Effect of yttrium and manganese addition on catalytic soot combustion activity and anti-high-temperature stability of CeO_(2) catalyst

In order to analyze the influence of the addition of yttrium and manganese on the soot combustion performance and high temperature stability of CeO_(2) catalyst,a series of Y/Mn-modified CeO_(2) catalysts were prepared.The effects of structural properties,textural properties,oxygen vacancies,Ce^(3+),surface adsorbed oxygen species,reduction properties and desorption properties of oxygen species on the activity were analyzed by various characterization methods.The results of the activity test show that the addition of manganese is beneficial to enhancement of the activity,while the addition of yttrium increases the amount of reactive oxygen species,but decreases the activity.After aging at 700℃,the activity of the CeMn catalyst decreases most sharply,while the catalytic activity of the CeY catalyst can be maintained to a certain extent.Interestingly,the addition of yttrium and manganese at the same time can stabilize the activity.The fundamental reason is that yttrium and manganese move to the surface of the solid solution after aging,which increases the reduction performance of the catalyst,thus contributing to the increase of activity.Although the activity of CeYMn catalyst decreases after aging at 800℃,it is still higher than that of other catalysts aged at 700℃.

Alkali/alkaline-earth metal-modified MnO_(x) supported on three-dimensionally ordered macroporous–mesoporous Ti_(x)Si+(1-x)O_(2) catalysts:Preparation and catalytic performance for soot combustion

The performance of catalysts used in after-treatment systems is the key factor for the removal of diesel soot,which is an important component of atmosphericfine particle emissions.Herein,three-dimensionally ordered macroporous–mesoporous Ti_(x)Si+(1-x)O_(2)(3DOM-m Ti_(x)Si+(1-x)O_(2)) and its supported MnO_(x)catalysts doped with different alkali/alkaline-earth metals (AMnO_(x)/3 DOM-m Ti_(0.7)Si_(0.3)O_(2)(A:Li,Na,K,Ru,Cs,Mg,Ca,Sr,Ba)) were prepared by mesoporous template (P123)-assisted colloidal crystal template (CCT) and incipient wetness impregnation methods,respectively.Physicochemical characterizations of the catalysts were performed using scanning electron microscopy,X-ray diffraction,N_(2)adsorption–desorption,H_(2)temperature-programmed reduction,O_(2)temperature-programmed desorption,NO temperature-programmed oxidation,and Raman spectroscopy techniques;then,we evaluated their catalytic performances for the removal of diesel soot particles.The results show that the 3DOM-m Ti_(0.7)Si_(0.3)O_(2)supports exhibited a well-defined 3DOM-m nanostructure,and AMnO_(x)nanoparticles with 10–50 nm were evenly dispersed on the inner walls of the uniform macropores.In addition,the as-prepared catalysts exhibited good catalytic performance for soot combustion.Among the prepared catalysts,CsMnO_(x)/3DOM-m Ti_(0.7)Si_(0.3)O_(2)had the highest catalytic activity for soot combustion,with T10,T50,and T90(the temperatures corresponding to soot conversion rates of 10%,50%,and 90%) values of 285,355,and 393℃,respectively.The high catalytic activity of the CsMnO_(x)/3 DOM-m Ti_(0.7)Si_(0.3)O_(2)catalysts was attributed to their excellent low-temperature reducibility and homogeneous macroporous–mesoporous structure,as well as to the synergistic effects between Cs and Mn species and between CsMnO_(x)and the Ti_(0.7)Si_(0.3)O_(2)support.

K-modified MnO_(δ)catalysts with tunnel structure and layered structure:Facile preparation and catalytic performance for soot combustion

Air pollution from particulate matter produced by incomplete combustion of diesel fuel has become a serious environmental pollution problem,which can be addressed by catalytic combustion.In this work,a series of K-modified MnO_(δ)catalysts with different microstructures were synthesized by the hydrothermal method,the relationship between structure of the catalysts and their catalytic performance for soot combustion was studied by characterization techniques and density functional theory(DFT)calculations.Results showed that the prepared catalysts had good catalytic performance for soot combustion and could completely oxidize soot at temperatures below 400℃.The cryptomelane-type K_(2−x)Mn_(8)O_(16)(K-OMS-2)with tunnel structure had excellent NO oxidation capacity and abundance of Mn^(4+)ions(Mn^(4+)/Mn^(3+)=1.24)with good redox ability,it demonstrated better soot combustion performance than layered birnessite-type K_(2)Mn_(4)O_(8)(K-OL-1).The T_(10),T_(50),T_(90)temperatures of KOMS-2 were 269,314,346℃,respectively.The K-OMS-2 catalyst also showed excellent stability after five catalytic cycles,with T_(10),T_(50),T_(90)values holding in the ranges of 270±2,316±2,348±3℃,respectively.

Facile preparation and efficient MnxCoy porous nanosheets for the sustainable catalytic process of soot

The pursuit of high-performance is worth considerable effort in catalysis for energy efficiency and environmental sustainability. To develop redox catalysts with superior performance for soot combustion, a series of Mn_(x)Co_(y) oxides were synthesized using MgO template substitution.This method greatly improves the preparation and catalytic efficiency and is more in line with the current theme of green catalysts and sustainable development. The resulting Mn_(1)Co_(2.3) has a strong activation capability of gaseous oxygen due to a high concentration of Co^(3+) and Mn^(3+). The Mn doping enhanced the intrinsic activity by prompting oxygen vacancy formation and gaseous oxygen adsorption. The nanosheet morphology with abundant mesoporous significantly increased the solid–solid contact efficiency and improved the adsorption capability of gaseous reactants. The novel design of Mn_(1)Co_(2.3)oxide enhanced its catalytic performance through a synergistic effect of Mn doping and the porous nanosheet morphology, showing significant potential for the preparation of high-performance soot combustion catalysts.

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.

Structure and catalytic property of CeO_2-ZrO_2-Fe_2O_3 mixed oxide catalysts for diesel soot combustion: Effect of preparation method

A series of Ceo.sFeo.30Zr0.20O2 catalysts were prepared by different methods （co-precipitations method, citric acid sol-gel method, impregnation method, physical mixed method, and hydrotherrnal method） and characterized by X-ray diffraction （XRD）, Raman spectroscopy, Brunauer-Emmett-Teller （BET） and H2-TPR measurements. Potential of the catalysts in the soot oxidation was evaluated in a temperature-programmed oxidation （TPO） apparatus. The results showed that all the Fe3＋ and Zr4＋ were incor- porated into ceria lattice to form a pure Ce-Fe-Zr-O solid solution for the co-precipitation sample, but two kinds of Fe phases ex- isted in the Ce-Fe-Zr-O catalysts prepared by other methods： Fe3＋ incorporated into CeO2 lattice and dispersed Fe2O3 clusters. The free Fe2O3 clusters could improve the activity of catalysts for soot oxidation comparing with the pure Ce-Fe-Zr-O solid solution owing to the synergetic effect between free Fe2O3 and surface oxygen vacancies. In addition, the activity of catalysts strongly relied on the surface reducibility of free Fe2O3 particles. Holding both abundant free Fe2O3 particles and high oxygen vacancy concentration, the hydrothermal Ce0.5Fe0.3Zr0.202 catalyst presented the lowest Ti （251℃, ignition temperature of soot oxidation） and Tm （310 ℃, maximum oxidation rate temperature） for soot combustion （with tight-contact between soot and catalysts） among the five samples. Even after aging at 800 ℃ for 10 h, the Ti and Tm were still relatively low, at 273 and 361 ℃, respectively, indicating high catalytic stability.

Promotional effects of cerium doping and NO_x on the catalytic soot combustion over MnMgAlO 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.

Catalytic combustion study of soot on Ce_(0.7)Zr_(0.3)O_2 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.

Efficient low-temperature soot combustion by bimetallic Ag–Cu/SBA-15 catalysts

In this study, the effects of copper（Cu） additive on the catalytic performance of Ag/SBA-15 in complete soot combustion were investigated. The soot combustion performance of bimetallic Ag–Cu/SBA-15 catalysts was higher than that of monometallic Ag and Cu catalysts. The optimum catalytic performance was acquired with the 5 Ag1-Cu0.1/SBA-15 catalyst, on which the soot combustion starts at Tig= 225°C with a T50= 285°C. The temperature for 50% of soot combustion was lower than that of conventional Ag-based catalysts to more than 50°C（Aneggi et al., 2009）. Physicochemical characterizations of the catalysts indicated that addition of Cu into Ag could form smaller bimetallic Ag–Cu nanolloy particles, downsizing the mean particle size from 3.7 nm in monometallic catalyst to 2.6 nm in bimetallic Ag–Cu catalyst. Further experiments revealed that Ag and Cu species elicited synergistic effects, subsequently increasing the content of surface active oxygen species. As a result, the structure modifications of Ag by the addition of Cu strongly intensified the catalytic performance.

Effects of Zr substitution on soot combustion over cubic fluorite-structured nanoceria:Soot-ceria contact and interfacial oxygen evolution

Ceria is widely used as a catalyst for soot combustion,but effects of Zr substitution on the reaction mechanism is ambiguous.The present work elucidates effects of Zr substitution on soot combustion over cubic fluorite-structured nanoceria.The nanostructured CeO_(2),Ce_(0.92)Zr_(0.08)O_(2),and Ce_(0.84)Zr_(0.16)O_(2)composed of 5-6 nm crystallites display T_(m-CO2)(the temperature at maximum CO_2 yield)at 383,355,and 375℃under 10 vol.%O_(2)/N_(2),respectively.The size of agglomerate decreases from 165.5 to 51.9-57.3 nm,which is beneficial for the sootceria contact.Moreover,Zr increases the amount of surface oxygen vacancies,generating more active oxygen(O_(2)^-and O^(-))for soot oxidation.Thus,the activities of Ce_(0.92)Zr_(0.08)O_(2)and Ce_(0.84)Zr_(0.16)O_(2)in soot combustion are better than that of CeO_(2).Although oxygen vacancies promote the migration of lattice O~(2-),the enriched surface Zr also inhibits the mobility of lattice O^(2-).Therefore,the T_(m-CO2)of Ce_(0.84)Zr_(0.1)6 O_(2)is higher than that of Ce_(0.92)Zr_(0.08)O_(2).Based on reaction kinetic study,soot in direct contact with ceria preferentially decomposes with low activation energy,while the oxidation of isolated soot occurs through diffusion with high activation energy.The obtained findings provide new understanding on the soot combustion over nanoceria.

Optimized Pt-MnO_(x) interface in Pt-MnO_(x)/3DOM-Al_(2)O_(3)catalysts for enhancing catalytic soot combustion

The catalysts of three-dimensionally ordered macroporous(3 DOM)Al_(2)O_(3)-supported core-shell structured Pt@MnOx nanoparticles(3 DOM-Pt@MnO_(x)/Al_(2)O_(3))were successfully prepared by the gas bubbling-assisted membrane reduction-precipitation(GBMR/P)method.Pt@MnO_(x)core-shell nanoparticles(NPs)are highly dispersed on the inner surface of 3 DOM-Al_(2)O_(3)support.Pt@MnOx/3 DOM-Al_(2)O_(3)catalysts,which combine both advantages of high-efficiency soot-catalyst contact by 3 DOM-Al_(2)O_(3)structure and the abundant active sites by the optimized Pt-MnO_(x)interface,exhibit high catalytic activities for soot combustion,and the catalytic activities are strongly dependent on the thickness of MnO_(x)shell.Among the catalysts,3 DOM-Pt@MnO_(x)/Al_(2)O_(3)-1 catalyst with optimized Pt-MnO_(x)interface shows the highest catalytic activity for soot combustion,i.e.,its values of T_(50)and S_(CO_(2))^(m) are 351℃and98.6%,respectively.The highest density of Pt-MnO_(x)active sites for adsorptio n-activation of gaseous O_(2)is responsible for enhancing catalytic activity for soot combustion.Pt@MnOx/3 DOM-Al_(2)O_(3)catalysts are promising to practical applications for the emission reduction of soot particles.

Synthesis and catalytic performance of macroporous La1-xCexCoO3 perovskite oxide catalysts with high oxygen mobility for catalytic combustion of soot

The disordered macroporous-mesoporous La1-xCexCoO3 catalysts were prepared by complexcombustion method with ethylene glycol as complexing agent at relatively low calcination temperature.The samples were characterized by means of X-ray diffraction,N2 adsorption-ndash;desorption,Xray photoelectron spectroscopy,transmission electron microscopy,hydrogen temperature-programmed reduction and soot temperature-programmed reduction,and so on.The results show that the use of complexing agent and relatively low calcination temperature increase the specific surface area of the catalyst and have abundant pore structure.The Ce ions introduced into lattice of LaCoO3 mainly exist in the form of tetravalent.At the same time,Ce ions enhance the redox performance of the catalyst and the mobility of active oxygen species,which enhances the catalytic activity of the catalyst for soot combustion.The results of activity test show that La0.9Ce0.1CoO3 catalyst exhibits the highest activity in the absence of NO and NO2,and its T10,T50 and T90 are 371,444,and 497℃,respectively.At the same time,a possible reaction mechanism is proposed in this study based on the turnover frequency(TOF) calculated by isothermal anaerobic titrations,XPS and XRD results.

Catalytic combustion of soot over Ru-doped mixed oxides catalysts

We employed modified substrates as outer heterogeneous catalysts to reduce the soot originating from the incomplete diesel combustion. Here, we proposed that ceria（CeO2）-based catalysts could lower the temperature at which soot combustion occurred from 610 oC to values included in the operation range of diesel exhausts（270–400 oC）. Here, we used the sol-gel method to synthesize catalysts based on mixed oxides（ZnO：CeO2） deposited on cordierite substrates, and modified by ruthenium nanoparticles. The presence of ZnO in these mixed oxides produced defects associated with oxygen vacancies, improving thermal stability, redox potential, sulfur resistance, and oxygen storage. We evaluated the morphological and structural properties of the material by X-ray diffraction（XRD）, Brumauer-emmett-teller method（BET）, temperature programmed reduction（H2-TPR）, scanning electron microscopy（SEM）, and transmission electron microscopy（TEM）. We investigated how the addition of Ru（0.5 wt.%） affected the catalytic activity of ZnO：CeO2 in terms of soot combustion. Thermogravimetric analysis（TG/DTA） revealed that presence of the catalyst decreased the soot combustion temperature by 250 oC, indicating that the oxygen species arose at low temperatures, which was the main reason for the high reactivity of the oxidation reactions. Comparative analysis of soot emission by diffuse reflectance spectroscopy（DRS） showed that the catalyst containing Ru on the mixed oxide-impregnated cordierite samples efficiently oxidized soot in a diesel stationary motor： soot emission decreased 80%.

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_(0.64)Mn_(0.36) catalyst,which shows a maximum rate temperature(T_(m)) at 306℃ for CO_(2) production in TPO curve.Compared with non-catalytic soot combustion,the T_(m) decreases by mo re than 270℃.Syste matical characte rization 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 O_(2),the promoting effect of Mn^(4+)is not obvious.

Modification of CeO_2-ZrO_2 catalyst by potassium for NOx-assisted soot oxidation

Potassium-modified ceria-zirconia catalyst was synthesized by wetness impregnation method. The ageing treatment was performed in static air at 800℃ for 20 hr to evaluate the thermal stability of the catalyst. The catalysts were characterized by X-ray diffraction, BET surface area, oxygen storage capacity, NOx-temperature programmed desorption and soot-temperature programmed oxidation measurements. By introduction of potassium, the maximum soot oxidation rate temperature （Tin） of the ceria-zirconia based catalyst decreased from 525 to 428℃ in the presence of NO under a loose contact mode. The shift of Tm of the K-modified catalyst after ageing is only 15℃. The enhanced activity of the aged catalyst mainly lies in the promotional effect of potassium on the NOx/oxygen storage capacity as well as the soot-catalyst contact.

NO_x-assisted soot oxidation over K/CuCe catalyst

CeO2 and CuOx-CeO2 supported potassium catalysts were synthesized by wetness impregnation method. The catalysts were characterized by BET, NO-TPO, NOx-TPD and soot-TPO measurements. By the decoration of potassium and copper, the maximum soot combustion temperature of the ceria-based catalyst decreased to 338 and 379 °C in the presence and absence of NO under a loose contact mode, re- spectively. The pronouncedly enhanced NO oxidation ability by copper introduction and NOx storage capacity by potassium modif...