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1.
The effect of Ce on the structure of MoVNbCeO multi-metal oxide catalysts and the performance of ethane selective oxidation was investigated. These multi-metal oxide catalysts with superior oxidizability exhibit high catalytic activity, and vanadium acts as the active center for ethane oxidation reaction. The improved catalytic activity is related to the increased V5+ content on the catalyst surface, which results from the enhanced transformation of the electrons between V and Ce. Moreover, Ce effectively promotes oxygen adsorption, activation, and mobility. And the presence of Ce can also prevent MoO3 formation and stabilize the Mo5O14-like structure. In addition, the catalyst with a moderate amount of Ce exhibits outstanding catalytic performance. Especially, the MVN-Ce catalyst with a Ce/V ratio of 0.1 exhibits the best performance: the total selectivity of the catalyst toward C2H4 and CH3COOH is the highest (72%) at the ethane conversion of 31%. Therefore, MoVNbCeO multi-metal oxides are promising candidates for selective oxidation.  相似文献   

2.
Mesoporous CeMnOx composite oxides catalysts were prepared by surfactant-assisted co-precipitation method and used for the catalytic oxidation of toluene.The effect of different cerium precursors[Ce(NO_3)_3 and(NH_4)_2 Ce(NO_3)_6] on catalyst structure,surface properties and toluene combustion activities of mesoporous CeMnO_x catalysts were investigated.The Ce(Ⅲ)MnO_x catalyst prepared from Ce(NO_3)_3 precursor shows higher catalytic activity,with a 90% conversion temperature of 240℃,which is better than the Ce(Ⅳ)MnO_x catalyst derived from(NH_4)_2 Ce(NO_3)_6] precursor.On the basis of characterizations,it reveals that abundant surface content of Mn~(4+),better redox behavior and larger concentration of surface active oxygen species are responsible for the excellent catalytic performance.  相似文献   

3.
Large amounts of water containing-ammonium nitrogen(NH4+-N)have attracted increasing attention.Catalytic ozonation technology,involving the generation of hydroxyl radical(OH)with strong oxidation ability,was originally utilized to degrade organic-containing wastewater.In this paper,Ce/MnOx composite metal oxide catalysts prepared with different preparation conditions were used to degrade wastewater containing inorganic pollutant(NH4+-N).The as-prepared catalyst features were characterized using X-ray diffraction(XRD),Brunauer-Emmett-Teller method(BET),scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDS),Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS)and H2-temperature programmed reduction(H2-TPR)techniques.The results show that the catalyst,prepared by conditions with precipitant Na2CO3 and Ce/Mn molar ratio 1:2 calcined at 400℃for 3 h in pH 11.0,displays the optimal performance,with the removal rate of NH4+-N and selectivity to gaseous nitrogen,88.14 wt%and 53.67 wt%,respectively.The effects of several operating factors including solution pH,initial NH4+-N concentrations and scavengers were evaluated.In addition,XRD patterns of catalyst with the best performance and the comparative study on decontamination of NH4+-N by various processes(O3,catalyst and catalyst/O3)show that the primary metal oxides are CeO2 and MnO2 in Ce/MnOx composite metal oxide catalysts,which have a synergistic effect on the catalytic ozonation of NH4+-N,and the new phase MnO2 plays a great role.After 5 consecutive use cycles,the degradation efficiency is declined slightly,and can still achieve better than 70 wt%over 1 h reaction.Additionally,the application of catalytic ozonation for actual wastewater on the removal rate of NH4+-N was investigated.Possible mechanism and degradation pathway of NH4+-N were also proposed.In a word,the application of CeO2-MnO2 composite metal oxide catalysts in catalytic ozonation can be regarded as an effective,feasible and promising method for the treatment of NH4+-N.  相似文献   

4.
A series of Ru supported on CeO2 and Ce0.7Zr0.3O2(CeZrO) was prepared by incipient-wet impregnation method and investigated in the catalytic wet oxidation of N,N-dimethyl formamide (DMF) in batch reactor. The physicochemical property of the catalysts was characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and thermogravimetry (TG). Compared with 3%Ru/CeO2, 3%Ru/Ce0.7Zr0.3O2 catalyst exhibits much higher performance for DMF degradation due to the promotion of Ru dispersion and the transfer of active oxygen, and 99% DMF conversion and 97% COD elimination are obtained at 453 K, 2.5 MPa oxygen pressure after 5 h. The reaction mechanism of DMF degradation was suggested. The carbonaceous species deposition and oxidation of Ru can be responsible for catalyst deactivation. And the catalyst activity can be recovered by air calcination and H2 reduction.  相似文献   

5.
The activity and hydrothermal stability of the Rh/Ce_xZr_(1-x)O_2(x=0,0.05,0.3,0.5) model three-way catalysts for gasoline vehicle emissions control were investigated in this work.Among the Rh/Ce_xZr_(1-)_xO_2 samples with different Ce/Zr ratios,the Rh/ZrO_2 sample exhibits a significantly better activity and hydrothermal stability than the rest of the samples.The impacts of having more Ce components in the Rh/Ce_xZr_(1-x)O_2 catalysts are associated with the strong Rh-O-Ce interaction that tends to over stabilize the rhodium species.A significant amount of such rhodium atoms can be found in the bulk of the support oxides after a hydrothermal aging at 1050℃ with 10% H_2 O in air for 12 h.Differently,the sintering of rhodium on the surface of Rh/ZrO_2 catalysts is the main reason for the catalyst deactivation during the hydrothermal aging.These findings provide an example where high dispersion of supported metal induced by strong metal-support interactions does not necessarily lead to high catalytic activity.  相似文献   

6.
In this work,tungsten oxide with different concentrations(0,0.4 at%,2.0 at% and 3.2 at%) was introduced to the ceria nanorods via a deposition-precipitation(DP) approach,and copper species of ca.10 at% were sequentially anchored onto the modified ceria support by a similar DP route.The aim of the study was to investigate the effect of the amount of tungsten oxide(0,0.4 at%,2.0 at%,and 3.2 at%) modifier on the copper-ceria catalysts for CO oxidation reaction and shed light on the structure-activity relationship.By the aids of multiple characterization techniques including N_2 adsorption,high-resolution transmission electron microscopy(HRTEM),powder X-ray diffraction(XRD),X-ray absorption fine structure(XAFS),and temperature-programmed reduction by hydrogen(H_2-TPR) in combination with the catalytic performance for CO oxidation reaction,it is found that the copper-ceria samples maintain the crystal structure of the fluorite fcc CeO_2 phase with the same nanorod-like morphology with the introduction of tungsten oxide,while the textural properties(the surface area,pore volume and pore size) of ceria support and copper-ceria catalysts are changed,and the oxidation states of copper and tungsten are kept the same as Cu~(2+)and W~(6+)before and after the reaction,but the introduction of tungsten oxide(WO_3)significantly changes the metal-support interaction(transfer the CuO_x clusters to Cu-[O_x]-Ce species),which delivers to impair the catalytic activity of copper-ceria catalysts for CO oxidation reaction.  相似文献   

7.
The effects of support materials on catalytic performance were investigated in catalytic removal of toluene. And the Mn–Ce binary oxides as active components were supported on ZrO2, SiO2, γ-Al2O3 and TiO2 support materials. Many techniques, including X-ray diffraction (XRD), Brunauer–Emmett–Teller method (BET), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and NH3-temperature-programmed desorption (NH3-TPD), were used to characterize physicochemical properties. Among the different catalysts, the MnCe/ZrO2 catalyst with the lowest specific surface area (39.7 m2/g) shows the best catalytic activity. In terms of toluene conversion, the activity order is as follows: MnCe/ZrO2 > MnCe/TiO2 ≈ MnCe/SiO2 > MnCe/Al2O3. The better performance of MnCe/ZrO2 should be attributed to the low-temperature reducibility, and abundant surface species (Mn4+ and lattice oxygen). And XPS and TPR results reveal that more surface abundant Mn and Ce elements generate good interaction in MnCe/ZrO2. The weak interaction between metal oxide and support also boosts the dispersion and complete reduction of MnCe oxides at low temperature. In addition, the in-situ DRIFTS results clarify that the carbonate species are main intermediates in MnCe/ZrO2 sample during surface reaction process.  相似文献   

8.
A CoCe/ZSM-5 catalyst was prepared by ultrasonic-assisted impregnation for the catalytic combustion of toluene.To study the effect of Na+on catalytic performance of CoCe/ZSM-5 catalysts,a series of different Si/Al ZSM-5 zeolites and catalysts doped with Na were synthesized.The experimental results show that 0.71 wt%Na+can inhibit active growth,generate more active small crystal grains,and promote improvement of the catalytic activity by the grain boundary segregation block mechanism,and the catalyst with 0.71 wt%of Na shows toluene conversion of 90 vol%at 250℃.Over 0.71 wt%of Na+content will neutralize the acid centre of the catalyst,lowering the specific surface area of the catalyst and resulting in a gradual decrease in the catalytic activity.  相似文献   

9.
The physicochemical properties of Pd and PdPt catalysts which possess different Ce doping position were investigated by techniques of TEM, XRD, N2 adsorption-desorption, XPS and FT-IR. The catalytic performance for methanol total oxidation was examined to study the effects of Ce adding position. CeO2Al2O3TiO2 (CAT) catalysts that Ce is directly introduced into support show higher reactivity and CO2 selectivity than CeO2/Al2O3TiO2 (Ce/AT) samples in which Ce is loaded by impregnation method. The characterization results reveal that the Ce doping position does not cause obvious otherness of basic crystalline phase and mesoporous structure of support. However, the Ce doping position affects the pore shapes of support and then influences the pore diameter. CAT catalysts possess more abundant adsorbed oxygen and more Ti3+ can transform the more gaseous oxygen into the active oxygen species on the catalyst surface, which is beneficial to the reaction. The AlOTi bridges in CAT facilitate the cooperation of Al and Ti species, which further speeds up the reaction rate.  相似文献   

10.
CexCoyCuz 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.  相似文献   

11.
Ce-or La-doped Cu/SSZ-13 catalysts were prepared by a hydrothermal method and Cu,Ce or La ions were incorporated through stepwise ion exchange,The catalyst activity was measured for the ammonia selective catalytic reduction reaction.The structure and composition of catalyst were characterized by using X-ray diffraction,scanning electron microscopy,inductively coupled plasma mass spectrometry solid-state NMR,NH_3-TPD techniques,and the active components were examined by XPS and XANES.The results indicate that the Ce and La doping can both completely preserve the SCR activity of Cu/SSZ-13 above 300℃,but there is also a decrease of activity below 200℃.On the other hand,Ce doping is beneficial to the formation of framework aluminum,stabilizes molecular sieve framework and Cu active sites of Cu/SSZ-13,thereby improves the catalyst hydrothermal stability.But La doping will decrease the amount of framework aluminum and Cu active sites of Cu/SSZ-13 after hydrothermally aging,even destroy zeolite CHA structure.This is quite harmful to the catalyst hydrothermal stability.  相似文献   

12.
In this study, a series of Hydrogen-Zeolite Socony Mobil-5-X (HZSM-5-X) catalysts were prepared by acid modification, then Ce/HZSM-5-X (X = 0, 0.2, 0.4, 1.0, 2.0) catalysts were prepared by impregnation method. The catalytic performance of the catalysts on dichloromethane (DCM) oxidation was investigated. Through different characterizations, HZSM-5-X exhibit high specific surface area, good redox ability, rich acidity and much suitable acidic site distribution after acid treatment. Among them, Ce/HZSM-5-0.4 shows better catalytic activity with the lowest by-product and the best CO2 yield. Its T90 is 302 °C and the CO2 yield of T90 is more than 80 wt%, which demonstrates that the acid modification of carrier plays the positive effect on the catalytic capacity for DCM oxidation.  相似文献   

13.
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 MnCeOx catalysts supported on palygorskite (Pal) and aluminium hydroxide (Al(OH)3). Our results indicate that the synergistic interaction in MnCeOx through the oxygen transfer mechanism from the oxygen reservoir CeO2 to MnOx 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. MnCeOx 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 MnCeOx 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.  相似文献   

14.
To probe the function of Ce on enhancing low-temperature stability of SAPO-34,Ce/SAPO-34 with different Ce contents was prepared via one-pot method and further treated at 70℃ in 80% relative humidity for 24 h.The structural results prove that the one-pot synthesis is an effective way to introduce Ce(Ce 0.325 wt%) without influencing micro-structural and chemical composition.The lowtemperature hydrothermal stability of Ce/SAPO-34 is enhanced by Ce loading.More than 92% CHA structure and total acidity are maintained over 0.188 wt% Ce/SAPO-34,while only about 20% of that left on pure H/SAPO-34.As Ce exists as Ce3+at exchange sites on the surface of SAPO-34,the results of the linear relationship between protected surface acidity and structure/acidity conservation manifest that Ce~(3+) effectively hinders the structural collapse.This study provides new insight into surface acidity protection for solving the problem of low-temperature hydrothermal stability of SAPO-34.  相似文献   

15.
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).  相似文献   

16.
A series of 3DOM CeMnO_3 perovskite catalysts were prepared by poly(methyl methacrylate) hardtemplating-excessive impregnation method at calcination temperature of x℃(x=600,700,800) and the heating rate of y ℃/min(y=1,2,5,10).The samples were characterized by Brunauer-Emmett-Teller method,scanning electron microscopy,transmission electron microscopy,H_2-temperature programmed reduction,X-ray photoelectron spectroscopy,X-ray diffraction,moreover,the effect of the calcination process on the catalytic activity of the samples were discussed by the catalytic combustion of toluene.The results show that the 3DOM CeMnO_3 catalysts calcined at 600℃ promote the formation of a perovskite structure,inhibit the reduction of the Mn~(4+) species in the catalyst with high temperature.The catalyst expresses the complete macroporous structure,large specific surface area(38.8 m~2/g),higher adsorption oxygen concentration and Mn~(4+) substance concentration,with a low T_(90%)=172℃.By preparing the catalysts at different calcination heating rates,it can be concluded that the catalyst possesses a high concentration of adsorbed oxygen and a low reduction temperature and a large specific surface area(40.42 m~2/g) greatly promotes adsorption stage catalytic oxidation reaction and catalytic combustion of toluene at low temperature under the heating rate of 5℃/min.When the heating rate is 1 ℃/min,the catalyst has a complete macroporous structure(250 nm),which is beneficial to the exchange of macromolecular substances during the catalytic reaction and the catalyst has a high concentration of lattice oxygen suitable for the catalysis of toluene in high temperature flue gas combustion.  相似文献   

17.
Zr-doped CuO-CeO_2 catalysts for CO selective oxidation were designed and prepared by the hydrothermal method and coprecipitation. The experimental samples were characterized by means of N_2 adsorption-desorption isotherms, powder X-ray diffraction, temperature-programmed reduction and Xray photoelectron spectroscopy. It is observed that the catalyst prepared by hydrothermal method exhibits larger specific surface area, smaller crystalline size and higher dispersion of active components compared with those of the catalyst obtained by coprecipitation. Meanwhile, redox properties of copper oxide are improved significantly and highly dispersed copper species providing CO oxidation sites are present on the surface. Furthermore, adsorptive centers of CO and active oxygen species increase on the copper-ceria interfaces. The Zr-doped CuO-CeO_2 catalyst prepared by hydrothermal method possesses superior catalytic activity and selectivity for selective oxidation of CO at low temperature compared with those of the sample prepared by coprecipitation. The temperature corresponding to 50% CO conversion is only 73 ℃ and the temperature span of total CO conversion is expanded from 120 to 160 ℃.  相似文献   

18.
So far,it is still a controversial issue which status of gold species is a better active site for catalyzing CO oxidation.Herein,the influence of the different atmospheres pretreatment(oxidative and reductive)on gold state of Au/La-CeOx(1 wt%gold loading)catalyst during CO oxidation was studied.The changes of Au species were monitored by combined in situ diffuse reflectance infrared Fourier transform spectroscopy(in situ DRIFTS)and X-ray photoelectron spectroscopy(XPS).For the sample pretreated with oxidative atmosphere,the data show that the initial Au3+is transformed to Auδ+(0<δ<1)during CO oxidation,which is a key step to lead to higher reactivity.For the sample after reductive atmosphere pretreatment,Auδ+is mixed with a small amount of Au0which can be converted to Auδ+with the increase of temperature in reaction.Meanwhile,the sample always maintains high activity during the reaction.Therefore,the Au?+obtained by reductive pretreatment is more active than the Au3+obtained by oxidative treatment in catalyzing CO oxidation.  相似文献   

19.
Spherical CeO2 synthesized by the hydrothermal process was used as support to prepare Pt/WO3/CeO2,and the effects of tungsten(W) contents on activity,stability and polychlorinated by-products were investigated to understand the role of W for vinyl chloride(VC) catalytic oxidation.The introduction of12 wt% W to Pt/CeO2(P12 WC) exhibits the highest catalytic activity with 90% conversion of VC at 250℃,meanwhile the stability improves and the polychlorinat...  相似文献   

20.
Cerium zirconium solid solution is a key washcoat material for automotive three-way catalysts(TWCs).However,improving the redox ability and high temperature thermal stability of cerium zirconium solid solution is still a challenge.In this paper,the cerium zirconium solid solution was prepared by a coprecipitation-hydrothermal method,and the effects of the ammonia concentration on their structures and redox properties were investigated.The results show that when the ammonia concentration is 0.8 mol/L,the aged sample(1100℃/10 h)of cerium zirconium solid solution has the highest specific surface area of 23.01 m2/g.Additionally,the increase of ammonia concentration improves the uniformity of phase compositions and increases the oxygen vacancies.When the ammonia concentration reaches 0.4 mol/L,the cerium zirconium solid solution exhibits the best redox activity,with the lowest reduction temperature of 565℃.Therefore,increasing ammonia concentration in the hydrothermal treatment is beneficial to the thermal stability and redox performance of cerium zirconium solid solution.  相似文献   

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