Promotion effect of H2 pretreatment on CeO2 catalyst for NH3-SCR reaction

In this study, the promotion effect of H₂ pretreatment on the SCR performance of CeO₂ catalyst was investigated based on the characterization results of XRD, H₂-TPR, Raman and in situ DRIFT techniques. Lower crystallinity, higher reducibility and surface acidity can be found on CeO₂-H catalyst. The results of DRIFT study reveal that the pretreatment of CeO₂ catalyst with H₂ can facilitate the adsorption of NH₃ and NO_x species, while the adsorbed NO_x is basically inactive in the NH₃-SCR reaction. Moreover, the reaction mechanism of the NH₃-SCR reaction over CeO₂ catalyst is not changed by H₂ pretreatment, which is mainly under the control of Eley-Rideal (E-R) mechanism. The enhanced SCR performance of CeO₂-H catalyst is mainly due to the promoted NH₃ adsorption and the subsequent facilitation of SCR reaction through E-R pathway.     

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 ...     

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.     

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...     

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.     

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...     

Sulfur poisoning and regeneration of MnOx-CeO2-Al2O3 catalyst for soot oxidation

MnOx-CeO2-Al2O3 mixed oxides were prepared by impregnating manganese and cerium precursors on alumina powders via a sol- gel deposition method. The oxide catalyst exhibited a poor resistance to sulfur dioxide after the treatment in 100 ppm SO2/air at 350 °C for 50 h. The formation of manganese sulfate and especially cerium sulfate reduced the availability of surface active metal oxides, blocked the pore structure and decreased the surface area of the catalyst. These changes in chemical and structural and textural properties resulted in a severe loss in the activities of the sulfated catalyst for NO and soot oxidation. The decomposition of sulfates was almost complete during the calcina-tion in air at 800 °C for 30 min, which partially recovered the surface active sites and the catalyst surface area despite the significant sintering of metal oxides. Consequently, the NOx-assisted soot oxidation activity of the catalyst was regenerated to some extent by the oxidation treatment.     

Effect of different doping elements on performance of Ce-Mn/TiO2 catalyst for low temperature denitration

Sm and Ho were doped in Ce-Mn/TiO₂ catalyst respectively to enhance its denitration performance at low temperature.X-ray diffraction(XRD),N₂ adsorption-desorption,X-ray photoelectron spectroscopy(XPS),NH₃-temperature programmed desorption(NH₃-TPD),H₂-temperature programmed reduction(H₂-TPR) and in situ diffuse reflectance infrared Fourier transform spectroscopy(DRIFTS) techniques were used to analyze the structure and performance ...     

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.     

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 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.     

Recovery of neodymium,dysprosium,and cobalt from NdFeB magnet leachate using an unsymmetrical dialkylphosphinic acid extractant,INET-3

Rare earths (REs) and Co are critical strategic resources.Their recovery is crucial for ensuring that their supplies are adequate and for reducing environmental pollution.End-of-life NdFeB magnets are important secondary RE sources.The separation of Dy,Nd,and Co from NdFeB leachate using a relatively new extractant (2,3-dimethylbutyl)(2,4,4'-trimethylpentyl)phosphinic acid (INET-3),was investigated in this study.The separation parameters,such as equilibrium pH,phase ratio,INET-3 concentration,and number of counter-current extraction stages,were optimised.The results show that INET-3 can separate Dy,Nd,and Co efficiently.For the preferential extraction of Dy from synthetic iron-free NdFeB leachate,the optimum equilibrium pH is 2.60.Under this condition,separation of Dy from the leachate requires four counter-current extraction stages at A/O (volume ratio of aqueous to organic)=1:2.This is demonstrated by a simulated four-stage counter-current extraction process.At equilibrium pH=2.52and A/O=1:2,98%of Dy is recovered with 95%purity.As to the subsequent separation of Nd from the leachate,nearly 100%is recovered with 99%purity through a simulated three-stage counter-current extraction process at equilibrium pH=5.33 and A/O=1:1.Approximately 95%of Co remains in the raffinate with 99.98%purity.     

SO2 poisoning and regeneration of Mn-Ce/TiO2 catalyst for low temperature NOx reduction with NH_3

SO2 poisoning and regeneration of Mn-Ce/TiO2 catalyst prepared by a novel co-precipitation method for low temperature selective catalytic reduction (SCR) of NOx with ammonia were investigated in this study. When 700 ppm SO2 was fed in, the Mn-Ce/TiO2 catalyst had good resistance to SO2, but the deactivation of Mn-Ce/TiO2 poisoned by SO2 still occurred. The NO conversion of Mn-Ce/TiO2 (the molar ra-tio of Ce to Ti is 0.075) catalyst decreased from 92.5% to 34.6% in 13 h. Characterizations of fresh and SO2-poisoned Mn-Ce/TiO2 catalysts were carried out by Brunauer-Emmett-Teller method (BET), ion chromatography (IC), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The characterized results indicated that the deposition of sulfates and nitrates on the surface made the catalyst deactivated. Water washing, thermal regeneration and reductive regeneration were used to regenerate the deactivated Mn-Ce/TiO2. And water washing showed best performance on the regeneration of poisoned catalysts, especially with ultrasonic vibration. The Mn-Ce/TiO2 catalyst showed high stability under a series of deactivation-regeneration experiments for ten cycles.     

Application of MnCeOx supported on palygorskite and Al(OH)3 for HCHO oxidation: Catalytic performance and stability

Indoor formaldehyde (HCHO) is an important air pollutant, while it is very difficult to reduce HCHO to low-level (e.g. <0.08 mg/m³). Catalytic oxidation at ambient temperature has been increasingly recognized as one of the important methods to mitigate HCHO pollution due to its good effectiveness, stability, and recyclability. To further improve the activity of catalytic oxidation, this study develops the integrated MnCeO_x catalysts supported on palygorskite (Pal) and aluminium hydroxide (Al(OH)₃). Our results indicate that the synergistic interaction in MnCeO_x through the oxygen transfer mechanism from the oxygen reservoir CeO₂ to MnO_x significantly improves the activity. Pal, Al(OH)₃, etc. were applied as the supports with a focus on their dispersion, microstructure, strength, and relative role. MnCeO_x can be anchored on the surface of Al(OH)₃ with high dispersion. With the integrated catalyst, HCHO concentration decreases from 1.012 to 0.086 mg/m³ within 48 h. Higher oxidation activity of MnCeO_x powder may be ascribed to the amount of active components on the surface. The incorporation of ZSM–5 and activated carbon can improve the adsorption of HCHO, and all integrated catalysts exhibit stronger activities, with HCHO being degraded to the level lower than 0.08 mg/m³. Meantime, the samples exhibit good stability and strength (20.2 MPa) without obvious decrease over five consecutive stability experiments.     

Multi-site occupancies and luminescence properties of cyan-emitting Ca9-xNaGd2/3(PO4)7:Eu2+phosphors for white light-emitting diodes

Cyan-emitting Ca₉NaGd_2/3(PO₄)₇:Eu²⁺phosphors were synthesized via high temperature solid-state route.X-ray powder diffraction(XRD)and scanning electron microscopy(SEM)were used to verify the phase and morphology of the Ca₉NaGd_2/3(PO₄)₇:Eu²⁺(CNGP:Eu²⁺)phosphors.The as-obtained phosphor exhibits a broad excitation band of 250-420 nm,which is near the ultraviolet region.An intense asymmetric cyan emission at 496 nm corresponds to the 5 d-4 f transition of Eu²⁺.The multiplesite luminescent properties of Eu²⁺ions in CNGP benefit from versatile structure ofβ-Ca3(PO4)2 compounds.The effective energy transfer distance is 5.46 nm(through the spectral overlap calculation),validating that the resonant energy migration type is via dipole-dipole interaction mechanism.Compared to the initial one at room temperature,the luminescent intensity of CNGP:Eu²⁺phosphor can maintain 77%as it is heated up to 420 K.A white light-emitting diode(WLED)with excellent luminesce nt properties was successfully fabricated.Moreover,the CIE chromaticity coordinates of fabricated WLED driven by changing current just change slightly.     

Synthesis and optical properties of novel double perovskite Ca_2MgTeO_6:Dy~(3+),Na~+ phosphors for white LEDs

Novel yellow-emitting phosphors of Dy~(3+)-doped double perovskite Ca_2 MgTeO_6 were synthesized by using a conventional high-temperature solid-state reaction.The phase purity,particle morphology,size distribution,elemental composition,luminescence properties,and luminescence decay curves of the resulting products were then analyzed in detail.The Ca2 MgTeO_6:Dy~(3+),Na~+ phosphors show three emission peaks after near-ultraviolet excitation at 350 nm,which correspond to ~4 F_(9/2)→~6 H_(11/2),~4 F_(9/2)→~6 H_(13/2),and ~4 F_(9/2)→~6 H_(13/2) transitions,respectively.Among them,the strongest peak is observed at 573 nm.The best doping content of Dy~(3+)in Ca_2 MgTeO_6:xDy~(3+),xNa~+ phosphors is x=5 mol%.The calculated critical distance of energy transfer between Dy~(3+) ions is 1.6 nm.Luminescence quenching is confirmed to be due to dipole-dipole interactions among Dy~(3+) ions.The phosphors show excellent thermal stability with high activation energy(0.27 eV).The Commission Internationale de l'Eclairage(CIE) chromaticity coordinates of the Ca_2 MgTeO_6 Dy~(3+),Na~+ phosphors are located in the yellow region.White light-emitting diodes(w-LEDs) were fabricated with a high color rendering index(R_a) of 88 and a good correlated color temperature(CCT) of 5440 K.All observed properties indicate that Ca_2 MgTeO_6:Dy~(3+),Na~+ phosphors have potential applications in display and photonic devices.     

Ni/Y_2O3-Al2O3 catalysts for hydrogen production from steam reforming of ethanol at low temperature

Y2O3-Al2O3 with different mole ratios of Y:Al were prepared by co-precipitation method. Catalysts Ni/Y2O3, Ni/Al2O3 and Ni/ Y2O3-Al2O3 were prepared by impregnation method. The result of BET showed that Al2O3 with relative high surface area was in favor of Ni distribution, whilst the TPR test demonstrated that composite support had appropriate synergistic effect between active constituent and sup-port, and NiO could be reduced more easily than loaded on the single support. H2-TPD test indicated that the catalyst NYA11 had lots of ac-tivity sites where H could be desorbed easily, which led to hydrogen-rich production over the catalyst. Composite support catalysts exhibited high activity for ethanol steam reforming (SRE), and the supported catalyst with composite of 1:1 mole ratio of Y:Al exhibited the optimum catalytic properties for SRE. Ethanol could be completely converted over catalyst NYA11 even at 450 °C, and there had no inactivation after 60 h continuous reaction, hydrogen yield appeared maximum 35.9% at 400 °C, and tended to increase with increasing H2O/EtOH molar ratio and feed flow rate.     

Optical and luminescence characteristics of Eu3+-doped B2O3:SiO2:Y2O3:CaO glasses for visible red laser and scintillation material applications

Europium(Eu~(3+)) doped glasses of chemical compositions(55-x)B_2O_3:10 SiO_2:25 Y_2O_3:10CaO:xEu_2O_3,where x denotes mol% and ranges 0≤ x ≤ 2.5, were synthesized by adopting conventional melt quenching technique, Physical properties like density, molar volume, polaron radius, inter-ionic distance and field strength of the glass samples were investigated to assess the impact of Eu_2O_3. Optical and luminescence properties of the glasses were characterized with optical absorption, photoluminescence,X-ray induced emission spectra, temperature dependence emission spectra and decay times. Judd-Ofelt(JO) intensity parameters(Ω_λ) of the glasses were evaluated based on the absorption spectrum of 0.5 mol%. JO parameters, calculated from absorption spectra with thermal corrections on oscillator strength, were used to evaluate radiative properties such as radiative transition probability(A_R),branching ratio(β_R), stimulated cross section emission(σ) and radiative lifetime(τ_R) for ~5D_0→~7 F_J(J = 0,1,2,3 and 4) transitions. The decay rate of ~5D_0 fluorescent level for all the glass samples was single exponential. Lifetimes of the ~5D_0 level were decreased with increasing concentrations of Eu~(3+)ions from 0.05 mol% to 2.5 mol% which might be due to energy transfer through cross-relaxation in the glasses. The chromaticity coordinates(x, y) were similar for all BSYCaEu glasses and were located at the red region of CIE 1931 color chromaticity diagram. Hence, these results confirm that the Eu~(3+) doped BSYCaEu glasses could be useful for visible red lasers and glass scintillation applications.