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1.
The La1−xKxMnO3 perovskite-type oxides whose sizes were in nanometric range were prepared by the citric acid-ligated method. The structures of these perovskite-type oxides were examined by XRD and FT-IR. The catalytic activity for the combustion of soot particulate was evaluated by a technique of the temperature-programmed reaction. In the LaMnO3 catalyst, the partial substitution of K for La at A-site enhanced the catalytic activity for the combustion of soot particle. In the La1−xKxMnO3 catalysts, the combustion temperature of soot particle decreases with increasing x values. The La1−xKxMnO3 oxides with the substitution quantity between x=0.20 and x=0.25 are good candidate catalysts for the soot particle removal reaction, and the combustion temperature of soot particle is between 285 and 430 °C when the contact of catalysts and soot is loose, and their catalytic activities for the combustion of soot particle are as good as supported Pt catalysts, which is the best catalyst system so far reported for soot combustion under loose contact conditions. 相似文献
2.
In order to elucidate the effect of support in the catalytic performance, two selected potassium-promoted catalysts (K1Cu/beta
and KCu2/Al2O3) were tested for the simultaneous NO
x
/soot removal from a simulated diesel exhaust. For comparative purpose, the behaviour of a platinum catalyst (Pt/beta) was
also studied. Isothermal experiments revealed that the potassium-promoted catalysts show a high activity for NO
x
/soot removal in the 350–450 °C temperature range. In addition, the catalysts present the advantage that the main reaction
products are N2 and CO2. Among the catalysts tested, KCu2/Al2O3 presents the best global performance at 450 °C: the highest soot consumption rate, even higher than the platinum catalysts,
and a high NO
x
reduction. 相似文献
3.
Reduction of lean NO2 with diesel soot over metal-exchanged ZSM5, perovskite and γ-alumina catalysts 总被引:1,自引:0,他引:1
Dae-Won Lee Seung-Jin Song Kwan-Young Lee 《Korean Journal of Chemical Engineering》2010,27(2):452-458
The catalytic performances of metal-exchanged ZSM5, perovskite and γ-alumina catalysts for the reduction of nitrogen dioxide (NO2) by diesel soot were investigated. The reaction tests were performed through temperature-programmed reaction (TPR), in which
NO2 and O2 were passed through a fixed bed of catalyst-soot mixture. On the three types of catalyst, NO2 was reduced to N2 by model soot (Printex-U) and most of the soot was converted into CO2. Pt-, Cu- and Co-exchanged ZSM5 catalysts exhibited reduction activities with conversions of NO2 into N2 of about 20%. Among the perovskite catalysts tested, La0.9K0.1FeO3 showed a 32% conversion of NO2 into N2. The catalytic activities of the perovskite catalysts were largely influenced by the number and stability of oxygen vacancies.
For the γ-alumina catalyst, the peak reduction activity appeared at a relatively high temperature of around 500 °C, but the NO2 reduction was more effective than the NO reduction, in contrast to the results of the ZSM-5 and perovskite catalysts. 相似文献
4.
Perovskite-type catalysts have been investigated for diesel soot combustion: (i) the LaCr0.9O3–
substoichiometric perovskite, (ii) K–La partially substituted chromites; (iii) Pt added ii-type perovskites. The catalysts prepared showed a progressively higher activity and potential for practical application in diesel particulate traps. Engine bench tests performed on a SiC wall-flow trap (Ibiden) lined with the La0.9K0.1Cr0.9O3–
+ 1 wt%Pt catalyst showed that the catalyst not only speeds up soot combustion on occasional trap heating (regeneration phase) but also prolongs the trap loading phase (soot accumulation during normal operation) as Pt active sites promote NO–NO2 oxidation, followed by the non-catalytic reaction of NO2 with the trapped soot. 相似文献
5.
Grisel Corro Umapada Pal Edgar Ayala Esmeralda Vidal Emmanuel Guilleminot 《Topics in Catalysis》2013,56(1-8):467-472
The catalytic behaviors of Ag, Cu, and Au loaded fumed SiO2 have been investigated for diesel soot oxidation. The diesel soot generated by burning pure Mexican diesel in laboratory was oxidized under air flow in presence of catalyst inside a tubular quartz reactor in between 25 and 600 °C. UV–Vis optical spectroscopy was utilized to study the electronic states of Ag, Cu, and Au(M) in M/SiO2 catalysts. The soot oxidation was seen to be strongly enhanced by the presence of metallic silver on 3 % Ag/SiO2 surface, probably due to the formation of atomic oxygen species during the soot oxidation process. The catalyst is very stable due to the stability of Ag0 species on the catalyst surface and high thermal stability of SiO2. Obtained results reveal that though the freshly prepared 3 % Cu/SiO2 is active for soot oxidation, it gets deactivated at high temperatures in oxidizing conditions. On the other hand, 3 % Au/SiO2 catalyst does not present activity for diesel soot oxidation in the conventional soot oxidation temperature range. The catalytic behaviors of the supported catalyst samples have been explained considering the electron donating ability of the metals to generate atomic oxygen species at their surface. 相似文献
6.
Structured catalysts prepared by means of coating cordierite monoliths with alumina-based suspensions containing transition metals such as Cu, Co and Fe and alkali/alkali-earth promoters such as K and Ba. Textural and structural features of these catalysts were analyzed by means of N2 adsorption and SEM. Their activity in the simultaneous removal of soot and NOx was assayed in a lab-scale installation, using a carbon black as diesel surrogate. Catalysts exhibited significant activity in deNOx and soot oxidation. K and Ba enhanced both NOx adsorption and soot–catalyst contact. However Ba contributed to a greater extent to the adsorption of N-species, which moreover presented higher thermal stability than on K-catalysts, and K showed higher mobility than Ba. Thus, Ba-containing catalysts showed increased activity towards NOx reduction but shifted to higher temperatures in comparison to K-catalysts, which on the other hand resulted more active towards soot oxidation than Ba-ones. Fe-based catalyst turned out to be less active both in soot oxidation and NOx reduction than Co and Cu-based ones. Intensive calcination of the catalysts at 800 °C for 5 h resulted in substantial loss of K and Ba. Loss of promoter depends, however, on the metal contained in the catalyst. In this sense Fe-containing catalysts showed higher stability. Calcination has a substantial effect on catalytic activity. Catalyst significantly lost their NOx adsorption capacity and showed similar activity than a catalyst prepared in absence of promoter, pointing to a substantial change in reaction mechanism and reaction predominantly occurring on metallic sites upon the loss of alkali/alkali-earth compound. 相似文献
7.
Promotion effect of Au on perovskite catalysts for the regeneration of diesel particulate filters 总被引:2,自引:0,他引:2
Four LaBO3 perovskite catalysts (B = Cr, Mn, Fe and Ni), also supporting 2% by weight of gold, were prepared via the so-called Solution Combustion Synthesis (SCS) method, and characterized by means of XRD, BET, FESEM-EDS, TEM, O2-TPD and CO-TPR analyses. The performance of these catalysts, in powder form, was evaluated towards the simultaneous oxidation of soot and CO. The 2 wt.% Au–LaNiO3 showed the best performance with a peak carbon combustion temperature of 431 °C and a half CO conversion of 156 °C. The same nano-structured catalyst, deposited by in situ SCS directly over a SiC filter and tested on real diesel exhaust gases, fully confirmed the encouraging results obtained with catalyst powder. 相似文献
8.
The diesel engine generally achieves the highest fuel, energy, and thermal efficiency due to its very high compression/expansion ratio (14:1 to 25:1). Diesel engines can have a thermal efficiency that exceeds 50%. The main problem is that they emit more pollution like fine black soot particulates (C8H to C10H) and nitrogen oxides (NOX). These pollutants have been causing serious problems for human health and the global environment and also impacts on the engine. There are many types of catalysts investigated for simultaneous control of these two pollutants, i.e., platinum group metals (PGM; Pt, Pd, Rh, and Ir) based, spinel-type oxides, hydrotalcite, rare earth metal oxides, mixed transient metal oxides, etc. The high raw material cost of PGM catalysts has become a significant issue, so developing non-PGM catalysts are one of the promising challenges. There are no extra reductants required because soot catalytically oxidizes itself in the presence of NOX at a faster rate than molecular oxygen and simultaneously NOX is reduced to nitrogen. The order of oxidation potential of NOX to oxidized soot in comparison to molecular oxygen is as follows: NO2 > NO > O2. To meet the very strict EPA US 2010 and Euro VI regulations of particulate matter (PM) and NOX for heavy-duty and light-duty vehicular stringent emission, it is very important to apply the integrated catalytic systems to significantly remove PM and NOX simultaneously. Many papers related to simultaneous control of soot and NOX over different catalysts have been published but till now some of effective catalysts showing high conversion at low temperatures (possibly within the range typical of diesel exhaust: 150–450°C) have not been reviewed. Thus, this article provides a summary of published information regarding the effective catalysts, their preparation methods, properties, and application for simultaneous control of diesel soot and NOX. 相似文献
9.
Eduard Emil Iojoiu Badr Bassou Nolven Guilhaume David Farrusseng Arnold Desmartin-Chomel Karine Lombaert Daniel Bianchi Claude Mirodatos 《Catalysis Today》2008,137(1):103
A methodology for the evaluation of diesel soot oxidation catalysts by high-throughput (HT) screening was developed. The optimal experimental conditions (soot amount, catalyst/soot ratio, type of contact, composition and flow rate of gas reactants) ensuring a reliable and reproducible detection of light-off temperatures in a 16 parallel channels reactor were set up. The temperature profile measured in the catalyst/soot bed under TPO conditions when the exothermic combustion of soot takes place was shown to provide an accurate measurement of the ignition. Its reproducibility and relevance were checked. The results obtained with a reference noble metal free catalyst (La0.8Cr0.8Li0.2O3 perovskite) agree very well with literature data. Qualitative mechanistic features could be derived from these experiments, stressing the likely limiting step of oxygen transfer from catalyst surface to soot particulates to ignite the soot combustion. Ceria material was shown to be more appropriate than perovskite one. From an HT screening of a large diverse library (over 100 mixed oxides catalysts) under optimized conditions, about 10 new formulations were found to perform better than selected noble metal free reference materials. 相似文献
10.
I. S. Mashkovskiy A. L. Tarasov L. M. Kustov M. P. Tsyurupa V. A. Davankov 《Catalysis in Industry》2012,4(3):155-161
A series of catalysts containing noble metals on a super-cross-linked polystyrene (SCP) support with a developed specific surface area (>1000 m2/g) and high thermal stability are prepared and studied to develop an effective catalyst for the low-temperature hydrogenation of aromatic hydrocarbons. A study of Pt- and Pd-containing catalysts based on SCP, carbon supports, and alumina in the hydrogenation of simple (benzene, toluene), branched (n-butylbenzene) and polycyclic (terphenyl) aromatic compounds is conducted. In the hydrogenation of aromatic hydrocarbons, the activity of the catalysts on SCP is comparable to or surpasses analogous catalysts based on Al2O3 and Sibunit in the content of noble metals; it is established that catalysts on SCP have greater selectivity in the hydrogenation of benzene in a benzene-toluene mixture. The electronic state of metals in the Pt(Pd)/SCP catalysts is studied by the IR spectroscopy of adsorbed CO. In testing the catalysts in the hydrogenation of terphenyl, it is found that Pt-containing catalyst on the SCP can operate in reversible hydrogenation-dehydrogenation cycles (terphenyl-tercyclohexane); this is promising for the use of such catalyst systems in creating composite materials for hydrogen storage. 相似文献
11.
A series of samples of La–Cr–O– perovskites were designed as catalysts for diesel soot combustion. They were prepared by using co-precipitation method, at ambient temperature using ammonia followed by a hydrothermal treatment (T = 200 °C, P = 20 atm, t = 24 h). All the chromium-containing precursors were then calcined at high temperature to develop the oxide catalyst. Two phase composition 86%LaCrO3–(14%) La2CrO6 or 94%LaCrO3–6%La2O3 were formed depending on the atmosphere of calcination (oxygen or hydrogen respectively) used. Their respective BET surface areas were 1.1 and 6.5 m2 g−1. Highly crystalline, pure phase of LaCrO3 and La2CrO6 powders were also prepared, with BET area of 4 and 3 m2 g−1, respectively. The crystalline structure and properties of all samples were characterised by X-ray diffraction (XRD), using Rietveld refinement, and temperature-programmed reduction (TPR) techniques. O2-TPD measurements performed on all samples showed the presence of suprafacial, weakly chemisorbed oxygen only for LaCrO3, which contributes actively to soot combustion. TPR study performed on all catalysts showed that while pure LaCrO3 and La2O3 samples did not reduce, the biphasic catalysts showed the presence of oxygen depletion peaks characteristic of lattice oxygen mobility in the samples at ca. 665 °C. Catalytic combustion of diesel soot was studied over all catalysts. The results showed that pure LaCrO3 exhibited significant catalytic activity which was sensitively affected by the modifier La2CrO6 or La2O3. 相似文献
12.
The physico-chemical properties of ceria (CeO2) and rare earth modified ceria (with La, Pr, Sm, Y) catalysts are studied and correlated with the soot oxidation activity
with using O2 and O2 + NO. CeO2 modified with La and Pr shows superior soot oxidation activity with O2 compared with the unmodified catalyst. The improved soot oxidation activity of rare earth doped CeO2 catalysts can be correlated to the increased meso/micro pore volume and the stabilisation of the external surface area. On
the other hand, unreducible ions decrease the intrinsic soot oxidation activity of rare earth modified ceria with both O2 and NO + O2 due to the decreased amount of redox surface sites. The catalyst bulk oxygen storage capacity is not a critical parameter
in determining the soot oxidation activity. The modification with Pr shows the best soot oxidation with both O2 and O2 + NO compared with all other catalysts. 相似文献
13.
Ilenia Rossetti Olga Buchneva Cesare Biffi Riccardo Rizza 《Applied catalysis. B, Environmental》2009,89(3-4):383-390
ABO3 perovskite-like catalysts are known to be sensitive to sulphur-containing compounds. Possible solutions to increase resistance to sulphur are represented by either catalyst bed protection with basic guards or catalyst doping with different transition or noble metals. In the present work La(1−x)A′xCoO3, La(1−x)A′xMnO3 and La(1−x)A′xFeO3, with A′ = Ce, Sr and x = 0, 0.1, 0.2, either pure or doped with noble metals (0.5 wt% Pt or Pd), were prepared in nano-powder form by flame-pyrolysis. All the catalysts were tested for the catalytic flameless combustion of methane, monitoring the activity by on-line mass spectrometry. The catalysts were then progressively deactivated in operando with a new procedure, consisting of repeated injection of some doses of tetrahydrothiophene (THT), usually employed as odorant in the natural gas grid, with continuous analysis of the transient response of the catalyst. The activity tests were then repeated on the poisoned catalyst. Different regenerative treatments were also tried, either in oxidising or reducing atmosphere.Among the unsubstituted samples, higher activity and better resistance to poisoning have been observed in general with manganites with respect to the corresponding formulations containing Co or Fe at the B-site. The worst catalyst showed LaFeO3, from both the points of view of activity and of resistance to sulphur poisoning. La0.9Sr0.1MnO3 showed, the best results, exhibiting very high activity and good resistance even after the addition of up to 8.4 mg of THT/g of catalyst. Interesting results were attained also by adding Sr to Co-based perovskites. Sr showed a first action by forcing Mn or Co in their highest oxidation state, but, in addition, it could also act as a sulphur guard, likely forming stable sulphates due to its basicity. Among noble metals, Pt doping proved beneficial in improving the activity of both the fresh and the poisoned catalyst. 相似文献
14.
《Applied catalysis. B, Environmental》2006,62(3-4):334-345
In this study, cobalt and lead based mixed oxide catalysts were tested for their soot oxidation ability. In addition to a mixed oxide formerly marketed as ceramic paint, a home made set was also prepared by incipient wetness impregnation of a cobalt oxide powder with a lead acetate solution and subsequent calcination. The materials investigated in this study were shown to decrease the peak combustion temperature of home made soot from 500 to 385 °C in air. Soot oxidation tests under inert (N2) atmospheres revealed that the oxidation took place by using the lattice oxygen of the catalyst. Reaction temperature could be further decreased when these mixed oxide catalysts were impregnated with platinum. An optimum platinum loading was determined as 0.5 wt% based on the peak combustion temperature of the soot. The role of Pt was to assist the oxygen transfer from the gas phase to the lattice. It was observed that NO2 is a better oxidizing agent as compared to air whereas NO had hardly any activity against soot oxidation reaction. When the mixed oxide catalyst was impregnated with platinum, the peak combustion temperature was measured as 310 °C in the presence of NOx and air. The catalyst's unique performance was in terms of the rate of soot oxidation. Under the experimental conditions studied here, the soot oxidation was so facile that the oxygen in the gas phase was completely depleted. This stream of oxygen depleted and CO enriched gas phase can be used to reduce NOx in the presence of a downstream or a co-catalyst. 相似文献
15.
Jong-Woo Jeong Byungchul Choi Myung Taeck Lim 《Journal of Industrial and Engineering Chemistry》2008,14(6):830-835
Catalytic oxidation activity of carbon-black (CB) simulating the soot of diesel particulate matters to CO2 over 3Pt/Al2O3, 3Pt5Mn/Al2O3 and 3Pt/30Ba–Al2O3 catalysts is investigated with model gases of diesel emission. In case of the large amount of CB compared to the amount of catalyst (3/1, w/w) in the mixture sample, insufficient oxygen at the point of sudden increase in the amount of CO2 is leaded to the partial oxidation using the lattice oxygen of the catalyst. And the peaks of CO2 after the first peak were attributed to the regional combustion of the CB, which was not in contact with catalyst particles. The fresh 3Pt5Mn was estimated to the oxidation states on the catalyst surface by XPS. For used sample at 700 °C, the BEs of Pt 4d5 was revealed to metallic state Pt(0) (314.4 eV) in a predominant levels compared with Pt(II) (317.3 eV). While BEs of Mn 2p were similar to that obtained from the fresh 3Pt5Mn. It is suggested that Pt is in charge of the roles in CB-oxidation, using the lattice oxygen of the catalyst. Two-stage catalytic system with the strategies of promoting the soot oxidation and NOx reduction, simultaneously, were composed of the CB oxidation catalyst and the diesel oxidation catalyst. The catalytic oxidation of CB was accelerated by activated oxidants and exothermic reaction resulted from the diesel oxidation catalyst, which lies in upstream of two-stage. But the system with the CB oxidation catalyst sited in the upstream showed the initiation of CB oxidation at a lower temperature than the other case. Two-stage catalytic system composed of 3Pt5Mn with CB in the upstream and DOC in the downstream showed high oxidation activity with 95% consumption rate of CB to the total loaded CB in the range of 100–500 °C during the TPR process. 相似文献
16.
A series of Mn-promoted BaAl2O4 catalysts were developed for catalytic soot combustion. These catalysts were characterized using XRD, BET, H2-TPR, O2-TPD, and in-situ DRIFTS. The results showed that an optimized combustion catalyst should accommodate barium and manganese with proper balance to promote soot combustion. A synergistic mechanism was suggested to explain the synergistic effect of manganese and barium: NO was trapped mainly as nitrites by barium, while the generated nitrites further transformed to nitrates facilitated by manganese, which finally oxidized soot into CO2. 相似文献
17.
A series of CuMgAl hydrotalcites derived oxides were prepared by co-precipitation and calcination methods and tested for the simultaneous catalytic removal of NOx and soot. The obtained samples were characterized by XRD, N2 adsorption-desorption, H2-TPR and ICP-AES techniques. The crystal phases, porous structures and redox properties of the catalysts were strongly influenced by Cu substitution contents and calcination temperatures. The CuMgAl mixed oxides with mesoporous properties exhibit high activity for the simultaneous NOx-soot removal. Among the tested catalysts, 3.0Cu-800 sample shows the best performance with the ignition temperature of soot = 260 °C and the total amounts of N2 = 6.0 × 10− 5 mol. Based on the experimental work, a primitive kinetics analysis was carried out from the non-steady (dynamic) TPR measurements. Linear Arrhenius plots of rates of CO2, N2 and N2O formation were observed around the onset of formation curves where the substantial amount of the soot still remains in the soot/catalyst mixture and the effective area of the soot/catalyst contact can be regarded as constant. Finally, a compensation effect was found for the formation of CO2, N2 and N2O over CuMgAl mixed oxides with CuO as the predominant phase. 相似文献
18.
Alkali-earth oxides and nitrates supported on alumina were studied as model systems for NOX storage/release. Their impact on the high-temperature soot oxidation has been investigated. The stability of surface nitrates and temperature of NOX release increase parallel to the basicity of the cation. The presence of soot decreases the temperature of NOX release. The storage capacity depends on the several factors, such as basicity, dispersion of the cation, and pre-treating conditions. Adsorption of NO with O2 at 200 °C leads to the formation of surface nitrates that mainly exist as ionic nitrates. Stored nitrates contribute to the soot oxidation and assist to lower the temperature of soot oxidation up to almost 100 °C. In the presence of only NOX storage material the efficiency of NOX utilization is, however, quite low, around 30%. Therefore, the presence of an oxidation catalyst is essential to increase the efficiency of NOX utilization for soot oxidation up to 140% and selectivity towards CO2. A combination of oxidation catalyst with NOX storage materials enables to lower the temperature of soot oxidation more than 100 °C for the Sr- and Ca-based systems. 相似文献
19.
Ag-Pt- and Pd-doped LaMnO3-based perovskite catalysts were prepared and their activity in the oxidation of toluene, n-heptane and ethanol was investigated. The activity of LaMnO3-based catalyst was very high in the oxidation of each compound tested. The Ag-doped catalyst was the most active in the oxidation of each compound and it displayed the highest BET specific surface area (SSA) also. The influence of Pt or Pd doping on perovskite activity is negligibly small. Pt-doped catalysts are slightly more active while Pd-doped catalysts are slightly less active than the pure perovskite. Thermogravimetric-differential thermal analysis (TG-DTA) for the catalyst precursor indicates that above 500 °C a perovskite structure began to form. The XRD analysis reveals the presence of the LaMnO3.15 perovskite phase and, additionally, the presence of some metal oxide phases (e.g. La2O2CO3, Mn2O3) and carbon. BET SSA measured after the oxidation tests was found to decrease for each catalyst. There was no relation between the chemical composition of the catalyst and the loss of SSA. 相似文献
20.
K. Wippermann B. Richter K. Klafki J. Mergel G. Zehl I. Dorbandt P. Bogdanoff S. Fiechter S. Kaytakoglu 《Journal of Applied Electrochemistry》2007,37(12):1399-1411
Cathode catalyst layers were prepared and characterized as part of membrane electrode assemblies (MEA) and catalyst coated
membranes (CCM) on the basis of carbon supported methanol tolerant RuSe
x
catalysts. Preparation parameters varied were: catalyst loading (0.5–2 mg RuSe
x
cm−2), PTFE content (0, 6, 18 wt.%), carbon support (Vulcan XC 72 or BP2000), and fraction of RuSe
x
in the carbon supported catalysts (20, 44, 47 wt.%). The MEAs and cathode catalyst layers were electrochemically characterized
under Direct Methanol Fuel Cell (DMFC) operating conditions by recording polarization curves, galvanostatic measurements,
and impedance spectra. The morphology of the catalyst layers was investigated by means of confocal laser scan microscopy (CLSM),
scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) measurements. MEAs
with Ru(44.0 wt.%)Se(2.8 wt.%)/VulcanXC72 cathode catalyst achieved the highest performance of all RuSe
x
catalysts investigated, i.e. ∼40 mW cm−2 at 80 °C under ambient pressure and λMeOH = λair = 4. This is 40% of the value obtained with commercial platinum cathode catalyst under the same operating conditions. The
RuSe
x
catalysts investigated are stable over a period of more than 1,000 h. This was confirmed by TEM and XRD measurements, where
no increase in mean RuSe
x
particle size (∼5 nm) after fuel cell operation was found. Enhancement of specific catalyst activity, mass transport, and
active surface offer potential for a further improvement of RuSe
x
catalyst layers. 相似文献