Effects of support property on the catalytic performance of CeO2-ZrO2-CrOx for 1,2-dichloroethane oxidation

HZSM-5, Al₂O₃, TiO₂ and SiO₂ supported CeO₂-ZrO₂-CrO_x catalysts were prepared by deposition-precipitation method and tested for deep catalytic oxidation of 1,2-dichloroethane（DCE）, as one of the common chlorinated organic pollutants. All the catalysts were characterized by means of N₂ adsorption-desorption, X-ray photoelectron spectroscopy（XPS）, ammonia-temperatureprogrammed desorption（NH₃-TPD） and hydrogen temperature-programmed reduction（H2-TPR）. The characterization results revealed that there was strongly synergistic effect between the oxidizability of CZCr species and the acidity of supports, which obviously promoted the catalytic activity for DCE degradation. 20% CZCr/HZSM-5 showed the highest activity and good durability during the long-term continuous test. The catalytic activity decreased in the order: 20%CZCr/HZSM-5>CZCr>20%CZCr/TiO₂>20%CZCr/Al₂O₃>20%CZCr/SiO₂.     

Theoretical consideration on composite oxide scales and coatings

The present paper discussed some fundamental aspects on composite oxide scales and coatings for protection of alloys from high temperature oxidation, the related thermodynamic conditions, special mechanical characteristics and a sealing mechanism. It was proposed that the oxide scales and coatings with a composite structure should possess superior mechanical properties than that with a single phase oxide. It also showed that the Al2O3 scales or coatings doped with Y2O3 and ZrO2 (or YSZ)-Al2O3 composite coatings possessed superior properties at high temperatures. In such composite oxide scales and coatings, the fracture resistance of the scales was increased by the toughening effect, the thermal stress was decreased owing to the increase of thermal-expansion coefficients, and Al2O3 phase could seal the alloy substrate well. In addition, the kinetic equation of thermal growth oxide on alloy covered with composite oxide coatings was derived.     

Synthesis and characterization of aluminum and AI/REE pillared clays and supported palladium catalysts for benzene oxidation

Volatile organic compounds (VOCs) are considered as a major pollutant in indoor and outdoor air.More stringent environmental regulations have been implemented in order to reduce the VOC emissions.One of the techniques available for destructive removal of VOCs is catalytic oxidation.In the present work,Al/Rare Earths (REE: Y,Ce,La,Pr and Nd) pillared clays (PILCs) were used to support 0.2 wt.% of palladium for the complete oxidation of low concentration of benzene.The supports and catalysts were characterized by XRD,N2 adsorp-tion/desorption,FTIR spectroscopy,HRTEM and H2-TPR techniques.The results indicated that after Al and Al/REE pillaring,the basal spac-ing,SBET,Amic and Vmic of Al and AlREE-PILC had a considerable increase compared with those of Na-mmt.Activity tests of deep oxidation of benzene showed that the catalytic activity of Pd catalysts supported on Al and AlREE-PILC were much higher than that on initial clays,which was due to the fact that optimized structure of PILCs,such as large basal spacing,high SBET and porosity,improved Pd dispersion and increased the active sites of Pd.Especially for Pd/AlCe-PILC,the temperature of complete oxidation was about 280 oC,exhibiting the highest catalytic activity.     

Low temperature selective catalytic reduction of NO by C3H6 over Ce Ox loaded on AC treated by HNO3

The activated carbons from coal were treated by HNO3(named as NAC) and used as carriers to load 7% Ce(named as Ce(0.07)/NAC) by impregnation method. The physical and chemical properties were investigated by thermogravimetric-differential thermal analysis(TG-DTA), Brunauer-Emmett-Teller(BET), X-ray diffraction(XRD), X-ray photoelectron spectra(XPS), scanning electron microscopy(SEM) and NH3-temperature programmed desorption(NH3-TPD) and NO-temperature programmed desorption techniques. The catalytic activities of Ce(0.07)/NAC were evaluated for the low temperature selective catalytic reduction(SCR) of NO with C3H6 using temperature-programmed reaction(TP-reaction) in NO, C3H6, O2 and N2 as a balance. The results showed that the specific surface area of Ce(0.07)/NAC was 850.8 m2/g and less than NAC, but Ce oxides could be dispersed highly on the activated carbons. Ce oxides could change acid sites and NO adsorption as well as oxygen-containing functional groups of activated carbons, and Ce4+ and Ce3+ coexisted in catalysts. The conversion of NO with C3H6 achieved 70% at 280 °C over Ce(0.07)/NAC, but with the increase of O2 concentration, heat accumulation and nonselective combustion were exacerbated, which could cause surface ashing and roughness, resulting in a sharp decrease of catalytic activities. The optimum O2 concentration used in the reaction system was 3% and achieved the high conversion of NO and the widest temperature window. The conversion of NO was closely related to the NO concentrations and [NO]/[C3H6] ratios, and the stoichiometric number was just close to 2:1, but the presence of H2 O could affect the denitration efficiency of catalyst.     

Controllable preparation of CeO2 nanostructure materials and their catalytic activity

Well-crystalline CeO2 nanostructures with the morphology of nanorods and nanocubes were synthesized by a template-free hydro-thermal method. X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) nitrogen adsorp-tion-desorption measurements were employed to characterize the synthesized materials. The reducibility and catalytic activity of nanostruc-tured CeO2 were examined by hydrogen temperature-programmed reduction (H2-TPR) and CO oxidation. The results showed that CeO2 nanorods could be converted into CeO2 nanocubes with the increasing of the reaction time and the hydrothermal temperature, CeO2 nanorods became longer gradually with the increasing of the concentrations of NaOH. H2-TPR characterization demonstrated that the intense low-temperature reduction peak in the CeO2 nanorods indicated the amount of hydrogen consumed is larger than CeO2 nanocubes. Meantime the CeO2 nanorods enhanced catalytic activity for CO oxidation, the total conversion temperature was 340 oC. The reasons were that CeO2 nanorods have much smaller crystalline sizes and higher surface areas than CeO2 nanocubes.     

Investigation of Pt-Dy co-doping effects on isothermal oxidation behavior of （Co,Ni）-based alloy

A Co32Ni21Cr8Al0.6Y (wt.%) alloy with and without doping 3 wt.% platinum, or co-doping 3 wt.% platinum and 0.1 wt.% dysprosium was produced by arc melting. The hardness of both base alloy and composition-modified alloy was measured by using a Vickers hardness tester. Isothermal oxidation tests at 1000 ℃ in static air atmosphere were conducted to assess the isothermal oxidation behavior of the alloys. The microstructure and composition of the tested alloys before and after oxidation were investigated by means of X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM) equipped with energy dispersive spectroscopy (EDS) and back scatter detector. Results showed that platinum had significant influence on microstructure of the tested alloy by the formation of β-(Ni,Pt)Al phase. Addition of 3 wt.% platinum could slightly increase the hardness of the tested alloy. Platinum accelerated phase transformation of alumina from metastable θ-Al 2 O 3 to stable α-Al 2 O 3 and suppressed the consumption of β-phase. Co-doping both 3 wt.% platinum and 0.1 wt.% dysprosium induced the fastest transformation of θto αalumina and the formation of a fine-grained oxide scales. The most effective reduction of oxidation rate was achieved by the Pt-Dy co-doping effects.     

Combustion synthesis and stability of nanocrystalline La2O3 via ethanolamine-nitrate process

Pure nanocrystalline La2O3 powders were successfully prepared by the combustion method.The effect of ethanolamine-to-nitrate ratio on phase composition and crystallite size of the combustion products was systematically investigated.Pure hexagonal La2O3 powders were almost formed in stoichiometric reaction(ψ=1.15),while metallic La phase was obtained in fuel-rich conditions(ψ≥3.0).The as-synthesized hexagonal La2O3 was found to be chemically unstable in ambient air since a complete transformation to hexagonal La(OH)3 was detected after 24 h exposure to air.The resulting hexagonal La(OH)3 showed an excellent ability to remove water pollutant and could nearly remove 100% of the Congo red at room temperature with a removal capacity of 143.5 mg Congo red/g.The phosphate adsorption data on hexagonal La(OH)3 agreed well with the Langmuir model with the estimated maximum adsorption capacity of 57.8 mg/g.     

Spectroscopic properties of Gd2Oa：Dy3＋ nanocrystals

Gd2O3:Dy3+ nanocrystals were synthesized via solvothermal method followed by a subsequent calcination.The samples were characterized by X-ray diffraction(XRD),transmission electron microsopy(TEM),Electronic dispersive X-ray spectroscopy(EDX),photoluminescence(PL)spectrum and decay curves.The effect of the annealing temperature on the crystallinity and particle size was studied;heat treatment improved the crystallinity of as-prepared nanocrystals as well as increased their particle size.The nanocryatals presented monodispersed spherical shape under TEM.Photoluminescence spectra showed that nanocrystal exhibited strong yellow emission corresponding to 4F9/2→6H13/2 transition(573 nm)of Dy3+ under UV light excitation,which broadened with the particle size decreased without structure changed.The theoretical mechanism of luminescence was explored and surface effect was thought to be the main reason.     

Microwave absorbing properties of NdFeCo magnetic powder

NdFeCo magnetic powder was prepared by the process of smelting,high-energy ball milling and oxidation heat treating.The effects of oxidation heat treatment and Co content on phase composition and microwave absorbing properties of NdFeCo magnetic powder were investigated by an X-ray diffractometer(XRD)and vector network analyzer.The minimum reflectivity of Nd23.25Fe36.75Co40 powder before oxidation heat treatment was-6.2 dB,and that of oxidized powder decreased to-14.0 dB.The microwave absorbing properties of NdFeCo magnetic powder could be improved effectively by oxidation heat treatment.With the increase of Co content,the Fe2O3 reduced and the Nd2O3 increased;Fe3Co7 phase appeared when the content of Co increased to 40%(mass ratio);the absorption peak was found to move towards lower frequency region first,and then it moved towards a higher frequency region.Nd23.25Fe66.75Co10 powder had better comprehensive properties in absorbing microwave in the frequency band of 3-13 GHz.The value of minimum reflectivity and absorption peak frequency,when the coating thickness(d)was 1.8 mm,were-19.7 dB and 4.8 GHz,respectively.     

Effect of the addition of rare earths on the activity of alumina supported copper cobaltite in CO oxidation,CH4 oxidationand NO decomposition

The effect of the addition of small amounts of rare earths(Ln=La, Ce, Nd and Gd) to alumina supported copper-cobalt spinel oxide on the catalysts efficiency in CO and CH4 oxidation and in NO decomposition was investigated. Samples of Ln/Cu Co/Al catalyst were prepared and characterized by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), atomic absorption spectroscopy(AAS), scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS), H2-temperature-programmed reduction(H2-TPR), electron paramagnetic resonance(EPR) spectroscopy and low temperature nitrogen adsorption. The results showed that the addition of rare earths changed the surface state of the alumina supported copper-cobalt spinel catalyst. As a result, partial reduction of copper species was observed as well as migration of these species between the surface and the bulk. The Ln/Cu Co/Al catalysts behaved differently in oxidation and reduction processes. In oxidation processes where oxide structure was important, Ce/Cu Co/Al and Nd/Cu Co/Al were the most active catalysts. The catalyst Ce/Cu Co/Al was the most active in the oxidation reactions because of the availability and favorable surface distribution of the redox couples Cu+/Cu2+ and Ce3+/Ce4+. In NO decompostion, Ln-modified catalysts significantly improved the selectivity of the process to N2.     

Catalytic performance for methane combustion of supported Mn-Ce mixed oxides

A series of supported Mn-Ce mixed oxide catalysts were prepared by the impregnation method and used for the oxidation of methane. The catalysts were characterized by N2 adsorption （BET）, X-ray diffraction （XRD）, laser Raman spectrum （LRS）, and temperature programmed reduction （TPR） techniques. The XRD and LRS results confirmed the high dispersion of active components or formation of solid solution between manganese and cerium oxides in the bulk and on the surface of mixed oxide catalysts. The reducibility was remarkably promoted by the stronger synergistic interaction between the two oxides from H2-TPR measurements. As expected, all the experimental mixed oxide catalysts showed excellent activity for methane combustion at low temperature. Especially, for the catalyst with Mn-Ce ratio 3：7, methane conversion reached 92% at a temperature as low as 470 ℃.     

Preparation of Au/CeO2 catalyst and its catalytic performance for HCHO oxidation

Aqueous precipitation and deposition-precipitation method were used to prepare CeO2 supports and Au/CeO2 catalysts, respectively. The effect of preparation condition of support on the catalyst activity was investigated. The catalytic combustion of HCHO was considered as the probe reaction for comparing the catalyst activity. The BET, X-ray diffraction, X-ray photoelectron spectroscopy （XPS）, and reduction （TPR） were carried out to analyze the influence factor on the catalysts activity. The results showed that the addition of dispersant and use of microwave in the support preparation procedure could be beneficial for enhancing the interaction of supports and gold species and thus improved the catalytic activity. The total conversion temperature for HCHO was 146 ℃ over AC400. With the modification during supports preparation process, the catalytic activity increased with total conversion temperature decreasing to 98 ℃. The results of XPS indicated that Au^0 and Au^＋1 species coexisted in these catalysts and the activity of catalyst correlated with Au^＋1/Au^0 ratio. Temperature-programmed reduction results demonstrated that the reduction peak appeared between 100-170 ℃ with the inducing of gold. The dependence of activity on the reduction peak temperature implied that ionic gold was catalytic activity component for HCHO oxidation.     

Synthesis of La_xK_(1–x)CoO_3 nanorod and their catalytic performances for CO oxidation

A series of Lax K1–x CoO3 nanorod oxides with perovskite structure were synthesized by sol-gel method using polyvinyl alcohol(PVA) as additive.These perovskite-type complex oxide catalysts were characterized by the techniques of X-ray diffraction(XRD),infrared(IR),Brumauer-Emmett-Teller(BET) and scanning electron microscopy(SEM).And the results showed that nanorods of La1–x Kx CoO3 perovskite-type complex oxides were fabricated by sol-gel method when the mass concentration of PVA was 4% and the calcined temperature kept at 700 ℃ for 4 h.The catalytic results of CO oxidation showed that the Lax K1–x CoO3 catalysts had high activity.LaCoO3 nanorods exposed more {110} plane than LaCoO3 nanoparticles,which was beneficial to the catalytic oxidation of CO.LaCoO3 nanorods had the best catalytic performance for the oxidation of CO.At 200 oC,the CO conversion could reach 100%.     

Removal of ammonia from aqueous solutions by catalytic oxidation with copper-based rare earth composite metal materials: catalytic performance, characterization, and cytotoxicity evaluation

Ammonia (NH3) has an important use in the chemical industry and is widely found in industrial wastewater. For this investigation of copper-based rare earth composite metal materials, aqueous solutions containing 400 mg/L of ammonia were oxidized in a batch-bed reac-tor with a catalyst prepared by the co-precipitation of copper nitrate, lanthanum nitrate and cerium nitrate. Barely any of the dissolved ammo-nia was removed by wet oxidation without a catalyst, but about 88% of the ammonia was reduced during we...     

Synthesis of mesoporous CeO2-MnOx binary oxides and their catalytic performances for CO oxidation

Mesoporous CeO2-MnOx binary oxides with different Mn/Ce molar ratios were prepared by hydrothermal synthesis and characterized by scanning electron microscopy （SEM）, N2 sorption, X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS） and H2 temperature-programmed reduction （H2-TPR）. The characterization results indicated that the CeO2-MnOx catalysts exhibited flower-like microspheres with high specific surface areas, and partial Mn cations could be incorporated into CeO2 lattice to form solid solution. The CeO2-MnOx catalysts showed better catalytic activity for CO oxidation than that prepared by the coprecipitation method. Furthermore, the CeO2-MnOx catalyst with Mn/Ce molar ratio of 1 in the synthesis gel （Ce-Mn-1） exhibited the best catalytic activity, over which the conversion of CO could achieve 90% at 135 ℃. This was ascribed to presence of more Mn species with higher oxida- tion state on the surface and the better reducibility over the Ce-Mn-I catalyst than other CeO2-MnOx catalysts.     

Modified-EISA synthesis of mesoporous high surface area CeO_2 and catalytic property for CO oxidation

Mesoporous CeO2 particles with high surface area were synthesized using a modified evaporation-induced self assembly(EISA) method which combined citric acid as complexing agent.As-prepared powder and further thermal treatment samples were characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),selected area electron diffraction(SAED),Fourier transform infrared spectrometer(FTIR),thermogravimetry and differential thermal analysis(TG-DTA),Brunauer-Emmett-Teller(BET) and Barrett-Joyner-Ha...     

In-situ synthesis of monolithic Cu-Mn-Ce/cordierite catalysts towards VOCs combustion

A monolithic series of Cu-Mn-Ce oxides supported on cordierites with different Cu/Mn/Ce molar ratios were prepared by the in-situ sol-gel method without any binder. The catalysts were characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), and Brunauer-Emmett-Teller method (BET) and examined in the catalytic combustion of volatile organic compounds (VOCs). The results showed that the well-dispersed nanometer particles of mixed oxides adhered firmly...     

Low-temperature catalytic oxidation of NO over Mn-Ce-O_x catalyst

A series of manganese-cerium oxide catalysts were prepared by different methods and used for low-temperature catalytic oxidation of NO in the presence of excess O2.Their surface properties were evaluated by means of BET and were characterized by using scanning electron microscopy(SEM) and X-ray diffractometer(XRD).The activity test of Mn-Ce-Ox catalysts showed that addition of Ce enhanced the activities of NO oxidation.The most active catalysts with a molar Ce/(Mn+Ce) ratio of 0.3 were prepared by co-precipitation method.The results showed that NO conversion reached 60% at 150 °C with a high space velocity of 50902 h-1.The effect of doping different rare earth oxides was also investigated and the addition of small amount of Ce not only increased the surface area of MnOx but also enhanced the dispersion of Mn species in the catalyst shown by BET,SEM and XRD.     

Synthesis of cerium-doped MCM-48 molecular sieves and its catalytic performance for selective oxidation of cyclohexane

Cerium-doped MCM-48 molecular sieves were synthesized hydrothermally and characterized by X-ray diffraction, nitrogen adsorption, transmission electron microscope, FT-IR spectroscopy, UV-visible spectroscopy, and Raman spectroscopy. The results showed that all the samples held the structure of MCM-48, and Ce could enter the framework of MCM-48. However, when Ce/Si molar ratio in the sampies was high （0.04 or 0.059）, there were CeO2 crystallites as secondary phase in the extraframework of MCM-48. Ce-doped MCM-48 was a very efficient catalyst for the oxidation of cyclohexane in a solvent-free system with oxygen as an oxidant. In the conditions of 0.5 MPa 02 and 413 K for 5 h, the conversion of cyclohexane was 8.1% over Ce-MCM-48-0.02, the total selectivity of cyclohexanol and cyclohaxnone was 98.7%. With an increase of Ce content, the conversion of cyclohexane and the selectivity to cyclohexanol decreased somewhat, but the selectivity to cyclohexanone increased.     

Preparation and characterization of nano-rare earth composite materials:application in selectivity catalytic oxidation of ammonia and its cytotoxicity study

The manufacture,physical characterization,environmental applications and cytotoxicity properties of nanocomposites consisting of CuO/CeO2 nano-rare earth composite materials prepared using the coprecipitation method at molar ratio of 6:4 with aqueous solutions of copper nitrate and cerium nitrate were reported.The performance of the selective catalytic oxidation of ammonia to N2(NH3-SCO) over a CuO/CeO2 nano-rare earth composite materials in a tubular fixed-bed reactor(TFBR) at temperatures from 423 to 673 K in the presence of oxygen was elucidated.The catalytic redox behavior was determined by cyclic voltammetry(CV).The nanocomposite particles were characterized by TEM,with a tiny particle size around 10 nm with high dispersion phenomena.Further,cell cytotoxicity and the percentage cell survival were determined by using 3-(4,5-dimethylthiazol-2-yl)-5(3-carboxymethoxyphenol)-2-(4-sulfophenyl)-2H-tetra-zolium(MTS) assay on human lung MRC-5 cell line.Experimental results showed that no apparent cytotoxicity was observed when the MRC-5 was exposed to the CuO/CeO2 nanocomposite materials.