Mn/beta and Mn/ZSM-5 for the low-temperature selective catalytic reduction of NO with ammonia: Effect of manganese precursors

Optimization of Photothermal Catalytic Reaction of Ethyl Acetate and NO Catalyzed by Biochar-Supported MnOx-TiO2 Catalysts

The substitution of ethyl acetate for ammonia in NH3-SCR provides a novel strategy for the simultaneous removal of VOCs and NO. In this study, three distinct types of biochar were fabricated through pyrolysis at 700 °C. MnOx and TiO2 were sequentially loaded onto these biochar substrates via a hydrothermal process, yielding a family of biochar-based catalysts with optimized dosages. Upon exposure to xenon lamp irradiation at 240 °C, the biochar catalyst designated as 700-12-3GN, derived from Ginkgo shells, demonstrated the highest catalytic activity when contrasted with its counterparts prepared from moso bamboo and loofah. The conversion efficiencies for NO and ethyl acetate (EA) peaked at 73.66% and 62.09%, respectively, at a catalyst loading of 300 mg. The characterization results indicate that the 700-12-3GN catalyst exhibits superior activity, which can be attributed to the higher concentration of Mn4+ and Ti4+ species, along with its superior redox properties and suitable elemental distribution. Notably, the 700-12-3GN catalyst has the smallest specific surface area but the largest pore volume and average BJH pore size, indicating that the specific surface area is not the predominant factor affecting catalyst performance. Instead, pore volume and average BJH pore diameter appear to be the more influential parameters. This research provides a reference and prospect for the resource utilization of biochar and the development of photothermal co-catalytic ethyl acetate and NO at low cost.

Selective Oxidation of Triethylamine Catalyzed by Mn-Ce/ZSM-5

The selective catalytic oxidation (SCO) of triethylamine (TEA) to harmless nitrogen (N₂), carbon dioxide (CO₂), and water (H₂O) is of green elimination technology. In this paper, Mn-Ce/ZSM-5 with different proportions of MnO_x/CeO_x were studied for the selective catalytic combustion of TEA. The catalysts were characterized by XRD, BET, H₂-TPR, XPS, and NH₃-TPD and their catalytic activities were analyzed. The results showed that MnO_x was the main active component. The addition of a small amount of CeO_x promotes the generation of high-valence Mn ions, which reduces the reduction temperature of the catalyst and increases the redox capacity of the catalyst. In addition, the synergistic effect between CeO_x and MnO_x significantly improves the mobility of reactive oxygen species on the catalyst, thus improving the catalytic performance of the catalyst. The catalytic oxidation performance of TEA over 15Mn5Ce/ZSM-5 is the highest. TEA can be completely converted at 220 °C, and the selectivity for N₂ is up to 80%. The reaction mechanism was studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS).

Bismuth-Decorated Beta Zeolites Catalysts for Highly Selective Catalytic Oxidation of Cellulose to Biomass-Derived Glycolic Acid

Catalytic conversion of cellulose to liquid fuel and highly valuable platform chemicals remains a critical and challenging process. Here, bismuth-decorated β zeolite catalysts (Bi/β) were exploited for highly efficient hydrolysis and selective oxidation of cellulose to biomass-derived glycolic acid in an O₂ atmosphere, which exhibited an exceptionally catalytic activity and high selectivity as well as excellent reusability. It was interestingly found that as high as 75.6% yield of glycolic acid over 2.3 wt% Bi/β was achieved from cellulose at 180 °C for 16 h, which was superior to previously reported catalysts. Experimental results combined with characterization revealed that the synergetic effect between oxidation active sites from Bi species and surface acidity on H-β together with appropriate total surface acidity significantly facilitated the chemoselectivity towards the production of glycolic acid in the direct, one-pot conversion of cellulose. This study will shed light on rationally designing Bi-based heterogeneous catalysts for sustainably generating glycolic acid from renewable biomass resources in the future.

Effect of MnOx/α-Fe2O3 Prepared from Goethite on Selective Catalytic Reduction of NO with NH3

A low-cost goethite and manganese acetate were used to prepare a MnOx/α-Fe2O3 composite catalyst by simple impregnation method for novel high-efficiency selective catalytic reduction (SCR) of NO with NH3, and its denitration performance of composite catalyst under different conditions was investigated in a thermal fixed-bed catalytic reaction system. The results showed that MnOx/α-Fe2O3 with Mn/Fe molar ratio of 0.1 and calcination temperature of 400 °C had the best low-temperature catalytic activity and wider reaction temperature window compared with α-Fe2O3. It achieved over 90% NO conversion efficiency with a space velocity of 72,000 h−1 at 200~350 °C and possessed a good resistance of H2O and SO2. Characterization by XRD, BET, H2-TPR, and NH3-TPD revealed that the main reason for the high catalytic activity of MnOx(0.1)/α-Fe2O3(400) was that the addition of Mn changed phase types of catalyst and valence composition of Fe, resulting in a larger specific surface area, more acidic sites, and higher redox performance.

Insight into the promoting effect of support pretreatment with sulfate acid on selective catalytic reduction performance of CeO2/ZrO2 catalysts

In this paper, sulfated ZrO₂ were synthesized via precipitation and impregnation method, and the promoting effects of support sulfation on selective catalytic reduction (SCR) performance of CeO₂/ZrO₂ catalysts were investigated. The results revealed that sulfated ZrO₂ could significantly enhance the SCR activity of CeO₂/ZrO₂ catalysts in a wide temperature range. Especially when S/Zr molar ratio was 0.1, CeO₂/ZrO₂-0.1S catalyst exhibited a large operating temperature window of 251 ∼ 500 °C and its N₂ selectivity was 100 % in the temperature range of 150 ∼ 500 °C. Moreover, CeO₂/ZrO₂-0.1S catalyst possessed a superior low-temperature activity over 0.1S-CeO₂/ZrO₂ catalyst. After exposing to 100 ppm SO₂ for 15 h, a high NO conversion efficiency of CeO₂/ZrO₂-0.1S catalyst (90.7 %) could still be reached. The characterization results indicated that ZrO₂ treated with a proper dosage of sulfate acid was beneficial to enlarge the specific surface area greatly. Sulfated ZrO₂ was also in favor of promoting the transformation of CeO₂ from crystalline state to highly-dispersed amorphous state, and inhibiting the transformation of ZrO₂ from tetragonal to monoclinic phase. It could also enhance the total surface acidity greatly with an increase in both Brønsted acid sites and Lewis acid sites, thus significantly improving NH₃ adsorption on catalyst surface. Besides, the promoting effect of support sulfation on SCR performance of CeO₂/ZrO₂ catalysts was also related with the enhanced redox property, higher Ce³⁺/(Ce³⁺+Ce⁴⁺) ratio and abundant surface chemisorbed labile oxygen. The in-situ DRIFTS results implied that nitrate species coordinated on the surface of CeO₂/ZrO₂-0.1S catalyst could participate in the Selective catalytic reduction with ammonia (NH₃-SCR) reactions at either medium or high temperature, suggesting that both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms might be followed in SCR reactions.

LaOx modified MnOx loaded biomass activated carbon and its enhanced performance for simultaneous abatement of NO and Hg0

A battery of agricultural straw derived biomass activated carbons supported LaOx modified MnOx (LaMn/BACs) was prepared by a facile impregnation method and then tested for simultaneous abatement of NO and Hg0. 15%LaMn/BAC manifested excellent removal efficiency of Hg0 (100%) and NO (86.7%) at 180 °C, which also exhibited splendid resistance to SO2 and H2O. The interaction between Hg0 removal and NO removal was explored; thereinto, Hg0 removal had no influence on NO removal, while NO removal preponderated over Hg0 removal. The inhibitory effect of NH3 was greater than the accelerative effect of NO and O2 on Hg0 removal. The physicochemical characterization of related samples was characterized by SEM, XRD, BET, H2-TPR, NH3-TPD, and XPS. After incorporating suitable LaOx into 15%Mn/BAC, the synergistic effect between LaOx and MnOx contributed to the improvement of BET surface area and total pore volume, the promotion of redox ability, surface active oxygen species, and acid sites, inhibiting the crystallization of MnOx. 15%LaMn/BAC has the best catalytic oxidation activity at low temperature. That might be answerable for superior performance and preferable tolerance to SO2 and H2O. The results indicated that 15%LaMn/BAC was a promising catalyst for simultaneous abatement of Hg0 and NO at low temperature.

The Deactivation Mechanism of the Mo-Ce/Zr-PILC Catalyst Induced by Pb for the Selective Catalytic Reduction of NO with NH3

As a heavy metal, Pb is one component in coal-fired flue gas and is widely considered to have a strong negative effect on catalyst activity in the selective catalytic reduction of NOx by NH3 (NH3-SCR). In this paper, we investigated the deactivation mechanism of the Mo-Ce/Zr-PILC catalyst induced by Pb in detail. We found that NO conversion over the 3Mo4Ce/Zr-PILC catalyst decreased greatly after the addition of Pb. The more severe deactivation induced by Pb was attributed to low surface area, lower amounts of chemisorbed oxygen species and surface Ce3+, and lower redox ability and surface acidity (especially a low number of Brønsted acid sites). Furthermore, the addition of Pb inhibited the formation of highly active intermediate nitrate species generated on the surface of the catalyst, hence decreasing the NH3-SCR activity.

Improving the Performance of Gd Addition on Catalytic Activity and SO2 Resistance over MnOx/ZSM-5 Catalysts for Low-Temperature NH3-SCR

SO2 poisoning is a great challenge for the practical application of Mn-based catalysts in low-temperature selective catalytic reduction (SCR) reactions of NOx with NH3. A series of Gadolinium (Gd)-modified MnOx/ZSM-5 catalysts were synthesized via a citric acid–ethanol dispersion method and evaluated by low-temperature NH3-SCR. Among them, the GdMn/Z-0.3 catalyst with the molar ratio of Gd/Mn of 0.3 presented the highest catalytic activity, in which a 100% NO conversion could be obtained in the temperature range of 120–240 °C. Furthermore, GdMn/Z-0.3 exhibited good SO2 resistance compared with Mn/Z in the presence of 100 ppm SO2. The results of Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction of H2 (H2-TPR) and temperature-programmed desorption of NH3 (NH3-TPD) illustrated that such catalytic performance was mainly caused by large surface area, abundant Mn4+ and surface chemisorbed oxygen species, strong reducibility and the suitable acidity of the catalyst. The in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS) results revealed that the addition of Gd greatly inhibited the reaction between the SO2 and MnOx active sites to form bulk manganese sulfate, thus contributing to high SO2 resistance. Moreover, in situ DRIFTS experiments also shed light on the mechanism of low-temperature SCR reactions over Mn/Z and GdMn/Z-0.3, which both followed the Langmuir–Hinshelwood (L–H) and Eley–Rideal (E–R) mechanism.

Theoretical Studies of DENOx SCR over Cu-, Fe- and Mn-FAU Catalysts

Ab initio calculations based on the density functional theory were used. A cluster model of the faujasite zeolite structure (Al2Si22O66H36) with metal particles adsorbed above the aluminium centres was used. The NO and NH3 adsorption processes, individual and co-adsorption, have been studied over metal nanoparticles bound into zeolite clusters. Several configurations, electronic structure (charges, bond orders) and vibration frequencies have been analyzed to determine feasible pathways for the deNOx reaction. The M2O dimers (M = Cu, Mn or Fe) were considered in relation to the previous studies of iron complexes.

Fabrication of a wide temperature Mn–Ce/TNU-9 catalyst with superior NH3-SCR activity and strong SO2 and H2O tolerance

A Mn–Ce/TNU-9 catalyst demonstrated excellent sulfur and water resistance and good catalytic stability in the NH₃-SCR reaction.

Effects of ferric and manganese precursors on catalytic activity of Fe-Mn/TiO2 catalysts for selective reduction of NO with ammonia at low temperature

Fe-Mn/TiO₂ catalysts were prepared through the wet impregnation process to selective catalytic reduction of NO by NH₃ at low temperature, and series of experiments were conducted to investigate the effects of key precursors on their SCR performance. Ferric nitrate, ferrous sulfate, and ferrous chloride were chosen as Fe precursors while manganese nitrate, manganese acetate, and manganese chloride as Mn precursors. These precursors had been commonly used to prepare Fe-Mn/TiO₂ catalysts by numerous researchers. The results showed that there were distinct differences in NO conversion efficiencies at low temperature of catalysts prepared with different precursors. Catalysts prepared with ferric nitrate and manganese nitrate precursors exhibited the best catalytic performance at low temperature, while three kinds of catalysts prepared with manganese chloride precursors exhibited significantly low catalytic activity. All catalysts were characterized by XRD, SEM, H₂-TPR, NH₃-TPD, and XPS. The results indicated that when the catalysts were prepared with manganese nitrate or manganese acetate as precursors, Mn⁴⁺ contents and O_β/(O_β + O_α) ratios decreased in an order of ferric nitrate > ferrous sulfate > ferrous chloride, which was consistent with the change of catalytic activities of the corresponding catalysts at low temperature. It can be found that the excellent catalytic performance of Fe(A)-Mn(a)/TiO₂ was ascribed to high redox property and enrichment of Mn⁴⁺species and surface chemical labile oxygen groups.

Modification of V2O5-WO3/TiO2 Catalyst by Loading of MnOx for Enhanced Low-Temperature NH3-SCR Performance

V₂O₅-WO₃/TiO₂ as a commercial selective catalytic reduction (SCR) catalyst usually used at middle-high temperatures was modified by loading of MnO_x for the purpose of enhancing its performance at lower temperatures. Manganese oxides were loaded onto V-W/Ti monolith by the methods of impregnation (I), precipitation (P), and in-situ growth (S), respectively. SCR activity of each modified catalyst was investigated at temperatures in the range of 100–340 °C. Catalysts were characterized by specific surface area and pore size determination (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR), etc. Results show that the loading of MnO_x remarkably enhanced the SCR activity at a temperature lower than 280 °C. The catalyst prepared by the in-situ growth method was found to be most active for SCR.

Highly efficient absorption of nitric oxide by RuIII(edta) aqueous solutions at low concentrations

In this paper, Ru^III(edta) was used as a highly efficient absorbent for the removal of NO due to its desirable properties of high NO affinity and oxygen insensitivity. The effects of the Ru^III(edta) concentration, reaction temperature, initial solution pH, oxygen concentration, inlet NO concentration, and liquid-to-gas ratio on denitration performance were examined. The results indicated that Ru^III(edta) showed excellent denitration performance at low concentrations and that an increase in the concentration of Ru^III(edta) resulted in an increase in NO removal efficiency. In addition, NO removal efficiency increased to its optimum value at first and then declined as both the reaction temperature and initial solution pH rose. The optimal reaction temperature and ideal initial solution pH were determined to be 45°C and 5.0 respectively. The suitable liquid-to-gas ratio was found to be 51.5 L/m³. NO removal efficiency was less affected by the oxygen concentration in the range of 0-12% due to a superior anti-oxidation performance at pH = 5.0. Furthermore, the NO removal efficiency decreased significantly as the inlet NO concentration increased. The addition of 5 wt% urea to an aqueous solution of Ru^III(edta) enhanced denitration performance, and an Ru^III(edta) and urea mixed solution were able to exceed 65.07% NO removal efficiency within 30 min under optimal experimental conditions. This work proposed an alternative absorbent for NO removal and provided fundamental data for industrial denitration with Ru^III(edta) absorbents.

Smart Modification of HZSM-5 with Manganese Species for the Removal of Mercury

In this study, a series of Mn-modified HZSM-5 samples were synthesized using the solid-state ion-exchange method, and the effects of the manganese loading amount, calcination temperature, reaction temperature, and gas components on mercury removal efficiency were systematically explored. Given that the mass ratio of HZSM-5 to KMnO₄ and the calcination and reaction temperatures were set to 10:2.6 and 400 and 150 °C, Hg⁰ removal efficiency could reach a peak value of 96.4% when exposed to the flue gas containing 5% O₂ and N₂ as the balance. Among the various gas components, O₂ and NO showed a positive impact on Hg⁰ removal; Hg⁰ removal efficiency could even reach ca. 100% when O₂ and NO were simultaneously introduced. In contrast, the introduction of SO₂ led to a decline of Hg⁰ removal efficiency by ca. 16%. In addition, Hg⁰ removal efficiency could still retain ca. 92% of that for the fresh sample after six regeneration and reuse cycles, which is indicative of a satisfactory stability and renewability. Finally, Mars-Maessen mechanisms dominated in the mercury chemical adsorption process.

Promoting Effect of Ti Species in MnOx-FeOx/Silicalite-1 for the Low-Temperature NH3-SCR Reaction

Manganese and iron oxides catalysts supported on silicalite-1 and titanium silicalite-1 (TS-1) are synthesized by the wet impregnation method for the selective catalytic reduction (SCR) of NOx with NH3 (NH3-SCR), respectively. The optimized catalyst demonstrates an increased NOx conversion efficiency of 20% below 150 °C, with a space velocity of 18,000 h−1, which can be attributed to the incorporation of Ti species. The presence of Ti species enhances surface acidity and redox ability of the catalyst without changing the structure of supporter. Moreover, further researches based on in situ NH3 adsorption reveal that Lewis acid sites linked to Mn4+ on the surface have a huge influence on the improvement of denitration efficiency of the catalyst at low temperatures.

Significantly enhanced Pb resistance of a Co-modified Mn–Ce–Ox/TiO2 catalyst for low-temperature NH3-SCR of NOx

Co modification can significantly improve the performance for low-temperature NH₃-SCR of NO_x and the Pb resistance of the Mn–Ce–O_x/TiO₂ catalyst.

Low Temperature deNOx Catalytic Activity with C2H4 as a Reductant Using Mixed Metal Fe-Mn Oxides Supported on Activated Carbon

The selective catalytic reduction of NOx (deNOx) at temperatures less than or at 200 °C was investigated while using C2H4 as the reductant and mixed oxides of Fe and Mn supported on activated carbon; their activity was compared to that of MnOx and FeOx separately supported on activated carbon. The bimetallic oxide compositions maintained high NO conversion of greater than 80–98% for periods that were three times greater than those of the supported monometallic oxides. To examine potential reasons for the significant increases in activity maintenance, and subsequent deactivation, the catalysts were examined by using bulk and surface sensitive analytical techniques before and after catalyst testing. No significant changes in Brunauer-Emmett-Teller (BET) surface areas or porosities were observed between freshly-prepared and tested catalysts whereas segregation of FeOx and MnOx species was readily observed in the mono-oxide catalysts after reaction testing that was not detected in the mixed oxide catalysts. Furthermore, x-ray diffraction and Raman spectroscopy data detected cubic Fe3Mn3O8 in both the freshly-prepared and reaction-tested mixed oxide catalysts that were more crystalline after testing. The presence of this compound, which is known to stabilize multivalent Fe species and to enhance oxygen transfer reactions, may be the reason for the high and relatively stable NO conversion activity, and its increased crystallinity during longer-term testing may also decrease surface availability of the active sites responsible for NO conversion. These results point to a potential of further enhancing catalyst stability and activity for low temperature deNOx that is applicable to advanced SCR processing with lower costs and less deleterious side effects to processing equipment.

Comparative study of mesoporous NixMn6−xCe4 composite oxides for NO catalytic oxidation

In this work, a series of mesoporous Ni_xMn_6−xCe ternary oxides were prepared to investigate their NO catalytic oxidation ability.

Performance of C2H4 Reductant in Activated-Carbon- Supported MnOx-based SCR Catalyst at Low Temperatures

Hydrocarbons as reductants show promising results for replacing NH3 in SCR technology. Therefore, considerable interest exists for developing low-temperature (<200 °C) and environmentally friendly HC-SCR catalysts. Hence, C2H4 was examined as a reductant using activated-carbon-supported MnOx-based catalyst in low-temperature SCR operation. Its sensitivity to Mn concentration and operating temperature was parametrically studied, the results of which showed that the catalyst activity followed the order of 130 °C > 150 °C > 180 °C with an optimized Mn concentration near 3.0 wt.%. However, rapid deactivation of catalytic activity also occurred when using C2H4 as the reductant. The mechanism of deactivation was explored and is discussed herein in which deactivation is attributed to two factors. The manganese oxide was reduced to Mn3O4 during reaction testing, which contained relatively low activity compared to Mn2O3. Also, increased crystallinity of the reduced manganese and the formation of carbon black occurred during SCR reaction testing, and these constituents on the catalyst’s surface blocked pores and active sites from participating in catalytic activity.

Promotional Effect of Cerium and/or Zirconium Doping on Cu/ZSM-5 Catalysts for Selective Catalytic Reduction of NO by NH3

The cerium and/or zirconium-doped Cu/ZSM-5 catalysts (CuCexZr1−xOy/ZSM-5) were prepared by ion exchange and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction by hydrogen (H2-TPR). Activities of the catalysts obtained on the selective catalytic reduction (SCR) of nitric oxide (NO) by ammonia were measured using temperature programmed reactions. Among all the catalysts tested, the CuCe0.75Zr0.25Oy/ZSM-5 catalyst presented the highest catalytic activity for the removal of NO, corresponding to the broadest active window of 175–468 °C. The cerium and zirconium addition enhanced the activity of catalysts, and the cerium-rich catalysts exhibited more excellent SCR activities as compared to the zirconium-rich catalysts. XRD and TEM results indicated that zirconium additions improved the copper dispersion and prevented copper crystallization. According to XPS and H2-TPR analysis, copper species were enriched on the ZSM-5 grain surfaces, and part of the copper ions were incorporated into the zirconium and/or cerium lattice. The strong interaction between copper species and cerium/zirconium improved the redox abilities of catalysts. Furthermore, the introduction of zirconium abates N2O formation in the tested temperature range.