Ce离子改性对Cu-SSZ-13催化剂NH3-SCR反应性能的影响研究

Cu-SSZ-13催化剂已被证实是高效NH₃-SCR催化剂。然而,其经过严重水热老化(950℃)后仍会导致不可逆失活。本文通过考察引入的第二活性金属(Ce)离子浓度对Cu-SSZ-13催化剂的活性位性质及其催化活性的影响,揭示了活性位与催化活性之间的关系。结果表明,Cu-SSZ-13中引入的Ce离子并不会成为NH₃-SCR反应的活性中心,而仅起到调节Cu活性位和表面酸性位的位置和数量的作用。通过XPS、H₂-TPR、NH₃-TPD和活性分析结果可知,低铈负载(约0.2%)下,少量的Ce可进入离子交换位点,有助于稳定SSZ-13骨架结构和抑制CuO_x团簇生成的作用(950℃老化后劣化率仅为6%),还能实现高铜负载(Cu负载量为3.01%)与丰富的L酸、B酸位,从而使其具有高的NO转化率、更宽的NO反应温度窗口和优异的水热稳定性。而引入过量的铈离子对Cu-SSZ-13的催化活性和水热稳定性产生不利影响,导致SCR性能下降。     

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.     

硫酸浓度对Mn改性稀土尾矿催化剂NH3-SCR脱硝性能的影响

利用硫酸预处理白云鄂博稀土尾矿,随后采用浸渍法使其负载5%乙酸锰,经微波焙烧制成脱硝催化剂,考察了硫酸浓度(0、0.5、1、3 mol/L)对催化剂脱硝性能的影响。通过XRD、NH₃-TPD、H₂-TPR和XPS对催化剂进行了表征。脱硝活性测试结果表明：催化剂在100～250℃的脱硝活性随着硫酸浓度的增加先提高后降低,当硫酸浓度为0.5 mol/L时达到最佳。较高浓度(3 mol/L)的硫酸大幅度降低了催化剂的低温活性。0.5 mol/L硫酸处理的催化剂具有较宽的温度窗口,在150～250℃范围内均有较好的活性,200℃时氮氧化物转化率达到92%。表征结果表明：负载的Mn元素以非晶态存在或高度分散在稀土尾矿表面;随着硫酸浓度的增加,催化剂表面Mn⁴⁺的浓度降低,其NH₃吸附能力和氧化还原能力均降低,从而脱硝性能降低。     

CeO2with diverse morphologies-supported IrOx nanocatalysts for efficient oxygen evolution reaction—Commemorating the 100th anniversary of the birth of Academician Guangxian Xu

IrOx-based catalysts are considered the most promising candidates for oxygen evolution reaction(OER)due to their high efficiency.However,improving their intrinsic catalytic activity is essential for practical application.In this work,CeO₂with three different morphologies(rod,cube,octahedron)and supported IrOx nanoparticles were fabricated,and they display morphology-dependent OER activity.The IrOx/CeO₂-rod shows the highest activity;the catalysts have a catalytic activity sequence of rod>cube>octahedron.A plausible mechanism was proposed:the CeO₂support with different morphologies modulates the electronic structure of IrOx by the synergistic interaction promoted by oxygen vacancies between the active component and the support,thereby altering the catalytic activity of the IrOx/CeO₂catalyst.     

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.     

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.     

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.     

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.     

Improved corrosion resistance and thermal stability of sintered Nd-Fe-B magnets with holmium substitution

The effects of Ho substitution for Nd on the microstructure, corrosion resistance and thermal stability of the Nd-Fe-B magnets were investigated. The(Nd,Ho)-O phase was formed with increasing Ho substitution. The results of potentiodynamic polarization and highly accelerated stress test show improved corrosion resistance with increasing Ho substitution. The optimum mass loss 0.29 mg/cm~2 is achieved.Moreover, the average temperature coefficients for remanence and coercivity in the range of 25-150℃are both closer to zero, indicating improved thermal stability. The mechanisms for the improved corrosion resistance and thermal stability are discussed in relation to the microstructure featuring the(Nd,Ho)-O phase.     

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 ...     

Design and synthesis of Fe-Ce-O@C with efficient photocatalytic activity

Fe-Ce-OH@AR14 was obtained via the adsorption of acid red 14(AR14) on Fe-Ce-OH prepared by the codeposition of cerium nitrate hexahydrate,ferric nitrate nonahydrate,and ammonia,and then Fe-Ce-O@C with high photocatalyic efficiency was synthesized by the calcination of Fe-Ce-OH@AR14 in N₂.For comparison,Fe-Ce-O was also prepared by the calcination of Fe-Ce-OH in N₂.The obtained materials were characte rized by X-ray diffraction(XRD),Raman,X-ray photoelectron spectroscopy(XPS...     

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 ...     

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.     

Rh/CeO2 composites prepared by combining dealloying with calcination as an efficient catalyst for CO oxidation and CH4 combustion

In this paper, a series of Rh/CeO₂ catalysts with three-dimensional porous nanorod frameworks and large specific surface area were prepared by chemical dealloying Al–Ce–Rh precursor alloys and then calcining in pure O₂. The effects of the Rh content and calcination temperature on CO oxidation and CH₄ combustion were studied, and the results reveal that the Rh/CeO₂ catalysts produced by dealloying melt-spun Al_91.3Ce₈Rh_0.7 alloy ribbons and then calcining at 500 °C exhibit the best catalytic activity, the reaction temperatures for the complete conversion of CO and CH₄ are as low as 90 and 400 °C, respectively. Furthermore, after 150 h of continuous testing at high concentrations of H₂O and CO₂, the nature of the catalyst is not irreversibly destroyed and can still return to its initial level of activity. This excellent catalytic activity is attributed to a portion of Rh being uniformly distributed on the CeO₂ nanorod surface in the form of nanoparticles, forming strong Rh–CeO₂ interfacial synergy. Another portion of Rh permeated into the CeO₂ lattice, which results in a significant increase in the number of oxygen vacancies in CeO₂, thus allowing more surface active oxygen to be adsorbed and converted from the gas phase. Moreover, the catalytic reaction can proceed even in an oxygen-free environment due to the excellent oxygen storage performance of the Rh/CeO₂ catalyst.     

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...