AMnO3 (A=La, Nd, Sm) and Sm1−xSrxMnO3 perovskites as combustion catalysts: structural, redox and catalytic properties

Catalytic combustion of methane has been investigated over AMnO₃ (A = La, Nd, Sm) and Sm_1−xSr_xMnO₃ (x = 0.1, 0.3, 0.5) perovskites prepared by citrate method. The catalysts were characterized by chemical analysis, XRD and TPR techniques. Catalytic activity measurements were carried out with a fixed bed reactor at T = 623–1023 K, space velocity = 40 000 N cm³ g⁻¹ h⁻¹, CH₄ concentration = 0.4% v/v, O₂ concentration = 10% v/v.

Specific surface areas of perovskites were in the range 13–20 m² g⁻¹. XRD analysis showed that LaMnO₃, NdMnO₃, SmMnO₃ and Sm_1−xSr_xMnO₃ (x = 0.1) are single phase perovskite type oxides. Traces of Sm₂O₃ besides the perovskite phase were detected in the Sm_1−xSr_xMnO₃ catalysts for x = 0.3, 0.5. Chemical analysis gave evidence of the presence of a significant fraction of Mn(IV) in AMnO₃. The fraction of Mn(IV) in the Sm_1−xSr_xMnO₃ samples increased with x. TPR measurements on AMnO₃ showed that the perovskites were reduced in two steps at low and high temperature, related to Mn(IV) → Mn(III) and Mn(III) → Mn(II) reductions, respectively. The onset temperatures were in the order LaMnO₃ > NdMnO₃ > SmMnO₃. In Sm_1−xSr_xMnO₃ the Sr substitution for Sm caused the formation of Mn(IV) easily reducible to Mn(II) even at low temperature. Catalytic activity tests showed that all samples gave methane complete conversion with 100% selectivity to CO₂ below 1023 K. The activation energies of the AMnO₃ perovskites varied in the same order as the onset temperatures in TPR experiments suggesting that the catalytic activity is affected by the reducibility of manganese. Sr substitution for Sm in SmMnO₃ perovskites resulted in a reduction of activity with respect to the unsubstituted perovskite. This behaviour was related to the reduction of Mn(IV) to Mn(II), occurring under reaction conditions, hindering the redox mechanism.     

A study of the abatement of VOC over V2O5–WO3–TiO2 and alternative SCR catalysts

The conversion of C3 organic compounds (propane, propene, 1- and 2-propanol, allyl alcohol, propanal, acrolein, acetone and 1- and 2-chloropropane) in the presence of excess oxygen has been investigated over two V–W–TiO₂ commercial SCR catalysts differing in the V content and over Mn–TiO₂ alternative SCR catalysts. V–W–Ti catalysts show poor activity in the oxidation of hydrocarbons and oxygenates and give significant amounts of partial oxidation products. Moreover they give rise to CO in excess of CO₂. The sample higher in V is more active. Mn–TiO₂ is definitely more active in oxidation of hydrocarbons and oxygenates, and produces, at total conversion, CO₂ as the only detectable product.

V–W–Ti catalysts are very active in dehydrochlorination of the two 2-chloropropane isomers and retain the same oxidation activity also in the presence of HCl. On the contrary, Mn-based catalysts in the presence of chlorocarbons convert into dehydrochlorination catalysts but lose their catalytic activity in oxidation. V–W–Ti catalysts can be used in Cl-containing atmospheres while Mn–TiO₂ can be proposed for DeNO_x and VOC abatement in Cl-free atmospheres such as for diesel engine exhaust gas purification.     

AFeO3 (A=La, Nd, Sm) and LaFe1−xMgxO3 perovskites as methane combustion and CO oxidation catalysts: structural, redox and catalytic properties

Catalytic methane combustion and CO oxidation were investigated over AFeO₃ (A=La, Nd, Sm) and LaFe_1−xMg_xO₃ (x=0.1, 0.2, 0.3, 0.4, 0.5) perovskites prepared by citrate method and calcined at 1073 K. The catalysts were characterized by X-ray diffraction (XRD). Redox properties and the content of Fe⁴⁺ were derived from temperature programmed reduction (TPR). Specific surface areas (SA) of perovskites were in 2.3–9.7 m² g⁻¹ range. XRD analysis showed that LaFeO₃, NdFeO₃, SmFeO₃ and LaFe_1−xMg_xO₃ (x·0.3) are single phase perovskite-type oxides. Traces of La₂O₃, in addition to the perovskite phase, were detected in the LaFe_1−xMg_xO₃ catalysts with x=0.4 and 0.5. TPR gave evidence of the presence in AFeO₃ of a very small fraction of Fe⁴⁺ which reduces to Fe³⁺. The fraction of Fe⁴⁺ in the LaFe_1−xMg_xO₃ samples increased with increasing magnesium content up to x=0.2, then it remained nearly constant. Catalytic activity tests showed that all samples gave methane and CO complete conversion with 100% selectivity to CO₂ below 973 and 773 K, respectively. For the AFeO₃ materials the order of activity towards methane combustion is La>Nd>Sm, whereas the activity, per unit SA, of the LaFe_1−xMg_xO₃ catalysts decreases with the amount of Mg at least for the catalysts showing a single perovskite phase (x=0.3). Concerning the CO oxidation, the order of activity for the AFeO₃ materials is Nd>La>Sm, while the activity (per unit SA) of the LaFe_1−xMg_xO₃ catalysts decreases at high magnesium content.     

Low-temperature SCR of NO with NH3 over AC/C supported manganese-based monolithic catalysts

Metal oxide/active carbon/ceramic (MO_x/AC/C) monolithic catalysts were prepared by impregnation method for selective catalytic reduction (SCR) of NO_x with NH₃ at low-temperature, and they also had been characterized by elemental analysis, N₂-BET, XRD, SEM and NO-TPD. The adsorption capability of the monolithic catalyst was greatly enhanced due to the attached active carbon. An ultrasonic treatment was used to improve the impregnation process, and which can increase their catalytic activities. More than 90% NO_x conversion could be achieved over the Mn-based monolithic catalysts at low-temperature, and which could be improved further by doping Ce, from 30% to 78% at 100 °C. Mn–Fe–Ce and Mn–V–Ce monolithic catalysts had better tolerance to SO₂ than Mn or Mn–Ce monolithic catalysts.     

Methane combustion and CO oxidation on LaAl1−xMnxO3 perovskite-type oxide solid solutions

Structural, redox and catalytic deep oxidation properties of LaAl_1−xMn_xO₃ (x=0.0, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0) solid solutions prepared by the citrate method and calcined at 1073 K were investigated. XRD analysis showed that all the LaAl_1−xMn_xO₃ samples are single phase perovskite-type solid solutions. Particle sizes and surface areas (SA) are in the 280–1180 Å and 4–33 m² g⁻¹ ranges, respectively. Redox properties and the content of Mn⁴⁺ were derived from temperature programmed reduction (TPR) with H₂. Two reduction steps are observed by TPR for pure LaMnO₃, the first attributed to the reduction of Mn⁴⁺ to Mn³⁺ and the second due to complete reduction of Mn³⁺ to Mn²⁺. The presence of Al in the LaAl_1−xMn_xO₃ solid solutions produces a strong promoting effect on the Mn⁴⁺→Mn³⁺ reducibility and inhibits the further reduction to Mn²⁺. Both for methane combustion and CO oxidation all Mn-containing perovskites are much more active than LaAlO₃, so pointing to the essential role of the transition metal ion in developing highly active catalysts. Partial dilution with Al appears to enhance the specific activity of Mn sites for methane combustion.     

Effect of Co content on the catalytic activity of CoSiBEA zeolite in the selective catalytic reduction of NO with ethanol: Nature of the cobalt species

The effect of Co content on the catalytic activity of CoSiBEA zeolites in the selective catalytic reduction (SCR) of NO with ethanol is investigated. The Co_xSiBEA zeolites (x = 0.3, 0.7, 3.6 and 6.75 Co wt.%) are prepared by a two-step postsynthesis method which allows to control the introduction of cobalt into zeolite and thus to obtain catalysts with specific Co sites. The nature of the active sites is characterized by XRD, diffuse reflectance UV–vis, H₂-TPR and XPS.

The catalytic activity of Co_xSiBEA strongly depends on the nature and environment of Co species. Zeolites with isolated lattice tetrahedral Co(II) (Co_0.3SiBEA and Co_0.7SiBEA samples) are active in SCR of NO with ethanol with selectivity toward N₂ exceeding 85% for NO conversion from 20 to 70%. When additional isolated extra-lattice octahedral Co(II) species appear (Co_3.6SiBEA sample), the full oxidation of ethanol by dioxygen becomes a very important reaction pathway. In presence of additional cobalt oxides (Co_6.75SiBEA sample), the activity and selectivity toward N₂ substantially change and full oxidation of ethanol to CO₂ is the main reaction pathway and full NO oxidation also takes place in the temperature range 550–775 K. The lack of correlation between the activity in SCR of NO with ethanol and NO oxidation to NO₂ suggests that the two reactions are more competitive than sequential.     

Catalytic properties of metal loaded silica-pillared manganese titanate for CO oxidation

Semiconducting microporous solids were prepared by pillaring layer structured manganese titanate, Rb_xMn_xTi_2−xO₄ (x=0.75) with silica. These solids were then chemically modified by loading various kinds of metals by cation exchange and impregnation methods. The samples with copper loaded by the impregnation method showed a high catalytic activity for the oxidation of carbon monoxide with oxygen. The highest activity was obtained for the sample with the copper content, [Cu]/[Cu+Mn]≈0.3; the CO conversion of more than 90% was achieved at 60°C. The high catalytic activity is attributed to the microporous pillared structure with a high porosity and the charge transfer between copper and the manganese titanate layers.     

Application of Ce0.33Zr0.63Pr0.04O2-supported noble metal catalysts in the catalytic wet air oxidation of 2-chlorophenol: Influence of the reaction conditions

In this work, different procedures, namely carbonate coprecipitation and modified solid–solid diffusion, were used to prepare hexaaluminate samples, unsupported or supported onto θ-Al₂O₃. These samples were used as catalyst for the methane total oxidation as synthesized or after impregnation of 1 wt% Pd. It was observed that the modified solid–solid diffusion procedure is an efficient method to obtain the hexaaluminate structure. At a theoretical ratio x of hexaaluminate onto Al₂O₃ less than 0.6 (xLa_0.2Sr_0.3Ba_0.5MnAl₁₁O₁₉ + (1−x)·Al₂O₃, with x = 0.25, 0.60), samples with high specific surface area and θ-Al₂O₃ structure are then obtained. Large differences in catalytic activity can be observed among the series of sample synthesized. All the pure oxide samples (i.e. without palladium) present low catalytic activity for methane total oxidation compared to a reference Pd/Al₂O₃ catalyst. The highest activity was obtained for the samples presenting a θ-Al₂O₃ structure (with x = 0.60) and a high surface area. Impregnation of 1 wt% palladium resulted in an increase in catalytic activity, for all the solids synthesized in this work. Even if the lowest light-off temperature was obtained on the reference sample, similar methane conversions at high temperature (700 °C) were obtained on the stabilized θ-Al₂O₃ solids (x = 0.25, 0.60). Moreover, the reference sample is found to strongly deactivate with reaction time at the temperature of test (700 °C), due to a progressive reduction of the PdO_x active phase into the less active Pd° phase, whereas excellent stabilities in reaction were obtained on the pure and palladium-doped hexaaluminate and supported θ-Al₂O₃ samples. This clearly showed the beneficial effect of the support for the stabilization of the PdO_x active phase at high reaction temperature. These properties are discussed in term of oxygen transfer from the support to the palladium particle. Oxygen transfer is directly related to the Mn³⁺/Mn²⁺ redox properties (in the case of the hexaaluminate and stabilized θ-Al₂O₃ samples), that allows a fast reoxidation of the metal palladium sites since palladium sites reoxidation cannot occur directly by gaseous dioxygen adsorption and dissociation on the surface.     

A study of anatase–supported Mn oxide as catalysts for 2-propanol oxidation

Several samples of TiO₂ (anatase)-supported Mn oxide XMn–TiO₂ (with X = 0.5, 1.0, 1.5 and 2.0, the theoretical monolayer fractions) have been prepared by a wet impregnation method and characterised by conventional techniques. Mn oxide was found to be well dispersed on the support surface as Mn³⁺species, while part of it is stabilised into the TiO₂ bulk as Mn⁴⁺species. This cation seem to hinder the support sintering and to favour the anatase to rutile phase transition at higher temperatures. Mn oxides supported on TiO₂ are stable and retain medium-high surface area in the 600–900 K range. They are less active than pure Mn oxides in the isopropanol oxidation but, above 600 K, allow complete oxidation of isopropanol to CO₂ only. FT–IR studies and the GC–MS analysis of some intermediate products allow us to confirm the 2-propanol total oxidation occurs through the previously proposed 2-propoxide/acetate/formate surface pathway.     

Catalytic oxidation of VOCs on Au/Ce-Ti-O

Ce_xTi_1−xO₂ oxides have been synthesised by sol–gel method with x varying from 0 to 0.3 and characterised by XRD and TPR. The structure of oxides changes with the Ce/Ti molar ratio. The presence of ceria in Ce-Ti oxides inhibits the phase transition from anatase to rutile. When x = 0.3 (Ce_0.3Ti_0.7O₂ sample), the solid presents an amorphous state. The TPR results indicate that the presence of Ti enhances the reducibility of cerium oxide species. Catalytic oxidation of propene is investigated on Ce-Ti oxides and the better conversion is obtained with Ce_0.3Ti_0.7O₂ but the CO₂ selectivity reaches 63% at 400 °C. Gold is then deposited on theses oxides to improve the catalytic activity. On the basis of characterisation data (H₂ TPR), it has been suggested that gold influences the reduction of the Ce-Ti oxide support and the catalytic activity to the propene oxidation. Thus, Au/Ce-Ti-O system catalysts are promising catalysts for propene oxidation.     

Development of new catalysts for N2O-decomposition from adipic acid plant

Direct decomposition of N₂O was investigated using simulated and real industrial gas stream coming from an adipic acid plant. Two different kinds of catalysts were studied: (i) LaB_1−xB′_xO₃ and CaB_1−xCu_xO₃ (B = Mn, Fe and B′ = Cu, Ni) perovskites (PVKs) and (ii) supported PVKs (10 or 20 wt.%) on γ-Al₂O₃ and CeO₂–ZrO₂. The structural modifications induced by the composition of PVK samples affect the catalytic performances: mixed oxide formation in CaMn_0.7Cu_0.3O₃ samples allows to reach the highest values of N₂O conversion while the effect of PVK phases is more controversial. The importance of copper on catalytic activities is confirmed by the investigation on CaMn_1−xCu_xO₃ samples. The best results were obtained with a CaMn_0.6Cu_0.4O₃ catalyst calcined at 700 °C for 5 h, in which the presence of copper maximises the Ca₃CuMnO₆ phase formation. The increase in Cu-content produces a large segregation of CuO despite PVK formation. The best catalyst was tested using industrial gas stream, showing good stability also in the presence of H₂O and O₂ (8% v/v ) after 1400 h on-stream. To increase surface area, Cu-containing PVKs were deposed on γ-Al₂O₃ and CeO₂–ZrO₂, and this latter has been recognised as the best support. Indeed, the activity of the PVKs supported on ceria–zirconia is comparable to and even better than that of the bulk catalysts. A possible explanation regards the support contribution in terms of activity and/or promotion of O₂ mobility which enhances the overall activity of the catalyst.     

Oxidation of CO over Ru containing perovskite type oxides

Perovskite type catalysts La_0.7Sr_0.3Cr_1−xRu_xO₃ (0.025 ≤ x ≤ 0.100) were synthesized by annealing a mixture of metal oxides and carbonates gradually up to 1000 °C in air, and characterized by XRPD, XPS, TPD, SEM-EDS and the van der Pauw method. The CO oxidation activity was investigated in a differential recycle reactor. According to the XRPD results, all samples achieved a perovskite structure, with a small presence of SrCrO₄ phase. The XPS results revealed that the surface composition of all samples differed considerably from the stoichiometric value with an important segregation of strontium and mainly ruthenium with regard to chromium at the surface of the catalysts. The sharp decrease of resistivity with increasing surface concentration of ruthenium and the independence of the resistivity on temperature for the sample with x = 0.100 imply the possible presence of SrRuO₃, La–Ru–O and highly dispersed RuO₂ (invisible by XRPD), known as good electric conductors, at the surface. The CO oxidation activity increases with increasing the degree of substitution (x). The surface concentrations of ruthenium are almost the same in the samples with x = 0.075 and 0.100. Those samples showed the similar values of resistivity in whole investigated temperature range and very close CO oxidation activity, which indicates that the concentration of Ru⁴⁺ in the surface region and its stability are determining factors for the CO oxidation activity. The main results of this study are that ruthenium perovskites have a high thermal stability and CO oxidation activity.     

Oxidation of unsymmetrical dimethylhydrazine over heterogeneous catalysts Solution of environmental problems of production, storage and disposal of highly toxic rocket fuels

The catalytic oxidation of unsymmetrical dimethylhydrazine (UDMH) by air has been studied in a vibro-fluidized catalyst bed laboratory kinetic setup over catalysts Cu_xMg_1−xCr₂O₄/γ-Al₂O₃, 32.9%Ir/γ-Al₂O₃ and β-Si₃N₄ in a temperature range 150–400 °C. The catalyst Cu_xMg_1−xCr₂O₄/γ-Al₂O₃ was found to be optimal regarding high yields of CO₂ and low yields of NO_x. A probable mechanism of UDMH heterogeneous catalytic oxidation is proposed. Catalyst Cu_xMg_1−xCr₂O₄/γ-Al₂O₃ has been further used in the pilot plant specially designed for the destruction of UDMH. Results of testing the main fluidized bed catalytic reactor for UDMH oxidation and the reactor for selective catalytic reduction of NO_x with NH₃ are presented. These results prove that the developed UDMH destruction technology is highly efficient and environmentally safe.     

Synthesis, characterization and catalytic activity for NO–CO reaction of Pd–(La, Sr)2MnO4 system

La_xSr_2−xMnO₄ (0 ≤ x ≤ 0.8) oxides were synthesized and single-phase K₂NiF₄-type oxides were obtained in the range of 0.1 ≤ x < 0.5. The catalytic activity of La_xSr_2−xMnO₄ for NO–CO reaction increased with increasing x in the range of solubility limit of La. La_0.5Sr_1.5MnO₄ showed the highest activity among La_xSr_2−xMnO₄ prepared in this study, but its activity was inferior to perovskite-type La_0.5Sr_0.5MnO₃. Among the Pd-loaded catalysts, however, Pd/La_0.8Sr_1.2MnO₄ showed the higher activity and the selectivity to N₂ than Pd/La_0.5Sr_0.5MnO₃ and Pd/γ-Al₂O₃. The excellent catalytic performance of Pd/La_0.2Sr_1.2MnO₄ could be ascribable to the formation of SrPd₃O₄ which was detected by XRD in the catalyst but not in the other two catalysts.     

Rh–La(Mn,Co)O3 monolithic catalysts for the combustion of methane under fuel-rich conditions

Novel Rh–La(Mn,Co)O₃ structured catalysts were developed for the partial oxidation of methane to syngas intended as a preliminary conversion step in combustion systems such as power turbines and utility burners employing a fuel-rich fuel-lean approach to reduce NO_x formation. Active components were impregnated on La–γ-Al₂O₃ washcoated honeycomb monoliths and the catalysts were characterised by BET, SEM/EDS, H₂-TPR, and in situ FT-IR under reaction conditions. Catalytic partial oxidation of methane was tested under both pseudo-isothermal and pseudo-adiabatic conditions showing that the process can be conducted with high yield and selectivity: improved and stable performances were found especially in the case of Rh–LaMnO₃ catalyst, due to the synergism between active sites and to the stabilization of the noble metal.     

CO oxidation over CuOx-CeO2-ZrO2 catalysts: Transient behaviour and role of copper clusters in contact with ceria

The effects of ZrO₂ content on the CO oxidation activity in a series of CuO_x/Ce_xZr_1−xO₂ (x = 0, 0.15, 0.5, 0.7 and 1) catalysts were investigated, both in the absence and in the presence of H₂, i.e. preferential CO oxidation—PROX. The investigation was performed under light-off conditions to focus the effects of transients and shut-down/start-up cycles on the performance; such phenomena are expected to affect the activity of PROX catalysts in small/delocalised fuel reformers. Evidence has been obtained for a transition from an “oxidized” towards a “reduced” state of the catalyst under the simulated PROX reaction conditions as a function of the reaction temperature, leading to different active species under the reaction conditions. Both CO oxidation activity and PROX selectivity appear to be affected by this process. IR characterisation of the surface copper species suggests an important role of reduced cerium sites in close contact with copper clusters on the CO oxidation activity at low temperatures.     

Oxygen storage capacity of La1−xBO3 perovskites (with A′ = Sr, Ce; B = Co, Mn)—relation with catalytic activity in the CH4 oxidation reaction

The aim of this work was to study the effect of cation-substitution on the reducibility of the perovskite, as well as the effect on the catalytic activity for the CH₄ oxidation reaction. Six perovskites (LaCoO₃, LaMnO₃, La_1−xSr_xMnO₃ (x = 0.2, 0.4), and La_1−xCe_xMnO₃ (x = 0.05, 0.1)) were synthesized by reactive grinding. The reducibility of the perovskite was studied by means of the oxygen storage capacity (OSC) measurement. OSC was performed at different temperatures on LaCoO₃ and LaMnO₃, in order to elucidate the different mechanisms of reduction involved at each temperature. The substituted samples showed that reduction profile is modified at high-substitution degrees; however, no differences were observed on the OSC values (amount of most active oxygen, calculated after one pulse of CO) between the pure lanthanum sample and the substituted ones.

Tested in the CH₄ oxidation reaction, the LaCoO₃ sample was found to present a little higher activity than LaMnO₃, even if the cobalt-based sample presented a smaller specific surface area. Moreover, all the substituted samples presented very slightly higher activities than the pure LaMnO₃ solid. Because of the supposed redox oxidation mechanism (Mars-Van-Krevelen), this agrees well with the OSC results obtained for the reducibility of the manganese on these samples, by which it was observed that substitution does not clearly affect the immediate reduction of the manganese.     

Synthesis and properties of lanthanum hexaaluminate ceramic La1−xCaxAl11−y−zMgyTizO18

The aim of the present work is to obtain ceramic materials with a hexagonal structure and high density, hardness and mechanical strength at lower synthesis temperature. Ceramic samples with nominal composition La_1−xCa_xAl_11−y−zMg_yTi_zO₁₈ (x=0–1; y=0–3; z=0–3,5) are prepared. The samples are sintered at temperature 1500 °C by one-stage and two-stage ceramic technology. By X-ray diffraction and scanning electron microscopy, predominant phase LaAl₁₁O₁₈ and second phases LaAlO₃ and -Al₂O₃ are identified. Ceramic materials are characterized with high physico-mechanical properties and may be find application for production of mill bodies and materials for immobilization of nuclear waste.     

Preparation of CexZr1−xO2 (x = 0.75, 0.62) solid solution and its application in Pd-only three-way catalysts

Nanoparticles of Ce_xZr_1−xO₂ (x = 0.75, 0.62) were prepared by the oxidation-coprecipitation method using H₂O₂ as an oxidant, and characterized by N₂ adsorption, XRD and H₂-TPR. Ce_xZr_1−xO₂ prepared had single fluorite cubic structure, good thermal stability and reduction property. With the increasing of Ce/Zr ratio, the surface area of Ce_xZr_1−xO₂ increased, but thermal stability of Ce_xZr_1−xO₂ decreased. The surface area of Ce_0.62Zr_0.38O₂ was 41.2 m²/g after calcination in air at 900 °C for 6 h. TPR results showed the formation of solid solution promoted the reduction of CeO₂, and the reduction properties of Ce_xZr_1−xO₂ were enhanced by the cycle of TPR-reoxidation. The Pd-only three-way catalysts (TWC) were prepared by the impregnation method, in which Ce_0.75Zr_0.25O₂ was used as the active washcoat and Pd loading was 0.7 g/L. In the test of Air/Fuel, the conversion of C₃H₈ was close to 100% and NO was completely converted at λ < 1.025. The high conversion of C₃H₈ was induced by the steam reform and dissociation adsorption reaction of C₃H₈. Pd-only catalyst using Ce_0.75Zr_0.25O₂ as active washcoat showed high light off activity, the reaction temperatures (T₅₀) of 50% conversion of CO, C₃H₈ and NO were 180, 200 and 205 °C, respectively. However, the conversions of C₃H₈ and NO showed oscillation with continuously increasing the reaction temperature. The presence of La₂O₃ in washcoat decreased the light off activity and suppressed the oscillation of C₃H₈ and NO conversion. After being aged at 900 °C for 4 h, the operation windows of catalysts shifted slightly to rich burn. The presence of La₂O₃ in active washcoat can enhance the thermal stability of catalyst significantly.     

Ce1−xCuxO2−x/Al2O3/FeCrAl catalysts for catalytic combustion of methane

A series of the Ce_1−xCu_xO_2−x/Al₂O₃/FeCrAl catalysts (x = 0–1) were prepared. The structure of the catalysts was characterized using XRD, SEM and H₂-TPR. The catalytic activity of the catalysts for the combustion of methane was evaluated. The results indicated that in the Ce_1−xCu_xO_2−x/Al₂O₃/FeCrAl catalysts the surface phase structure were the Ce_1−xCu_xO_2−x solid solution, -Al₂O₃ and γ-Al₂O₃. The surface particle shape and size were different with the variety of the molar ratio of Ce to Cu in the Ce_1−xCu_xO_2−x solid solution. The Cu component of the Ce_1−xCu_xO_2−x/Al₂O₃/FeCrAl catalysts played an important role to the catalytic activity for the methane combustion. There were the stronger interaction among the Ce_1−xCu_xO_2−x solid solution and the Al₂O₃ washcoats and the FeCrAl support.