SCR Activity Research Articles

Influence of CePO4 with different crystalline phase on selective catalytic reduction of NOx with ammonia

A series of cerium phosphate catalysts with different crystal phases were synthesized by hydrothermal method and co-precipitation method. Hexagonal cerium phosphate (CePO4-H) shows better NH3-SCR denitration activity than monoclinic cerium phosphate (CePO4-M) and mixed phases of CePO4-H and CePO4-M. Moreover, CePO4-H also exhibits excellent activity stability with stream time and cycling stability. Various characterizations were carried out to explain the effects of different crystal phases of CePO4 on the activity. Among these catalysts, CePO4-H has much stronger surface acidity that is conducive to the adsorption and activation of NH3, and more surface adsorbed oxygen species that can effectively improve SCR activity. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were performed to investigate the adsorption and reaction of NH3 and NOx on CePO4-H and CePO4-M, and the results suggest that the better activity over CePO4-H follows mainly the Eley–Rideal mechanism in the activity temperature window (300–500 °C) with 100% NO conversion.

A novel CNTs functionalized CeO2/CNTs–GAC catalyst with high NO conversion and SO2 tolerance for low temperature selective catalytic reduction of NO by NH3

Low−temperature selective catalytic reduction of NOx by NH3 (NH3−SCR) for diminishing SO2 poisoning remains an issue in flue gas denitrification (DeNOx). Herein, A novel CNTs functionalized low temperature NH3−SCR catalyst CeO2/CNTs−GAC was prepared, which showed high NO conversion activity (100% at 150 °C) and SO2 resistance. The addition of CNTs restrained SO2 adsorption but improved the selective adsorption of NO, which restricted the deposition of (NH4)2SO4 and/or Ce2(SO4)3, and resulted in high SO2 resistance. The addition of CNTs facilitated the diffusion and transportation of NH3 and NO, and the electron transfer on CeO2/CNTs−GAC, leading to higher content of Ce3+ and adsorbed O species on the CeO2/CNTs−GAC surface and promoted formation of surface-adsorbed oxygen OA. Therefore, CeO2/CNTs−GAC provided abundant NO adsorption and activation sites, facilitating “fast SCR” reaction and enhancing the NH3−SCR reaction. The proposed CeO2/CNTs−GAC catalyst exhibited higher NH3−SCR activity, N2 selectivity, catalytic durability and SO2 resistance than CeO2/GAC.

A Probe into the Low-Temperature SCR Activity: NO Oxidative Activation to Nitrite-Intermediates

A Probe into the Low-Temperature SCR Activity: NO Oxidative Activation to Nitrite-Intermediates

Improved NH3-SCR deNOx activity and tolerance to H2O & SO2 at low temperature over the NbmCu0.1-mCe0.9Ox catalysts: Role of acidity by niobium doping

A series of NbmCu0.1-mCe0.9Ox catalysts were synthesized with the help of citric acid method, and used for the selective catalytic reduction of NOx with NH3 (NH3-SCR). The catalytic performance of the NbmCu0.1-mCe0.9Ox samples was greatly improved after the introducing of niobium. Among all catalysts, the Nb0.06Cu0.04Ce0.9Ox catalyst revealed the best low-temperature SCR activity, higher N2 selectivity and extraordinary SO2 and H2O durability with 100% NO conversion at 150–390 °C. The various characterization techniques were carried out to investigate the effect of niobium doping on the physical structures, surface properties and NH3-SCR activity of catalysts. Results reveal that the oxidation ability decrease but the acidity is enhanced with the Nb addition. The improved acidity by niobium doping is considered the primary cause for the superior deNOx performance of the Nb0.06Cu0.04Ce0.9Ox catalyst at low temperature, which can offset the negative effects of the reduced oxidation ability on activity. Furthermore, in situ DRIFTS results were applied for the investigation of the reaction process in detail.

Balancing redox and acidic properties for optimizing catalytic performance of SCR catalysts: A case study of nanopolyhedron CeOx-supported WOx

For the selective catalytic reduction of NOx with NH3 (NH3-SCR) reaction, how to precisely adjust the reducibility and surface acidity over SCR catalysts remains a fundamental challenge. Here, a very facile and effective way, the addition of WOx species using an incipient wetness impregnation method, to balance the redox and acidic properties of CeOx for optimizing its SCR performance was proposed. Especially, nanopolyhedron CeOx with predominately exposed (111) facet was prepared as the support of WyCe catalysts. As an effective surface modifier, the WOx species could not only suppress the over-oxidation of NH3 over CeOx by partially covering oxygen vacancies, but also supply abundant Brønsted and Lewis acid sites, which stemmed from WO, WOW, CeOW bonds and electronically deficient unsaturated Cen+, Wn+ cations, respectively. As a result, the SCR activity and N2 selectivity of WyCe catalysts were significantly improved at the same time, through the balance between the redox and acidic properties. The above results might open a new avenue for the design and preparation of more efficient SCR catalysts.

Optimizing acid promoters of Ce-based NH3-SCR catalysts for reducing NOx emissions

WO3 and MoO3 are often used as acidic promoters to modify vanadium based and non-vanadium based composite oxide catalysts, meanwhile, the NH3-SCR performance of the catalysts could be evidently improved. Generally, WO3 and MoO3 are believed to play the same role in V2O5-based and other composite oxide NH3-SCR catalysts. Interestingly, our recent work found that there are significant differences between WO3 and MoO3 in improving the NH3-SCR performance of CeZrOx. The operating temperature window of WO3/CeZrOx (222−454 °C) is 76 °C wider than that of MoO3/CeZrOx (254−410 °C) for NH3-SCR reaction. WO3/CeZrOx exhibits higher NOx removal efficiency than MoO3/CeZrOx in the whole temperature range. The similarities and differences in the effects of the acid promoters WO3 and MoO3 on the NH3-SCR performance of Ce-based catalysts are systematically investigated by Vis-Raman, XRD, XPS, NH3/O2/NOx-TPD, H2-TPR, NO/NH3-oxidation and in situ DRIFTS. Noteworthy, stronger interaction between MoO3 and CeZrOx than WO3 and CeZrOx leads to less oxygen vacancies and Lewis acid sites on the surface of MoO3/CeZrOx as well as strong oxidation property, which inhibit the NOx adsorption but contribute to the peroxidation of NH3 on MoO3/CeZrOx, reflecting its poor SCR activity. This work provides an in-depth understanding of the intrinsic effects of WO3 and MoO3 on the NH3-SCR performance of CeZrOx-based catalysts.

Promotional effect of ceria on the catalytic behaviour of new V2O5–WO3–TiO2 aerogel solids for the DeNOx process

New cerium and/or tungsten modified V2O5–TiO2 aerogel catalysts (V2O5–TiO2,V2O5–WO3–TiO2, V2O5–CeO2–TiO2 and V2O5–WO3–CeO2–TiO2) were successfully developed, by associating the sol gel procedure and supercritical drying approach. A combination of various analytical techniques, including XRD, N2-Physisorption at 77 ​K, DRUV-Vis spectroscopy, NH3-TPD and H2-TPR, was used to characterize the obtained solids. Their catalytic performances were evaluated in the low temperature NO-SCR by NH3. The results reveal that all the materials exhibit high cristallinity of TiO2 anatase phase and developed mesoporous texture. The addition of tungsten (W) increases the surface acidity of V2O5–TiO2 and thereby enhances its reactivity at high temperatures (>420 ​°C). However, the addition of cerium (Ce) improves the redox properties of the latter catalyst and increases significantly its NO-SCR reactivity, especially at low temperatures. The NO-SCR activity increases over the aerogel systems, in the 200–400 ​°C temperature range, following this order: V2O5–WO3–TiO2 ​< ​V2O5–TiO2 ​< ​V2O5–CeO2–TiO2 ​< ​V2O5–WO3–CeO2–TiO2. The new V2O5–WO3–CeO2–TiO2 system was found to be the most active catalyst for converting NO into N2 (with 60% and 90% NO conversions at 250 ​°C and between 320 and 420 ​°C, respectively). The highest SCR activity of this new aerogel solid if compared to the other samples was essentially correlated with a good reactivity of its acidic and redox sites which in turn was related to the existence of strong interactions between cerium and the other active elements (mostly Ce↔ V and Ce ↔ W).

Insight into the Promoting Role of Er Modification on SO2 Resistance for NH3-SCR at Low Temperature over FeMn/TiO2 Catalysts

Er-modified FeMn/TiO2 catalysts were prepared through the wet impregnation method, and their NH3-SCR activities were tested. The results showed that Er modification could obviously promote SO2 resistance of FeMn/TiO2 catalysts at a low temperature. The promoting effect and mechanism were explored in detail using various techniques, such as BET, XRD, H2-TPR, XPS, TG, and in-situ DRIFTS. The characterization results indicated that Er modification on FeMn/TiO2 catalysts could increase the Mn4+ concentration and surface chemisorbed labile oxygen ratio, which was favorable for NO oxidation to NO2, further accelerating low-temperature SCR activity through the “fast SCR” reaction. As fast SCR reaction could accelerate the consumption of adsorbed NH3 species, it would benefit to restrain the competitive adsorption of SO2 and limit the reaction between adsorbed SO2 and NH3 species. XPS results indicated that ammonium sulfates and Mn sulfates formed were found on Er-modified FeMn/TiO2 catalyst surface seemed much less than those on FeMn/TiO2 catalyst surface, suggested that Er modification was helpful for reducing the generation or deposition of sulfate salts on the catalyst surface. According to in-situ DRIFTS the results of, the presence of SO2 in feeding gas imposed a stronger impact on the NO adsorption than NH3 adsorption on Lewis acid sites of Er-modified FeMn/TiO2 catalysts, gradually making NH3-SCR reaction to proceed in E–R mechanism rather than L–H mechanism.

Microkinetic study of NO oxidation, standard and fast NH3-SCR on CeWOx at low temperatures

A comprehensive microkinetic model was established to describe NO oxidation, standard SCR and fast SCR on CeWOx at low temperatures for the first time, providing an in-depth understanding of the NH3-SCR mechanism. The model divided the NH3 adsorption sites into two groups, including sites that could prohibit NO adsorption and that could not affect NO adsorption. Different rate-limiting steps during NO oxidation, standard and fast SCR were identified, and different reaction orders toward NO, NH3 and NO2 were obtained in different reactions. The mechanisms of standard and fast SCR were quite similar. Both the Eley-Rideal and Langmuir-Hinshelwood mechanisms were present, and the reaction between nitrites and adsorbed NH3 made the main contribution to the NOx conversion. The apparent activation energy was affected by the reaction between nitrites and adsorbed NH3 and the reaction between NO and NH4NO3, and the activation energy of the latter reaction was higher. The activation energy of fast SCR was higher than that of standard SCR due to a greater contribution by the reaction between NO and NH4NO3, but larger amounts of nitrites and NH4NO3 caused higher activity for fast SCR than standard SCR. The sites for NO adsorption to produce nitrites were low in number but highly active, which might be a reason why CeWOx is highly active for standard SCR under high gas hourly space velocity, and increasing the sites for NO adsorption might be an effective way to accelerate NH3-SCR. This work provides guiding information for the development of new and effective NH3-SCR catalysts.

Enhancement of Ce doped La–Mn oxides for the selective catalytic reduction of NOx with NH3 and SO2 and/or H2O resistance

• A–bit doping is more favorable for improving SCR activity than that of B–bit doping. • A–bit doping enhances SO 2 resistance, but B–bit doping improves N 2 selectivity. • A–bit or B–bit doping can form the perovskite structure but the exposed plane changes. • A–bit doping increases Mn 4+ content but B–bit doping decreases Mn 4+ content. Cerium modified La–Mn oxides for NH 3 –SCR at low temperature is prepared by one–step synthesis method and characterized. The results showed that the perovskite La–Mn oxides at A–bit doped by Ce is more favorable for NOx removal than B–bit doping and achieves about 80% conversion of NOx at 120°C and about 100% in the range temperature of 180–220°C as well as good SO 2 and/or H 2 O resistance. However, LaMn 0.8 Ce 0.2 O 3 (B–bit doping) has better N 2 selectivity than La 0.8 Ce 0.2 MnO 3 (A–bit doping) and LaMnO 3 . The generated N 2 O and NO 2 influence the N 2 selectivity in the NH 3 –SCR reaction, but N 2 O is from the NH 3 oxidation while NO 2 is from the NO oxidation. The perovskite La–Mn oxides at A–bit or B–bit doped by Ce are able to maintain the perovskite structure of LaMnO 3.15 but the exposed plane shifts from (104) to (110). However, for both doped samples, some CeOx and Mn 3 O 4 are spilled out from the perovskite structure of La–Mn oxides. A–bit ions doped by Ce can increase Mn 4+ relative content, specific surface area, available oxygen and surface acid amount, while B–bit doping decreases Mn 4+ relative content and adsorbed oxygen and increases Ce 4+ relative content. After SO 2 resistance testing, the formation of (NH 4 ) 2 SO 4 and MnSO 4 on all catalysts is inevitable, but the binding force of the formed metal sulfate is different on catalyst surface, resulting in the difference of its resistance to sulfur.

MnOx location on MnOx-ZSM-5 to influence the catalytic activity for selective catalytic reduction of NOx by NH3

MnOx-ZSM-5 catalysts with different MnOx location were synthesized and their catalytic performances are investigated for selective catalytic reduction of NOx with NH3 (NH3-SCR). MZ-150 that MnOx clusters are dispersed on the outside of ZSM-5 exhibits higher catalytic activity at low temperature than MZ-25 of MnOx nanoparticles encapsulated in the channels of the support. The characteristics results show that the excellent redox ability and the dominant Mn3+ species over MZ-150 improve the oxidation of NO to NO2 and the formation of unstable NOx intermediates, enhancing the low-temperature SCR activity. For MZ-25, the confinement effect of ZSM-5 leads to a large NOx adsorption capacity, but the generated NOx species are stable, which could be the important reason for the poor activity at low temperature. This work reveals the relationship between the location of MnOx nanoparticles and the SCR properties, which can provide a new idea for designing the low-temperature zeolite catalysts.

Remarkable low temperature catalytic activity for SCR of NO with propylene under oxygen-rich conditions over Mn0.2La0.07Ce0.05Ox/ZSM-5 catalyst

Unlike NH3-SCR systems, even in oxygen-poor conditions, SCR of NO with propylene traditionally exhibited good catalytic activity only at high temperature (≥300 °C) due to the reduction properties of propylene. Most of the researches of low temperature HC-SCR are still focused on the development of noble metal (Ag, Pt, Pd, Rh etc.) catalysts. Herein, a series of rare earth metals LayCez co-doped Mn-based microporous zeolite ZSM-5 (MnxLayCez/ZSM-5) were prepared by co-impregnation method. Under the simulated oxygen-rich condition of actual diesel engines, we first reported a non-noble metal catalyst that exhibited high activity (≥90%) and selectivity (≥90%) for low temperature (180–270 °C) C3H6-SCR. The excellent low temperatures catalytic performance could be attributed to the more Brønsted acid sites, the higher superficial dispersion of manganese species, the more oxygen vacancy and the larger pore size (4.42 nm) characterized by XRD, SEM, HR-TEM, HAADF-STEM, NH3-TPD, H2-TPR and FT-IR. Moreover, the XPS results showed that the introduction of La could effectively enhance the oxygen vacancies of manganese oxide and cerium oxide, which significantly increase the chemical adsorption of NO, reducing the reaction activation energy, and promoting the conversion of NO under low-temperature. These advantages suggest the material has huge application potential in the deNOX process.

Ultralow specific surface area vermiculite supporting Mn-Ce-Fe mixed oxides as “curling catalysts” for selective catalytic reduction of NO with NH3

In this study, the ultralow specific surface area clay vermiculite (VMT) was selected to be a catalyst support for the NH3-SCR process, and the active components MnCeFeOx loaded on vermiculite was just like curling on ice from the TEM results. The de-NOx performance of Mn–Ce–Fe/VMT exhibited almost complete NO conversion with a gas hourly space velocity (GHSV) of 15,300 h−1 at 150 °C, which was 25% and 10% higher than that of Mn/VMT and Mn–Ce/VMT, respectively. Ce and Fe co-doping improved the BET surface area, the quantities of active Mn4+, the acid sites and NH3 adsorption energy of Mn/VMT, all of which contributed to the increase in low-temperature SCR activity. In situ DRIFT measurements suggested that NOx removal over Mn–Ce–Fe/VMT followed both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms at 150 °C, but the E-R mechanism played a dominant role. Corresponding Mn–Ce–Fe/VMT monolithic catalysts reached 90% NO conversion with a GHSV of 4000 h-1.

Preparation of MnOx/CNTs Catalyst by In situ Precipitation Method for Low-Temperature NO Reduction with NH3

Background: V2O5–WO3(MoO3)/TiO2 catalyst, as the core of selective catalytic reduction of NO with NH3 (SCR) has some drawbacks, such as high working temperature window (300- 400°C), toxicity of V-based catalyst and so on. Therefore, the development of the catalyst with better low temperature denitration activity and weaker toxicity are necessary. Objective: The study aimed at the development of highly dispersed MnOx/CNTs catalysts with excellent denitration activity at 80-180°C, and weaker toxicity of MnOx. It is worth noting that an in-situ precipitation method based on the reaction of manganese acetate and sodium carbonate, is advantageous for the in-situ deposition of the active component, and the catalytic activity. Methods: MnOx/CNTs catalysts with different Mn/C molar ratios were fabricated by in-situ precipitation method due to the reaction of manganese acetate and sodium carbonate. The microstructure, crystalline property, the content of the surface element, valence state, redox property, and catalytic activity were confirmed by FESEM, TEM, XRD, XPS, TPD, and fixed-bed reactor. Results: The as-prepared MnOx/CNTs catalysts exhibited outstanding low temperature SCR activity. The NO conversion of the optimum 1.2% MnOx/CNTs catalyst reached 57.4-89.2% at 80-180oC, which resulted from the amorphous MnOx catalysts, having a higher ratio of Mn4+/Mn3+ and OS/(OS+OL). Conclusion: MnOx/CNTs catalysts have been prepared by the in-situ precipitation method based on the reaction of manganese acetate and sodium carbonate. The resultant MnOx/CNTs catalysts presented excellent low temperature denitration activity between 80°C and 180°C. Among them, the 1.2% MnOx/CNTs catalyst exhibited the first rate low temperature denitration activity, and the denitration activity reached 57.4-89.2%, which may be due to the presence of the weakly crystalline or amorphous MnOx, having higher ratio of Mn4+/Mn3+ and OS/(OS+OL).

Precursor Effect on Mn-Fe-Ce/TiO2 Catalysts for Selective Catalytic Reduction of NO with NH3 at Low Temperatures

Preparation of Mn/TiO2, Mn-Fe/TiO2, and Mn-Fe-Ce/TiO2 by the deposition-precipitation (DP) method can afford very active catalysts for low-temperature NH3-SCR (selective catalytic reduction of NO with NH3). The effect of precursor choice (nitrate vs. acetate) of Mn, Fe, and Ce on the physiochemical properties including thermal stability and the resulting SCR activity were investigated. The resulting materials were characterized by N2-Physisorption, XRD (Powder X-ray diffraction), XPS (X-ray photoelectron spectroscopy), H2-TPR (temperature-programmed reduction with hydrogen), and the oxidation of NO to NO2 measured at 300 °C. Among all the prepared catalysts 5MnAce/Ti, 25Mn0.75AceFe0.25Nit/Ti, and 25Mn0.75AceFe0.20NitCe0.05Ace/Ti showed superior SCR activity at low temperature. The superior activity of the latter two materials is likely attributable to the presence of amorphous active metal oxide phases (manganese-, iron- and cerium-oxide) and the ease of the reduction of metal oxides on TiO2. Enhanced ability to convert NO to NO2, which can promote fast-SCR like pathways, could be another reason. Cerium was found to stabilize amorphous manganese oxide phases when exposed to high temperatures.

Impact of toluene poisoning on MnCe/HZSM-5 SCR catalyst

Increasing attentions have been drawn towards the simultaneous removal of toluene in current existing NH3-SCR unit. The development of dual-functional catalysts and the understanding of impact induced by toluene addition are momentous but lacking. Herein, a well-reported MnOx-CeO2 catalyst was chosen as active phase to assess the role of HZSM-5 in this simultaneous removal process. HZSM-5 was found to supply more acid sites especially Lewis acid on the MnOx-CeO2 catalyst. A MnCe/HZSM-5 catalyst with a SiO2/Al2O3 molar ratio of 25 delivered a broad active temperature window of 200–400 °C with NO conversion > 80% and possessed a stable N2 selectivity > 96% in NH3-SCR reaction. Also, it was able to maintain above 60% of toluene conversion in the range of 200–400 °C. More Lewis acid sites, together with abundant Mn4+, Ce3+ and active surface oxygen that formed via the interaction between Mn4+/Mn3+ and Ce4+/Ce3+ (Mn3+ + Ce4+ ↔ Mn4+ + Ce3+), contributed to the superior catalytic performance of MnCe/HZSM-5 with lower SiO2/Al2O3 ratio. A reversible catalyst deactivation in NH3-SCR induced by toluene was found. Toluene was prone to reacting with NH3 forming nitriles, which infringed the active sites and decreased the available coordinated NH3 on Lewis acid sites. In addition, the suppression of NO oxidation to NO2 that decreasing the percentage of “fast SCR” process, and the inhibition of NH3 activation to NH2 species also contributed to the lower SCR activity in the presence of toluene over MnCe/HZSM-5.

Low temperature performance and sulfur resistance enhancement of Mn-Ce oxides supported on W-modified MWCNT for NH3-SCR removal of NOx

ABSTRACT To eliminate nitrogen oxides (NOx), composite carrier-supported catalysts (Mn-Ce/MWCNT-W) and traditional catalysts (Mn-Ce/MWCNT and W-Mn-Ce/MWCNT) were prepared using an ultrasonic impregnation method that preformed low-temperature ammonia-selective catalytic reduction (SCR) removal of NOx. The promotion effects of MWCNT-W composite carriers for low temperature SCR activities and SO2 tolerance of the catalysts were systematically investigated. Compared to traditional catalyst, Mn-Ce/MWCNT-W catalyst, with a 30% WOx/MWCNT mass ratio, demonstrated improved SCR activity and high N2-selectivity from 100°C to 200°C. A series of characterizations were carried out and it was found that there were more redox sites and the stronger the NH3 adsorption capacity over the composite carrier-supported catalysts than traditional catalysts. Also, with this composite carrier-supported catalyst, the improvement of SCR reaction was considered to be from the abundance of high valence state Mn and well dispersed active components. Notably, compared to traditional catalyst, the composite carrier-supported catalyst exhibited the stronger sulfur resistance. Thus, using MWCNT-W composite carriers to prepare Mn-Ce/MWCNT-W catalysts resulted in excellent NOx conversion and SO2 resistance at low temperatures. Implications: LT NH3-SCR of NOx is an effective way to remove NOx from stationary sources. The physicochemical properties of the support not only affect a catalyst’s LT SCR activity but also affect the catalyst’s anti-poisoning performance. The modified carriers could promote active component dispersion, which is conducive to SCR reaction. However, for LT SCR reactions, few reports have addressed the design and preparation of composite carrier-supported catalysts. The goal of this study was to design and synthesize Mn-Ce/MWCNT-W catalysts and to observe the influence of composite support in Mn-based catalysts on LT SCR activity and sulfur resistance.

New Mn-TiO2 aerogel catalysts for the low-temperature selective catalytic reduction of NOx

A new series of Mn-based catalysts (Mn-TiO2, Ce-Mn-TiO2, Mn-TiO2-SO42–, and Ce-Mn-TiO2-SO42–) were successfully elaborated using the sol–gel method associated with supercritical drying approach for the low-temperature NO-SCR by NH3. The physicochemical properties of aerogel powders were examined by XRD, N2-Physisorption at 77 K, NH3-TPD, H2-TPR, and DRUV-Vis spectroscopy. It was shown that all the catalysts develop essentially the diffraction peaks of TiO2 anatase phase and are characterized by a nanometer size (ranging between ~5 and 9 nm), developed mesoporous texture, high surface area (SBET > 104 m2/g) and large porosity (VPT > 0.24 cm3/g). The incorporation of Ce and/or SO42– influences differently the structural, textural, acidic, and redox properties of Mn-derived sol–gel catalysts and consequently affects their SCR activity. High NO conversions (>75%) into essentially N2O are obtained at low temperatures (150–270 °C) over Mn-TiO2 and Ce-Mn-TiO2 aerogel systems. The addition of sulfate modifies the nature of Mn species and noticeably reduces the low-temperature reactivity of catalysts (T < 300 °C). However, it induces, thanks to the contribution of many strong acid sites, a substantial increase of the NO conversion into N2 at higher temperatures (T > 300 °C) leading to highly active and N2-selective Mn-TiO2-SO42– and Ce-Mn-TiO2-SO42– sulfated catalysts. Above 90% NO conversion into N2 (100%) was reached, in the NO-SCR by NH3, over the new Ce-Mn-TiO2-SO42– aerogel catalyst, in the 450–500 °C temperature range.

Promoting effect of Sb on the selective catalytic reduction of NO with NH3 over CeVO4 catalyst

A series of Sb-doped CeVO4 samples were synthetized by hydrothermal method and used in selective catalytic reduction of NO with NH3. Contrasted with other catalysts, Sb2CeVO4 possessed superior NH3-SCR activity and excellent SO2 tolerance. Besides, the characterization results testified that Sb species in Sb2CeVO4 could reduce the crystallization of CeVO4, and improve the surface acidity and reducibility. Moreover, the existence of Sb3+ was beneficial to generate more surface adsorbed oxygen species. Based on the in situ DRIFT spectra, more ad-NH3 and ad-NOx species with higher reactivity were obtainable on Sb2CeVO4 catalyst compared with that on CeVO4 catalyst, which also contributed to enhancing the SCR activity by Langmuir-Hinshelwood (L-H) mechanism effectively.

Copper Doping Promotion on Ce/CAC-CNT Catalysts with High Sulfur Dioxide Tolerance for Low-Temperature NH3–SCR

The stumbling block to the ever-increasing need for improving air quality remains nitrogen oxides (NOx). The copper-introduced Ce/CAC-CNT (CuxCe/CAC-CNTs) catalyst using the in situ-growth-prepared activated carbon and carbon-nanotube composite (CAC-CNT) carrier with high sulfur dioxide tolerance was successfully applied to low-temperature NH3–SCR in this study. The findings indicate that the CuxCe/CAC-CNTs obtained at a 0.2 Cu/Ce molar ratio and the calcination temperature of 450 °C showed the highest 100% NO conversion with 95.8% N2 selectivity at 150 °C and 10 000 h–1. The incorporation of Cu improved the Cu0.2Ce/CAC-CNTs in Lewis acid, lattice oxygen (31.99%), and Ce3+ (26.03%). The accelerated NH3 adsorption on acid sites, the encouraging electron transfer by the Ce4+ + Cu+ ↔ Ce3+ + Cu2+ redox circle, and the more surface chemisorbed oxygen (Oβ) improved the catalytic activity of Cu0.2Ce/CAC-CNTs. The NH3–SCR of Cu0.2Ce/CAC-CNTs largely follows the L–H mechanism, together with a certain degree of “Fast SCR.” The added Cu species effectively prevented surface SO2 adsorption and oxidation, and the Cu0.2Ce/CAC-CNTs restored more than 94% SCR activity after 8 h of poisoning in 50 ppm SO2 and 5 vol % H2O.