Enhancement of potassium resistance of Ce-Ti oxide catalyst for NH3-SCR reaction by modification with holmium

Alkali metal K in exhaust gas has a deactivation effect on NH₃-SCR catalysts.In this work,it is discovered that the addition of Ho on CeTi catalyst can remarkably strengthen its K tolerance.The conclusions of Brunauer-Emmett-Teller(BET),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),NH₃ temperature programmed desorption(NH₃-TPD)and H₂temperature programmed reduction(H₂-TPR)analyses demonstrate that the enhancement of K resistance mainly originates from its stronger surface acidity and redox capability,the higher concentration of Ce³⁺species and surface chemisorbed oxygen.In situ DRIFT analysis reveals that the introduction of Ho on CeTi can remarkably improve the adsorption of NH₃ and NO_x species on catalyst surface,accompanied by the intensified reactivity of ad-NH₃ species,which should also administer to improve the K resistance.     

Promoting effect of tantalum and antimony additives on deNOx performance of Ce3Ta3SbOx for NH3-SCR reaction and DRIFT studies

A superior Ce-Ta-Sb composite oxide catalyst prepared using homogeneous precipitation method exhibited excellent deNOx efficiency and nearly 100% N_2 selectivity with broad operation temperature window and better resistance to higher space velocity, meanwhile strong resistance to H_2 O and SO_2. This catalyst was systematically characterized using XRD, N_2 adsorption, SEM, TEM, XPS, ESR, Raman, H_2-TPR,NH3-TPD and in situ DRIFTS. There exists a synergistic effect between Ce, Ta and Sb species. It is further indicated that the prominent deNOx performance of the Ce3 Ta3 SbOx catalyst is attributed to the elevated Ce3+ concentrations, abundant active surface oxygen species, as well as surface acidity and reducibility,which is closely linked with the synergistic effect between Ce, Sb and Ta species. Results from DRIFTS reveal that the reaction mechanism of surface-adsorbed NH3 and NO_x species is linked to temperature,the L-H mechanism mainly occurs at low temperature(300 ℃),while the E-R mechanism occurs at high temperature(300 ℃). Overall,these findings indicate that Ce3 Ta3 SbOx is promising for NO_x practical abatement.     

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.     

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.     

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...     

Low-temperature NH_3-SCR of NO_x over MnCeO_x/TiO_2 catalyst:Enhanced activity and SO_2 tolerance by modifying TiO_2 with Al_2O_3

A series of TiO_2-Al_2 O_3 composites with Al/Ti molar ratios of 0.1,0.2,and 0.4 were synthesized by a coprecipitation method and used as supports to prepare supported MnCeO_x catalysts by an impregnation method.The physico-chemical properties of the samples were extensively characterized by N2 physisorption,X-ray diffraction,Raman spectroscopy,scanning electron micro scopy and energy-dispersive Xray spectroscopy element mapping,X-ray photoelectron spectroscopy,H_2-temperature programmed reduction,ammonia temperature programmed desorption,and in-situ diffuse reflectance infrared Fourier transform spectroscopy.The catalytic activity and resistance to water vapor and SO_2 of the asprepared catalysts for the SCR of NO_x with NH3 were evaluated at 50-250℃ and GHSV of 80000 mL/(g_(cat)·h).The results reveal that MnCeO_x/TiO_2-Al_2 O_3 exhibits higher activity and better SO2 tolerance than MnCeO_x/TiO_2.Combining with the characterization results,the enhanced activity and SO2 tolerance of MnCeO_x/TiO_2-Al_2 O_3 can be mainly attributed to higher relative concentrations of Mn~(4+)and chemisorbed oxygen species,stronger reducibility,and larger adsorption capacity for NH3 and NO,which originate from the larger specific surface area and pore volume,higher dispersion of Mn and Ce species compared with MnCeO_x/TiO_2.Moreover,in situ DRIFTS was used to investigate the reaction mechanism,and the results indicate that the NH3-SCR reaction over MnCeO_x/TiO_2 and MnCeO_x/TiO_2-Al_2 O_3 takes place by both the E-R and L-H mechanisms.     

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 ...     

Getting insights into gas-phase sulfation effect on catalytic performance of praseodymium oxides in NH3-SCR of NO

Sulfation treatment has been widely used to promote the catalytic performance of ceria(CeO₂) based catalysts for the selective catalytic reduction of NO by NH₃(NH₃-SCR of NO).Praseodymium oxide(PrO_x),another commonly used rare earth material with similar structural properties as CeO₂,also shows satistactory redox properties due to the facile redox cycle of Pr³⁺■Pr⁴⁺.In this work,gas phase sulfation treatment with varied...     

Promoting effect and mechanism of neodymium on low-temperature selective catalytic reduction with NH3 over Mn/TiO2 catalysts

Series of Mn/TiO₂ catalysts modified with various contents of Nd for low-temperature SCR were synthesized. It can be found that the appropriate amount of Nd can markedly reduce the take-off temperature of Mn/TiO₂ catalyst to 80 °C and NO_x conversion is stabilized over 90% in the wide temperature range of 100–260 °C. 0.1Nd–Mn/Ti shows higher N₂ selectivity and better SO₂ resistance than Mn/Ti catalyst. The results reveal that Nd-doped Mn/TiO₂ catalyst exhibits larger BET surface area and better dispersion of active component Mn₂O₃. XPS results indicate that the optimal 0.1Nd–Mn/Ti sample possesses higher concentration of Mn⁴⁺ and larger amount of adsorbed oxygen at the surface compared with the unmodified counterpart. In situ DRIFTS show that the surface acidity is evidently increased after adding Nd, especially, the Lewis acid sites, and the intermediate (-NH₂) is more stable. The reaction mechanism over Mn/Ti and 0.1Nd–Mn/Ti catalysts obey the Eley-Rideal (E-R) mechanisms under low temperature reaction conditions. H₂-TPR results show that Nd–Mn/TiO₂ catalyst exhibits better low-temperature redox properties.     

Hydrogen production from ammonia decomposition over Ni/CeO2 catalyst: Effect of CeO2 morphology

Ammonia(NH₃) decomposition to release CO_x-free hydrogen(H₂) over non-noble catalysts has gained increasing attention.In this study,three nanostructured CeO₂ with different morphologies,viz.rod(R).sphere(Sph),and spindle(Spi),were fabricated and served as supports for Ni/CeO₂ catalyst.The CeO₂supports are different in particle sizes,specific surface area and porosity,resulting in the formation of Ni nanoparticles with distinguished...     

Effects of cerium and vanadium on the activity and selectivity of MnOx-TiO2 catalyst for low-temperature NH3-SCR

MnOx-TiO2,CeO2-MnOx-TiO2 and V2O5-MnOx-TiO2 catalysts for low-temperature NH3-SCR were prepared by sol-gel method.The results showed that both cerium and vanadium prevented the transformation of anatase TiO2 to the rutile phase.The addition of vanadium oxide induced the segregation of crystalline Mn2O3,which contributed little to low-temperature SCR and ammonia oxidation,from the MnOx-TiO2 solid solutions.However,the selectivity of the V-containing catalyst was almost 100% due to the decreased ammonia consump-tion and enhanced adsorption capacity of ammonia on Br(?)nsted acid sites at relatively high temperatures.The electron-donating effect of ce-rium reduced the Mn4+/Mn3+ ratio to some extent,resulting in a decreased activity for ammonia oxidation.This,in combination with the en-hanced ammonia adsorption capacity by Cen+ as additional Lewis acid sites,endowed the Ce-doped catalyst a higher N2 selectivity than MnOx-TiO2 despite the slightly elevated light-off temperature for NO conversion.     

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...     

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.     

Revealing active species of CePO4 catalyst for selective catalytic reduction of NOx with NH3

Revealing the active species of the catalyst is conducive to the design of more efficient catalyst.Herein,we tried to demonstrate the roles of amorphous and crystalline structures on CePO₄ catalyst during selective catalytic reduction(SCR) of NO_x by NH₃.Higher calcination temperature promotes the transfer of amorphous structure to crystalline structure on the surface of CePO₄.Both amorphous and crystalline CePO₄ species on CePO-X samples can...     

Promotional effect of CO pretreatment on CuO/CeO2 catalyst for catalytic reduction of NO by CO

The CuO/CeO2 catalysts were investigated by means of X-ray diffraction(XRD),laser Raman spectroscopy(LRS),X-ray photoelectronic spectroscopy(XPS),temperature-programmed reduction(TPR),in situ Fourier transform infrared spectroscopy(FTIR) and NO+CO reaction.The results revealed that the low temperature(150 °C) catalytic performances were enhanced for CO pretreated samples.During CO pretreatment,the surface Cu+/Cu0 and oxygen vacancies on ceria surface were present.The low valence copper species activated the adsorbed CO and surface oxygen vacancies facilitated the NO dissociation.These effects in turn led to higher activities of CuO/CeO2 for NO reduction.The current study provided helpful understandings of active sites and reaction mechanism in NO+CO reaction.     

Catalytic combustion of toluene on Pt/Al2O3 and Pd/Al2O3 catalysts with CeO2,CeO2-Y2O3 and La2O3 as coatings

CeO₂,La₂O₃,and CeO₂-Y₂O₃ oxides were coated on the surface of spherical granular AI₂O₃(3-5 mm)through impregnation method,and proved as better supports of Pd and Pt catalysts.The influences of rare earth metal doping on the adsorption rates of Pd and Pt ions,as well as the catalytic performance,were investigated.Results show that the H₂PtCl₆·6H₂O adsorption rates of the Al     

CeO2 and CeO2-based nanomaterials for photocatalytic,antioxidant and antimicrobial activities

Cerium oxide(CeO₂),one of the most significant rare-earth oxides,has attracted considerable interest over the past decades.This is primarily due to the ease in Ce³⁺/Ce⁴⁺ redox ability as well as other factors that affect the efficacy of CeO₂ and CeO₂-based materials.CeO₂ and CeO₂-based materials have shown enhanced responses in catalytic and photocatalytic activities for environmental and biological applications.In addi...     

Magnetic composite Fe3O4/CeO2 for adsorption of azo dye

In this paper, magnetic composite Fe₃O₄/CeO₂ (MC Fe/Ce) was synthesized via CeO₂ covered onto the surface of Fe₃O₄ by sol-precipitation method. The as-synthesized samples were characterized by FE-SEM, XRD, SEM-EDS and FT-IR spectrum. The pseudo-second-order (PSO) kinetic can describe well the adsorption of Acid black 210 (AB210) onto the as-obtained MC Fe/Ce of which the adsorption isotherm fits the Langmuir adsorption model better than Freundlich adsorption model. Furthermore, the maximum monolayer adsorption capacity of MC Fe/Ce is about 93 mg/g, which is 6 times more than that of commercial CeO₂ for AB210. Moreover, the removal rate of the adsorbates for AB210 is 82.3% after first adsorption and still about 70% the fourth forth adsorption experiments within 120 min, which demonstrates that the obtained MC Fe/Ce has outstanding adsorption capacity and good stability. Additionally, the composite can be easily separated from aqueous solution in a few seconds with an external magnetic field due to its magnetic property, which is vital and has potential for its practical applications.     

Effect of interaction between different CeO2 plane and platinum nanoparticles on catalytic activity of Pt/CeO2 in toluene oxidation

The plane exposure of support vitally affects the catalytic performance of the catalyst. In this work, CeO₂ nanorods ((110) plane exposure), nano-octahedrons ((111) plane exposure) and nano-cubes ((100) plane exposure) were prepared as the supports of Pt/CeO₂ samples to investigate the effect of CeO₂ plane exposure on total toluene oxidation. Characterizations reveal that the (110) plane of CeO₂ is more helpful to the dispersion of Pt species, followed by (111) face. The improved dispersion of Pt species can enhance the metal-supports interaction, which promotes the electron transfer of CeO₂ carrier to Pt nanoparticles and the adsorption-activation of O₂, thereby facilitating the total oxidation of toluene via the Langmuir–Hinshelwood (L-H) mechanism. Therefore, Pt/CeO₂-r (nanorods) sample expresses excellent catalytic performance of toluene oxidation. Finally, the procedure of toluene total oxidation was studied by in-situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. We expect that this work can contribute to the development of an effective sample for the decomposition of volatile organic compounds (VOCs).     

Influence of CeO_2 loading on structure and catalytic activity for NH_3-SCR over TiO_2-supported CeO_2

A series of supported CeO_2/TiO_2 catalysts were prepared to explore the influence of CeO_2 loading on these catalysts for the selective catalytic reduction of NO_3 by NH_3(NH_3-SCR).The catalysts were investigated in detail by means of XRD,Raman,H_2-TPR,NH_3-TPD,XPS,in situ DRIFTS,and NH3-SCR reaction.The activity of the catalyst is closely related to the content of CeO_2.When the loading of CeO_2 is near the dispersion capacity(1.16 mmol Ce~(4+)/100 m~2 TiO_2),the catalytic activity is better.This may be because that the dispersed CeO_2 is the active species and the catalyst has appropriate redox property,along with the larger amounts of surface Ce content and surface adsorbed oxygen species.Finally,a possible reaction mechanism via the Langmuir-Hinshelwood(L-H) mechanism is tentatively proposed to further understand the NH_3-SCR reaction.