Preparation and reaction mechanism of novel CexCoyCuz oxide composite catalysts towards oxidation of o-xylene

Ce_xCo_yCu_z oxide composite catalysts were prepared by using polyethylene glycol, citrate sol–gel method combined with PMMA template for the oxidation of o-xylene. The catalysts were characterized by the X-ray diffraction (XRD), H₂-temperature programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR), etc. The catalytic activity for o-xylene was investigated. The catalytic degradation pathway and mechanism of o-xylene were inferred. The results show that CeO₂ is mainly present on the surface of all catalysts. The surface area of Ce₂Co₁Cu₁ is up to 77.2 m²/g, and the average pore size is 10.62 nm. It exhibits redox and sufficient Ce⁴⁺ and Ce³⁺, and reactive oxygen species, and has maximum O–H and CO in the five catalyst samples. The catalytic activity of Ce₂Co₁Cu₁ is the best at low temperature, with the T₅₀ and T₉₀ values of 235 and 258 °C at a space velocity of 32000 h^?1, respectively. The o-xylene is oxidized to o-methyl benzaldehyde, and then further oxidized to o-methylbenzoic acid, and finally CO₂ and H₂O are formed.     

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.     

MCM-41 supported nano-sized CuO-CeO_2 for catalytic combustion of chlorobenzene

In this paper,MCM-41 was synthesized by a soft template technique and MCM-41 supported CuO-CeO_2 nano-sized catalysts with different Cu/Ce molar ratios were prepared by a deposition-precipitation method.N_2 adsorption,HRTEM-EDS,H_2-TPR,XPS characterization,as well as catalytic activity and durability tests for the catalytic combustion of chlorobenzene(CB) were conducted to explore the relationship between the structure and catalytic performance of the catalysts.It is revealed that cuCe(6:1)/MCM-41 has the highest activity and can completely catalyze the degradation of CB at 260℃.The reasons for the high activity of the catalysts are as follows:MCM-41,a type of mesoporous material which has large pore size and large specific surface area,is suitable as a catalyst carrier.The average diameter of nano-sized CuO and CeO_2 particles is about 3-5 nm and adding CeO_2 improves the dispersion of active component CuO,which are highly and evenly dispersed on the surface of MCM-41.Characterization results also explain why MCM-41 supported CuO-CeO_2 with appropriate proportion can highly enhance the catalytic activity.The reason is that CeO_2 acting as an oxygen-rich material can improve the mobility of oxygen species through continuous redox between Ce~(4+)and Ce~(3+),and improve the catalytic performance of CuO for CB combustion.Besides,CuCe(6:1)/MCM-41 also displays good durability for CB combustion,both in the humid condition and in the presence of benzene,making it a promising catalytic material for the elimination of chlorinated VOCs.     

Synthesis and characterization of YAG: Ce3+ fluorescence powders by co-precipitation method

YAG:Ce³⁺(Yttrium aluminum garnet) fluorescence powders were successfully prepared by co-precipitation method using aluminum nitrate, yttrium nitrate, cerous nitrate as the starting materials and ammonium carbonate as precipitant. The products were characterized by X-ray powder diffraction, luminescence spectrometer, transmission electron microscope (TEM). The XRD results showed that the obtained YAG:Ce³⁺ fluorescence powders had the crystalline structures of YAG at calcinations temperature of 900 °C and the TEM results showed that the grain diameters were about 100 nm. The YAG:Ce³⁺ fluorescence powders, synthesized by co-precipitation method, had the best luminescence property when the Ce doping amount was x=0.06 in the molecular formula of Y_3-xCe_xAl₅O₁₂, the calcinations time was 2 h and the calcinations temperature was 1000 °C.     

Promotional effects of cerium doping and NOx on the catalytic soot combustion over MnMgAIO hydrotalcite-based mixed oxides

A series of MnMgA10 samples with different amounts of Ce doping were facilely prepared using coprecipitation method and their catalytic soot combustion activity was evaluated by temperature programmed oxidation reaction （TPO）. The methods of X-ray diffraction （XRD）, Brumauer-Emmett-Teller （BET）, H2-TPR, NO-TPO and in situ 1R were used to characterize the physio- chemical properties of these samples. Dopant Ce improved the soot combustion performance of MnMgA10 catalyst due to the en- hanced redox ability. Introduction of NOx led to the further increase of catalytic soot oxidation activity on these samples. Over Ce-containing samples, the catalytic activity was slightly decreased as the amount of dopant Ce increased in 02. Diftbrently, in NO＋O2, a certain amount of dopant Ce was much more favorable and excess amount of Ce resulted in a sharp drop of the catalytic soot combustion activity. Both NO： and nitrates were found to have great contributions to the effects of NOx on the soot combustion activity of Ce-doped catalysts. More NO2 was generated as dopant Ce increased. When appropriate amount of Ce was introduced, the as-formed NO2 was stored as bridging bidentate nitrate on Mn-Ce site, which was confirmed to have higher reactivity with soot than nitrite or monodentate nitrate on Mn and/or Ce sites. Overall, Mno.sMg2.sCeo.lAlo.90 was considered as the most potential catalyst for soot combustion.     

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.     

Effects of different introduction methods of Ce4+ and Zr4+ on denitration performance and anti-K poisoning performance of V2O5-WO3/TiO2 catalyst

The purpose of this work is to explore the effects of the introduction methods of Ce⁴⁺ and Zr⁴⁺ on the physicochemical properties, activity, and K tolerance of V₂O₅-WO₃/TiO₂ catalyst for the selective catalytic reduction of NO_x by NH₃. Four different methods, namely pre-impregnation, post-impregnation, co-impregnation, and co-precipitation, were used to synthesize a series of V₂O₅-WO₃-TiO₂-CeO₂-ZrO₂ catalysts. The catalysts were characterized by XRD, BET, NH₃-TPD, XPS, and H₂-TPR techniques. Moreover, the activity and anti-K poisoning performance were tested by an NH₃-SCR model reaction. The results show that the introduction of Ce⁴⁺ and Zr⁴⁺ can improve the catalytic performance of V₂O₅-WO₃/TiO₂ catalyst, but the impregnation method cannot enhance the anti-K poisoning performance. Ce⁴⁺ and Zr⁴⁺ introduced by co-precipitation method can effectively improve the tolerance of K, which is mainly due to the incorporation of Ce⁴⁺ and Zr⁴⁺ into TiO₂ lattice to form a uniform TiO₂-CeO₂-ZrO₂ solid solution, resulting in the optimal surface acidity and redox performance, and reducing the decreases caused by K-poisoning. Furthermore, based on the best introduction method, we further optimized the molar ratio of Ce⁴⁺/Zr⁴⁺. It is found that the catalyst exhibits the best anti-K poisoning performance when the molar ratio of Ce⁴⁺/Zr⁴⁺ is 2:1.     

Luminescence properties of BaAl12O19:Tb,Ce and energy transfer between Ce3+, Tb3+

BaAl₁₂O₁₉:Tb,Ce phosphors were prepared by sol-gel technique, the crystalline structures of samples characterized by XRD, and the luminescence properties and energy transfer between Ce³⁺ and Tb³⁺ were investigated. The results indicated that the emission intensity and the excitation wavelength range of Tb³⁺ increased when Ce³⁺ was doped. It demonstrated that the Ce³⁺ added in the BaAl₁₂O₁₉:Tb could deliver energy to Tb³⁺, and Ce³⁺ was not luminous by itself. The relative emission intensity of Tb³⁺ at wavelength of 548 nm was the strongest by Tb³⁺/Ce³⁺ ratio of 2:1, when excited at 310 nm, which was the characteristic adsorption wavelength of Ce³⁺.     

Performance of mesoporous CeO2-Cr2O3 mixed metal oxides applied to benzene catalytic combustion

In this paper,a hydrothermal method was used to prepare(Ce,Cr)-MOF with different Ce/Cr molar ratios and then a series of CeO₂-Cr₂O₃ mixed metal oxides(CeCr-MMO) with mesoporous structure were prepared by thermal decomposition of these MOFs at different temperatures.After a series of characterization techniques were applied to test the physicochemical properties of the materials,it is found that thermal decomposition temperature(TDT) and Ce/Cr molar ratios have i...     

The standard gibbs energy of formation of CeF3 and its activity coefficient in cryolite

Literature data are analyzed to give the activity coefficient (γ_Ce) of Ce in dilute solution in Al as log₁₀γ_Ce = −11 356/T + 4.261 referred to liquid Ce as standard state. Measurements were made in the range of 977 to 1288 K of the equilibrium Al (1) + CeF₃ (s) = AlF₃ (s) + Ce(Al) and give, by a third-law calculation, °G ^o = 183 360 + 19.456T joules, and Δ _{fH 298} ^o of CeF₃ = −1701 kJ mol⁻¹. Values of the partition coefficient of Ce between Al and molten cryolite then give activity coefficients of CeF₃ in solution. These activity coefficients decrease as the NaF/AlF₃ ratio is raised, showing acid behavior of CeF₃. It appears to dissolve mainly in the form of Na₂CeF₅.     

Solid-state preparation of mesoporous Ce-Mn-Co ternary mixed oxide nanoparticles for catalytic degradation of methylene blue

Mesoporous Ce-Mn-Co ternary metal oxide was fabricated via an efficient oxalate-precursor-based soft reactive grinding route and used to activate H_2 O_2 for advanced oxidation of methylene blue in water.In addition,Mn-Co binary oxide and pure Co_3 O_4 and Mn_3 O_4 were also synthesized as reference catalysts.These catalysts were characterized by X-ray diffraction,N2 adsorption-desorption,H2-temperature programmed reduction,transmission electron microscopy,scanning electron microscopy and X-ray photoelectron spectroscopy.The results demonstrate that part of the Ce and Mn can be incorporated into the lattice of Co_3 O_4 and cause severe lattice distortion of the unit cell.Compared with the single or binary system,Ce-Mn-Co ternary metal oxide exhibits the best activity in methylene blue removal and nearly100% decomposition rate and 84% COD removal rate can be achieved in 12 h,and with degradation rate of93.5% after three rounds.These results are primarily attributed to the synergistic effect of Ce,Mn and Co,which can promote the formation of more lattice defects,higher specific surface area and smaller particle size.Quenching tests show that hydroxyl radicals(·OH) play more dominant role than superoxide radicals(·O_2~-).Kinetic studies were studied and the activation energies of all the catalysts were calculated.     

Synthesis and electrochemical properties of Ce-doped LiNi_（1/3）Mn_（1/3）Co_（1/3）O_2 cathode material for Li-ion batteries

The layered material of Ce-doped LiNi1/3Mn1/3Co1/3O2 with α-NaFeO2 was synthesized by a co-precipitation method. X-ray diffraction (XRD) showed that Ce-doped LiNi1/3Mn1/3Co1/3O2 had the same layered structure as the undoped LiNi1/3Mn1/3Co1/3O2. The scanning electron microscopy (SEM) images exhibited that the particle size of Ce-doped LiNi1/3Mn1/3Co1/3O2 was smaller than that of the undoped LiNi1/3Mn1/3Co1/3O2. The Ce-doped LiNi1/3Mn1/3Co1/3O2 samples were investigated on the Li extraction/insertion performances through charge/discharge, cyclic voltammogram (CV), and electrochemical impedance spectra (EIS). The optimal doping content of Ce was x=0.02 in the LiNi1/3-xMn1/3Co1/3CexO2 samples to achieve high discharge capacity and good cyclic stability. The electrode reaction reversibility was enhanced, and the charge transfer resistance was decreased through Ce-doping. The improved electrochemical performances of the Ce-doped LiNi1/3Mn1/3Co1/3O2 cathode materials were attributed to the addition of Ce4+ ion by stabilizing the layer structure.     

Optical characteristics of Ce,Eu:YAG single crystal grown by Czochralski method

Eu-doped Ce:YAG single crystal (SC) was fabricated by the Czochralski method. The crystal structure, optical and photoelectric property of the constructed w-LED was investigated. The XRD and HRTEM results show that YAG crystal structure has little change when Eu³⁺, Ce³⁺ are doped. Absorption spectra and photoluminescence spectra show that the Ce,Eu:YAG single crystal can effectively absorb the 460 nm blue light to form a broadband emission center at 530 nm, decay curves of the crystal show that the energy transfer between Ce³⁺ and Eu³⁺ is highly suppressed. Compared with commercial Ce:YAG phosphor, Ce,Eu:YAG exhibits better thermal stability.     

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...     

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.     

Phase relations,microstructure, and valence transition studies on CaZr_(1-x)Ce_xTi_2O_7(0.0≤x≤1.0) system

In this study, Ce-doped zirconolite was synthesized through high-temperature solid-state reaction at 1250 ℃ in air for 96 h. The crystal phase.microstructure and valence transition were studied by X-ray diffraction(XRD), scanning electron microscopy(SEM), and X-ray photoelectron spectroscopy(XPS).Phase relations of CaZr_(1-x)Ce_xTi_2O_7 systems were determined by XRD analyses and Rietveld refinements.Four different phases are identified, namely zirconolite, perovskite, pyrochlore, and cerianite. The phase transformation(2M-zirconolite → 4M-zirconolite → Ce-pyrochlore) is caused by cations rearrangement as cerium content increases. The solubility limit of cerium ions in CaZr_(1-x)Ce_xTi_2O_7 system is estimated to be approximately 0.80. Under sintering air atmosphere, partial reduction of Ce~(4+) in Ce~(3+) is detected in Ce 3d XPS spectra, and the ratio of Ce~(3+) and Ce~(4+) significantly decreases as cerium content increases.     

A novel Eu3+-doped phosphor-in-glass for WLEDs and the effect of borophosphate matrix

Phosphor-in-glass(PiG) is a potential color convertor for high power WLEDs.A novel glass matrix with advanced performance is still a challenge.Recently,Eu³⁺ doped glass matrix has attracted much consideration mainly due to its red compensation.A new borophosphate matrix to realize Eu³⁺ red light was designed in the Na₂O-ZnO-P₂O₅-B₂O₃-Eu₂O₃ system.Meanwhile,a series of PiGs composed of different con...     

Optical studies of Y_3(Al,Ga)_5O_(12):Ce~(3+),Cr~(3+),Nd~(3+) nano-phosphors obtained by the Pechini method

The Y3(AI,Ga)_5O_(12):Ce~(3+),Cr~(3+),Nd~(3+)(YAGG) nano-phosphors with homogeneous particle-size distribution,low aggregation and average crystalline size of about 65 nm were obtained using a modified Pechini method.Only slight aggregation of the crystallites occurs after post-annealing at 1100℃.The intense Ce~(3+)bands in the excitation spectra of the Ce~(3+),Cr~(3+),Nd~(3+)co-doped materials monitoring the Cr~(3+) emission at 690 nm indicate energy transfer from Ce~(3+) to Cr~(3+).Weak Nd~(3+) lines are observed,as well.In addition,the emission of Nd~(3+)at 1060 nm with excitation of Ce~(3+) and Cr~(3+) confirms the Ce~(3+)/Cr~(3+)to Nd~(3+)energy transfer.The short average luminescence decay times for the Ce~(3+) emission indicate the Ce~(3+)/Cr~(3+)to Nd~(3+)energy transfer.Eventually,the Y_3(AI,Ga)_5O_(12):Ce~(3+),Cr~(3+),Nd~(3+) nano-phosphors exhibit persistent luminescence originating from the 4f~3→4f~3 transitions of Nd~(3+) which matches well to the first biological window to be used in bioimaging applications.     

Luminescent properties of β-Lu2Si2O7:RE(RE=Ce, Tb) nanoparticles by sol-gel method

Nanoscale RE³⁺ (RE=Ce, Tb) doped and codoped lutetium pyrosilicate Lu₂Si₂O₇ (LPS) phosphors were prepared by using the sol-gel method. Heat treatment was performed in the temperature range from 900 to 1100 °C. The crystal structure was analyzed by X-ray diffraction (XRD). The results showed that the β-type structure of LPS was obtained at 1100 °C. The excitation spectra in the UV and VUV ranges and the emission spectra of the samples were measured at room temperature, and their luminescent properties were studied. The energy transfer from Ce³⁺ to Tb³⁺ in the codoped samples were observed and discussed.