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1.
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
2.
This study deals with the development of a laboratory bench for the practical evaluation of catalysts that are useful for the direct conversion of NO x and soot in the exhaust of diesel engines. The employed model exhaust is generated by using a diffusion burner with additionally dosing some gaseous components to the burner gas to obtain a realistic feed composition. The produced soot is extensively characterized by employing thermogravimetry, transmission electron microscopy, N 2 physisorption and temperature programmed techniques. The results of the different characterization methods show that the present soot is suitable for the intended catalytic investigations. The simultaneous conversion of NO x and soot is examined like in practice, i.e. the soot is separated from the tail gas by a diesel particulate filter (DPF) that is coated with the catalyst. The deposited soot is then catalytically converted by NO x and O 2 to form N 2 and CO 2. The conversions of NO x and soot are measured by exclusively applying gas analysers, whereby a special experimental procedure is developed to determine the soot removal. Hence, additional soot related analytics are not required. To show the suitability of the constructed bench a Pt/Fe 2O 3/β-zeolite sample is taken as test catalyst that is reported to be very active in NO x/soot reaction. The measurements performed with and without catalyst clearly show the effect of the used sample in simultaneous NO x/soot conversion. We therefore consider the constructed laboratory bench to be a useful tool for testing and ranking catalytic materials. 相似文献
3.
The influence of NO on the oxidation of metal (cerium, copper, and iron)-activated soot was studied. Without NO in the gas phase, the activation energy of soot is ≈170 kJ/mol, independent of the type of metal applied in the soot. The rate-limiting step in the oxidation with oxygen is probably the decomposition of surface oxygen complexes. In presence of NO, the oxidation rate of soot mixed with a supported platinum catalyst is increased significantly, especially for cerium-activated soot. The activation energy of the oxidation reaction is decreased by the presence of NO in the gas phase. The increase in reaction rate as a result of NO and a platinum catalyst is explained by a cycle of two catalytic reactions, where platinum oxidises NO to NO 2, which subsequently oxidises soot using cerium as a catalyst, forming NO which can participate in the reaction more than once. This oxidation mechanism can be put into practice by combining a platinum-activated particulate trap with a combination of platinum and cerium fuel additives. This combination might be a breakthrough in the search for an applicable catalytic soot removal system. 相似文献
4.
NO x adsorption/desorption capacities of barium aluminates and BaSnO 3 were measured under representative exhaust gas mixture at temperatures below 550°C and compared to those of bulk BaO. The capacities are high and the test of sorption–desorption is reproducible on barium aluminate and BaSnO 3, while this is not the case on BaO. The difference is due to the electronic environment of barium oxide. If BaO is not engaged in a chemical bond, progressive formation of high stability carbonates is observed. This is not the case with barium aluminate and BaSnO 3, where carbonation does not take place because the competition between nitrate and carbonate formation is in favour of the nitrate due to its chemical nature. An N-bounded nitrate, with IR frequencies at 1360 and 1415 cm −1, is formed on barium aluminate and BaSnO 3 and not on bulk BaO. 相似文献
6.
In order to elucidate the effect of support in the catalytic performance, two selected potassium-promoted catalysts (K1Cu/beta
and KCu2/Al 2O 3) 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 N 2 and CO 2. Among the catalysts tested, KCu2/Al 2O 3 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
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.
Preliminary studies on a series of nanocomposite BaO–Fe ZSM-5 materials have been carried out to determine the feasibility of combining NO x trapping and SCR-NH 3 reactions to develop a system that might be applicable to reducing NO x emissions from diesel-powered vehicles. The materials are analysed for SCR-NH 3 and SCR-urea reactivity, their NO x trapping and NH 3 trapping capacities are probed using temperature programmed desorption (TPD) and the activities of the catalysts for promoting the NH 3 ads + NO/O 2 → N 2 and NO x ads + NH 3 → N 2 reactions are studied using temperature programmed surface reaction (TPSR). 相似文献
9.
Kinetic and in situ spectroscopic studies of Co–Pt/MFI and Co–Pt/HY catalysts for the selective reduction of NO x with propylene in the presence of oxygen were carried out. The results of catalytic tests of Co–Pt/MFI showed that the addition of Pt to Co based catalyst improved the activity, but a small increase in selectivity to N 2O (15–20%) was observed. In the case of Co–Pt/HY catalyst, the addition of Pt improved the activity more significantly and however, a larger increase in selectivity to N 2O (6–72%) was obtained. It was also found from the results of FT-IR studies of Co–Pt/MFI that the reduction of NO to N 2 was as follows: firstly the oxidation of NO to NO 2 occurred over metallic Pt and NO 2 forms Co–NO 2, Co–ONO, and/or Co–ONO 2; secondly, the partial oxidation of C 3H 6 was happened over Brønsted acid sites and the reaction of NO 2 formed on Co sites with partial oxidized C 3H 6 produced organo-nitro species. These species were dehydrated and isomerized to form isocyanate. Finally, [NCO] type intermediates react with NO from gas phase to selectively yield N 2. 相似文献
10.
Nano-structured perovskite-type lanthanum ferrites La 1 − xA xFe 1 − yB yO 3 (where A = Na, K, Rb and B = Cu), prepared by the solution combustion synthesis (SCS) method and characterized by BET, XRD, FESEM, AAS and catalytic activity tests in microreactors as well as on an engine bench, proved to be effective in the simultaneous removal of soot and NO, the two prevalent pollutants in diesel exhaust gases in the temperature range 350–450 °C. The best compromise between soot and nitrogen oxide abatement was shown by the La-K-Cu-FeO 3 catalyst which displayed the highest catalytic activity towards carbon combustion and the highest NO conversion activity. 相似文献
11.
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
12.
Co 3O 4–CeO 2 type mixed oxide catalyst compositions have been prepared by using co-precipitation method and, their catalytic activity towards diesel particulate matter (PM)/carbon oxidation has been evaluated under both loose and tight contact conditions. These catalysts show excellent catalytic activity for PM/carbon oxidation, despite their low surface area. The activation energy observed for non-catalyzed and catalyzed reactions are 163 kJ/mol and 140 kJ/mol, respectively, which also confirm the catalytic activity of catalyst for carbon/soot oxidation. The promotional effects of an optimum amount of cobalt oxide incorporation in ceria and presence of a small amount of potassium appears to be responsible for the excellent soot oxidation activity of this mixed oxide type material. The catalytic materials show good thermal stability, while their low cost will also add to their potential for practical applications. 相似文献
13.
A method to quantify DRIFT spectral features associated with the in situ adsorption of gases on a NO x adsorber catalyst, Pt/K/Al 2O 3, is described. To implement this method, the multicomponent catalyst is analysed with DRIFT and chemisorption to determine that under operating conditions the surface comprised a Pt phase, a pure γ-Al 2O 3 phase with associated hydroxyl groups at the surface, and an alkalized-Al 2O 3 phase where the surface –OH groups are replaced by –OK groups. Both DRIFTS and chemisorption experiments show that 93–97% of the potassium exists in this form. The phases have a fractional surface area of 1.1% for the 1.7 nm-sized Pt, 34% for pure Al 2O 3 and 65% for the alkalized-Al 2O 3. NO 2 and CO 2 chemisorption at 250 °C is implemented to determine the saturation uptake value, which is observed with DRIFTS at 250 °C. Pt/Al 2O 3 adsorbs 0.087 μmol CO 2/m 2and 2.0 μmol NO 2/m 2, and Pt/K/Al 2O 3 adsorbs 2.0 μmol CO 2/m 2and 6.4 μmol NO 2/m 2. This method can be implemented to quantitatively monitor the formation of carboxylates and nitrates on Pt/K/Al 2O 3 during both lean and rich periods of the NO x adsorber catalyst cycle. 相似文献
14.
Meso- or micro/mesoporous supports (NbMCM-41 and NaY + NbMCM-41, respectively) were tested for Pt loading. The effects of the support structure and composition on the metal oxidation and on nitrate storage properties were pointed out in the SCR for NO x removal. Nitrate species were found directly related to the catalytic performance of Pt. Niobium from NbMCM-41 matrix in Pt/NbMCM-41 play the role of NO x storage species, whereas in the presence of NaY in the support, sodium cations act as storage for NO x. 相似文献
15.
The effect of different reducing agents (H 2, CO, C 3H 6 and C 3H 8) on the reduction of stored NO x over PM/BaO/Al 2O 3 catalysts (PM = Pt, Pd or Rh) at 350, 250 and 150 °C was studied by the use of both NO 2-TPD and transient reactor experiments. With the aim of comparing the different reducing agents and precious metals, constant molar reduction capacity was used during the reduction period for samples with the same molar amount of precious metal. The results reveal that H 2 and CO have a relatively high NO x reduction efficiency compared to C 3H 6 and especially C 3H 8 that does not show any NO x reduction ability except at 350 °C over Pd/BaO/Al 2O 3. The type of precious metals affects the NO x storage-reduction properties, where the Pd/BaO/Al 2O 3 catalyst shows both a high storage and a high reduction ability. The Rh/BaO/Al 2O 3 catalyst shows a high reduction ability but a relatively low NO x storage capacity. 相似文献
16.
A La–Sr–Cu–O–S system with K 2NiF 4 perovskite-type structure has been studied as a novel SO x-resistant combustion catalyst. The XRD result implied that sulfur is incorporated into the structure as non-sulfate-type cations. An introduction of sulfur with highly positive valence (S 6+ or S 4+) into the lattice requires the charge compensation by decreasing the oxidation number of Cu. This is accompanied by the creation of more reducible Cu species, which would achieve the light-off of catalytic C 3H 6 oxidation at lower temperatures. More important feature of sulfur-containing compounds is that the catalytic C 3H 6 oxidation was significantly accelerated by addition of SO 2 to the gas feed. The catalytic performance for the oxidation of C 3H 6 and CO and the reduction of NO was finally evaluated in a simulated automotive exhaust in the presence of SO 2. 相似文献
17.
Reaction activities of several developed catalysts for NO oxidation and NO x (NO + NO 2) reduction have been determined in a fixed bed differential reactor. Among all the catalysts tested, Co 3O 4 based catalysts are the most active ones for both NO oxidation and NO x reduction reactions even at high space velocity (SV) and low temperature in the fast selective catalytic reduction (SCR) process. Over Co 3O 4 catalyst, the effects of calcination temperatures, SO 2 concentration, optimum SV for 50% conversion of NO to NO 2 were determined. Also, Co 3O 4 based catalysts (Co 3O 4-WO 3) exhibit significantly higher conversion than all the developed DeNO x catalysts (supported/unsupported) having maximum conversion of NO x even at lower temperature and higher SV since the mixed oxide Co-W nanocomposite is formed. In case of the fast SCR, N 2O formation over Co 3O 4-WO 3 catalyst is far less than that over the other catalysts but the standard SCR produces high concentration of N 2O over all the catalysts. The effect of SO 2 concentration on NO x reduction is found to be almost negligible may be due to the presence of WO 3 that resists SO 2 oxidation. 相似文献
18.
The Co/MFI(SiO 2/Al 2O 3 = 30) were prepared by a precipitation method with NaOCl in alkali solutions exhibited high activities to N 2 at 250 °C for the selective catalytic reduction (SCR) of NO x. These catalysts showed two UV–vis bands at 700 and 400 nm, indicating the presence of octahedral Co(III) as well as tetrahedral Co(II). The high SCR activity over such Co(III, II)/MFI(30) seems to come from Co(III)---O moieties. The Co(II)MFI(30) catalysts prepared from Co(II)Cl 2 exhibited low SCR activities due to the presence of tetrahedral Co(II) ions in MFI. Less CO formation occurred over Co/MFI catalysts. The Fe/MFI(30) catalyst exhibited high activity due to the presence of some Fe---O species in MFI but more amount of CO were produced during SCR. H/MFI(30) catalyst exhibited a good SCR activity. However, more amount of carbonaceous deposits were produced on it. The correlation between acid concentration and SCR activity was discussed over H/MFIs. 相似文献
19.
The presence of sulfur in automotive exhaust is known to be detrimental to lean-NO x traps as SO 2 is oxidized to SO 3 that competes with NO 2 for sites on the trap and is difficult to remove. In this study the effect of adding Cu to the prototypical Pt–BaO/γ-Al 2O 3 formulation on the system's tolerance for sulfur was investigated. It was found that in the absence of sulfur, Cu decreases the performance in terms of both NO x storage capacity and reduction of NO x to N 2 during regeneration. In the presence of SO 2, Cu provides a significant improvement in sulfur tolerance so that, after sulfur exposure, the storage capacity of the Cu-modified material can exceed that of the baseline material. The sulfur tolerance afforded by Cu is attributed to a moderation in the activity for SO 2 oxidation resulting from the formation of a Pt–Cu bimetallic phase. The propensity for NO oxidation is also modified, but to a lesser effect. Evidence for the bimetallic phase is provided by temperature-programmed reduction (TPR) and electron microscopy. The impact of SO 2 on the Cu-modified material is greater during the regenerative reduction cycle. In this case, the results suggest that sulfur blocks Pt and possibly Cu sites and that the sulfur is not removed by oxidation during the subsequent storage cycle. Hence, activity lost during the reduction cycle is not restored. In contrast, sulfur that blocks Pt sites on the baseline material during the reduction cycle is subsequently oxidized and desorbs from the Pt, restoring the activity. However, some of the resulting SO 3 reacts with the BaO to form BaSO 4, and there is a partial loss of storage capacity. 相似文献
20.
This study addresses the catalytic reaction of NO x and soot into N 2 and CO 2 under O 2-rich conditions. To elucidate the mechanism of the soot/NO x/O 2 reaction and particularly the role of the catalyst -Fe 2O 3 is used as model sample. Furthermore, a series of examinations is also made with pure soot for reference purposes. Temperature programmed oxidation and transient experiments in which the soot/O 2 and soot/NO reaction are temporally separated show that the NO reduction occurs on the soot surface without direct participation of the Fe 2O 3 catalyst. The first reaction step is the formation of CC(O) groups that is mainly associated with the attack of oxygen on the soot surface. The decomposition of these complexes leads to active carbon sites on which NO is adsorbed. Furthermore, the oxidation of soot by oxygen provides a specific configuration of active carbon sites with suitable atomic orbital orientation that enables the chemisorption and dissociation of NO as well as the recombination of two adjacent N atoms to evolve N 2. Moreover, carbothermal reaction, high resolution transmission electron microscopy and isotopic studies result in a mechanistic model that describes the role of the Fe 2O 3 catalyst. This model includes the dissociative adsorption of O 2 on the iron oxide, surface migration of the oxygen to the contact points of soot and catalyst and then final transfer of O to the soot. Moreover, our experimental data suggest that the contact between both solids is maintained up to high conversion levels thus resulting in continuous oxygen transfer from catalyst to soot. As no coordinative interaction of soot and Fe 2O 3 catalyst is evidenced by diffuse reflectance infrared Fourier transform spectroscopy a van der Waals type interaction is supposed. 相似文献
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