Low-temperature deNOx Research Articles

Metals doping effect of perovskite–type La-Mn oxides for NH3-SCR reaction at low temperature

Doping of perovskites with the heteroatoms has emerged as an additional lever, a dimension beyond structural perfection and compositional distinction, for the alteration of many properties of perovskites. In this work, a series of different metals were doped via citric acid sol–gel method to investigate their influences on the structure and catalytic performance of La-Mn perovskite oxides for NH3-SCR reaction. It is found that Zr doped La-Mn oxides (LMZr) displays better low-temperature deNOx performance (T90 = 118 °C) than other metal doped catalysts. Such a result is mainly attributed to the increase of Lewis acid sites, surface Mn4+ and adsorbed oxygen species. Besides, La-Mn perovskite doped with Sr, Ce, Y and Al can also obviously improve low-temperature deNOx activity and N2 selectivity. These doped metals mainly change the electron transfer between different cations, thus changing the valence distribution of Mn on the surface, meanwhile, metal doping changes the crystalline size of the catalysts, thereby affecting the adsorption and activation of NH3 and O2 involved in the removal of NO. Although other metal doping alters the tolerance of the La-Mn catalyst to SO2 and/or H2O, SO2 is inevitably oxidized to S6+ and deposits on the catalyst surface. Zr or Ce doping significantly enhances the tolerance to SO2 and/or H2O, but they have a different mechanism. Zr reduces the deposition rate of sulfate while Ce reacts with SO2 to form Ce2(SOx)3 to protect Mn active species. This paper highlights the importance of Lewis acid, Mn4+ content and adsorbed oxygen in the NH3-SCR reaction.

Significant Effects of Adding Mode on Low-Temperature De-NOx Performance and SO2 Resistance of a MnCeTiOx Catalyst Prepared by the Co-Precipitation Method

Significant Effects of Adding Mode on Low-Temperature De-NOx Performance and SO2 Resistance of a MnCeTiOx Catalyst Prepared by the Co-Precipitation Method

Effect of crystalline TiO2 on V2O5WO3/TiO2 as tunable low-temperature shift De-NOx catalyst

Based on the crystalline size of anatase TiO2, a series of tunable low-temperature shift V2O5-WO3/TiO2 (VW/Ti) catalysts for NH3 selective catalytic reduction (NH3-SCR) of NOx were prepared by impregnation process. These catalysts contained a loading amount of 2 wt% WO3 and either 2 or 5 wt% V2O5. The tunable low-temperature shift De-NOx performance of the VW/Ti catalysts was significantly enhanced and dramatically decreased after heat treatment of TiO2 from 100 °C to 700 °C (Ti100 ∼ Ti700). Nearly 100 % De-NOx efficiency was achieved at a gas hourly space velocity (GHSV) of 60,000 h−1. A notable shift from higher to lower temperatures was observed from V2W2/Ti100 to V2W2/Ti600; however, the activity was lost for V2W2/Ti650 to V2W2/Ti700. When the V2O5 loading increased from 2 wt% to 5 wt%, the V5W2/Ti600 showed the highest De-NOx efficiency at 225 °C, demonstrating a remarkable synergistic effect compared to the V2W2/Ti100 catalyst, which achieved maximum efficiency at 375 °C. The De-NOx performance and low-temperature shift effect of these catalysts were elucidated by considering TiO2 crystalline size, the synergistic effect between V2O5 content and TiO2, and the V4+/V5+ oxidation state of V2O5 in the catalyst. Additionally, the high crystalline TiO2-based V2W2/Ti600 catalyst prepared in this study is expected to effectively decompose NOx at low temperatures, in contrast to the low crystalline TiO2-based V2W2/Ti100 catalyst.

Three-dimensionally ordered macroporous CeZrVOx catalyst with remarkable NH3-SCR performance and SO2 tolerance: Key roles of the morphology and highly dispersed V species

Developing effective low-temperature deNOx catalysts with high activity, SO2 tolerance, and stability is crucial yet challenging. Thus, in this work, CeZrVOx catalyst with a three-dimensional ordered macroporous structure was successfully prepared using the PMMA hard template method, and the catalyst has a macropore diameter of up to 110−140 nm. The modification with highly dispersed V significantly enhances the low-temperature activity and broadens the activity temperature window of the catalyst. This is mainly attributed to the increased number of surface acid sites, as well as the higher proportion of Ce3+ and active surface oxygen species induced by V modification. The V species prepared by this method are highly dispersed on the CeZrOx solid solution and combine with Ce to form CeVO4, which is also an important factor in enhancing catalytic activity. The catalyst does not react with SO2 to produce inactive sulfate species; even the formed cerium sulfate species are beneficial for high-temperature performance. More importantly, due to its unique interconnected three-dimensional ordered structure, the catalyst can significantly inhibit the blockage and coverage of NH4HSO4 on the catalyst, thereby exhibiting remarkable resistance to physical poisoning caused by SO2. Even in high concentrations of sulfur-containing atmospheres, the catalyst still shows high catalytic activity. This work offers meaningful guidance into developing denitration catalysts that show superior performance and robust resistance to both physical and chemical poisoning induced by SO2.

Low-temperature deNOx performance and mechanism: a novel FeVO4/CeO2 catalyst for iron ore sintering flue gas

Low-temperature deNOx performance and mechanism: a novel FeVO4/CeO2 catalyst for iron ore sintering flue gas

Structural properties and low-temperature NH3-SCR activity of CeO2-MnOx mixed oxides catalyst in the microwave field

The NH3-SCR technology, based on CeO2-MnOx catalysts, is of great significance for NOx removal at low temperatures. Microwave irradiation, as an effective heating approach, can enhance the low-temperature NH3-SCR activity of catalysts. Herein, the structure-activity relationship of CeO2-MnOx oxides catalysts was explored under microwave irradiation. The MnOx catalyst and Ce-Mn(1:1) mixed oxide catalyst exhibited good low-temperature de-NOx performance in the microwave field. With the increase of microwave irradiation intensity and time, the structure and phase composition of MnOx material underwent significant changes. CeO2 played a key role in maintaining the structural stability of the Ce-Mn(1:1) catalyst. In addition, microwave irradiation affected the redox properties and acidity of the catalyst, regulating the catalytic performance. Suitable microwave operation conditions were conducive to increasing the number of acidic sites and enhancing the redox properties, which improved the low-temperature catalytic activity of the catalyst.

Collaborative optimization of de-NOx & NH4HSO4 decomposition over Cu-based LDO catalysts: Perspective from the acidic and redox properties

Low temperature de-NOx catalyst with excellent resistance to ammonium bisulfate (ABS) is of great practical significance. Study about the simultaneous optimization of de-NOx performance and ABS resistance by acidic and redox properties regulation is imperative. In this work, the influence of the acidic and redox properties to the de-NOx & ABS decomposition performance was investigated via three Cu-based LDO model catalysts with distinct surface chemical character. Test results indicated that the low temperature de-NOx performance of both the modified Cu2NiAl-LDO and Cu2CoAl-LDO catalysts was slightly improved, while their in situ ABS resistance behavior was remarkably different (Cu2CoAl-LDO > Cu3Al-LDO > Cu2NiAl-LDO). TPDC and TPSR test evidenced that the ABS thermal decomposition or its reactivity with NOx was facilitated over Cu2CoAl-LDO catalyst, but inhibited over Cu2NiAl-LDO catalyst. Characterizations revealed the Cu2CoAl-LDO catalyst with stronger redox property could contribute to ABS decomposition, while more weak acid sites on Cu2NiAl-LDO catalyst induced a negative effect for ABS decomposition. Our study might provide guidance on the rational design of de-NOx & anti-ABS catalysts for future studies.

Rational design on hierarchically porous Cu/ZSM-5 zeolite for promoting low-temperature NH3-SCR performance based on protectively alkali-etching strategy

In this study, organic structure-directing agents (OSDA) of TPA+ are used as templating agents to synthesize zeolites with different topologies, and are also served as protectants for alkali treatment to inhibit the severe silicon extraction from zeolite skeleton. The TPA+ cations could be bound to the negatively charged Al sites in the framework, so we prepared a series of Cu-based ZSM-5 catalysts with mesoporous/microporous composite structure by using TPA+ cation as a protectant for alkali treatment and evaluated the pore structures by using the hierarchy factor (HF). The results show the hierarchically mesoporous/microporous structure of the alkali-etched catalyst with the maximal HF (0.115) effectively improved the low-temperature activity on selective catalytic reduction (SCR) of NO by ammonia, achieving a complete NOx to N2 conversion at 225–400 ºC. It was shown that the TPA+ cation played an important role on protecting the crystallinity, long-range order, and pore connectivity of zeolites, and substantially widened the mesopore volume with the loss of a small portion of micropores. In addition, the alkali treatment strategy involving protectant was systematically studied, including the corresponding effect on the pore structure, redox ability, acidity, and copper ion dispersion. The N2 adsorption-desorption experiments revealed that the maximization of the HF can be obtained by adjusting the ratio of protectant to etchant (TPA+/OH-). Among them, the Cu/ZSM-5 catalyst associated with the ratio of TPA+/OH-=0.4 and the best activity has a maximum surface area of 515 m2/g, which enhances the mesopore volume (0.325 cm3/g) by approximately three times simultaneously with only a 16.9% loss of the micropore volume (0.154 cm3/g). The hierarchically porous zeolites not only enhance the diffusion of mobile hydrated copper ions and ammonia-solvated copper complexes, but also facilitate the dispersion of copper ions. This work provides a feasible strategy to rapidly enhance the low-temperature deNOx efficiency on the zeolite catalysts.

Engineering the surface properties of CeVO4 catalysts to improve low temperature De-NOx performance through regulating pH value in synthesis process

The presence of quick electron transfer in metal oxides can well promote selective catalytic reduction (SCR) of NOx with NH3. Here, a series of CeVO4-X (X = 4, 6, 8, 10 and 12) catalysts with engineering the surface properties were successfully synthesized via controlling pH values in the hydrothermal process. The catalysts were evaluated in the NH3-SCR reaction in the temperature range of 90–420 °C. Among them, the CeVO4-8 catalyst with nanorods structure displayed the highest catalytic activity, achieving over 90 % NO conversion between 180 and 390 °C. It also showed high N2 selectivity and good tolerance to H2O and SO2. The effect of different pH values on the catalytic activity and microstructure of CeVO4 catalysts was comprehensively characterized using various techniques such as XRD, Raman, SEM, HR-TEM, N2 adsorption-desorption, H2-TPR, O2/NH3/NO-TPD, XPS, and in-situ DRIFTS. The characterization results revealed that the variation in catalytic activity among these catalysts is attributed to the difference in their surface properties, which were tuned by changing the pH values during synthesis process, despite having the same crystal phase of CeVO4. The superior catalytic performance of the CeVO4-8 catalyst, particularly at low temperature, can be attributed to its higher specific surface area, enhanced acidity, and the electron transfer between cerium and vanadium species (Ce4+ + V4+ ↔ Ce3+ + V5+), consequently resulting in increased redox capacity and facilitating the adsorption and activation of NH3 and NO molecules. This study broadens the applications of CeVO4 in the field of low temperature NOx removal.

Low-temperature selective catalytic reduction of NOx with NH3: Exploring the mechanism of enhancing H2O tolerance through methylation functionalization and structural regulation in IPAx-Mn-BTC

In the selective catalytic reduction (SCR) of NOx with NH3, it is crucial to design low-temperature de-nitrification (de-NOx) catalysts with high H2O tolerance. Here, we developed a type of low-temperature de-NOx catalyst (IPAx-Mn-BTC) with strong H2O tolerance through methyl functionalization. In the presence of the optimal catalyst (IPA50-Mn-BTC), the NOx conversion only decreased from 97% to 90% after introducing 6% H2O for 6 h at low temperature of 150 °C. The results of in-situ DRIFTS and density functional theory calculations confirm that the de-NOx reaction process and the generation of intermediate states that occur on the surface of the IPA50-Mn-BTC are not affected by H2O. The elimination of the small pore size (< 4.3 nm) and the diminished H2O adsorption energy resulted from methyl functionalization are the key factors behind the improved H2O tolerance. This work provides a new approach for designing low-temperature de-NOx catalysts with high H2O tolerance.

Improved N2 Selectivity of MnOx Catalysts for NOx Reduction by Engineering Bridged Mn3+ Sites

Mn-based catalysts are promising for selective catalytic reduction (SCR) of NOx with NH3 at low temperatures due to their excellent redox capacity. However, the N2 selectivity of Mn-based catalysts is an urgent problem for practical application owing to excessive oxidizability. To solve this issue, we report a Mn-based catalyst using amorphous ZrTiOx as the support (Mn/ZrTi-A) with both excellent low-temperature NOx conversion and N2 selectivity. It is found that the amorphous structure of ZrTiOx modulates the metal-support interaction for anchoring the highly dispersed active MnOx species and constructs a uniquely bridged Mn3+ bonded with the support through oxygen linked to Ti4+ and Zr4+, respectively, which regulates the optimal oxidizability of the MnOx species. As a result, Mn/ZrTi-A is not conducive to the formation of ammonium nitrate that readily decomposes to N2O, thus further increasing N2 selectivity. This work investigates the role of an amorphous support in promoting the N2 selectivity of a manganese-based catalyst and sheds light on the design of efficient low-temperature deNOx catalysts.

Insight into the low-temperature DeNOx performance of copper-based oxides: Perspective from the valence state distribution

Understanding the effect of CuOx valence state specifically is significant for constructing high-performance Cu based oxide catalyst for low-temperature selective catalytic reduction of NO with NH3 (NH3-SCR). In this work, CuOx with different valence state including Cu2O, Cu2O-CuO and CuO particles are synthetized as model catalysts, which present same variation laws in catalytic performance at 180 ℃, 210 ℃ and 240 ℃. NH3-SCR catalytic performance of Cu2O-CuO heterojunction is the best, CuO exhibits good catalytic activity, while Cu2O possesses excellent N2 selectivity. Experimental results combined with density functional theory (DFT) calculations reveal that Cu2+ favor to form monodentate nitrate and possess strong ability of activation and dehydrogenation of NH3. The energy barrier for the form of NH2* is 79.5 kJ/mol, which is much lower than that for Cu+. While Cu+ is beneficial to NH3 and NOx adsorption and the form of bidentate nitrate, which have a positive impact on improving the selectivity of N2. Moreover, the collaboration of Cu2+ and Cu+ facilitates the redox capability and the form of surface adsorbed oxygen species, thus the reaction progress is further promoted. The SCR reaction catalyzed by three samples are dominated mainly by Langmuir-Hinshelwood (L-H) mechanism at 180 ℃. While at 240 ℃, the reaction over Cu2O follows Eley-Rideal (E-R) mechanism, during which the rate-limiting step is the internal hydrogen transfer procedure (NH2NO*→NHNOH*). Over CuO, the reaction follows L-H mechanism, the process of atomic isomerism (NHNOH*+ *→N2*+H2O*) is the rate-determining step. The energy barriers are 136 and 146 kJ/mol, respectively. This work may supply important theoretical support for the preparation of high-performance Cu-based oxide catalysts.

Role of Ce in promoting low-temperature performance and hydrothermal stability of Ce/Cu-SSZ-13 in the selective catalytic reduction of NOx with NH3

With the increase of car ownership, new challenges are posed to the treatment of mobile source exhaust gas, especially denitration (de-NOx). It is urgent to develop highly efficient de-NOx catalyst with a wide working temperature window. In this work, a series of Ce modified Cu-SSZ-13 molecular sieves (Ce/Cu-SSZ-13) are prepared by ion exchange method with different exchange times (x = 1, 2, 4, 8 h), and the role of Ce in promoting low-temperature de-NOx performance and hydrothermal stability of Ce/Cu-SSZ-13 in the selective catalytic reduction (SCR) of NOx are investigated. Both the low-temperature de-NOx performance and the hydrothermal stability of Cu-SSZ-13 are enhanced due to the modification of Ce, especially the Ce/Cu-SSZ-13 with an exchange time of 2 h. Both Ce/Cu-SSZ-13 and Cu-SSZ-13 present more than 95 % NOx conversion in the temperature region of 210–600 °C, and Ce modification significantly improves the NOx conversion in the low-temperature range (120–210 °C). It is revealed that the acidity, the surface Cu2+/Cu+ ratio and the NH3 adsorption amount on Cu-SSZ-13 increase after Ce ion exchange, and the active component Cu2+ migrates to the more stable six-membered ring due to the modification of Ce, all of which have promote the improvement of NH3-SCR de-NOx performance. Furthermore, in the process of hydrothermal aging, the presence of Ce protects the framework of Cu-SSZ-13, acidic sites and active component Cu2+, which greatly improves the hydrothermal stability of Cu-SSZ-13 molecular sieve. In addition, in-situ DRIFTS shows that the developed Ce/Cu-SSZ-13 follows dual mechanisms of Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) to undergo NH3-SCR reaction. This work provides a new idea for improving the low-temperature de-NOx performance and hydrothermal stability of Cu-SSZ-13.

Low-temperature DeNOx characteristics and mechanism of the Fe-doped modified CeMn selective catalytic reduction catalyst

Low-temperature deNOx selective catalytic reduction (SCR) catalysts are of great significance to prolong catalyst life and reduce flue gas temperature. In this work, the low-temperature deNOx performance of different zFeCexMny catalysts was investigated on a simulated flue gas fixed-bed experimental bench. BET, XRD, XPS, NH3-TPD, and in situ FT-IR were used to characterize the physical-chemical properties of the samples. The optimum ratio and deNOx mechanism of the catalysts were explored. The results show 4FeMn7Ce3 doped with 4 wt% Fe based on Mn7Ce3 has the best deNOx performance. Its deNOx efficiency is over 90% at 120–220 °C and GHSV = 50,000 h−1, with the peak value of 98% at 150 °C. The Fe doping makes the oxide distributed uniformly on the catalyst's surface, promotes the valence cycle of the catalyst, yields more Mn4+ and Ce3+ species, and prompts the optimal deNOx temperature to the low temperature direction. Meanwhile, Lewis acid sites on the catalyst's surface are enhanced, which can promote the amide species formation that is beneficial for the deNOx reaction. Combined with in situ FTIR, the E-R mechanism and the L-H mechanism coexist in the deNOx process of zFeCexMny catalysts. These findings are helpful for the development of high-performance low-temperature deNOx catalysts.

Rational Regulation of Reducibility and Acid Site on Mn-Fe-BTC to Achieve High Low-Temperature Catalytic Denitration Performance.

Selective catalytic reduction with ammonia is the mainstream technology of flue gas denitration (de-NOx). The reducibility and acid site are two important factors affecting the de-NOx performance, and effective regulation between them is the key to obtain a highly efficient de-NOx catalyst. Herein, a series of Mn-Fe-BTC with different ratios of Mn and Fe are synthesized, among which 2Mn-1Fe-BTC with 2:1 molar ratio of Mn and Fe has excellent low-temperature (LT) de-NOx performance (above 90% NO conversion between 60 and 270 °C) and good tolerance to H2O and SO2 poisoning (88% NO conversion at 150 °C with 100 ppm of SO2 and/or 6% H2O). It is revealed that the reducibility properties and acid sites of Mn-Fe-BTC can be flexibly tuned by the ratio of Mn and Fe. The difference in electronegativity between Fe and Mn leads to the redistribution of valence electrons, which enables the controllable reducibility of Mn-Fe-BTC. Furthermore, different amounts of Mn and Fe lead to different electron transport, which determines the type and number of acid sites. The synergistic effect of Mn and Fe endows Mn-Fe-BTC with enhanced surface molecular adsorption capacity and enables the catalyst to selectively chemisorb NH3 and NO at different active sites. This research provides guidance for the flexible regulation of reducibility and acid site of LT de-NOx catalyst.

MnCe/GAC-CNTs catalyst with high activity, SO2 and H2O tolerance for low-temperature NH3-SCR

SO2 and H2O tolerance is a crucial issue for low-temperature selective catalytic reduction of NO with NH3 (NH3-SCR) in practical application. In the present work, MnCe/GAC-CNTs catalysts were prepared and showed high activity, SO2 and H2O tolerance for low-temperature NH3-SCR. The catalysts were characterized by SBET, XPS, XRD, NH3−TPD, and DRIFTs. MnCe/GAC-CNTs exhibited higher catalytic activity and H2O + SO2 tolerance than CeO2/GAC-CNTs due to electron transfer between Ce and Mn species (Ce4+ + Mn3+ ↔ Ce3+ + Mn4+) accompanied with higher proportion Ce3+, and the improvement of surface acidity concentration and strength. Besides, Mn addition inhibited the oxygen inhibitory effect, enhanced the adsorption of NO, and increased the proportion diameter, which were beneficial to SO2/H2O resistance. Furthermore, the presence of Mn suppressed the formation of hydroxyl group, inhibited the adsorption of SO2, ultimately limited electron transfer between SO2 and Ce4+, which led to high SO2 tolerance of the MnCe/GAC–CNTs catalyst. Therefore, MnCe/GAC-CNTs catalyst with high deNOx performance and SO2/H2O tolerance, showed the potential of practical low-temperature deNOx application.

Superior CuMgFe mixed oxide catalysts engineered by tuning the redox cycle for enhancing NOx removal performance

In this work, the CuMgFe layered double hydroxides (CuMgFe-LDH) with different Cu/Mg/Fe molar ratios were fabricated, and derived catalysts (CuMgFe-LDO) were tested in the removal of NOx by selective catalytic reduction with NH3 (NH3-SCR). Cu/Mg/Fe molar ratios of LDH precursors were systematically identified to achieve optimal catalytic performance. The results showed that the denitration performances of the as-acquired catalysts were vulnerable to the Cu/Mg/Fe molar ratios. The Cu0.5Mg2.5Fe1-LDO catalyst displayed the superior activity (the NOx conversion was 80% at the range of 180–250 °C) and SO2 resistance (the NOx conversion was decreased by 18% in 8 h when 100 ppm SO2 was introduced at 210 °C). Multiple characterization techniques revealed that superior catalytic performance of Cu0.5Mg2.5Fe1-LDO could be attributed to the well dispersed active ingredients and the electron transfer between copper and iron species (Cu++Fe3+↔Fe2++Cu2+), consequently resulting in higher specific surface area, enhanced acidity, increased redox capacity, and improved cycle reactions of Cu++Fe3+↔Fe2++Cu2+. This work provides a fundamental understanding on Cu++Fe3+↔Fe2++Cu2+ synergistic effect of NH3-SCR and expand the applications of LDH in the field of low-temperature de-NOx.

Gd-Mn-Ti composite oxides anchored on waste coal fly ash for the low-temperature catalytic reduction of nitrogen oxide

Nitrogen oxide (NOx) is a typical atmospheric pollutant that harms the environment and human body, and selective catalytic reduction with NH3 (NH3-SCR) is one of the most effective technologies to deal with its emissions at present. In this work, the Gd-Mn-Ti composite oxides are anchored on waste coal fly ash (CFA) as catalyst for the reduction of NOx by the NH3-SCR technology. The developed 0.2Gd-Mn-Ti/CFA catalyst presents above 90% de-NOx efficiency from 120 to 330 °C with a wide temperature window. The reasons can be ascribed to the facts that the introduction of appropriate Gd can increase the acid sites, improve the redox environment and elevate the content of surface Mn4+ and chemical adsorption oxygen (Oα). In addition, the interaction between Gd-Mn-Ti composite oxides and between active components and carrier also plays a positive role for the excellent reaction activity. Additionally, both E-R and L-H mechanisms are included in the NH3-SCR reaction over Gd-Mn-Ti/CFA catalyst. This work opens up a new way for the utilization of waste CFA, and provides a reference for the design and preparation of Mn-based low-temperature de-NOx catalysts with wide temperature windows.

Bimetallic modification of MnFeOx nanobelts with Nb and Nd for enhanced low-temperature de-NOx performance and SO2 tolerance

Nitrogen oxide (NOx) is one of the key factors contributing to air pollution, and selective catalytic reduction with ammonia (NH3-SCR) is widely used for denitrification (de-NOx). To effectively deal with the NOx pollution, it is urgent to develop efficient catalyst working at below 300 °C with a wide operating temperature window. Herein, a series of ferromanganese oxides (MnFeOx) nanobelts are bimetallically modified with niobium (Nb) and neodymium (Nd) for the first time via electrospinning method. The resultant MnFeNbNdOx catalysts present improved low-temperature de-NOx performance and sulfur dioxide (SO2) tolerance, particularly MnFeNb0.2Nd0.1Ox who achieves a NOx conversion up to over 90 % during the range of 120–330 °C and an enhanced tolerance of water (H2O) and SO2. Experimental and theoretical calculations confirm that strong adsorption of nitric oxide (NO) and ammonia (NH3) and weak adsorption of SO2 with the synergy of Nd, Nb and Mn enable MnFeNb0.2Nd0.1Ox excellent SCR activity and good SO2 tolerance. In-situ diffuse reflectance infrared Fourier transform spectra (DRIFTS) further reveal that the de-NOx reaction over MnFeNb0.2Nd0.1Ox follows both Eley-Rideal (E-R) and Langmuir-Hinshel-wood (L-H) mechanisms. This study will inspire the further design and study of the synergy of transition metals and rare earth elements for de-NOx.

Insight into the sulfur resistance of manganese oxide for NH3-SCR: Perspective from the valence state distributions

The multiple valence states distributions (VSDs) endowed the catalyst with excellent low temperature de-NOx activity, while little is known about whether the SO2 resistance can be affected by VSDs modulation. In this context, three model manganese oxide catalysts (MnO2, Mn2O3 and Mn3O4) with different valence state distributions were fabricated and evaluated in the NH3-SCR reaction under the presence of SO2. The results show that the three catalysts exhibited a valance-state-dependent SO2 resistance (Mn3O4 > Mn2O3 > MnO2) under the SCR atmosphere with the presence of 100 ppm SO2 at 100 °C within 7 h. Thermal regeneration analysis revealed the overall deactivation was dominated by the remarkably different reversible activity loss proportions, which were found proportionally correlated to the superficial Mn4+/Mnn+ content of the catalysts. Further characterizations indicated the Mn3O4 catalyst with more basic sites and less bulk-like sulfate formation could be the reason for its more slowly deactivation within the limited test period. However, the overall number of basic sites on MnOx is still critically insufficient for longer SO2 resistance test. This work clarified the deactivations details of MnOx from the perspective of valence state distributions, which can provide references for the design of better low temperature SO2-tolerant de-NOx catalyst.