SO2 Tolerance Research Articles

Effect of Ceria Precursor on the Physicochemical and Catalytic Properties of Mn–W/CeO2 Nanocatalysts for NH3 SCR at Low Temperature

A series of Mn–W/CeO2 catalysts were synthesized by employing Ce–NO-R nanorods [Ce(NO3)3·6H2O as the precursor] and Ce–Cl-C nanocubes and Ce–Cl-R nanorods (CeCl3·7H2O as the precursor) as the supports, and their structures and catalytic performances in NOx removal were investigated. TEM results demonstrate that the morphology of the CeO2 species is associated with the Ce precursor. The activity results show that the NOx conversion in Mn–W/Ce–NO-R is greater than 96% at 150 °C, which is much higher than those in Mn–W/Ce–Cl-R and Mn–W/Ce–Cl-C. At the same time, Mn–W/Ce–NO-R exhibits strong SO2 tolerance and excellent H2O resistance. DFT modeling shows that NO adsorbs over Mn–W/Ce–NO-R{110} by forming ONO*, whereas NO prefers to adsorb on the O vacancies in Mn–W/Ce–Cl-C{100}. Moreover, the superior catalytic performance of Mn–W/Ce–NO-R is associated with its greater amounts of surface Ce3+ and Mn4+ species, surface acid sites, and active oxygen species, resulting in the promotion of the reactions according t...

Solvothermal synthesis of well-designed ceria-tin-titanium catalysts with enhanced catalytic performance for wide temperature NH3-SCR reaction

Ternary mixed ceria-titanium catalysts doping tin were synthesized by a solvothermal method and applied to selective catalytic reduction (SCR) of NO with NH3. The Sn doping catalyst showed better low-temperature activity compared with unmodified catalyst, which exhibited an extraordinarily wide operation window ranging from 180 to 460 °C and better the tolerance of H2O or SO2. Powder X-ray diffraction (XRD), laser Raman spectroscopy (Raman), fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), BET surface area by N2-adsorption-desorption, hydrogen temperature-programmed reduction (H2-TPR), ammonia temperature-programmed desorption (NH3-TPD) were performed to study the structure, redox ability and surface acidity for the CeSnTiOx catalyst. Notably, the addition of Sn could prominently modify and optimize the structure of mixed metal oxides. Meanwhile, it was verified that synergistic interaction between of Ce and Sn surprisingly produced, and crystal defects, oxygen vacancies, acid sites as well as the specific surface areas evidently increased. In addition, the uniform pore channel was also beneficial to NH3-SCR. Especially, the electron interaction between Sn and Ce in reaction could greatly improve the SCR performance and H2O/SO2 durability.

Photo-assisted selective catalytic reduction of NO by Z-scheme natural clay based photocatalyst: Insight into the effect of graphene coupling

Photo-assisted selective catalytic reduction (photo-SCR) has been recognized as a promising strategy for NOx removal in recent decade, however rational designing of efficient and low-cost catalyst for photo-SCR remains to be a challenge. In the present work, natural one-dimension attapulgite (ATP) clay was initially coated with perovskite oxides by sol–gel method, and then coupled with reduced graphene oxide (rGO) by electrostatic assembly. XRD, TEM, Raman, UV–Vis, XPS, NH3-TPD, H2-TPR and in situ EPR were employed to characterize the products. Results indicated that the framework was coherently integrated by ATP skeleton, LaCoO3 particles and rGO nanosheet, while rGO behaved as excellent electronic transmission mediator between ATP and LaCoO3 to achieve indirect Z-scheme system, thus significantly improved the charge-separation efficiency and redox ability of the nanocomposite. In situ EPR revealed that the photogenerated holes in the catalysts were captured by NH3 to produce NH2 radical, which produced NH2NO intermediate followed by decomposing into N2 and H2O. Photo-SCR of NO was performed using LaCoO3/ATP/rGO as catalyst under simulated solar-light irradiation. Results indicated that the introduction amount of rGO had critical effect on the NO conversion efficiency, which reached as high as 95% conversion rate and 100% N2 selectivity even under room temperature when the mass content of rGO was optimized to 0.6 wt%. In addition, SO2 and H2O tolerance experiment did not find noticeable deactivation of the obtained Z-scheme photocatalyst, which was attributed to the synergistic resistance effect between ATP and rGO.

Denitrification performance of non-pitch coal-based activated coke by the introduction of MnOx–CeOx–M (FeOx, CoOx) at low temperature

Modified activated coke was prepared by the introduction of MnOx, CeOx, and M (FeOx, CoOx) into non-pitch coal-based activated coke (NPAC) using a novel non-pitch binder. The modified non-pitch coal-based activated coke was characterized in detail by N2 physical adsorption, thermogravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, fourier transform infrared spectroscopy, temperature-programmed reduction of H2, temperature-programmed desorption of NH3, and its catalytic activity was examined by the selective catalytic reduction of NO with NH3 at low temperature. In addition, the SO2 and H2O tolerance was investigated. The results indicated that compared to MnOx–CeOx–4.39, Mn–Ce–Co/NPAC-7 and Mn–Ce–Fe/NPAC-7 exhibit considerably higher catalytic activities while simultaneously maintaining NOx removal rates of 78.98% and 77.85%, respectively, at 150°C. The high catalytic performance of Mn–Ce–Co/NPAC-a and Mn–Ce–Fe/NPAC-a is related to several better properties compared to MnOx–CeOx–4.39, namely, considerably higher specific surface areas and percentages of Oα/(Oα+Oβ+Oγ) and Ce3+/(Ce3++Ce4+), more easily reduced of Mn species, high reducibility, and more acidic sites. Furthermore, Mn–Ce–Co/NPAC-7 and Mn–Ce–Fe/NPAC-7 exhibited specific resistance to SO2 and H2O poisoning, and the SO2 deactivation mechanism was proposed.

Study on improving the SO2 tolerance of low-temperature SCR catalysts using zeolite membranes: NO/SO2 separation performance of aluminogermanate membranes

A novel idea is proposed to improve the SO2 tolerance of low-temperature selective catalytic reduction (SCR) catalysts by using a RHO zeolite membrane to separate NO from SO2 to reduce the contact between SO2 and the SCR catalysts. RHO zeolite membranes were prepared on a macroporous stainless steel tube. The results from XRD and SEM measurements indicated that the crystals on the surface were pure RHO zeolites and a uniform and continuous layer of RHO zeolite membrane covered the surface of the support. Permeation measurements using different feed gases indicated that the prepared RHO zeolite membrane could effectively separate NO from SO2. A maximum NO/SO2 selectivity of 36.14 was obtained when using NO/SO2/N2 mixtures. The SO2 permeation decreased a lot in the present of water. Surface diffusion and activated diffusion were believed to be the main transport mechanisms of the RHO zeolite membrane.

Support effect of the supported ceria-based catalysts during NH3-SCR reaction

To investigate how the physicochemical properties and NH3-selective catalytic reduction (NH3-SCR) performance of supported ceria-based catalysts are influenced as a function of support type, a series of CeO2/SiO2, CeO2/γ-Al2O3, CeO2/ZrO2, and CeO2/TiO2 catalysts were prepared. The physicochemical properties were probed by means of X-ray diffraction, Raman spectroscopy, Brunauer-Emmett-Teller surface area measurements, X-ray photoelectron spectroscopy, H2-temperature programmed reduction, and NH3-temperature programmed desorption. Furthermore, the supported ceria-based catalysts' catalytic performance and H2O + SO2 tolerance were evaluated by the NH3-SCR model reaction. The results indicate that out of the supported ceria-based catalysts studied, the CeO2/γ-Al2O3 catalyst exhibits the highest catalytic activity as a result of having a high relative Ce3+/Ce4+ ratio, optimum reduction behavior, and the largest total acid site concentration. Finally, the CeO2/γ-Al2O3 catalyst also presents excellent H2O + SO2 tolerance during the NH3-SCR process.

Use of Native Yeast Strains for In-Bottle Fermentation to Face the Uniformity in Sparkling Wine Production.

The in-bottle fermentation of sparkling wines is currently triggered by few commercialized Saccharomyces cerevisiae strains. This lack of diversity in tirage yeast cultures leads to a prevalent uniformity in sensory profiles of the end products. The aim of this study has been to exploit the natural multiplicity of yeast populations in order to introduce variability in sparkling wines throughout the re-fermentation step. A collection of 133 S. cerevisiae strains were screened on the basis of technological criteria (fermenting power and vigor, SO2 tolerance, alcohol tolerance, flocculence) and qualitative features (acetic acid, glycerol and H2S productions). These activities allowed the selection of yeasts capable of dominating the in-bottle fermentation in actual cellar conditions: in particular, the performances of FX and FY strains (isolated in Franciacorta area), and OX and OY strains (isolated in Oltrepò Pavese area), were compared to those of habitually used starter cultures (IOC18-2007, EC1118, Lalvin DV10), by involving nine wineries belonging to the two Consortia of Appellation of Origin. The microbiological analyses of samples have revealed that the indigenous strains showed an increased latency period and a higher cultivability along the aging time than the commercial starter cultures do. Results of chemical analyses and sensory evaluation of the samples after 18 months sur lies have shown that significant differences (p < 0.05) were present among the strains for alcoholic strength, carbon dioxide overpressure and pleasantness, whereas they were not observed for residual sugars content, titratable acidity or volatile acidity. Indigenous S. cerevisiae exhibited comparable values respect to the commercial starter cultures. The ANOVA has also proven that the base wine formulation is a key factor, by significantly affecting (p < 0.01) some oenological parameters of wine, like alcoholic strength, volatile acidity, carbon dioxide overpressure, titratable acidity and dry extract. The use of native yeast strains for the re-fermentation step can be considered a convenient way for introducing differentiation to the final product without modifying the traditional technology. In a perspective of “precision enology,” where the wine is designed on specific vine cultivars and microorganisms, this work underlines that exploring yeast biodiversity is a strategic activity to improve the production.

Influence of Mn/Ce ratio on the physicochemical properties and catalytic performance of graphene supported MnOx-CeO2 oxides for NH3-SCR at low temperature

A series of MnOx-CeO2/graphene catalysts prepared by a hydrothermal method with different molar ratios of Mn/Ce active components were loaded on graphene for low-temperature SCR of NOx with NH3. Experimental results indicated that these catalysts exhibited excellent low-temperature SCR activities and strong resistance against SO2. The characterization results indicated that manganese and cerium oxides dispersed on the surface of graphene uniformly, and that manganese oxide existed in different forms of crystallinities (MnO, Mn3O4, and MnO2). The MnOx-CeO2(8:1)/GR displayed superior activity, high N2 selectivity, and good resistance to H2O and SO2, which would be very attractive for the application in controlling NOx emission from flue gas. Its excellent catalytic performance and SO2 tolerance at low temperature were attributed to the high content of manganese with high oxidation valence, increased chemisorbed oxygen on the surface, more active sites, and the strong interaction between MnOx-CeO2 active sites and graphene support.

Effect of Ce/Y Addition on Low-Temperature SCR Activity and SO2 and H2O Resistance of MnOx/ZrO2/MWCNTs Catalysts

The effects of SO2 and H2O on the low-temperature selective catalytic reduction (SCR) activity over MnOx/ZrO2/MWCNTs and MnOx/ZrO2/MWCNTs catalysts modified by Ce or Y was studied. MnCeZr and MnYZr catalysts reached nearly 100% and 93.9% NOx conversions at 200 °C and 240 °C, respectively. They displayed a better SO2 tolerance, and the effect of H2O was negligible. The structural properties of the catalysts were characterized by XRD, H2-TPR, XPS, and FTIR before and after the reaction. The results showed that Ce could increase the mobility of the oxygen and improve the valence and the oxidizability of manganese, while the effect of Y was the opposite. This might be the main reason why the catalytic activity of MnCeZr was better than MnYZr in the presence or absence of SO2 and H2O. Doping Ce or Y broadened the active temperature window. Ce or Y, which existed in the catalysts with a high dispersion or at the amorphous state, preferred to react with SO2 to form sulfate species, and protected the manganese active sites from combing with SO2 to some extent, which coincided with the theory of ionic polarization.

V2O5-decorated Mn-Fe/attapulgite catalyst with high SO2 tolerance for SCR of NOx with NH3 at low temperature

Fe-based catalysts were widely reported with high N2 selectivity in the NH3-SCR reaction in recent years. Unfortunately, the Fe-based catalysts usually exhibit poor NOx conversion at low temperature. In order to solve this problem, MnO2 was chosen to enhance the low temperature activity of the catalyst. In this work, V2O5-decorated Mn-Fe/attapulgite (V@Mn-Fe/ATP) with high SO2 tolerance were prepared by impregnation and sol-gel methods and used for selective catalytic reduction of NO by NH3 (NH3-SCR). In addition, γ-Fe2O3/ATP and Mn-Fe/ATP were also prepared for comparison with the V@Mn-Fe/ATP. The as-prepared catalysts were characterized by XRD, TEM, BET, H2-TPR, NH3-TPD, and XPS. It could be deduced from TEM, XRD, and BET, the specific surface area was improved due to a uniform V2O5 layer formed on the Mn-Fe/ATP surface. The results of XPS and NH3-TPD illustrated that the coating of V2O5 could also enhance the amount of surface chemisorbed oxygen and acidic sites, which play significant influence on oxidation of NO and NH3 absorption during NH3-SCR and are also beneficial to increase SCR reaction rates. Moreover, the test of SO2 tolerance and stability demonstrated that the V2O5 layer could effectively inhibit SO2 poisoning and improve the stability of catalysts. Therefore, the V@ Mn-Fe/ATP was proved to be an excellent catalyst for NH3-SCR.

Promotional mechanisms of activity and SO2 tolerance of Co- or Ni-doped MnOx-CeO2 catalysts for SCR of NOx with NH3 at low temperature

Metals doped MnOx-CeO2 catalysts with a molar ratio of M:Mn:Ce=1:4:5 (M=Cu, Co, Cr, Ni, Fe, Sn, Mg) were prepared by a co-precipitation method for low-temperature selective catalytic reduction of NOx with NH3 (NOx-NH3-SCR). The results showed Co/Ni doped catalysts had high SCR performance and good tolerance to SO2. Solid solutions with higher surface area and smaller pore size were obtained over Co/Ni doped catalysts. XPS analysis presented Co/Ni doped catalysts had more chemisorbed oxygen, more active sites (Mn3+ and Mn4+) and higher ratio of Ce4+/Ce3+, which were favorable for improving the SCR activity accompanied by the fast-SCR due to a high activity for NO oxidation to NO2. The in-situ DRIFTS revealed NOx-absorbed species over Co/Ni doped catalysts tended to bidentate nitrate without influences by SO2, which further transformed to monodentate nitrate producing new Brønsted acid sites for adsorbing NH4+. While that over MnOx-CeO2 catalyst was more in favor of monodentate nitrite species, significantly inhibiting by SO2. Thermogravimetric analysis (TGA) presented the formations of ammonium sulfate and metal sulfate species over Co/Ni doped catalysts were markedly inhibited. The possible SCR reaction pathways and mechanisms of SO2 tolerance were proposed over Co/Ni doped catalysts contrasted to MnOx-CeO2 catalyst.

Cerium-loaded MnO x /attapulgite catalyst for the low-temperature NH 3 -selective catalytic reduction

Abstract A series of MnO2/attapulgite (ATP) and n(Ce):n(Mn)/ATP (molar ratios) catalysts were prepared and investigated for the selective catalytic reduction of NO by NH3 (NH3-SCR) at low temperature. The results showed that the 7 wt % MnO2/ATP exhibited the best NOx conversion (85% at 300 °C) among all MnO2/ATP catalysts of different mass ratios. The introduction of cerium enhanced the NOx conversion at low temperature, and so Ce–MnOx/ATP can reach the highest NOx conversion (95% at 300 °C). Meanwhile, the as-prepared catalysts were characterized by XRD, TEM, BET, H2-TPR, NH3-TPD, and XPS. It can be deduced from TEM, XRD, and BET, MnOx nanorods in this work mainly existed in the β-MnO2, and cerium highly dispersed on the surface of ATP to form porous structure and thus improved the deNOx performance. Moreover, the study of SO2 tolerance demonstrated that cerium can effectively inhibit SO2 poison. XPS results illustrated that Ce could enhance Mn4+ content on the surface of the catalyst and thus lead to high SCR activity. Therefore Mn(1):Ce(0.25)/ATP was proved to be an excellent catalyst for NH3-SCR.

Effect of barium sulfate modification on the SO2 tolerance of V2O5/TiO2 catalyst for NH3-SCR reaction

Sulfur poisoning of V2O5/BaSO4–TiO2 (VBT), V2O5/WO3–TiO2 (VWT) and V2O5/BaSO4–WO3–TiO2 (VBWT) catalysts was performed in wet air at 350°C for 3hr, and activities for the selective catalytic reduction of NOx with NH3 were evaluated for 200–500°C. The VBT catalyst showed higher NOx conversions after sulfur poisoning than the other two catalysts. The introduction of barium sulfate contributed to strong acid sites for the as-received catalyst, and eliminated the redox cycle of active vanadium oxide to some extent, which resulted in a certain loss of activity. Readily decomposable sulfate species formed on VBT-S instead of inactive sulfates on VWT-S. These decomposable sulfates increased the number of strong acid sites significantly. Some sulfate species escaped during catalyst preparation and barium sulfate was reproduced during sulfur poisoning, which protects vanadia from sulfur oxide attachment to a great extent. Consequently, the VBT catalyst exhibited the best resistance to sulfur poisoning.

Identification of Zygosaccharomyces mellis strains in stored honey and their stress tolerance.

To screen yeast with high sugar tolerance and evaluate their stress tolerance, six yeast strains were selected from 17 stored honey samples. The species were identified through 26S rRNA sequencing. Their stress tolerance was determined via the Durham fermentation method and ethanol production ability was determined via flask fermentation. The results demonstrated that all the six strains were Zygosaccharomyces mellis. Their sugar, ethanol, and acid tolerance ranges were 500-700 g/L, 10-12% (v/v), and pH 2.5-4.5, respectively. The SO2 tolerance was 250 mg/L. Among the six strains, 6-7431 had the best stress tolerance with sugar tolerance of 700 g/L, ethanol tolerance of 12% (v/v), and acid tolerance of pH 2.5. Furthermore, the strain of 6-7431 had the highest percentage of ethanol production at the same initial sugar content as the other strains. Therefore, the selected six yeast strains would be promising fermentation yeasts for wine-making, ethanol production, or other fermentation purposes.

Novel hollow microspheres MnxCo3−xO4 (x = 1, 2) with remarkable performance for low-temperature selective catalytic reduction of NO with NH3

Hollow microspheres MnCo2O4 and CoMn2O4 have been synthesized by a facile solvothermal route followed by pyrolysis of the carbonate counterparts and carbon microspheres, using carbon microspheres as the template. The NH3-selective catalytic reduction reaction was used to test the catalytic activity. The obtained hollow microspheres are composed of numerous primary particles with sizes of tens of nanometers, giving a porous shell. The obtained CoMn2O4 microsphere shows better low-temperature catalytic activity and N2 selectivity than MnCo2O4 microsphere in the NH3-selective catalytic reduction reaction. The X-ray photoelectron spectroscopy results demonstrate that CoMn2O4 microsphere has a relatively higher number content of Mn3+ and chemisorbed oxygen species. The temperature-programmed desorption by ammonia and in situ diffuse reflectance infrared Fourier transform spectroscopy results indicate that the CoMn2O4 microsphere possesses stronger Lewis acid strength than the MnCo2O4 microsphere. Additionally, the CoMn2O4 microsphere also presented outstanding stability, H2O resistance and SO2 tolerance. The NH3-SCR reaction mechanism is proposed that NH3(g) is adsorbed on the surface of Lewis acid sites and Bronsted acid sites in the shape of NH4 + ions and gaseous NH3. Besides, the adsorption of NO could exist in the form of gaseous or oxide ions NO2 − on the surface of catalysts.The adsorbed NH3 species could react with NO2 − species easily to produce NH4NO2, which subsequently to produce the innocuous N2 and H2O.

Three-dimensional ordered mesoporous CeXZr1−XO2 for selective catalytic reduction removal of NOX with NH3

A series of highly ordered mesoporous CeXZr1−XO2 (x represents the mole ratio of Ce), were fabricated for NH3-SCR of NOX using KIT-6 as a hard template, which have been characterized by TEM, XRD, BET, BJH, XPS, H2-TPR, NH3-TPD and in-situ DRIFT, showing superior composite crystal microstructure, uniform mesopore diameter and larger surface area. Among all the mesoporous CeXZr1−XO2 samples (x=0, 0.25, 0.33, 0.5, 0.67, 0.75 and 1), mesoporous Ce0.67Zr0.33O2 showed the best NH3-SCR activity to clean NOX, and 100% NOX conversion ratio at 325°C can be reached, as well as excellent H2O or SO2 tolerance and best thermal stability. Furthermore, the addition of ZrO2 content enhanced the thermal performance and redox ability of mesoporous CexZr1−xO2, which were favorable for their excellent NH3-SCR performance. Finally, a possible redox reaction mechanism of NH3-SCR reaction over the mesoporous CeXZr1−XO2 was proposed.

Highly selective catalytic reduction of NO via SO2/H2O-tolerant spinel catalysts at low temperature.

Selective catalytic reduction of NOX by hydrogen (H2-SCR) in the presence of oxygen has been investigated over the NiCo2O4 and Pd-doped NiCo2O4 catalysts under varying conditions. The catalysts were prepared by a sol-gel method in the presence of oxygen within 50–350 °C and were characterized using XRD, BET, EDS, XPS, Raman, H2-TPR, and NH3-TPD analysis. The results demonstrated that the doped Pd could improve the catalyst reducibility and change the surface acidity and redox properties, resulting in a higher catalytic performance. The performance of NiCo1.95Pd0.05O4 was consistently better than that of NiCo2O4 within the 150–350 °C range at a gas hourly space velocity (GHSV) of 4800 mL g−1 h−1, with a feed stream containing 1070 ppm NO, 10,700 ppm H2, 2 % O2, and N2 as balance gas. The effects of GHSV, NO/H2 ratios, and O2 feed concentration on the NO conversion over the NiCo2O4 and NiCo1.95Pd0.05O4 catalysts were also investigated. The two samples similarly showed that an increase in GHSV from 4800 to 9600 mL h−1 g−1, the NO/H2 ratio from 1:10 to 1:1, and the O2 content from 0 to 6 % would result in a decrease in NO conversion. In addition, 2 %, 5 %, and 8 % H2O into the feed gas had a slightly negative influence on SCR activity over the two catalysts. The effect of SO2 on the SCR activity indicated that the NiCo1.95Pd0.05O4 possesses better SO2 tolerance than NiCo2O4 catalyst does.Graphical abstractThe NiCo1.95Pd0.05O4 catalyst achieved over 90 % NO conversion with N2 selectivity of 100 % in the 200∼250 °C range than the maximum 40.5 % NO conversion over NiCo2O4 with N2 selectivity of approximately 80 % in 350 °C.

The catalytic performance of Mn/TiWOx catalyst for selective catalytic reduction of NOx with NH3

A series of Mn/TiWOx catalysts were prepared and used in NH3-SCR reaction for NOx emission control. The experimental results showed that the SCR activities of Mn/TiWOx catalysts are higher than that of Mn/TiO2 catalyst. After that, several characterization techniques including XRD, H2-TPR, NH3-TPD, XPS were used to investigate the effect of TiWOx support on the SCR performance of Mn/TiWOx (1:1) catalyst. The stronger reducibility and NH3 adsorption capacity, and more surface chemisorbed oxygen of Mn/TiWOx (1:1) should all contribute to its better SCR performance. Moreover, Mn/TiWOx (1:1) catalyst shows higher N2 selectivity, better SO2 tolerance and stability than Mn/TiO2 catalyst. The results of in situ DRIFT study revealed that the NH3-SCR reactions over Mn/TiO2 and Mn/TiWOx (1:1) were all followed the Langmuir–Hinshelwood mechanism, in which the SCR reaction takes place between the adsorbed NH3 species and NOx species.

H2O and SO2 tolerance, activity and reaction mechanism of sulfated Ni–Ce–La composite oxide nanocrystals in NH3-SCR

Ceria-based catalysts exhibit excellent performance at mediate-high temperature in selective catalytic reduction (SCR) of NO with NH3. However, their activities are severely restrained in the presence of H2O and SO2. In this work, Ni–Ce–La composite oxide nanocrystals were synthesized. After sulfation, it showed excellent H2O and SO2 tolerance. The catalysts were studied by inductively coupled plasma (ICP), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), temperature-programmed desorption (TPD), in situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS), Brunauer–Emmett–Teller (BET) surface area and thermogravimetry (TG). The H2O and SO2 tolerance of Ce-based catalysts and sulfation mechanism and its effect on the SCR activity were investigated. After sulfation, the increase in proportion of Ce3+/(Ce3++Ce4+), the formation of SO42− and the increase of NH3 adsorptivity all illustrate that sulfation increases the Brönsted acid sites of samples. The mainly reserved Lewis acid sites and the newly formed Brönsted acid sites contribute to the excellent SCR activity. A shrinking core model was proposed to explain the process of sulfation. The reaction process mostly follows L–H mechanism. After sulfation, Ni–Ce–La composite oxide increases NH3 adsorptivity and remains good NO adsorptivity, which greatly enhances resistance to H2O and SO2.

Effect of V2O5 Additive on the SO2 Resistance of a Fe2O3/AC Catalyst for NH3-SCR of NOx at Low Temperatures

The effect of vanadium oxide on an iron-based catalyst supported on activated carbon (AC) in the selective catalytic reduction of NOx by NH3 (NH3-SCR) was investigated in this work. A series of vanadium-modified Fe2O3/AC catalysts were prepared by a coimpregnation method. The addition of a small amount of vanadium oxide contributed to the higher dispersion of iron species on the surface of the catalyst. Among various vanadium-modified iron catalysts supported on AC, 3% Fe–0.5% V achieved the best SCR activity and SO2 tolerance. In the presence of H2O, SO2 had a severe deactivation effect on both vanadium- and non-vanadium-modified catalysts, yet the inhibition effect of H2O and SO2 was reversible on 3% Fe–0.5% V at relatively low space velocity. It was found that the vanadium additive promoted the formation of sulfate species. The formed sulfate species increased the surface acidity and thus enhanced the tolerance toward SO2.