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1.
Small Co clusters ( d<10 nm) supported over mixed La–Co–Fe perovskites were successfully synthesized. These catalysts were active for Fischer–Tropsch (FT). Depending on the Co to Fe ratios the mixed perovskite exhibited two different forms: the rhombohedral phase of LaCoO 3 is maintained for the mixed perovskite when x>0.5, the orthorhombic phase of LaFeO 3 is found for x<0.5. Interestingly only one of these structures is active for the FT reaction: the orthorhombic structure. This is most likely due to the capacity of this material to maintain its structure even with a high number of cation vacancies. These cations (mostly Co) were on purpose extracted and reduced. Magnetic measurements clearly showed their metallic nature. Rhombohedral Co–Fe mixed perovskites ( x≥0.5) cannot be used as precursors for Fischer–Tropsch catalysts: their partial reduction only consists in a complete reduction of Co 3+ into Co 2+. The partial reduction of orthorhombic perovskites (x<0.5) leads to active Fischer–Tropsch (FT) catalysts by formation of a metal phase well dispersed on a cation-deficient perovskite. The FT activity is related to the stability of the precursor perovskite. When initially calcined at 600 °C, a maximum of 8.6 wt.% of Co0 can be extracted from LaCo0.40Fe0.60O3 (compared to only 2 wt.% after calcination at 750 °C). The catalyst is then composed of Co0 particles of 10 nm on a stable deficient perovskite LaCo0.053+Fe0.603+O2.40. Catalytic tests showed that up to 70% in the molar selectivity for hydrocarbons was obtained at 250 °C, 40% of which was composed of the C2–C4 fraction. 相似文献
2.
In order to elucidate the superior start-up activity of LaFePdO x catalysts in practical automotive emission control, the redox property of Pd species in a Perovskite-type LaFe 0.95Pd 0.05O 3 catalyst was studied at temperatures ranging from 100 to 400 °C using X-ray spectroscopic techniques. In a reductive atmosphere, and even at temperatures as low as 100 °C, Pd 0 species is partially segregated out onto the catalyst surface from the B-site of the Perovskite-type matrix of LaFe 0.95Pd 0.05O 3. Passing through successive oxidizing atmospheres, the segregated Pd 0 species is re-oxidized into Pd 2+ at 200–300 °C. The formation of a solid solution between the re-oxidized Pd species and the Perovskite-type matrix begins to be seen at around 400 °C and accelerates at higher temperatures. Thus a quasi-reversible redox reaction between the surface Pd 0 and the cationic Pd in the LaFe 0.95Pd 0.05O 3 matrix takes place. The start-up activity of LaFePd xO x catalysts can be attributed to Pd 0 that segregates under the reductive atmosphere which is a natural part of the redox fluctuation in automotive exhaust gases at 100–200 °C. 相似文献
3.
Supported LaCoO 3 perovskites with 10 and 20 wt.% loading were obtained by wet impregnation of different Ce 1−xZr xO 2 ( x = 0–0.3) supports with a solution prepared from La and Co nitrates, and citric acid. Supports were also prepared using the “citrate method”. All materials were calcined at 700 °C for 6 h and investigated by N 2 adsorption at −196 °C, XRD and XPS. XRD patterns and XPS measurements evidenced the formation of a pure perovskite phase, preferentially accumulated at the outer surface. These materials were comparatively tested in benzene and toluene total oxidation in the temperature range 100–500 °C. All catalysts showed a lower T50 than the corresponding Ce 1−xZr xO 2 supports. Twenty weight percent LaCoO 3 catalysts presented lower T50 than bulk LaCoO 3. In terms of reaction rates per mass unit of perovskite calculated at 300 °C, two facts should be noted (i) the activity order is more than 10 times higher for toluene and (ii) the reverse variation with the loading as a function of the reactant, a better activity being observed for low loadings in the case of benzene. For the same loading, the support composition influences drastically the oxidative abilities of LaCoO 3 by the surface area and the oxygen mobility. 相似文献
4.
Supported LaCoO 3 perovskites with 10 wt.% loading were prepared by impregnation of different supports containing ceria with a solution of La and Co nitrates and citric acid. All precursors were calcined at 700 °C for 5 h. XRD investigations indicated the perovskite formation via “citrate” precursor only on ceria support. All catalysts were tested for toluene total oxidation in the temperature range 100–600 °C. In spite of a large surface area, alumina-supported perovskites showed a lower global activity. It appears then the necessity of the presence of a perovskite phase for good oxidative activity. In terms of reaction rates higher reaction rates per perovskite weight were observed for all supported catalysts when compared to bulk LaCoO 3. 相似文献
5.
The nucleation and growth of Pd clusters in mordenite were investigated using in situ extended X-ray absorption fine structure (EXAFS) spectroscopy and Fourier transform infrared (FTIR) spectroscopy of absorbed CO. Calcination of [Pd(NH 3) 4] 2+-exchanged mordenite at 350°C in O 2 results in decomposition of the amine complex and formation of square-planar Pd 2+ oxo species within the mordenite pores. Reduction of these species at 150°C in H 2 yields Pd clusters with an average nuclearity of 3. On an average two 2.22 Å Pd-O bonds are associated with each Pd 3 cluster; we infer that this interaction serves to anchor the clusters within the pores. After reduction at 150°C, the FTIR spectrum of irreversibly adsorbed CO is indicative of a mixture of Pd +, Pd δ+, and Pd 0 carbonyl species. Reduction at 350°C produces larger intrazeolitic Pd clusters (average nuclearity of 6) that exhibit only a weak interaction with the mordenite, as evidenced by their facile aggregation in the presence of CO at 30°C. Reduction at 450°C yields large 20 Å Pd clusters that we infer are located on external mordenite surfaces or locally disrupt the intracrystalline structure. 相似文献
6.
Supported LaCoO 3 perovskites with 2, 5, 10, 15, 20 and 30 wt.% loading were prepared by impregnation of a Ce 0.8Zr 0.2O 2 support (40 m 2 g −1) with: (i) a solution of La and Co nitrates and (ii) a “citrate” solution, namely containing La and Co nitrates, and citric acid. All precursors were decomposed and calcined at 700 °C for 5 h. XRD investigations indicated the formation of a pure perovskite phase only if citrates were used. These materials were tested as catalysts for methane combustion in the temperature range 300–700 °C. All catalysts showed a lower T50 (the temperature at which the conversion level of methane is 50%) than the Ce 0.8Zr 0.2O 2 support or non-supported LaCoO 3. The activity increased continuously with the perovskite loading. The samples prepared from citrates were slightly more active than from nitrates. This is due to a more homogeneous surface, as indicated by XPS measurements. The presence of a well-characterized perovskite phase (as opposed to highly dispersed elements) seems necessary for good activity. A higher reaction rate per perovskite weight is observed for low loadings when compared to bulk LaCoO 3, but the variation with perovskite loading presents a breakpoint, suggesting complex interactions in the catalysts or in the oxidation mechanism. In spite of the experimental impossibility to evaluate the area developed by the supported perovskite, an approximative approach strongly suggests a synergy between the support and supported species. 相似文献
7.
Pechini route (M.P. Pechini. U.S. Patent no. 3,330,697 (1967)) was used for supporting perovskite – like systems LaBO 3 (B = Mn, Fe, Co, Ni, Cu) on thin-wall (0. 35 mm) cordierite honeycomb support with low thermal expansion coefficient to prepare stable to thermal shocks supported catalysts for high-temperature processes of ammonia oxidation into NO in nitric acid production. In this preparation route, perovskites (2–6%) have nearly uniform distribution in the walls as well as form surface grainy perovskite layer 2–3 μm thick that may be also important for the high temperature processes occurring at short contact times. Cordierite supported lanthanum manganite and cobaltite are the most active in the reaction of ammonia oxidation into NO especially when supported twice or on a secondary sublayer (Ln 2O 3, ZrO 2, MeO, LaBO 3). 相似文献
8.
Nanometer perovskite-type oxides La 1−xSr xMO 3−δ (M = Co, Mn; x = 0, 0.4) have been prepared using the citric acid complexing-hydrothermal-coupled method and characterized by means of techniques, such as X-ray diffraction (XRD), BET, high-resolution scanning electron microscopy (HRSEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), and temperature-programmed reduction (TPR). The catalytic performance of these nanoperovskites in the combustion of ethylacetate (EA) has also been evaluated. The XRD results indicate that all the samples possessed single-phase rhombohedral crystal structures. The surface areas of these nanomaterials ranged from 20 to 33 m 2 g −1, the achievement of such high surface areas are due to the uniform morphology with the typical particle size of 40–80 nm (as can be clearly seen in their HRSEM images) that were derived with the citric acid complexing-hydrothermally coupled strategy. The XPS results demonstrate the presence of Mn 4+ and Mn 3+ in La 1−xSr xMnO 3−δ and Co 3+ and Co 2+ in La 1−xSr xCoO 3−δ, Sr substitution induced the rises in Mn 4+ and Co 3+ concentrations; adsorbed oxygen species (O −, O 2−, or O 22−) were detected on the catalyst surfaces. The O 2-TPD profiles indicate that Sr doping increased desorption of the adsorbed oxygen and lattice oxygen species at low temperatures. The H 2-TPR results reveal that the nanoperovskite catalysts could be reduced at much lower temperatures (<240 °C) after Sr doping. It is observed that under the conditions of EA concentration = 1000 ppm, EA/oxygen molar ratio = 1/400, and space velocity = 20,000 h −1, the catalytic activity (as reflected by the temperature ( T100%) for EA complete conversion) increased in the order of LaCoO 2.91 ( T100% = 230 °C) ≈ LaMnO 3.12 ( T100% = 235 °C) < La 0.6Sr 0.4MnO 3.02 ( T100% = 190 °C) < La 0.6Sr 0.4CoO 2.78 ( T100% = 175 °C); furthermore, there were no formation of partially oxidized by-products over these catalysts. Based on the above results, we conclude that the excellent catalytic performance is associated with the high surface areas, good redox properties (derived from higher Mn 4+/Mn 3+ and Co 3+/Co 2+ ratios), and rich lattice defects of the nanostructured La 1−xSr xMO 3−δ materials. 相似文献
9.
The active site in ZSM-5 zeolite-supported palladium, which shows the catalytic activity for NO reduction with methane as a reducing agent, has been investigated qualitatively and quantitatively by means of NO chemisorption and NaCl titration, comparing with PdO supported on silica. Palladium species in 0.4 wt.% Pd loaded H-ZSM-5 can adsorb NO equimolarly after calcination at 773 K, and almost all the NO was desorbed at around 673 K, while the palladium species on PdO/SiO 2 hardly adsorbed NO. The palladium species in Pd(0.4)/H-ZSM-5 are ion-exchangeable with Na + in NaCl solution, indicating that they exist in a cationic state of an isolated Pd 2+. This method for quantitative analysis of the isolated Pd 2+ cations is named as ‘NaCl titration’. The amount of the isolated Pd 2+ cationic species increased with increasing palladium content on Pd/H-ZSM-5, and PdO co-existed above 1 wt.%. The amount of the isolated Pd 2+ cation was unchanged after the reaction of NO 2–CH 4, NO 2–CH 4–O 2, or CH 4–O 2 at 673 K, while the adsorbed amount of NO per the Pd 2+ as determined by NO-TPD decreased after the NO 2–CH 4–O 2 reaction. It was found by NaCl titration that the catalytic activity of Pd/H-ZSM-5 for NO 2–CH 4–O 2 reaction increased with increasing amount of the isolated Pd 2+ cationic species up to 0.7 wt.%, while the increase in the amount of PdO led to decrease in selectivity towards NO 2 reduction. The palladium species that are active and selective for NO reduction with CH 4 will be proposed. 相似文献
10.
Well crystallised aluminium borate Al 18B 4O 33 has been synthesised from alumina and boric acid with a BET area of 18 m 2/g after calcination at 1100 °C. Afterwards, 2 wt.% Pd/Al 18B 4O 33 was prepared by conventional impregnation of Pd(NO 3) 2 aqueous solution and calcination in air at 500 °C. The catalytic activity of Pd/Al 18B 4O 33 in the complete oxidation of methane was measured between 300 and 900 °C and compared with that of Pd/Al 2O 3. Pd/Al 18B 4O 33 exhibited a much lower activity than Pd/Al 2O 3 when treated in hydrogen at 500 °C or aged in O 2/H 2O (90:10) at 800 °C prior to catalytic testing. Surprisingly, a catalytic reaction run up to 900 °C in the reaction mixture induced a steep increase of the catalytic activity of Pd/Al 18B 4O 33 which became as active as Pd/Al 2O 3. Moreover, the decrease of the catalytic activity observed around 750 °C for Pd/Al 2O 3 and attributed to PdO decomposition into metallic Pd was significantly shifted to higher temperatures (820 °C) in the case of Pd/Al 18B 4O 33. The existence of two distinct types of PdO species formed on Al 18B 4O 33 and being, respectively, responsible for the improvement of the activity at low and high temperature was proposed on the basis of diffuse reflectance spectroscopy and temperature-programmed desorption of O 2. 相似文献
11.
CO and CH 4 combined oxidation tests were performed over a Pd (70 g/ft 3)/Co 3O 4 monolithic catalyst in conditions of GHSV = 100,000 h −1 and feed composition close to that of emission from bi-fuel vehicles. The effect of SO 2 (5 ppm) on CO and CH 4 oxidation activity under lean condition ( λ = 2) was investigated. The presence of sulphur strongly deactivated the catalyst towards methane oxidation, while the poisoning effect was less drastic in the oxidation of CO. Saturation of the Pd/Co 3O 4 catalytic sites via chemisorbed SO 3 and/or sulphates occurred upon exposure to SO 2. A treatment of regeneration to remove sulphate species was attempted by performing a heating/cooling cycle up to 900 °C in oxidizing atmosphere. Decomposition of PdO and Co 3O 4 phases at high temperature, above 750 °C, was observed. Moreover, sintering of Pd 0 and PdO particles along with of CoO crystallites takes place. 相似文献
12.
A 5 wt% CoO x/TiO 2 catalyst has been used to study the effect of calcination temperature on the activity of this catalyst for CO oxidation at 100 °C under a net oxidizing condition in a continuous flow type fixed-bed reactor system, and the catalyst samples have been characterized using TPD, XPS and XRD measurements. The catalyst after calcination at 450 °C gave highest activity for this low-temperature CO oxidation, and XPS measurements yielded that a 780.2-eV Co 2p 3/2 main peak appeared with this catalyst sample and this binding energy was similar to that measured with pure Co 3O 4. After calcination at 570 °C, the catalyst, which had possessed practically no activity in the oxidation reaction, gave a Co 2p 3/2 main structure peak at 781.3 eV which was very similar to those obtained for synthesized Co nTiO n+2 compounds (CoTiO 3 and Co 2TiO 4), and this catalyst sample had relatively negligible CO chemisorption as observed by TPD spectra. XRD peaks indicating only the formation of Co 3O 4 particles on titania surface were developed in the catalyst samples after calcination at temperatures ≥350 °C. Based on these characterization results, five types of Co species could be modeled to exist with the catalyst calcined at different temperatures. Among these surface Co species, the Type A clean Co 3O 4 particles were predominant on a sample of the catalyst after calcination at 450 °C and highly active for CO oxidation at 100 °C, and the calcination at 570 °C gave the Type B Co 3O 4 particles with complete Co nTiO n+2 overlayers inactive for this oxidation reaction. 相似文献
13.
A novel technique for the preparation of highly dispersed rare-earth perovskite LaCoO 3 catalysts was developed. Using the conventional complexation and pyrolysis methods, an etchable component, zinc oxide (ZnO), was introduced into the precursor by adding zinc nitrate during preparation. After calcination, the independent ZnO phase was extracted by an aqueous NH 4Cl solution, resulting in well-dispersed LaCoO 3 catalysts with a surface area of over 30 m 2/g. DTA-reaction tests using CO oxidation as the model reaction were performed as a quick means to illustrate the higher catalytic oxidation activities of the prepared LaCoO 3 catalysts mainly due to their high surface area. 相似文献
14.
A 1% Pd catalyst (38% dispersion) was prepared by impregnating a γ-alumina with palladium acetylacetonate dissolved in acetone. The behaviour of this catalyst in oxidation and steam reforming (SR) of propane was investigated. Temperature-programmed reactions of C 3H 8 with O 2 or with O 2 + H 2O were carried out with different stoichiometric ratios S( S =[O 2]/5[C 3H 8]). The conversion profiles of C 3H 8 for the reaction carried out in substoichiometry of O 2 ( S < 1) showed two discrete domains of conversion: oxidation at temperatures below 350°C and SR at temperatures above 350°C. The presence of steam in the inlet gases is not necessary for SR to occur: there is sufficient water produced in the oxidation to form H 2 and carbon oxides by this reaction. Contrary to what was observed with Pt, an apparent deactivation between 310 and 385°C could be observed with Pd in oxidation. This is due to a reduction of PdO x into Pd 0, which is much less active than the oxide in propane oxidation. Steam added to the reactants inhibits oxidation while it prevents the reduction of PdO x into Pd 0. Compared to Pt and to Rh, Pd has a higher thermal resistance: no deactivation occurred after treatment up to 700°C and limited deactivation after treatment up to 900°C, provided that the catalyst is maintained in an oxygen-rich atmosphere during the cooling. 相似文献
15.
The TiO 2 supported noble metal (Au, Rh, Pd and Pt) catalysts were prepared by impregnation method and characterized by means of X-ray diffraction (XRD) and BET. These catalysts were tested for the catalytic oxidation of formaldehyde (HCHO). It was found that the order of activity was Pt/TiO 2 Rh/TiO 2 > Pd/TiO 2 > Au/TiO 2 TiO 2. HCHO could be completely oxidized into CO 2 and H 2O over Pt/TiO 2 in a gas hourly space velocity (GHSV) of 50,000 h −1 even at room temperature. In contrast, the other catalysts were much less effective for HCHO oxidation at the same reaction conditions. HCHO conversion to CO 2 was only 20% over the Rh/TiO 2 at 20 °C. The Pd/TiO 2 and Au/TiO 2 showed no activities for HCHO oxidation at 20 °C. The different activities of the noble metals for HCHO oxidation were studied with respect to the behavior of adsorbed species on the catalysts surface at room temperature using in situ DRIFTS. The results show that the activities of the TiO 2 supported Pt, Rh, Pd and Au catalysts for HCHO oxidation are closely related to their capacities for the formation of formate species and the formate decomposition into CO species. Based on in situ DRIFTS studies, a simplified reaction scheme of HCHO oxidation was also proposed. 相似文献
16.
The effect of Pd-loading on Pd-NaZSM-5 and Pd-NaMordenite catalysts prepared by ion exchange was studied for methane combustion with excess oxygen (1% CH 4, 18% O 2, balance N 2) in the temperature range 40–500°C. Fresh and calcined samples (3 h, 450°C) showed methane conversions proportional to Pd-loading on Pd-NaZSM-5 catalysts, while conversions decreased with Pd-loading on calcined Pd-NaMordenite catalysts. TOF (number of methane molecules converted per second per Pd 2+ ion) for over exchanged Pd-NaZSM5-116 was low as compared to under exchanged Pd-NaZSM5-80 and Pd-NaZSM5-58 samples. Close TOF's were found for the last two samples at 330°C. TOF differences in Pd-NaMordenite catalysts demonstrate the heterogeneity of Pd +2 sites due to structurally nonidentical locations of cations. TOF's appear to be related to Na/Pd ratios in both catalyst types. Apparent activation energies for Pd-NaZSM-5 materials are higher than those for Pd-NaMordenite catalysts. 相似文献
17.
In situ X-ray diffraction (XRD) and quasi in situ X-ray photoelectron spectroscopy (XPS) measurements were complementary used to investigate structural and surface modifications of a palladium-supported on LaCoO 3 perovskite catalyst under various controlled atmospheres, particularly during the reduction of NO by hydrogen under lean conditions, in the presence of a large excess of oxygen. An extensive reduction of the perovskite was evidenced during the pre-activation thermal treatment of the palladium-supported catalyst under hydrogen at 773 K leading to the formation of Pd particles in contact with Co0 and La2O3. In the presence of an excess of oxygen, the catalyst structure changes during the reaction. The reduced solid is progressively transformed into LaCoO3 in the range of 873–1173 K. However, such a bulk transformation probably occurs at lower temperatures at the surface of the solid according to XPS analyses. At the same time, the binding energy (BE) level of the Pd 3d5/2 photopeak increases up to 337.5 eV which reveals the stabilisation of oxidic palladium species in a different chemical environment than that corresponding to PdO. Such changes induced different catalytic properties of the catalyst during the reduction of NO by H2. 相似文献
18.
Pd/Nb 2O 5/Al 2O 3 catalysts were investigated on propane oxidation. Diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS) analysis suggested that monolayer coverage was attained between 10 and 20 wt.% of Nb 2O 5. Temperature programmed reduction (TPR) evidenced the partial reduction of niobium oxide. The maximum propane conversion observed on the Pd/10% Nb 2O 5/Al 2O 3 corresponded to the maximum Nb/Al surface ratio. The presence of NbO x polymeric structures near to the monolayer could favor the ideal Pd 0/Pd 2+ surface ratio to the propane oxidation which could explain the promoting effect of niobium oxide. 相似文献
19.
Palladium (Pd) supported on CeO 2-promoted γ-Al 2O 3 with various CeO 2 (ceria) crystallinities, were used as catalysts in the methane steam reforming reaction. X-ray diffraction (XRD) analysis, FTIR spectroscopy of adsorbed CO, and X-ray photoelectron spectroscopy (XPS) were employed to characterize the samples in terms of Pd and CeO 2 structure and dispersion on the γ-Al 2O 3 support. These results were correlated with the observed catalytic activity and deactivation process. Arrhenius plots at steady-state conditions are presented as a function of CeO 2 structure. Pd is present on the oxidized CeO 2-promoted catalysts as Pd 0, Pd + and Pd 2+, at ratios strongly dependent on CeO 2 structure. XRD measurements indicated that Pd is well dispersed (particles <2 nm) on crystalline CeO 2 and is agglomerated as large clusters (particles in 10–20 nm range) on amorphous CeO 2. FTIR spectra of adsorbed CO revealed that after pre-treatment under H 2 or in the presence of amorphous CeO 2, partial encapsulation of Pd particles occurs. CeO 2 structure influences the CH 4 steam reforming reaction rates. Crystalline CeO 2 and dispersed Pd favor high reaction rates (low activation energy). The presence of CeO 2 as a promoter conferred high catalytic activity to the alumina-supported Pd catalysts. The catalytic activity is significantly lower on Pd/γ-Al 2O 3 or on amorphous (reduced) CeO 2/Al 2O 3 catalysts. The reaction rates are two orders of magnitude higher on Pd/CeO 2/γ-Al 2O 3 than on Pd/γ-Al 2O 3, which is attributed to a catalytic synergism between Pd and CeO 2. The low rates on the reduced Pd/CeO 2/Al 2O 3 catalysts can be correlated with the loss of Pd sites through encapsulation or particle agglomeration, a process found mostly irreversible after catalyst regeneration. 相似文献
20.
The objective of this work was to study the promotional effect of Pt on Co-zeolite (viz. mordenite, ferrierite, ZSM-5 and Y-zeolite) and Co/Al 2O 3 on the selective catalytic reduction (SCR) of NO x with CH 4 under dry and wet reaction stream. After being reduced in H 2 at 350°C, the PtCo bimetallic zeolites showed higher NO to N 2 conversion and selectivity than the monometallic samples, as well as a combination of the latter samples such as mechanical mixtures or two-stage catalysts. After the same pretreatment, under wet reaction stream, the bimetallic samples were also more active. Among the other catalysts studied with 5% of water in the feed, (NO = CH 4 = 1000 ppm, O 2 = 2%), the NO conversion dropped to zero over Co 2.0Mor at 500°C and GHSV = 30,000 h −1, whereas it is 20% in Pt 0.5Co 2.0Mor. In Pt/Co/Al 2O 3 the NO x conversion dropped below 5% with only 2% of water under the same reaction conditions. The specific activity given as molecules of NO converted per total metal atom per second were 16.5 × 10 −4 s −1 for Pt 0.5Co 2.0Fer, 13 × 10 −4 s −1 for Pt 0.5Co 2.0Mor, 4.33 × 10 −4 s −1 for Pt 0.5Co 2.0ZSM-5 and 0.5 × 10 −4 s −1 for Pt/Co/Al 2O 3. The Y-zeolite-based samples were inactive in both mono and bimetallic samples. The species initially present in the solid were Pt° and Co°, together with Co 2+ and Pt 2+ at exchange positions. Co° seems not to participate as an active site in the SCR of NO x. Those species remained after the reaction but some reorganization occurred. A synergetic effect among the different species that enhances both the NO to NO 2 reaction, the activation of CH 4 and also the ability of the catalyst to adsorb NO, could be responsible for the high activity and selectivity of the bimetallic zeolites. 相似文献
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