共查询到20条相似文献,搜索用时 31 毫秒
1.
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 (N 2) 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 NO 2 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 NO x 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 NO x in the presence of a downstream or a co-catalyst. 相似文献
2.
This paper deals with the activity of bimetallic potassium–copper and potassium–cobalt catalysts supported on alumina for the reduction of NO x with soot from simulated diesel engine exhaust. The effect of the reaction temperature, the soot/catalyst mass ratio and the presence of C 3H 6 has been studied. In addition, the behavior of two monometallic catalysts supported on zeolite beta (Co/beta and Cu/beta), previously used for NO x reduction with C 3H 6, as well as a highly active HC-SCR catalyst (Pt/beta) has been tested for comparison. The preliminary results obtained in the absence of C 3H 6 indicate that, at temperatures between 250 and 400 °C, the use of bimetallic potassium catalysts notably increases the rate of NO x reduction with soot evolving N 2 and CO 2 as main reaction products. At higher temperatures, the catalysts mainly favor the direct soot combustion with oxygen. In the presence of C 3H 6, an increase in the activity for NO x reduction has been observed for the catalyst with the highest metal content. At 450 °C, the copper-based catalysts (Cu/beta and KCu2/Al 2O 3) show the highest activity for both NO x reduction (to N 2 and CO 2) and soot consumption. The Pt/beta catalyst does not combine, at any temperature, a high NO x reduction with a high soot consumption rate. 相似文献
3.
Potassium-loaded lanthana is a promising catalyst to be used for the simultaneous abatement of soot and NO x, which are the main diesel-exhaust pollutants. With potassium loadings between 4.5 and 10 wt.% and calcination temperatures between 400 and 700 °C, this catalyst mixed with soot gave maximum combustion rates between 350 and 400 °C in TPO experiments, showing a good hydrothermal stability. There was no difference in activity when it was either mixed by grinding in an agate mortar or mixed by shaking in a sample bottle (tight and loose conditions, respectively). Moreover, when the K-loaded La 2O 3 is used as washcoat for a cordierite monolith, there were found no significant differences in the catalytic behaviour of the system, which implies its potentiality for practical purposes. The influence of poisons as water and SO2 was investigated. While water does not affect the soot combustion activity, SO2 slightly shift the TPO peak to higher temperature. Surface basicity, which is a key factor, was analysed by measuring the interactions of the catalytic surface with CO2 using the high frequency CO2 pulses technique, which proved to be very sensitive, detecting minor changes by modifications in the dynamics of the CO2 adsorption–desorption process. Water diminishes the interaction with CO2, probably as a consequence of an adsorption competition. The SO2 treated catalyst is equilibrated with the CO2 atmosphere more rapidly if compared with the untreated one, also showing a lower interaction. The lower the interaction with the CO2, the lower the activity. Differential scanning calorimetric (DSC) results indicate that the soot combustion reaction coexists with the thermal decomposition of hydroxide and carbonate species, occurring in the same temperature range (350–460 °C). The presence of potassium increases surface basicity shifting the endothermic decomposition signal to higher temperatures. We also found that NO2 strongly interacts with both La2O3 and K/La2O3 solids, probably through the formation of monodentate nitrate species which are stable under He atmosphere until 490 °C. These nitrate species further react with the solid to form bulk nitrate compounds. The addition of Cobalt decreases the nitrates stability and catalyses the NOx to N2 reduction under a reducing atmosphere, which is a necessary step for a working NOx catalytic trap. Preliminary studies performed in this work demonstrated the feasibility of using these catalysts to simultaneously remove NOx and soot particles from diesel exhausts. The nitrate formation is still observed during the catalytic combustion of soot in the presence of NOx, making our K/La2O3 a very interesting system for practical applications in simultaneous soot combustion and NOx storage in diesel exhausts. 相似文献
4.
This paper deals with the activity of the KCu and KCo catalysts supported on beta-zeolite for the simultaneous NO x/soot removal from a simulated diesel exhaust, containing C 3H 6 as model hydrocarbon. In order to reveal the effect of potassium, the corresponding monometallic catalysts (Co/beta and Cu/beta) were analyzed and different potassium loadings were used. In addition, for comparative purpose, the performance of a platinum based catalyst (Pt/beta) was studied. All noble-free catalysts show, at 450 °C, a high activity for the simultaneous NO x/soot removal. Among them, K1Cu/beta presents the best global performance at 350 and 450 °C achieving a high soot consumption rate (comparable to platinum catalysts) and the highest NO x reduction. In contrast to platinum catalysts, K1Cu/beta has the advantage that the main reaction products are N 2 and CO 2. 相似文献
5.
A catalytically assisted ceramic combustor for a gas turbine was designed and tested to achieve low NO x emissions. This combustor is composed of a burner and a ceramic liner. The burner consists of an annular preburner, six catalytic combustor segments and six premixing nozzles, which are arranged in parallel and alternately. In this combustor system, catalytic combustion temperature is controlled under 1000 °C, premixed gas is injected from the premixing nozzles to the catalytic combustion gas and lean premixed combustion over 1300 °C is carried out in the ceramic liner. This system was designed to avoid catalyst deactivation at high temperature and thermal shock fracture of the ceramic honeycomb monolith of the catalyst. A 1 MW class combustor was tested using LNG fuel. Firstly, NO x emissions from the preburner were investigated under various pressure conditions. Secondly, two sets of honeycomb cell density catalysts and one set of thermally pretreated catalysts ware applied to the combustor, and combustion tests were carried out under various pressure conditions. As a result, it was found that the main source of NO x was the preburner, and total NO x emissions from the combustor were approximately 4 ppm (at 16% O 2) at an adiabatic combustion temperature of 1350 °C and combustor inlet pressure of 1.33 MPa. 相似文献
6.
Ceria (CeO 2) and rare-earth modified ceria (CeReO x with Re = La, Pr, Sm, Y) catalysts are prepared by nitrate precursor calcination and are characterised by BET surface area, XRD, H 2-TPR, and Raman spectroscopy. Potential of the catalysts in the soot oxidation is evaluated in TGA with a feed gas containing O 2. Seven hundred degree Celsius calcination leads to a decrease in the surface area of the rare-earth modified CeO 2 compared with CeO 2. However, an increase in the meso/macro pore volume, an important parameter for the soot oxidation with O 2, is observed. Rare-earth ion doping led to the stabilisation of the CeO 2 surface area when calcined at 1000 °C. XRD, H 2-TPR, and Raman characterisation show a solid solution formation in most of the mixed oxide catalysts. Surface segregation of dopant and even separate phases, in CeSmO x and CeYO x catalysts, are, however, observed. CePrO x and CeLaO x catalysts show superior soot oxidation activity (100% soot oxidation below 550 °C) compared with CeSmO x, CeYO x, and CeO 2. The improved soot oxidation activity of rare-earth doped CeO 2 catalysts with O 2 can be correlated with the increased meso/micro pore volume and stabilisation of external surface area. The segregation of the phases and the enrichment of the catalyst surface with unreducible dopant decrease the intrinsic soot oxidation activity of the potential CeO 2 catalytic sites. Doping CeO 2 with a reducible ion such as Pr 4+/3+ shows an increase in the soot oxidation. However, the ease of catalyst reduction and the bulk oxygen-storage capacity is not a critical parameter in the determination of the soot oxidation activity. During the soot oxidation with O 2, the function of the catalyst is to increase the ‘active oxygen’ transfer to the soot surface, but it does not change the rate-determining step, as evident from the unchanged apparent activation energy (around 150 kJ mol −1), for the catalysed and un-catalysed soot oxidation. Spill over of oxygen on the soot surface and its subsequent adsorption at the active carbon sites is an important intermediate step in the soot oxidation mechanism. 相似文献
7.
A series of Pt and Pt,Cu supported catalysts were prepared by wet impregnation of Mg–Al supports obtained from hydrotalcite-type (HT) precursor compounds. These novel NO x storage-reduction (NO xSR) catalysts show improved performances in NO x storage than Pt,Ba/alumina NO xSR catalysts at reaction temperatures lower than 200 °C. These catalysts show also improved resistance to deactivation by SO 2. The effect is attributed to the formation of well dispersed Mg(Al)O particles which show good NO x storage properties. The promoted low temperature activity is explained by the lower basicity of the Mg(Al)O mixed oxide in comparison to BaO, which induces on one hand a lower inhibition on Pt activity (NO to NO 2 oxidation and/or hydrocarbon oxidation) due to electronic effect, and on the other hand a lower thermal stability of the stored NO x. The presence of Cu slightly inhibits activity at low temperature, although improves activity and resistance to deactivation at 300 °C. On these catalysts FT-IR characterization evidences the formation of a Pt–Cu alloy after reduction. 相似文献
8.
A catalytic deSoot–deNO x system, comprising Pt and Ce fuel additives, a Pt-impregnated wall-flow monolith soot filter and a vanadia-type monolithic NH 3-SCR catalyst, was tested with a two-cylinder DI diesel engine. The soot removal efficiency of the filter was 98–99 mass% with a balance temperature (stationary pressure drop) of 315 °C at an engine load of 55%. The NO x conversion ranged from 40 to 73%, at a NH 3/NO x molar ratio of 0.9. Both systems were measured at a GHSV of 52 000 l/(l h). The maximum NO x conversion was obtained at 400 °C. The reason for the moderate deNO x performance is discussed. No deactivation was observed after 380 h time on stream. The NO x emission at high engine loads is around 15% lower than that of engines running without fuel additives. 相似文献
9.
In order to improve a “Three Function Catalysts Model”, the present paper deals with alumina based catalysts containing cobalt and palladium for the NO reduction by methane. The deNOx temperature window was estimated by adsorption and subsequent desorption of NO in lean conditions. Two NOx desorption peaks were detected for both catalysts. For Pd(0.63)Co(0.58)/Al2O3, the two desorption peaks appeared at 205 and 423 °C, whereas for Pd(0.14)Co(0.57)/Al2O3, the maxima desorption temperature peaks were at 205 and 487 °C. In addition, NO oxidation was also studied to evaluate the catalyst first function. It was found that, the oxidation begins on Co–Pd/Al2O3 around 250 °C. On Pd(0.63)Co(0.58)/Al2O3, 8% of deNOx were found in the range of the second NOx desorption peak temperature (410 °C). During TPSR, CxHyOz species such as formaldehyde were detected. These oxygenate species are the reactive intermediate for deNOx by methane. 相似文献
10.
The effect of introduction of alkalies (Me = Li, K, Cs) into SrTiO 3 on the physico-chemical properties of resulted materials and their catalytic activity in soot combustion was studied. Two groups of SrTiO 3 based perovskites were prepared: substituted in A-position of the structure (Sr 1 − xMe xTiO 3, x = 0.05–0.2) and impregnated with the same amount of alkali metals. Prepared materials exhibit low specific surface area and perovskite structure, only these ones impregnated with the highest amount of Cs (K) show weak XRD signals of Me 2O. TPD-O 2 experiments show bimodal profiles of O 2 desorption curves with maximums corresponding to individual step of alkali nitrates thermal decomposition. It is supposed that second peak of O 2 desorption from impregnated SrTiO 3 can be related to reversible decomposition of MeNO 3. XPS shows that surface of SrTiO 3 substituted with K (Cs) is much richer in these elements than the surface of impregnated one. Prepared materials lower the temperature of soot ignition from 530 (inert) to 470 °C for SrTiO 3 and to 302–303 °C for Sr 0.8K 0.2TiO 3 and Sr 0.8K 0.2TiO 3, respectively. Substituted materials are more active in soot combustion than impregnated ones. A mechanism explaining effect of alkali metals nitrate addition to SrTiO 3 on its catalytic activity in soot combustion is proposed. 相似文献
11.
The emissions of CO 2, NO x and SO 2 from the combustion of a high-volatile coal with N 2- and CO 2-based, high O 2 concentration (20, 50, 80, 100%) inlet gases were investigated in an electrically heated up-flow-tube furnace at elevated gas temperatures (1123–1573 K). The fuel equivalence ratio, φ, was varied in the range of 0.4–1.6. Results showed that CO 2 concentrations in flue gas were higher than 95% for the processes with O 2 and CO 2-based inlet gases. NO x emissions increased with φ under fuel-lean conditions, then declined dramatically after φ=0.8, and the peak values increased from about 1000 ppm for the air combustion process and 500 ppm for the O 2(20%)+CO 2(80%) inlet gas process to about 4500 ppm for the oxygen combustion process. When φ>1.4 the emissions decreased to the same level for different O 2 concentration inlet gas processes. On the other hand, NO x emission indexes decreased monotonically with φ under both fuel-lean and fuel-rich combustion. SO 2 emissions increased with φ under fuel-lean conditions, then declined slightly after φ>1.2. Temperature has a large effect on the NO x emission. Peak values of the NO x emission increased by 50–70% for the N 2-based inlet gas processes and by 30–50% for the CO 2-based inlet gas process from 1123 to 1573 K. However, there was only a small effect of temperature on the SO 2 emission. 相似文献
12.
A new NO x storage-reduction electrochemical catalyst has been prepared from a polycrystalline Pt film deposited on 8 mol% Y 2O 3-stabilized ZrO 2 (YSZ) solid electrolyte. BaO has been added onto the Pt film by impregnation method. The NO x storage capacity of Pt-BaO/YSZ system was investigated at 350 °C and 400 °C under lean conditions. Results have shown that the electrochemical catalyst was effective for NO x storage. When nitric oxides are fully stored, the catalyst potential is high and reaches its maximum. On the other hand, when a part of NO and also NO 2 desorb to the gas phase, the catalyst potential remarkably drops and finally stabilizes when no more NO x storage occurs but only the reaction of NO oxidation into NO 2. Furthermore, the investigation has clearly demonstrated that the catalyst potential variation versus temperature or chemical composition is an effective indicator for in situ following the NO x storage-reduction process, i.e. the storage as well as the regeneration phase. The catalyst potential variations during NO x storage process was explained in terms of oxygen coverage modifications on the Pt. 相似文献
13.
A catalytically assisted low NO x combustor has been developed which has the advantage of catalyst durability. Combustion characteristics of catalysts at high pressure were investigated using a bench scale reactor and an improved catalyst was selected. A combustor for multi-can type gas turbine of 10 MW class was designed and tested at high-pressure conditions using liquefied natural gas (LNG) fuel. This combustor is composed of a burner system and a premixed combustion zone in a ceramic type liner. The burner system consists of catalytic combustor segments and premixing nozzles. Catalyst bed temperature is controlled under 1000°C, premixed gas is injected from the premixing nozzles to catalytic combustion gas and lean premixed combustion is carried out in the premixed combustion zone. As a result of the combustion tests, NO x emission was lower than 5 ppm converted at 16% O 2 at a combustor outlet temperature of 1350°C and a combustor inlet pressure of 1.33 MPa. 相似文献
14.
Several hexaaluminate-related materials were prepared via hydrolysis of alkoxide and powder mixing method for high temperature combustion of CH 4 and C 3H 8, in order to investigate the effect of the concentration of the fuels, O 2 and H 2O on NO x emission and combustion characteristics. Among the hexaaluminate catalysts, Sr 0.8La 0.2MnAl 11O 19− prepared by the alkoxide method exhibited the highest activity for methane combustion and low NO x emission capability. NO x emission at 1500 °C was increased linearly with O 2 concentration, whereas water vapor addition decreased NO x emission in CH 4 combustion over the Sr 0.8La 0.2MnAl 11O 19− catalyst. In the catalytic combustion of C 3H 8 over the Sr 0.8La 0.2MnAl 11O 19− catalyst, the amount of NO x emitted was raised in the temperature range between 1000 and 1500 °C when the C 3H 8 concentration increased from 1 to 2 vol.%. It was found that NO x emission in this temperature range was reduced effectively by adding water vapor. 相似文献
15.
In this paper, previously reported findings and new results presented here are discussed with the main objective of establishing the reaction mechanism for soot oxidation on different supports and catalysts formulations. Catalysts containing Co, K and/or Ba supported on MgO, La 2O 3 and CeO 2 have been studied for diesel soot catalytic combustion. Among them, K/La 2O 3 and K/CeO 2 showed the best activity and stability for the combustion of soot with oxygen. A reaction mechanism involving the redox sites and the surface-carbonate species takes place on these catalysts. On the other hand, Co,K/La 2O 3 and Co,K/CeO 2 catalysts display activity for the simultaneous removal of soot and nitric oxide. The soot–catalyst contacting phenomenon was also addressed. A synergic La–K effect was observed in which the mechanical mixtures of soot with K–La 2O 3 showed higher combustion rates than those observed when K and La were directly deposited on the soot surface. The effect of the addition of Ba was explored with the aim of promoting the interaction of the solid with NO 2, thus combining the NO x catalytic trap concept with the soot combustion for filter regeneration. Ba/CeO 2 and Ba,K/CeO 2 were effective in NO x absorption as shown in the microbalance experiments. However, the formation of stable nitrate species inhibits the soot combustion reaction. 相似文献
16.
Ceria (CeO 2) and rare-earth modified ceria (CeReO x with Re = La 3+, Pr 3+/4+, Sm 3+, Y 3+) supports and Pt impregnated supports are studied for the soot oxidation under a loose contact with the catalyst with the feed gas, containing NO + O 2. The catalysts are characterised by XRD, H 2-TPR, DRIFT and Raman spectroscopy. Among the single component oxides, CeO 2 is significantly more active compared with the other lanthanide oxides used in this study. Doping CeO 2 with Pr 3+/4+ and La 3+ improved, however, the soot oxidation activity of the resulting solid solutions. This improvement is correlated with the surface area in the case of CeLaO x and to the surface area and redox properties of CePrO x catalyst. The NO conversion to NO 2 over these catalysts is responsible for the soot oxidation activity. If the activity per unit surface area is compared CePrO x is the most active one. This indicates that though La 3+ can stabilise the surface area of the catalyst in fact it decreases the soot oxidation activity of Ce 4+. The lattice oxygen participates in NO conversion to NO 2 and the rate of this lattice oxygen transfer is much faster on CePrO x. In general, the improvement of the soot oxidation is observed over the Pt impregnated CeO 2 and CeReO x catalysts, and can be correlated to the presence of Pt°. The surface reduction of the supports in the presence of Pt occurred below 100 °C. The surface redox properties of the support in the Pt catalysts do not have a significant role in the NO to NO 2 conversion. In spite of the lower surface area, the Pt/CeYO x and Pt/CeO 2 catalysts are found to be more active due to larger Pt crystal sizes. The presence of Pt also improved the CO conversion to CO 2 over these catalysts. The activation energy for the soot oxidation with NO + O 2 is found to be around 50 kJ/mol. 相似文献
17.
The simultaneous removal of carbon particulate and NO x has been studied over perovskite-type oxides prepared by malic acid method. The catalysts were modified to enhance the activity by substitution of metal into A- or B-site of perovskite oxide. In the LaCoO 3 catalyst, the partial substitution of Cs into A-site enhanced the catalytic activity in the combustion of soot particulate and NO reduction. In La 1−xCs xCoO 3 catalysts, the ignition temperature of carbon particulate decreases with increasing x values and shows almost constant values at substitution of x>0.2 and NO conversion also shows the similar tendency. In the Cs-substituted oxide, the ignition temperature of carbon particulate slightly decreased in the order Co>Mn>Fe of B-site metal cation but NO conversion showed almost similar values. With increasing NO concentration, NO conversion decreased but the ignition temperature moved to high temperature when the NO concentration was higher than 1000 ppm. The carbon particulate played an important role on the reduction of NO, but NO had little effect on the oxidation of carbon particulate. 相似文献
18.
Manganese–cerium mixed oxide catalysts with different molar ratio Mn/(Mn + Ce) (0, 0.25, 0.50, 0.75, 1) were prepared by citric acid method and investigated concerning their adsorption behavior, redox properties and behavior in the selective catalytic reduction of NO x by NH 3. The studies based on pulse thermal analysis combined with mass spectroscopy and FT-IR spectroscopy uncovered a clear correlation between the dependence of these properties and the mixed oxide composition. Highest activity to nitrogen formation was found for catalysts with a molar ratio Mn/(Mn + Ce) of 0.25, whereas the activity was much lower for the pure constituent oxides. Measurements of adsorption uptake of reactants, NO x (NO, NO 2) and NH 3, and reducibility showed similar dependence on the mixed oxide composition indicating a clear correlation of these properties with catalytic activity. The adsorption studies indicated that NO x and NH 3 are adsorbed on separate sites. Consecutive adsorption measurements of the reactants showed similar uptakes as separate measurements indicating that there was no interference between adsorbed reactants. Mechanistic investigations by changing the sequence of admittance of reactants (NO x, NH 3) indicated that at 100–150 °C nitrogen formation follows an Eley–Rideal type mechanism, where adsorbed ammonia reacts with NO x in the gas phase, whereas adsorbed NO x showed no significant reactivity under conditions used. 相似文献
19.
A series of 1 wt.%Pt/ xBa/Support (Support = Al 2O 3, SiO 2, Al 2O 3-5.5 wt.%SiO 2 and Ce 0.7Zr 0.3O 2, x = 5–30 wt.% BaO) catalysts was investigated regarding the influence of the support oxide on Ba properties for the rapid NO x trapping (100 s). Catalysts were treated at 700 °C under wet oxidizing atmosphere. The nature of the support oxide and the Ba loading influenced the Pt–Ba proximity, the Ba dispersion and then the surface basicity of the catalysts estimated by CO 2-TPD. At high temperature (400 °C) in the absence of CO 2 and H 2O, the NO x storage capacity increased with the catalyst basicity: Pt/20Ba/Si < Pt/20Ba/Al5.5Si < Pt/10Ba/Al < Pt/5Ba/CeZr < Pt/30Ba/Al5.5Si < Pt/20Ba/Al < Pt/10BaCeZr. Addition of CO 2 decreased catalyst performances. The inhibiting effect of CO 2 on the NO x uptake increased generally with both the catalyst basicity and the storage temperature. Water negatively affected the NO x storage capacity, this effect being higher on alumina containing catalysts than on ceria–zirconia samples. When both CO 2 and H 2O were present in the inlet gas, a cumulative effect was observed at low temperatures (200 °C and 300 °C) whereas mainly CO 2 was responsible for the loss of NO x storage capacity at 400 °C. Finally, under realistic conditions (H 2O and CO 2) the Pt/20Ba/Al5.5Si catalyst showed the best performances for the rapid NO x uptake in the 200–400 °C temperature range. It resulted mainly from: (i) enhanced dispersions of platinum and barium on the alumina–silica support, (ii) a high Pt–Ba proximity and (iii) a low basicity of the catalyst which limits the CO 2 competition for the storage sites. 相似文献
20.
The activity of several catalysts are studied in the soot combustion reaction using air and NO/air as oxidising agents. Over Al 2O 3-supported catalysts NO (g) is a promoter for the combustion reaction with the extent of promotion depending on the Na loading. Over these catalysts SO 42− poisons this promotion by preventing NO oxidation through a site blocking mechanism. SiO 2 is unable to adsorb NO or catalyse its oxidation and over SiO 2-supported Na catalysts NO (g) inhibits the combustion reaction. This is ascribed to a competition between NO and O 2. Over Fe-ZSM-5 catalysts the presence of a NO x trapping component does not increase the combustion of soot in the presence of NO (g) and it is proposed that this previously reported effect is only seen under continuous NO x trap operation as NO 2 is periodically released during regeneration and thus available for soot combustion. Experiments during which the [NO] (g) is varied show that CO, rather than an adsorbed carbonyl-like intermediate, is formed upon reaction between NO 2 (the proposed oxygen carrier) and soot. 相似文献
|