31.2486.913.16.6120.010.569.50.44
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

Zhou, T.; Jin, J.; Zhang, H. Mn-Ce Catalysts/LDPC Modified by Mo for Improving NH3-SCR Performance and SO2 Resistance at Low Temperature. Metals 2023, 13, 938. https://doi.org/10.3390/met13050938

AMA Style

Zhou T, Jin J, Zhang H. Mn-Ce Catalysts/LDPC Modified by Mo for Improving NH3-SCR Performance and SO2 Resistance at Low Temperature. Metals. 2023; 13(5):938. https://doi.org/10.3390/met13050938

Chicago/Turabian Style

Zhou, Tao, Jiang Jin, and Hua Zhang. 2023. "Mn-Ce Catalysts/LDPC Modified by Mo for Improving NH3-SCR Performance and SO2 Resistance at Low Temperature" Metals 13, no. 5: 938. https://doi.org/10.3390/met13050938

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