Er-modified MnOx for selective catalytic reduction of NOx with NH3 at low temperature: Promoting effect of erbium on catalytic performance

Various Er modified MnO_x catalysts were synthesized using co-precipitation approach and tested in the selective catalytic reduction of NO_x by ammonia(NH₃-SCR).Catalysts were analyzed with various characterization techniques,and it is found that the doping of Er can enormously enhance the catalytic performance of MnOx catalyst.MnEr_0.1 demonstrates advantageous catalytic performance in the NH₃-SCR reaction owing to rich surface acidic sites,hi...     

Effect of manganese and/or ceria loading on V_2O_5-MoO_3/TiO_2 NH_3 selective catalytic reduction catalyst

The effect of manganese and/or ceria loading of V_2 O_5-Mo_O_3/TiO_2 catalysts was investigated for selective catalytic reduction(SCR) of NO_x by NH_3.The manganese and/or ceria loaded V_2 O_5-MoO_3/TiO_2 catalysts we re prepared by the wetness impregnation method.The physicochemical characteristics of the catalysts were thoroughly characterized.The catalytic performance of 1.5 wt% V_2 O_5-3 wt% MoO_3/TiO_2(V1.5 Mo3/Ti) is greatly enhanced by addition of 2.5 wt% MnO_x and 3.0 wt% CeO_2(V1.5 Mo3 Mn2.5 Ce3/Ti) below450℃.Compared with the V1.5 Mo3/Ti catalyst with NO_x conversion of 75% at 275 ℃,V1.5 Mo3 Mn2.5 Ce3/Ti exhibits higher NO_x conversion of 84% with good resistance to SO_2 and H_2 O at a gas hourly space velocity value of 150000 h~(-1).The active manganese,cerium,molybdenum,and vanadium oxide species are highly dispersed on the catalyst surface and some synergistic effects exist among these species.Addition of MnO_x significantly enhances the redox ability of the cerium,vanadium,and molybdenum species.Addition of Ce increases the acidity of the catalyst.More active oxygen species,including surface chemisorbed oxygen,form with addition of Mn and/or Ce.Because of the synergistic effects,appropriate proportions of manganese in different valence states exist in the catalysts.In summary,the good redox ability and the strong acidity contribute to the high NH3-SCR activity and N2 selectivity of the V1.5 Mo3 Mn2.5 Ce3/Ti catalyst in a wide temperature range.And the V1.5 Mo3 Mn2.5 Ce3/Ti catalyst shows good resistance to H_2 O and SO2 in long-time catalytic testing,which can be ascribed to the highly sulfated species adsorbed on the catalyst.     

Catalytic ozonation of NH4+-N in wastewater over composite metal oxide catalyst

Large amounts of water containing-ammonium nitrogen(NH₄⁺-N)have attracted increasing attention.Catalytic ozonation technology,involving the generation of hydroxyl radical(OH)with strong oxidation ability,was originally utilized to degrade organic-containing wastewater.In this paper,Ce/MnOx composite metal oxide catalysts prepared with different preparation conditions were used to degrade wastewater containing inorganic pollutant(NH₄⁺-N).The as-prepared catalyst features were characterized using X-ray diffraction(XRD),Brunauer-Emmett-Teller method(BET),scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDS),Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS)and H₂-temperature programmed reduction(H₂-TPR)techniques.The results show that the catalyst,prepared by conditions with precipitant Na₂CO₃ and Ce/Mn molar ratio 1:2 calcined at 400℃for 3 h in pH 11.0,displays the optimal performance,with the removal rate of NH₄⁺-N and selectivity to gaseous nitrogen,88.14 wt%and 53.67 wt%,respectively.The effects of several operating factors including solution pH,initial NH₄⁺-N concentrations and scavengers were evaluated.In addition,XRD patterns of catalyst with the best performance and the comparative study on decontamination of NH₄⁺-N by various processes(O₃,catalyst and catalyst/O₃)show that the primary metal oxides are CeO₂ and MnO₂ in Ce/MnOx composite metal oxide catalysts,which have a synergistic effect on the catalytic ozonation of NH₄⁺-N,and the new phase MnO₂ plays a great role.After 5 consecutive use cycles,the degradation efficiency is declined slightly,and can still achieve better than 70 wt%over 1 h reaction.Additionally,the application of catalytic ozonation for actual wastewater on the removal rate of NH₄⁺-N was investigated.Possible mechanism and degradation pathway of NH₄⁺-N were also proposed.In a word,the application of CeO₂-MnO₂ composite metal oxide catalysts in catalytic ozonation can be regarded as an effective,feasible and promising method for the treatment of NH₄⁺-N.     

Effect of calcination process on performance of 3DOM CeMnO_3 catalysts

A series of 3DOM CeMnO_3 perovskite catalysts were prepared by poly(methyl methacrylate) hardtemplating-excessive impregnation method at calcination temperature of x℃(x=600,700,800) and the heating rate of y ℃/min(y=1,2,5,10).The samples were characterized by Brunauer-Emmett-Teller method,scanning electron microscopy,transmission electron microscopy,H_2-temperature programmed reduction,X-ray photoelectron spectroscopy,X-ray diffraction,moreover,the effect of the calcination process on the catalytic activity of the samples were discussed by the catalytic combustion of toluene.The results show that the 3DOM CeMnO_3 catalysts calcined at 600℃ promote the formation of a perovskite structure,inhibit the reduction of the Mn~(4+) species in the catalyst with high temperature.The catalyst expresses the complete macroporous structure,large specific surface area(38.8 m~2/g),higher adsorption oxygen concentration and Mn~(4+) substance concentration,with a low T_(90%)=172℃.By preparing the catalysts at different calcination heating rates,it can be concluded that the catalyst possesses a high concentration of adsorbed oxygen and a low reduction temperature and a large specific surface area(40.42 m~2/g) greatly promotes adsorption stage catalytic oxidation reaction and catalytic combustion of toluene at low temperature under the heating rate of 5℃/min.When the heating rate is 1 ℃/min,the catalyst has a complete macroporous structure(250 nm),which is beneficial to the exchange of macromolecular substances during the catalytic reaction and the catalyst has a high concentration of lattice oxygen suitable for the catalysis of toluene in high temperature flue gas combustion.     

Study on catalytic combustion of benzene over cerium based catalyst supported on cordierite

A series of MnCeOx catalysts supported on cordierite honeycomb (Cord) were prepared by a combustion synthesis method using Mn(NO3)2 , Ce(NO3 )2·6H2O and citric acid. The effect of the molar ratio of Mn/Ce, calcination time, the amount of citric acid and the effect of water vapor on the catalytic properties for the complete oxidation of benzene were investigated. These catalysts were characterized by X-ray diffraction (XRD), H 2 temperature-programmed reduction (H2 -TPR), O2 temperature programmed desorption (O2 -TPD) and scanning electron microscopy (SEM) techniques. The results indicated that the MnCeOx /Cord catalyst with Mn/Ce molar ratio of 1:1, calcining for 7h and M n+ /(citric acid) molar ratio of 6 exhibited the highest catalytic activity. When the concentration of benzene was 1500 ppm and the gaseous hourly space velocity was 20000h -1 , the conversion of toluene was 99.1% at the reaction temperature of 300 oC.     

Doping effect of rare earth metal ions Sm3+, Nd3+ and Ce4+ on denitration performance of MnOx catalyst in low temperature NH3-SCR reaction

The MnXO_x catalysts(i.e.,MnSmO_x,MnNdO_x,MnCeO_x) were prepared by reverse co-precipitation method and used for NH₃-SCR reaction.It is found that MnCeO_x catalyst presents the best low tempe rature catalytic activity(higher than 90% NO_x conversion in the te mperature range from 125 to 225℃)and excellent H₂O+SO₂ resistance.In order to explore the reason for this result,the characterization of X-ray diff...     

Enhancing low-temperature NH3-SCR performance of Fe–Mn/CeO2 catalyst by Al2O3 modification

In the work, supported catalysts of FeO_x and MnO_x co-supported on aluminum-modified CeO₂ was synthesized for low-temperature NH₃-selective catalytic reduction (NH₃-SCR) of NO. Impressively, the SCR activity of the obtained catalyst is markedly influenced by the adding amount of Al and the appropriate Ce/Al molar ratio is 1/2. The activity tests demonstrate that Fe–Mn/Ce1Al2 catalyst shows over 90% NO conversion at 75–250 °C and exhibits better SO₂ resistance compared to Fe–Mn/CeO₂. Fe–Mn/Ce1Al2 shows the expected physicochemical characters of the ideal catalyst including the larger surface and increased active reaction active sites by controlling the amount of Al doping. Also, the better catalytic activity is well correlated with the present advantaged surface adsorption oxygen species, Mn⁴⁺ species, Ce³⁺ species and the enhanced reducibility of Fe–Mn/Ce1Al2, which is superior to the Fe–Mn/CeO₂ catalyst. More importantly, we further demonstrate that the amount and strength of surface acid sites are improved by Al-doping and more active intermediates (monodentate nitrate) is generated during NH₃-SCR reaction. This work provides certain insight into the rational creation of simple and practical denitration catalyst environmental purification.     

Novel promoting effects of cerium on the activities of NO_x reduction by NH_3 over TiO_2-SiO_2-WO_3 monolith catalysts

A series of catalysts were prepared by doping different loadings of CeO2 over TiO2-SiO2-WO3 and used for the selective catalytic reduction of NOx by NH3. The experimental results showed that the selective catalytic reduction（SCR） performance and SO2-resistant ability of TiO2-SiO2-WO3 were greatly enhanced by the introduction of cerium. The catalyst containing 10% CeO2 showed the highest NO conversion in a wide temperature range and good N2 selectivity with broad operation temperature window at the gas hourly space velocity（GHSV） of 30000 h–1, which was a very promising catalyst for NOx abatement from diesel engine exhaust. The catalysts were characterized by X-ray diffraction（XRD）, scanning electron microscopy with energy dispersive X-ray spectroscopy（SEM-EDS）, N2 adsorption-desorption（BET） and X-ray photoelectron spectroscopy（XPS）. The characterization results showed that the bigger pore radius, higher surface atomic concentration and dispersion of Ce and the abundant adsorbed oxygen on the surface of catalyst contributed to the best NH3-SCR performance of CeO2/TiO2-SiO2-WO3 catalyst containing 10% CeO2.     

Novel Mn-Ce bi-oxides loaded on 3D monolithic nickel foam for low-temperature NH3-SCR de-NOx:Preparation optimization and reaction mechanism

This study explored the superior citrate method(CM)to synthesize Mn-Ce bi-oxides on 3 D monolithic Ni-foam(NF)catalysts for the selective catalytic reduction of NO by NH₃(NH₃-SCR).The 17 wt%Mn(7)Ce(3)O_x/NF(CM-17)catalyst shows the NO_xconversion of 98.7%at 175℃and 90%in the presence of 10 vol%H2 O.It is revealed that the combination of surface-active oxygen(formed by high-level oxygen vacancies)and strongly oxidized Mn4+species promots the Fast-SCR reactions,in which Mn4+species play a leading role in NH₃-SCR reaction,and the unsaturated Ni atoms and also Ce3+species promote electron exchange and thus improve the redox performance.The coexistence mechanisms of Fast-SCR reactions and E-R pathways are observed over Mn-CeO_x/NF catalyst,which may be promoted by the Br?nsted sites at low temperature.In addition,the heat resistance,stability,3 D monolithic porous structure and excellent physical properties of foam nickel provide a unique growth substrates for catalysts preparation and reaction sites for NO_xpurification.Therefore,industrial application of Mn-Ce bioxides loaded on 3 D monolithic is proposed to be achieved through reasonable preparation methods.     

One-pot synthesis of Cu-Ce co-doped SAPO-5/34 hybrid crystal structure catalysts for NH_3-SCR reaction with SO_2 resistance

SAPO-34,SAPO-5/34 based catalysts doped with Cu,Ce as active components were synthesized via a one-pot hydrothermal method by using different amounts of additive(a-cellulose),and their catalytic activities were measured for selective catalytic reduction(SCR) of NO with NH3.The synthesized Cu-Ce co-doped products switch from cubic SAPO-34,to flower-like aggregated SAPO-5/34,hybrid crystal SAPO-5/34,and finally to spherical aggregated SAPO-34 with the increase of α-cellulose amount.The Cu-Ce co-doped SAPO-5/34 hybrid crystal structure catalysts with 0.75 mol ratios of C/P(Cu-Ce/SP-0.75)exhibit excellent NH3-SCR activity with higher than 90% NO_x conversion in the temperature range of 180-450℃,at WHSV of 20000 mL/(g·h).Furthermore,the catalyst displays outstanding sulfur resistance and NO_X conversion maintains above 90% at 200-450℃ after adding 100 ppm of SO_2.The characteristic results suggest that the high deNO_X performance of Cu-Ce/SP-0.75 is due to the enhanced accessibility,abundant activity species,excellent redox property and high adsorptive and activated capacity for NH3.     

Influence of MnO2 modification methods on the catalytic performance of CuO/CeO2 for NO reduction by CO

In order to investigate the influence of MnO2 modification methods on the catalytic performance of CuO/CeO2 catalyst for NO reduction by CO,two series of catalysts(xCuyMn/Ce and xCu/yMn/Ce) were prepared by co-impregnation and stepwise-impregnation methods,and characterized by means of X-ray diffraction(XRD),Raman spectra,H2-temperature programmed reduction(H2-TPR),in situ diffuse reflectance infrared Fourier transform spectra(in situ DRIFTS) techniques.Furthermore,the catalytic performances of these catalysts were evaluated by NO+CO model reaction.The obtained results indicated that:(1) The catalysts acquired by co-impregnation method exhibited stronger interaction owing to the more sufficient contact among each component of the catalysts compared with the catalysts obtained by stepwise-impregnation method,which was beneficial to the improvement of the reduction behavior;(2) The excellent reduction behavior was conducive to the formation of low valence state copper species(Cu+/Cu0) and more oxygen vacancies(especially the surface synergetic oxygen vacancies(SSOV,Cu+-□-Mn(4–x)+)) during the reaction process,which were beneficial to the adsorption of CO species and the dissociation of NO species,respectively,and further promoted the enhancement of the catalytic performance.Finally,in order to further understand the difference between the catalytic performances of these catalysts prepared by co-impregnation and stepwise-impregnation methods,a possible reaction mechanism(schematic diagram) was tentatively proposed.     

Ce–Ti catalysts modified with copper and vanadium to effectively remove slip NH3 and NOx from coal-fired plants

In this work, V/Ce–Ti catalysts were modified with different kinds of transition metals (Cu, Fe, Co, Mn) by sol–gel and impregnation methods. The NH₃ oxidation performance of them was tested to select the most active catalyst in NH₃-selective catalytic oxidation (NH₃–SCO). The effect of NO, SO₂ and H₂O was also investigated. The experimental results indicate that 1% Cu–V/Ce–Ti catalyst exhibits the most significant ability to remove slip ammonia discharged from coal-fired plants and its NH₃ conversion efficiency reaches 90% at 300 °C. In addition, 97% NO_x can be removed when NO is introduced in the gas. Cu–V/Ce–Ti catalyst also obtains good resistance to H₂O and SO₂. Based on the characterization experiment, the introduced Cu and V are highly dispersed on Ce–Ti catalyst and they can increase the redox properties and the number of acidic sites. Besides, the redox cycles among Cu, V and Ce species on Cu–V/Ce–Ti catalyst surface are conducive to generating more active oxygen and promoting the oxidation capacity of the catalyst.     

Promotion effect of niobium on ceria catalyst for selective catalytic reduction of NO with NH3

The CeO₂, Ce–Nb–O_x and Nb₂O₅ catalysts were synthesized by citric acid method and the promotion effect of Nb on ceria for selective catalytic reduction (SCR) of NO with NH₃ was investigated. The catalytic activity measurements indicate that the mixed oxide Ce–Nb–O_x presents a higher SCR activity than the single oxide CeO₂ or Nb₂O₅ catalyst. In addition, the Ce–Nb–O_x catalyst shows high resistance towards H₂O and SO₂ at 280 °C. The Raman, X-ray photoelectron spectra and temperature programmed reduction with H₂ results indicate that the incorporation of Nb provides abundant oxygen vacancies for capturing more surface adsorbed oxygen, which provides a superior redox capability and accelerates the renewal of active sites. Furthermore, the Fourier transform infrared spectra and temperature programmed desorption of NH₃ results suggest that niobium pentoxide shows high surface acidity, which is partly retained in the Ce–Nb–O_x catalyst possessing a high content of Lewis and Brønsted acid sites. Therefore, the incorporation of Nb improves both the redox and acidic capacities of Ce–Nb–O_x catalyst for the SCR reaction. Here, the redox behavior is primarily taken on Ce and the acidity is well improved by Nb, so the synergistic effect should exist between Ce and Nb. In terms of the reaction mechanism, in situ DRIFT experiments suggest that both NH₃ on Lewis acid sites and NH₄⁺ on Brønsted acid sites can react with NO species, and adsorbed NO and NO₂ species can both be reduced by NH₃. In the SCR process, O₂ primarily acts as the accelerant to improve the redox and acid cycles and plays an important role. This work proves that the combination of redox and acidic properties of different constituents can be feasible for catalyst design to obtain a superior SCR performance.     

Effect of preparation method on MnOx-CeO2 catalysts for NO oxidation

The NO oxidation reaction was studied over MnO_x-CeO₂ catalysts prepared by co-precipitation, impregnation and mechanical mixing method, respectively. It was found that the co-precipitation was the most active and a 60% NO conversion was achieved at 250 °C. X-ray diffraction (XRD), Brumauer-Emmett (BET), H₂-temperature programmed reduction (H₂-TPR) and oxygen storage capacity (OSC) techniques were employed to characterize the physical and chemical properties of the catalysts. XRD results showed that amorphous MnO_x or Mn-O-Ce solid solution existed in co-precipitation and impregnation prepared sample, while crystalline MnO_x was found in mechanical mixing catalyst. A larger surface area was observed on co-precipitation prepared catalyst compared to those prepared by impregnation and mechanical mixing. The strong interaction between MnO_x and CeO₂ enhanced the reducibility of the oxides and increased the amount of Mn⁴⁺ and activated oxygen, which are favorable for NO oxidation to NO₂.     

Extruded monolith MnOx-CeO2-TiO2 catalyst for NH3-SCR of low temperature flue gas from an industry boiler: Deactivation and recovery

The selective catalytic reduction(SCR) of NO_x with NH₃(NH₃-SCR) technology has been widely applied for reducing NO_x emissions from stationary and mobile sources.In this work,the extruded monolith MnO_x-CeO₂-TiO₂ catalyst was installed in a cement kiln for NH₃-SCR of NO_x,where the flue gas temperature was 110-140℃.It is found that the monolith catalyst is severely deactivated after operating for abou...     

In-situ DRIFT assessment on strengthening effect of cerium over FeO_x/TiO_2 catalyst for selective catalytic reduction of NO_x with NH_3

Fe-based catalysts have a great potential to be used for selective catalytic reduction(SCR) of NO_x with NH3 reaction due to their low cost,nontoxicity and excellent catalytic activity.The aim of this paper is to investigate Ce doping effect on activity of NH_3-SCR over the FeO_x/TiO_2 catalyst.In-situ diffuse reflectance infrared fourier transform(DRIFT) technology was utilized to verity the adsorbed species on the surface of FeO_x/TiO_2 and FeO_x-CeO_2/TiO_2 catalysts.With respect to the obtained results,among the four catalysts studied,the FeO_x-CeO_2/TiO_2 with the FeO_x/CeO_2 ratio of 3/8 shows the best NO conversion more than 98%in the temperature range of 230—350℃,The active centers for NH_3 adsorption and activation are assigned to Lewis acid sites over the FeO_x-CeO_2/TiO_2 and monodentate nitrates can act as the key intermediate in the NH3-SCR.Moreover,both of Langmuir-Hinshelwood and Eley-Rideal mechanisms are observed over the FeO_x-CeO_2/TiO_2 catalysts in the SCR.     

Effects of cerium and tungsten addition on acid–base properties of spindle-like α-Fe2O3 in low-temperature SCR of NOx with NH3

Low-temperature selective catalytic reduction (SCR) is important for the elimination of NO_x from stationary sources. In the present study, the loading of Ce and W on α-Fe₂O₃ was achieved through the integration of single-mode microwave and incipient wetness impregnation (IWI) methods. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images reveal that the structure of α-Fe₂O₃ is spindle-like, and the structure remains unchanged after the introduction of Ce and/or W. The results of NH₃-SCR investigation demonstrate that NO_x conversion over Ce–W/α-Fe₂O₃ is more than 85% at 300 °C, which is much higher than that over Ce/α-Fe₂O₃ and α-Fe₂O₃. Our studies illustrate that the addition of Ce can significantly increase the amount of surface oxygen vacancies as well as sites of moderate basicity. On the other hand, the addition of W can obviously decrease the amount of basic sites and increase the number of Brønsted acid sites. The synergistic effect of Ce and W addition on balancing acidity/basicity properties accounts for the high activity of Ce₂₀W₁₀/α-Fe₂O₃ for NO_x removal at low temperatures. The study provides insight into the relationship between acidity/basicity properties and catalytic performance of Ce–W/α-Fe₂O₃ catalysts, which is beneficial to the design of high-performance NH₃-SCR catalyst for NO_x removal at low temperatures.     

Promotional mechanism of activity of CeEuMnOx ternary oxide for low temperature SCR of NOx

Due to strong synergistic effect of the elements,a series of XEuMnO_x ternary oxides(X=Ce,Ni,Co,Sb,Sn,Mo) were synthesized by one-pot co-precipitation method,and composite components were identified and optimized to maintain high activity and superior SO₂ and H₂O endurance in selective catalytic reduction of NO_x with NH₃(NH₃-SCR).NO_x conversion of CeEuMnO_x ternary oxide catalysts attains more than 90% at 100-2...     

Sm-MnOx catalysts for low-temperature selective catalytic reduction of NOx with NH3: Effect of precipitation agent

A series of Sm-Mn mixed oxide catalysts were prepared via precipitation using various precipitants,namely Na₂CO₃(NH₄)₂CO₃,and NH₃·H₂O,and evaluated for the selective catalytic reduction(SCR) of NO_x with NH₃ at low temperatures.Various characterisation techniques were used to determine the physicochemical properties of the catalysts,and it is found that their catalytic performance is greatly influen...     

Comparative study of La_(1-x)Ce_xMnO_(3+δ) perovskites and Mn-Ce mixed oxides for NO catalytic oxidation

A series of La_(1-x)Ce_xMnO_(3+δ)(x=D,0.05,0.1,0.2,and 0.3) perovskites and Mn-Ce mixed oxides were prepared.Their physico-chemical properties were systematically characterized and the NO oxidation activities of the catalysts were investigated.The La_(0.9)Ce_(0.1)MnO_(3+δ) has the best activity among all of the catalysts,with a maximum NO conversion of 85% at 300℃.The characterization results indicate that the doping of Ce improves the properties of the perovsidtes in terms of the specific surface area,the average valence state of Mn ions,the number of reactive oxygen species and the NO_x desorption behaviors.The Mn-Ce mixed oxide calcined at 500℃ shows a similar NO oxidation activity with La_(0.9)Ce_(0.1)MnO_(3+δ).However,the activity of the mixed oxide obtained at 750℃ decreases a lot,which results from the loss of active sites and active oxygen species.