Fabrication of wide temperature lanthanum and cerium doped Cu/TNU-9 catalyst with excellent NH3-SCR performance and outstanding SO2+H2O tolerance

The effects of La on the catalytic performance,SO₂ and H2O resistance of Cu-Ce/TNU-9 catalyst were studied in the selective catalytic reduction of NO_x via ammonia(NH₃-SCR).The results show that the La doped Ce-Cu/TNU-9(CCL/T9) catalyst exhibits better SCR performance than Ce-Cu/TNU-9(CC/T9) and Cu/TNU-9(C/T9) in the wide temperature window(200-450 ℃) due to La benefiting from enhancing Cu⁺+Ce⁴⁺?Cu²⁺-+Ce³⁺ to facilitate ...     

Effect of surface manganese oxide species on soot catalytic combustion of Ce–Mn–O catalyst

Constructing cerium and manganese bimetallic catalysts with excellent catalytic performance for soot combustion is the research frontier at present. In order to find out the key factors for catalytic soot combustion of Ce–Mn–O catalysts, a series of Ce–Mn–O catalysts with different Ce/Mn proportions were prepared by co-precipitation method. The activity test results show that it increases first and then decreases with the increase of Mn content. The best catalytic activity is obtained for Ce_0.64Mn_0.36 catalyst, which shows a maximum rate temperature (T_m) at 306 °C for CO₂ production in TPO curve. Compared with non-catalytic soot combustion, the T_m decreases by more than 270 °C. Systematical characterization results suggest that when the adsorbed surface oxygen, lattice oxygen, specific surface area and total reduction amount of the catalysts reach a certain value, the key factors leading to the difference of catalytic activity become the readily reducible and highly dispersed surface manganese oxide species and contact performance of the external surface. The surface manganese oxide species is beneficial to improving the low-temperature reducibility of catalysts and the porous surface is conducive to the contact between catalyst and soot. Furthermore, for the soot combustion reaction containing only O₂, the promoting effect of Mn⁴⁺ is not obvious.     

One-pot synthesis of CNT-SAPO-34 composite supported copper and cerium catalysts with excellent surface resistance to SO2 and H2O in NH3-SCR

CuCe/CNT_x-SAPO-34(x=0,0.5,1,2) with various CNT doping quantities were synthesized through the one-pot hydrothermal synthesis method using CNT and SAPO-34 as composite supporters.The selected CuCe/CNT₁-SAPO-34 catalyst exhibits remarkable SCR activity and high H₂O/SO₂ resistance in a wide temperature range of 200-450℃.X-ray diffraction(XRD),N₂ adsorption-desorption,scanning electron microscopy(SEM),X-ray photoelectro n spectroscopy(XPS),H     

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.     

Highly efficient K-doped Mn-Ce catalysts with strong K-Mn-Ce interaction for toluene oxidation

In this study,K_x-Mn-Ce catalysts prepared by sol-gel method were investigated for toluene oxidation.Compared with Mn-Ce,the catalytic performance of K_x-Mn-Ce was further improved.X-ray diffraction(XRD),high resolution transmission electron microscopy(HRTEM) and Raman analyses demonstrate that K ions enter the lattice of CeO₂ and disperse uniformly.The results of X-ray photoelectron spectroscopy(XPS),H₂-temperature programmed reduction(H₂-TPR...     

Effect of coating modification of cordierite carrier on catalytic performance of supported NiMnO3 catalysts for VOCs combustion

NiMnO_3 perovskite catalysts supported on cordierite modified by Ce_xZr_(1-x)O_2 coatings were prepared using impregnation and sol-gel methods for catalytic combustion of single/double component VOCs at different concentrations and GHSV of 15,000 h~(-1), which were characterized by BET, XRD, SEM, FT-IR, H_2-TPR and O_2-TPD. After coating modification, the specific surface area of catalysts is improved obviously.Among the catalysts, the Ce_(0.75)Zr_(0.25)O_2 coating modified NiMnO_3 catalyst exhibits the best catalytic activity for VOCs combustion with 95.6% conversion at 275 ℃ and has stable activity when catalyst is embalmed at 800 ℃. In addition, the catalyst also presents the excellent water-resistant and conversion stability over time-on-stream condition. The reason is that Ce_(0.75)Zr_(0.25)O_2 coating can promote more lattice distortion and defects and smaller crystal size, which improve oxygen transfer capability and dispersion of active component.     

Constructing a high concentration CuO/CeO2 interface for complete oxidation of toluene: The fantastic application of spatial confinement strategy

In this paper,CeO₂ substrate was prepared by the sol-gel method,further CuO was introduced by adding the copper complexes with chelating agents into the sol-gel precursors of CeO₂,in which different chelating agents(β-cyclodextrin,glucose and trimesic acid) were tried.This synthesis method helps the CuO species to disperse very uniformly in the CeO₂ substrates.When the amount of copper oxide is up to33 mol%,the CuO/CeO₂ samples can still maintain a hig...     

Synergetic catalytic removal of chlorobenzene and NOx from waste incineration exhaust over MnNb0.4Ce0.2Ox catalysts: Performance and mechanism study

Nb doped MnCe_0.2O_x complex oxides catalysts prepared via a homogeneous precipitation method were investigated for synergistic catalytic removal of NO_x and chlorobenzene (CB) at low temperatures. The MnNb_0.4Ce_0.2O_x catalyst with a molar ratio of Nb/Mn = 0.4 exhibits excellent activity and the NO_x and CB removal efficiency reaches 94.5% and 96% at 220 °C, respectively. Furthermore, the NO_x and CB removal efficiency of MnNb_0.4Ce_0.2O_x still remains above 80% after injecting 300 ppm SO₂ and 7 vol% H₂O for 36 h. In addition, the presence of CB and NO_x + NH₃ can improve the NO_x and CB removal efficiency of MnNb_0.4Ce_0.2O_x, respectively. The analysis results from N₂-BET, Py-IR, H₂-TPR and NH₃-TPD reveal that the introduction of Nb increases the average pore size, pore volume and surface area, promoted the growth of Lewis acid amount obviously, and enhances redox ability of MnCe_0.2O_x at 100–250 °C. Moreover, the molecular migration process of NO_x, NH₃, CB and SO₂ in NH₃-SCR and CB oxidation reaction over MnNb_0.4Ce_0.2O_x catalysts were systematically studied. In situ DRIFTS, FT-IR and XPS also confirm that the adsorption of sulfate species and SO₂ on the surface of MnNb_0.4Ce_0.2O_x is inhibited effectively by the introduction of Nb in the presence of SO₂ and H₂O. Moreover, Nb additives also enhance the structural stability of MnNb_0.4Ce_0.2O_x, due to the interactions among Mn, Nb and Ce. The NH₃-TPD, H₂-TPR and in situ DRIFTS results also confirm that the MnNb_0.4Ce_0.2O_x still retains abundant acid sites and high redox ability in the presence of SO₂ and H₂O. In summary, MnNb_0.4Ce_0.2O_x catalysts represent a promising and effective candidate for controlling NO_x and CB at low temperatures.     

Lanthanum-doped Cu-Mn composite oxide catalysts for catalytic oxidation of toluene

CuMn mixed oxides catalysts doped with La were prepared following a co-precipitation method and used for the catalytic oxidation of toluene. Catalysts properties of the catalysts were investigated by X-ray diffraction, N_2 adsorption/desorption,scanning electron microscopy, H_2-temperature-programmed reduction(H_2-TPR), O_2-temperature-programmed desorption(O_2-TPD) and X-ray photoelectron spectroscopy techniques. Characterization data reveal that the phase change and decrease in crystallinity of the La-doped catalysts increase the number of oxygen vacancies. Improvements in reducibility and an increase in the amount of chemisorbed oxygen of the La-doped catalysts were also verified by H_2-TPR and O_2-TPD. The activity of the CuMn mixed oxides catalysts is significantly improved by the addition of a nominal amount of La. The CuMn/La-4 mol% catalyst exhibits the best catalytic activity, with a 90%conversion temperature of 255 ℃,attributed to a high Mn~(3+)ratio, superficial chemisorbed oxygen,and high surface area. This study indicates La to be a promising dopant for Cu-Mn catalysts toward toluene oxidation.     

Preparation of M/Ce1–xTixO2 (M=Pt,Rh, Ru) from sol-gel method and their catalytic oxidation activity for diesel soot

A series of Ce_1–xTi_xO₂ mixed oxide catalysts were synthesized by sol-gel method and then loading of noble metal (M = Pt, Rh, Ru) was used for soot oxidation. Ti-doped Ce_1–xTi_xO₂ catalysts (x is the molar ratio of Ti/(Ti + Ce) and ranges from 0.1 to 0.5) exhibit much better oxidation performance than CeO₂ catalyst, and the Ce_0.9Ti_0.1O₂ catalyst calcined at 500 °C has the best catalysis activity. Each noble metal (1 wt%) was supported on Ce_0.9Ti_0.1O₂ (M/C9T1) and the properties of the catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman, Brunauer–Emmett–Teller (BET) method, and H₂-temperature programmed reduction (H₂-TPR) results. Results show that the introduction of Ti into CeO₂ forming Ti-O-Ce structure enhances the catalytic activity and increases the number of oxygen vacancies at the catalyst surface. The noble metal is highly dispersed over Ce_0.9Ti_0.1O₂, and M/C9T1 catalysts present enhanced activity in comparison to Ce_0.9Ti_0.1O₂. It is found that noble metals can greatly increase the activity of the catalyst and the corresponding oxidation rate of soot can enhance the electron transfer capacity and oxygen adsorption capacity of the catalyst. A small amount of Ti doping in CeO₂ can significantly improve the activity of the catalyst, while a large amount of Ti reduces the performance of the catalyst because a large amount of Ti is enriched on the surface of the catalyst, which hinders the contact and reaction between the catalyst and the soot.     

Active oxygen species and oxidation mechanism over Ce-doped LaMn_(0.8)Ni_(0.2)O_3/hierarchical ZSM-5 in pentanal oxidation

Hierarchical ZSM-5(HZ) molecular sieves based on fly ash were synthesized using a method combining water heat treatment with step-by-step calcination.The coupling catalysts between La_(1-x)Ce_xMn_(0.8)-Ni_(0.2)O_3(x ≤ 0.5) perovskites and HZ were prepared through the impregnation method,which were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),high-resolution transmission electron microscopy(HRTEM),N_2 adsorption,X-ray photoelectron spectroscopy(XPS),NH_3-temperature programmed desoprtion(NH_3-TPD),H_2-temperature programmed reduction(H_2-TPR) and O_2-TPD techniques and investigated regarding pentanal oxidation at 120-390℃ to explore the effects of Ce doping on the catalytic activity and the active oxygen species of the coupling catalysts,meanwhile,the reaction mechanism and pathway of pentanal oxidation were also studied.The results reveal that Ce substitution at La sites can change the electronic interactions between all the elements and promote the electronic transfer among La,Ce,Ni,Mn and HZ,influencing directly the physicochemical characteristics of the catalysts.Moreover,the amount and transfer ability of surface adsorbed oxygen(O_2~-and O~-)regarded as the reactive oxygen species and the low temperature reducibility are the main influence factors in pentanal oxidation.Additionally,La_(0.8)Ce_(0.2)Mn_(0.8)Ni_(0.2)O_3/HZ exhibits the best catalytic activity and deep oxidation capacity as well as a better water resistance due to its larger amount of surface adsorbed oxygen species and higher low temperature reducibility.What's more,appropriate Ce substitution can significantly enhance the amount of O_2~-ions,which can distinctly enhance the catalytic activity of the catalyst,and moderate acid strength and appropriate acid amount can also facilitate the improvement of the pentanal oxidation activity.It is found that there is a synergic catalytic effect between surface acidity and redox ability of the catalyst.According to the in situ DRIFTS and GC/MS analyses,pentanal can be oxidized gradually to CO_2 and H_2 O by the surface oxygen species with the form of adsorption in air following the Langmuir-Hinshelwood(L-H) reaction mechanism.Two reaction pathways for the pentanal oxidation process are proposed,and the conversion of the formates to carbonates may be one of the main rate-determining steps.     

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...     

Catalytic feasibility of Ce-doped LaCoO3 systems for chlorobenzene oxidation: An analysis of synthesis method

A family of Ce-doped LaCoO₃ perovskites are presented as possible catalysts for Cl–VOCs elimination. These materials with different contents of Ce were obtained through the citrate and the reactive grinding methods. The insertion of Ce in the original perovskite structure favours the presence of Co²⁺/Co³⁺ and Ce³⁺/Ce⁴⁺ redox pairs and a higher content of oxygen vacancies that enhances the catalytic performance in chlorobenzene combustion based on differential kinetics studies. The family obtained by the grinding method presents a performance as high as that synthesized by citrate method. Thus, the reactive grinding is a feasible green chemistry alternative to obtain a catalyst with the same performance as that obtained from traditional methods. Finally, the stability of samples was evaluated under total combustion reaction conditions showing an excellent activity during 45 h time on stream.     

Structure and catalytic property of CeO2-ZrO2-Fe2O3 mixed oxide catalysts for diesel soot combustion： Effect of preparation method

A series of Ce0.5Fe0.30Zr0.20O2 catalysts were prepared by different methods(co-precipitations method, citric acid sol-gel method, impregnation method, physical mixed method, and hydrothermal method) and characterized by X-ray diffraction(XRD), Raman spectroscopy, Brunauer-Emmett-Teller(BET) and H2-TPR measurements. Potential of the catalysts in the soot oxidation was evaluated in a temperature-programmed oxidation(TPO) apparatus. The results showed that all the Fe3+ and Zr4+ were incorporated into ceria lattice to form a pure Ce-Fe-Zr-O solid solution for the co-precipitation sample, but two kinds of Fe phases existed in the Ce-Fe-Zr-O catalysts prepared by other methods: Fe3+ incorporated into CeO2 lattice and dispersed Fe2O3 clusters. The free Fe2O3 clusters could improve the activity of catalysts for soot oxidation comparing with the pure Ce-Fe-Zr-O solid solution owing to the synergetic effect between free Fe2O3 and surface oxygen vacancies. In addition, the activity of catalysts strongly relied on the surface reducibility of free Fe2O3 particles. Holding both abundant free Fe2O3 particles and high oxygen vacancy concentration, the hydrothermal Ce0.5Fe0.3Zr0.2O2 catalyst presented the lowest Ti(251 °C, ignition temperature of soot oxidation) and Tm(310 °C, maximum oxidation rate temperature) for soot combustion(with tight-contact between soot and catalysts) among the five samples. Even after aging at 800 °C for 10 h, the Ti and Tm were still relatively low, at 273 and 361 °C, respectively, indicating high catalytic stability.     

Possible negative influences of increasing content of cerium on activity and hydrothermal stability of Rh/ceria-zirconia three-way catalysts

The activity and hydrothermal stability of the Rh/Ce_xZr_(1-x)O_2(x=0,0.05,0.3,0.5) model three-way catalysts for gasoline vehicle emissions control were investigated in this work.Among the Rh/Ce_xZr_(1-)_xO_2 samples with different Ce/Zr ratios,the Rh/ZrO_2 sample exhibits a significantly better activity and hydrothermal stability than the rest of the samples.The impacts of having more Ce components in the Rh/Ce_xZr_(1-x)O_2 catalysts are associated with the strong Rh-O-Ce interaction that tends to over stabilize the rhodium species.A significant amount of such rhodium atoms can be found in the bulk of the support oxides after a hydrothermal aging at 1050℃ with 10% H_2 O in air for 12 h.Differently,the sintering of rhodium on the surface of Rh/ZrO_2 catalysts is the main reason for the catalyst deactivation during the hydrothermal aging.These findings provide an example where high dispersion of supported metal induced by strong metal-support interactions does not necessarily lead to high catalytic activity.     

CO oxidation and 4-nitrophenol reduction over ceria-promoted platinum nanoparticles impregnated with ZSM-5 zeolite

Active new ceria-promoted platinum supported on ZSM-5 catalysts were prepared and characterized by X-ray diffraction(XRD),Fourier transform infrared spectra(FTIR),transform electron microscopy(TEM),temperature programmed desorption(TPD),and FTIR of CO adsorption.The samples were prepared by the incipient wetness impregnation method and calcined at 500℃.The XRD patterns and FTIR spectra prove that the zeolite framework is kept unaltered after metal loadings.TEM images prove the presence of Pt nan...     

Selective catalytic reduction of NOx with NH3 over core-shell Ce@W catalyst

An environmentally benign WO₃ wrapped cubic CeO₂ core–shell catalyst (Ce@W) was developed for the selective catalytic reduction of NO_x with NH₃. Compared with CeW particles prepared via the conventional co-precipitation method, this core–shell catalyst not only displays higher tolerance to SO₂ and H₂O, but also exhibits a wider activity temperature window of 250–450 °C, in which NO_x conversion and N₂ selectivity reaches 100%. The improved performance of Ce@W catalysts can be contributed to the strong interactions between CeO₂ (100) and WO₃, which generates more Ce³⁺ and surface chemisorbed oxygen. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) reveal that the more thermally stable Brønsted acid sites on Ce@W lead to its excellent high-temperature activity.     

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.     

Promoting effect of microwave irradiation on CeO_2-TiO_2 catalyst for selective catalytic reduction of NO by NH_3

In this work we prepared several CeO₂-TiO₂ catalysts for the NH₃-SCR reactionusing co-precipitation with assistance of microwave irradiation. The catalytic NH₃-SCR activities over CeO₂-TiO₂ catalysts at low temperatures are largely enhanced by the treatment of microwave irradiation, the operation temperature window is also broadened. For better understanding the promotion mechanism, the catalyst prepared by conventional co-precipitation with and without microwave irradiation treatment was characterized with H₂-TPR, NH₃-TPD, XPS, XRD and BET. Microwave irradiation treatment accelerates the crystallite rate of CeO₂-TiO₂ catalysts, and greatly enlarges their surface area by adjusting their microstructures. The resistance to SO₂ and H₂O is also improved via regulating the hierarchical pore structure by the microwave irradiation. Microwave irradiation treatment can also improve the redox property and increase the acid sites over the catalyst surfaces. The result of in situ DRIFTS suggests that the microwave irradiation treatment generates more Brønsted acid sites on CeO₂-TiO₂-2 h catalyst, helpful in SCR reactions. XPS results show that after microwave irradiation on the CeO₂-TiO₂ catalysts, the surface demonstrates an elevated concentration of chemisorbed oxygen, consequently leading to better oxidation of NO to NO₂. Additionally, the molar ratio of Ce³⁺/Ce⁴⁺ has been elevated after being treated by microwave irradiation, a vital factor in enhancing the NH₃-SCR activities.     

Promotional effects of samarium on Co3O4 spinel for CO and CH4 oxidation

A series of Co3O4 spinel catalysts modified by Sm were prepared by co-precipitation method and tested for CH4 and CO oxidation.The addition of a small amount of Sm into Co3O4 led to an improvement in the catalytic activity for both reactions.Co0.98Sm0.02 and Co0.95Sm0.05,the two samples with Co/Sm molar ratio of 0.98/0.02 and 0.95/0.05 in sequence,showed the similar and the highest activity for CH4 oxidation,with CH4 complete conversion at 450 oC.In contrast,Co0.90Sm0.10 was the most active sample for CO oxidation,with CO complete conversion at 120 oC.The catalysts were characterized by techniques of N2 adsortion-desorption with Brunauer-Emmett-Teller technique(N2-BET),X-ray powder diffraction(XRD),thermal gravity analysis-differential scanning calorimetry(TGA-DSC),H2 temperature programmed reduction(H2-TPR) and X-ray photoelectron spectroscopy analysis(XPS).Compared with pure Co3O4,for Co1–x Smx catalysts with 0.02≤x≤0.10,the addition of a small amount of Sm resulted in the formation of spinel Co3O4 and amorphous SmCoO3,hence increasing the number of Co3+ and the active surface oxygen species,which was responsible for the improvement of the activity.Co0.95Sm0.05 catalyst showed not only high thermal stability and activity but also good reaction durability in the presence of 5% water vapor for CH4 oxidation.