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

A series of MnMgAlO 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 IR were used to characterize the physiochemical properties of these samples.Dopant Ce improved the soot combustion performance of MnMgAlO catalyst due to the enhanced 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 O2.Differently,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 NO2 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,Mn0.5Mg2.5Ce0.1Al0.9O was considered as the most potential catalyst for soot combustion.     

Preparation of ultrafine Ce-based oxide nanoparticles and their catalytic performances for diesel soot combustion

The ultrafine Ce-based oxide nanoparticles with different element dopings （Zr, Y） were synthesized by the method of mi- cropores-diffused coprecipitation （MDC） using ammonia solution as the precipitation agent. The activities of the catalysts for soot oxidation were evaluated by the temperature-programmed oxidation （TPO） reaction. Ce-based oxides prepared in this study exhibited high catalytic activity for soot oxidation under tile condition of loose contact between soot particles and catalysts, and the catalytic ac- tivity ofultrafine Ce0.gZr0 iO2 nanoparticle for soot combustion was the highest, whose/＂10, Ts0 and Sco2m was 364, 442 ~C and 98.3%, respectively. All catalysts were systematically characterized by means of X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, Brumauer-Emett-Teller （BET）, Fourier transform infrared spectroscopy （FT-IR） and UV-Vis diffuse reflectance spectroscopy （UV-Vis DRS）. It was indicated that the MDC method could prepare the ultrafine Ce-bascd oxide nanoparticles whose the crystal lattice were perfect, and the BET surface area and average crystal size of the ultrafine nanoparticles changed with the different element dopings （Zr, Y）. The H2-TPR measurements showed that the ultrafine Ce-based ox- ide nanoparticles with the doping-Zr cation could be favorable for improving the redox property of the catalysts.     

Effect of Fe2O3 Loading Amount on Catalytic Properties of Monolithic Fe2O3/Ce0.67Zr0.33O2 -Al2O3 Catalyst for Methane Combustion

Ce0.67Zr0.33O2-Al2O3 solid solution was prepared by the co-precipitation method. Fe2O3-based catalysts supported on the solid solution were obtained by the impregnation method. The article revealed that the optimal loading amount of Fe2O3 on Ce0.67Zr0.33 O2-Al2O3 in our experimental condition for catalytic combustion of methane was 8% （ mass fraction）. The prepared catalysts were characterized by BET, TPR, XRD analyses, and their catalytic activity was investigated after being calcined at 873 K and after being aged in water gas at 1273 K. When the loading amount of Fe203 was 8% （ mass fraction）, the catalyst held the highest activity, and the best temperature speciality and thermal stability. The complete-conversion temperature of methane for fresh and aged sample was 788 and 838 K, respectively. The range between the light-off temperature and the complete-conversion temperature was only 15 K. The characterization results of XRD indicated that Fe2O3 was well dispersed on the Ce0.67Zr0.33O2-Al2O3 matrix. The results of BET and TPR were in good harmony with the catalytic activity results.     

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.     

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.     

Effect of Novel Supporter on Catalytic Combustion of Methane

A new catalyst support, Ce-Mg-O, was prepared in a novel way macromolecule surfactant modified method and was used as a catalyst support for low-temperature methane combustion. The results indicate that the new type of FeOx/Ce- Mg-O catalyst exhibits high activity in low-temperature methane combustion, such that the T90 at which 90% conversion of methane occurs can be obtained at 560 ℃. The structure of the catalyst and the effect of the supporter on catalytic activity were characterized by transmission electronic microscopy （TEM）, X-ray diffraction （XRD）, and temperature-programmed reduction （TPR）. The results indicate that the high catalytic activity of FeOx/Ce-Mg-O over methane combustion is strongly dependent on the particle size, typical crystal phase of the Ce-Mg-O, and the interaction of FeOx and Ce-Mg-O.     

Effect of Complex Agents on Structure and Activity of Fe-Substituted Rare Earth Hexaaluminate Catalysts for Methane Combustion

A series of catalysts were prepared by using complex sol-gel methods.Experimental results confirm the effect of different agents on structure and activity of Fe-substituted rare earth hexaaluminate catalyst (LaFeAl11 O19 ) for methane combustion.The catalyst is yielded by complex sol-gel, respectively using three different complex agents (maltose, glucose and citric acid).XRD demonstrated that haxaaluminate is the major phase of catalyst prepared by maltose,while LaAlO3 is the major one of the catalyst by glucose and citric acid.At the same time, there is a little LaFeO3 and surface areas as well as 29.5 nm particle diameter when the complex agent is maltose.However, T10 ( temperature for 10% conversion of methane) and T100 ( temperature for 100% conversion of methane) for catalyst by glucose is 543 and 758 ℃, which is the best among the three complex agents for methane combustion.     

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.     

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.     

Cerium,manganese and cerium/manganese ceramic monolithic catalysts.Study of VOCs and PM removal

Ceramic supported cerium, manganese and cerium-manganese catalysts were prepared by direct impregnation of aqueous precursor, and characterized by scanning electron microscopy(SEM), X-ray diffraction(XRD), Brunauer-Emmett-Teller method(BET), temperature programmed reduction(H_2-TPR), X-ray photoelectron spectroscopy(XPS) acidity measurements and electrical conductivity. The catalytic activity was evaluated for volatile organic compounds(VOC)(ethanol, methyl ethyl ketone and toluene) oxidation. Additionally, catalysts were tested in particulate matter(PM) combustion. The characterization results indicated that Ce was in the form of Ce~(4+) and Ce~(3+), and Mn existed in the form of Mn~(4+) and Mn~(3+) on the surface of the Mn/AC sample and in the form of Mn~(4+) in the Ce/Mn/AC monolith. VOC oxidation results revealed that the Ce/Mn/AC sample showed an excellent performance compared with ceramic supported CeO_2(Ce/AC) and MnO_x(Mn/AC) samples. The PM combustion was also higher on Ce/Mn/AC monoliths. The enhanced catalytic activity was mainly attributed to the Ce and Mn interaction which enhanced the acidity, conductivity and the reducibility of the oxides.     

Effect of metal doping into Ce0.5Zr0.5O2 on catalytic activity of MnOx/Ce0.5-xZr0.5-xM0.2xOy/Al2O3 for benzene combustion

The research investigated the effect of doping two metals separately or together into Ce0.5Zr0.5O2 on the catalytic activity of MnOx/Ce0.5–xZr0.5–xM0.2xOy/Al2O3 (M=Y, Mn, Y and Mn) for catalytic combustion of benzene. The prepared catalysts were characterized by X-ray diffraction (XRD), surface area analysis, oxygen storage capacity (OSC), and H2-temperature programmed reduction (H2-TPR). Cata-lytic test was performed on a conventional fixed bed flow reactor. The characterization results revealed that Y and Mn ions entered into the ceria-zirconia mixed oxides framework, which improved the textural properties and greatly promoted the MnOx dispersion on the support surface. The complete conversion temperature of benzene on MnOx/Ce0.4Zr0.4Y0.1Mn0.1Oy /Al2O3 was 563 K, and the selectivity of carbon dioxides was 99%. This catalyst could be applied in a wide range of GHSV and wide concentration condition, showing great potential for application.     

Promotional effect of CeO2 and Y2O3 on CuO/ZrO2 catalysts for methane combustion

Catalytic combustion of methane was conducted by using a Cu-based catalyst prepared by the plasma-assisted impregnation method. The properties of the catalysts were surveyed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (H2-TPR). The results showed that the activity of CuO/ZrO2 with the CeO2 and Y2O3 was obviously increased compared with the CuO/ZrO2 catalyst, which was examined in relation to the structure and surface characteristics and might be correlated with their surface oxygen species and redox properties. Among the investigated catalysts, the Ce-CuO/ZrO2 sample exhibited the highest activity for methane combustion.     

Preparation and characterizations of Ce-Cu-O monolithic catalysts for ethyl acetate catalytic combustion

Ce-Cu-O monolithic catalysts were prepared by using Ce0.9Cu0.1O1.9 solid solution or nitrate as precursors,and their catalytic performance for the combustion of ethyl acetate were studied.The catalysts calcined at a low temperature showed high catalytic activities.When calcined at high temperatures,the catalyst with Ce0.9Cu0.1O1.9 solid solution as precursor remained a high activity,while the catalyst with metal nitrates as precursors exhibited a suppressed reactivity.Therefore,the catalyst prepared with th...     

Synthesis of neodymium modified CeO2-ZrO2-Al2O3 support materials and their application in Pd-only three-way catalysts

Ce-Zr-Al-Nd2O3 (CZAN) support materials were prepared by co-precipitation and impregnation methods, respectively. They were characterized by X-ray diffraction (XRD), low temperature nitrogen adsorption-desorption, oxygen pulsing technique, H2-temperature pro-grammed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS). The Pd-only three-way catalysts (Pd-TWC) supported on these materials were prepared by incipient wetness method and studied by activity tests. The results demonstrated that the CZAN supports obtained by the two methods showed better structural, textural and redox properties than the CZA without Nd2O3, and the addition of Nd2O3 improved the catalytic activity of TWC. Especially, the CZAN-i support prepared by impregnation method had better thermal stability and redox prop-erty. Meanwhile, the Pd/CZAN-i catalyst exhibited the best catalytic performance. XPS measurements indicated that the Nd-modified sam-ples possessed more Ce3+ and oxygen vacancies on the surface of samples, which led to a better redox property. The excellent redox property of support materials helped to improve the catalytic activity of TWC.     

Roles of Lewis and Brnsted acid sites in NO reduction with ammonia on CeO_2-ZrO_2-NiO-SO_4~(2-) catalyst

Nickel and sulfate co-modified CeO2-ZrO2 catalysts were prepared by sol-gel method. The catalysts were characterized by XRD, FTIR, XPS, NH3 chemisorption and NH3-SCR activity tests. The results showed that the enhanced acidity of CeO2-ZrO2 catalysts by nickel and sulfate co-modification was responsible for the broadened temperature window and improved the selectivity to N2 in NH3-SCR deNOx. The introduction of nickel to CeO2-ZrO2 solid solutions resulted in more Ce3+ on surface of catalyst, leading to an in...     

Ce-modified AlZr pillared clays supported-transition metals for catalytic combustion of chlorobenzene

In this article, we provided a one-step hydrothermal method to prepare composite AlZr pillaring agents, and synthesized AlZr-pillared clays (AlZr-PILC) via ion exchange. Compared with conventional methods, our method successfully shortened synthetic routes and greatly reduced consumption of the materials. Then, AlZr-PILC-supported manganese and cerium oxide catalysts were obtained by impregnation method. The compositions and properties of these catalysts were characterized by some technical means. The energy dispersive X-ray spectroscopy clearly shows the existence of Mn, Ce, and O, which indicates the successful loading of the active components on the surface of AlZr-PILC. Meanwhile, the results of X-ray diffraction (XRD) and N₂ adsorption experiments demonstrate that the synthesized AlZr-PILC outperforms the raw clays (Na-mmt) and mononuclear Al-PILC in the catalytic combustion of chlorobenzene. XRD and high-resolution transmission electron microscopy also proves that the high activity of them is related to the high dispersion of the oxides and the exposure of more active sites. H₂-temperature-programmed reduction shows that cerium can promote the redox cycles of the manganese system through the strong interactions between MnO₂, CeO₂ and AlZr-PILC. In particular, MnCe(9:1)/AlZr-PILC shows the best catalytic activity in the catalytic combustion of chlorobenzene.     

Catalytic combustion study of soot on Ce0.7Zr0.3O2 solid solution

The Ce0.7Zr0.3O2 solid solution and CeO2 were prepared using the sol-gel method. The phase structure, crystallite sizes and the reducibility of the catalysts were characterized by XRD and H2-TPR techniques. XRD results indicated that Zr^4＋ had replaced part of Ce^4＋ to form a fluorite-like solid solution, which was favorable to obtain ultrafine nanoparticles. The ratio of main HE consumption for Ce0.7Zr0.3O2：CeO2 was 4.4：1.0, implying that the solid solution could improve the reducibility compared to the single CeO2. The Ce0.7Zr0.3O2 solid solution catalyst showed a sharp combustion peak at 397 ℃, which was 200 ℃ lower than that of the single soot. The good catalytic activity of the Ce0.7Zr0.3O2 was attributed to the formation of nano-CeO2-based solid solution, which enhanced the reducibility and then improved the combustion activity. As Ce0.7Zr0.3O2 could be easily reduced to Ce0.7Zr0.3O2-x meanwhile, after oxygenation, the Ce0.7Zr0.3O2.x was recovered to Ce0.7Zr0.3O2 completely. A catalytic combustion reaction mechanism was proposed： the Ce0.7Zr0.3O2 was reduced to Ce0.7Zr0.3O2-x by the reaction with carbon and then it was recovered to Ce0.7Zr0.3O2-x by the interaction with O2.     

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 ...     

激光处理制备La_(0.6)Ba_(0.4)Co_(0.2)Fe_(0.8)O_3钙钛矿催化剂

通过柠檬酸络合树脂法合成了钙钛矿催化剂La0.6Ba0.4Co0.2Fe0.8O3前驱体,然后分别对前驱体以不同功率和扫描速度的激光扫描及高温焙烧进行处理。用XRD、XPS方法测定了催化剂的结构并测定了催化剂的甲烷燃烧活性。结果表明,适当激光条件下制备的催化剂活性明显高于高温焙烧的催化剂。激光制备催化剂高活性的原因可归因于,激光处理的特点使催化剂形成较小的晶粒度、存在的夹杂相造成晶格缺陷。     

Influence of preparation method on performance of a metal supported perovskite catalyst for combustion of methane

A different method was employed for the preparation of a metal supported perovskite catalyst for the catalytic combustion of methane.The prepared metallic catalysts were characterized by means of X-ray diffractometer(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),and also by ultrasonic and thermal shock tests and catalytic activity.It was found that the process factors during the preparation,e.g.the preparation of the catalyst precursor and the coating slurry,the calcination te...