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1.
In this study, we examine the interaction of N2O with TiO2(1 1 0) in an effort to better understand the conversion of NOx species to N2 over TiO2-based catalysts. The TiO2(1 1 0) surface was chosen as a model system because this material is commonly used as a support and because oxygen vacancies on this surface are perhaps the best available models for the role of electronic defects in catalysis. Annealing TiO2(1 1 0) in vacuum at high temperature (above about 800 K) generates oxygen vacancy sites that are associated with reduced surface cations (Ti3+ sites) and that are easily quantified using temperature programmed desorption (TPD) of water. Using TPD, X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS), we found that the majority of N2O molecules adsorbed at 90 K on TiO2(1 1 0) are weakly held and desorb from the surface at 130 K. However, a small fraction of the N2O molecules exposed to TiO2(1 1 0) at 90 K decompose to N2 via one of two channels, both of which are vacancy-mediated. One channel occurs at 90 K, and results in N2 ejection from the surface and vacancy oxidation. We propose that this channel involves N2O molecules bound at vacancies with the O-end of the molecule in the vacancy. The second channel results from an adsorbed state of N2O that decomposes at 170 K to liberate N2 in the gas phase and deposit oxygen adatoms at non-defect Ti4+ sites. The presence of these O adatoms is clearly evident in subsequent water TPD measurements. We propose that this channel involves N2O molecules that are bound at vacancies with the N-end of the molecule in the vacancy, which permits the O-end of the molecule to interact with an adjacent Ti4+ site. The partitioning between these two channels is roughly 1:1 for adsorption at 90 K, but neither is observed to occur for moderate N2O exposures at temperatures above 200 K. EELS data indicate that vacancies readily transfer charge to N2O at 90 K, and this charge transfer facilitates N2O decomposition. Based on these results, it appears that the decomposition of N2O to N2 requires trapping of the molecule at vacancies and that the lifetime of the N2O–vacancy interaction may be key to the conversion of N2O to N2. 相似文献
2.
Runduo Zhang Houshang Alamdari Serge Kaliaguine 《Applied catalysis. B, Environmental》2007,72(3-4):331-341
A series of La(Co, Mn, Fe)1−x(Cu, Pd)xO3 perovskites having high specific surface areas and nanosized crystal domains was prepared by reactive grinding. The solids were characterized by N2 adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed desorption (TPD) of O2, NO + O2, C3H6, in the absence or presence of 5% H2O, Fourier transform infrared (FTIR) spectroscopy, as well as activity tests towards NO reduction by propene under the conditions of 3000 ppm NO, 3000 ppm C3H6, 1% O2, 0 or 10% H2O, and 50,000 h−1 space velocity. The objective was to investigate the influence of H2O addition on catalytic behavior. A good performance (100% NO conversion, 77% N2 yield, and 90% C3H6 conversion) was achieved at 600 °C over LaFe0.8Cu0.2O3 under a dry feed stream. With the exposure of LaFe0.8Cu0.2O3 to a humid atmosphere containing 10% water vapor, the catalytic activity was slightly decreased yielding 91% NO conversion, 51% N2 yield, and 86% C3H6 conversion. A competitive adsorption between H2O vapor with O2 and NO molecules at anion vacancies over LaFe0.8Cu0.2O3 was found by means of TPD studies here. A deactivation mechanism was therefore proposed involving the occupation of available active sites by water vapor, resulting in an inhibition of catalytic activity in C3H6 + NO + O2 reaction. This H2O deactivation was also verified to be strictly reversible by removing steam from the feed. 相似文献
3.
Juan Antonio Martín Malcolm Yates Pedro vila Silvia Surez Jesús Blanco 《Applied catalysis. B, Environmental》2007,70(1-4):330-334
Nitric oxide and nitric dioxide compounds (NOx) present in stack gases from nitric acid plants are usually eliminated by selective catalytic reduction (SCR) with ammonia. In this process, small quantities of nitrous oxide (N2O) are produced. This undesirable molecule has a high greenhouse gas potential and a long lifetime in the atmosphere, where it can contribute to stratospheric ozone depletion. The influence of catalyst composition and some operating variables were evaluated in terms of N2O formation, using V2O5/TiO2 catalysts. High vanadia catalyst loading, nitric oxide inlet concentration and reaction temperature increase the generation of this undesirable compound. The results suggest that adsorbed ammonia not only reacts with NO via SCR, but also with small quantities of oxygen activated by the presence of NO. The mechanism proposed for N2O generation at low temperature is based on the formation of surface V–ON species which may be produced by the partial oxidation of dissociatively adsorbed ammonia species with NO + O2 (eventually NO2). When these active sites are in close proximity they can interact to form an N2O molecule. This mechanism seems to be affected by changes in the active site density produced by increasing the catalyst vanadia loading. 相似文献
4.
Koichi Yuzaki Takayoshi Yarimizu Kenji Aoyagi Shin-ichi Ito Kimio Kunimori 《Catalysis Today》1998,45(1-4):129-134
The study of catalytic decomposition of nitrous oxide to nitrogen and oxygen over Rh catalysts supported on various supports (USY, NaY, Al2O3, ZrO2, FSM-16, CeO2, La2O3) showed that the activities of Rh/Al2O3 and Rh/USY (ultrastable Y zeolite) catalysts were comparable to or higher than the other catalysts reported in the literatures. The catalytic activity of N2O decomposition was sensitive not only to the Rh dispersion but also to the preparation variables such as the Rh precursors and the supports used. A pulsed N2O experiment over a Rh/USY catalyst suggested that the catalytic N2O decomposition occurs on oxygen-covered surface and that O2 may be freed on collision of N2O molecules with the adsorbed oxygen atoms. 相似文献
5.
High thermal conductive β-SiC for selective oxidation of H2S: A new support for exothermal reactions
P. Nguyen D. Edouard J.-M. Nhut M.J. Ledoux Ch. Pham C. Pham-Huu 《Applied catalysis. B, Environmental》2007,76(3-4):300-310
This study aims at synthesizing a new by substituting 1 atom% Pd2+ in ionic state in TiO2 in the form of Ti0.99Pd0.01O1.99 with oxide-ion vacancy. The catalyst was synthesized by solution combustion method and was characterized by XRD and XPS. The catalytic activity was investigated by performing CO oxidation, hydrocarbon oxidation and NO reduction. A reaction mechanism for CO oxidation by O2 and NO reduction by CO was proposed. The model based on CO adsorption on Pd2+ and dissociative chemisorption of O2 in the oxide-ion vacancy for CO oxidation reaction fitted the experimental for CO oxidation. For NO reduction in presence of CO, the model based on competitive adsorption of NO and CO on Pd2+, NO chemisorption and dissociation on oxide-ion vacancy fitted the experimental data. The rate parameters obtained from the model indicated that the reactions were much faster over this catalyst compared to other catalysts reported in the literature. The selectivity of N2, defined as the ratio of the formation of N2 and formation of N2 and N2O, was very high compared to other catalysts and 100% selectivity was reached at temperature of 350 °C and above. As the N2O + CO reaction is an intermediate reaction for NO + CO reaction, it was also studied as an isolated reaction and the rate of the isolated reaction was less than that of intermediate reaction. 相似文献
6.
The selective catalytic reduction (SCR) of NOx (NO + NO2) by NH3 in O2 rich atmosphere has been studied on Cu-FAU catalysts with Cu nominal exchange degree from 25 to 195%. NO2 promotes the NO conversion at NO/NO2 = 1 and low Cu content. This is in agreement with next-nearest-neighbor (NNN) Cu ions as the most active sites and with NxOy adsorbed species formed between NO and NO2 as a key intermediate. Special attention was paid to the origin of N2O formation. CuO aggregates form 40–50% of N2O at ca. 550 K and become inactive for the SCR above 650 K. NNN Cu ions located within the sodalite cages are active for N2O formation above 600 K. This formation is greatly enhanced when NO2 is present in the feed, and originated from the interaction between NO (or NO2) and NH3. The introduction of selected co-cations, e.g. Ba, reduces very significantly this N2O formation. 相似文献
7.
The pathway for selective reduction of NOx by methane over Co mordenite cataysts has been studied by comparing the rates of the individual reactions (NO oxidation, CH4 oxidation, NO2 reduction) with that of the combined reaction (NO + O2 + CH4). Co(+2) was exchanged into H-MOR and Na-MOR to give catalysts with different metal loading and number of support protons. Additionally, exchanged Co(+2) ions were precipitated with NaOH to produce dispersed cobalt oxide on Na-MOR. The NO oxidation rate is the same for ion exchanged Co(+2) ions in H-MOR and Na-MOR, but the rate of Co(+2) ions is much lower than that of cobalt oxide. NO oxidation equilibrium is obtained only for those catalysts with high metal loading, cobalt oxide or run at low GHSV. Under the conditions of selective catalytic reduction, methane oxidation by O2 is low for all catalysts. The turnover frequency of Co on Na-MOR, however, is higher than that on H-MOR. The rate of NO2 reduction to N2 is directly proportional to the number of support acid sites and independent of the amount of Co. Comparison of the rates and selectivities for the individual reactions with the combined reaction of NO + O2 + CH4 indicates that there are two types of catalysts. For the first, the NO oxidation is in equilibrium and the rate determining step is reduction of NO2. For these catalysts, the rate (and selectivity) for formation of N2 is identical from NO + O2 + CH4 and NO2 + CH4. These catalysts have high metal loading and few acid sites. Nevertheless, the rate of N2 formation increases with increasing number of protons. For the second type of catalyst, NO oxidation is not in equilibrium and is the rate limiting step. For these catalysts the rate of N2 formation increases with increasing metal loading. Neither catalyst type, however, is optimized for the maximum formation of N2. By using a mixture of catalysts, one with high NO oxidation activity and one with a large number of Brønsted acid sites, the rate of N2 is greater than the weighted sum of the individual catalysts. The current results support the proposal that the pathway for selective catalytic reduction is bifunctional where metal sites affect NO oxidation, while support protons catalyze the formation of N2. 相似文献
8.
An effect of oxygen species formed from O2, N2O and NO on the selectivity of the catalytic oxidation of ammonia was studied over a polycrystalline Pt catalyst using the temporal analysis of products (TAP) reactor. The transient experiments were performed in the temperature range between 773 and 1073 K in a sequential pulse mode with a time interval of 0.2 s between the pulses of the oxidant (O2, N2O and NO) and NH3. In contrast to adsorbed oxygen species formed from NO, those from O2 and N2O reacted with ammonia yielding NO. It is suggested that the difference between these oxidising agents may be related to the different active sites for dissociation of O2, N2O and NO, where oxygen species of various Pt-O strength are formed. Weaker bound oxygen species, which are active for NO formation, originate from O2 and N2O rather than from NO. These species may be of bi-atomic nature. 相似文献
9.
Shin-ichi Tanaka Koichi Yuzaki Shin-ichi Ito Hiroshi Uetsuka Satoshi Kameoka Kimio Kunimori 《Catalysis Today》2000,63(2-4):413-418
N2O decomposition on an unsupported Rh catalyst has been studied using tracer technique in order to reveal the reaction mechanism. N216O was pulsed onto 18O/oxidized Rh catalyst at 220°C and desorbed O2 molecules (m/e=32,34,36) were monitored by means of mass spectrometer. The 18O fraction in the desorbed dioxygen was the same value as that on the surface oxygen. The result shows that the O2 molecules desorb via Langmuir–Hinshelwood mechanism, i.e., the desorption of dioxygen through the recombination of adsorbed oxygen. On the other hand, TPD measurements in He showed that desorption of oxygen from the Rh black catalyst occurred at the higher temperatures. Therefore, reaction-assisted desorption of oxygen during N2O decomposition reaction at the low temperature was proposed. 相似文献
10.
Tanja Kolli Katariina Rahkamaa-Tolonen Ulla Lassi Auli Savim ki Riitta L. Keiski 《Catalysis Today》2005,100(3-4):297-302
The effect of the Pd addition method into the fresh Pd/(OSC + Al2O3) and (Pd + OSC)/Al2O3 catalysts (OSC material = CexZr1−xO2 mixed oxides) was investigated in this study. The CO + NO and CO + NO + O2 model reactions were studied over fresh and aged catalysts. The differences in the fresh catalysts were insignificant compared to the aged catalysts. During the CO + NO reaction, only small differences were observed in the behaviour of the fresh catalysts. The light-off temperature of CO was about 20 °C lower for the fresh Pd/(OSC + Al2O3) catalyst than for the fresh (Pd + OSC)/Al2O3 catalyst during the CO + NO + O2 reaction. For the aged catalysts lower NO reduction and CO oxidation activities were observed, as expected. Pd on OSC-containing alumina was more active than Pd on OSC material after the agings. The activity decline is due to a decrease in the number of active sites on the surface, which was observed as a larger Pd particle size for aged catalysts than for fresh catalysts. In addition, the oxygen storage capacity of the aged Pd/(OSC + Al2O3) catalyst was higher than that of the (Pd + OSC)/Al2O3 catalyst. 相似文献
11.
M.N. Debbagh C. Salinas Martínez de Lecea J. Prez-Ramírez 《Applied catalysis. B, Environmental》2007,70(1-4):335-341
The catalytic reduction of N2O by CH4, CO, and their mixtures has been comparatively investigated over steam-activated FeZSM-5 zeolite. The influence of the molar feed ratio between N2O and the reducing agents, the gas-hourly space velocity, and the presence of O2 on the catalytic performance were studied in the temperature range of 475–850 K. The CH4 is more efficient than CO for N2O reduction, achieving the same degree of conversion at significantly lower temperatures. The apparent activation energy for N2O reduction by CH4 was very similar to that of direct N2O decomposition (140 kJ mol−1), being much lower for the N2O reduction by CO (60 kJ mol−1). This suggests that the reactions have a markedly different mechanism. Addition of CO using equimolar mixtures in the ternary N2O + CH4 + CO system did not affect the N2O conversion with respect to the binary N2O + CH4 system, indicating that CO does not interfere in the low-temperature reduction of N2O by CH4. In the ternary system, CO contributed to N2O reduction when methane was the limiting reactant. The conversion and selectivity of the reactions of N2O with CH4, CO, and their mixtures were not altered upon adding excess O2 in the feed. 相似文献
12.
Takeshi Nobukawa Kou Sugawara Kazu Okumura Keiichi Tomishige Kimio Kunimori 《Applied catalysis. B, Environmental》2007,70(1-4):342-352
Sharp NO and O2 desorption peaks, which were caused by the decomposition of nitro and nitrate species over Fe species, were observed in the range of 520–673 K in temperature-programmed desorption (TPD) from Fe-MFI after H2 treatment at 773 K or high-temperature (HT) treatment at 1073 K followed by N2O treatment. The amounts of O2 and NO desorption were dependent on the pretreatment pressure of N2O in the H2 and N2O treatment. The adsorbed species could be regenerated by the H2 and N2O treatment after TPD, and might be considered to be active oxygen species in selective catalytic reduction (SCR) of N2O with CH4. However, the reaction rate of CH4 activation by the adsorbed species formed after the H2 and N2O or the HT and N2O treatment was not so high as that of the CH4 + N2O reaction over the catalyst after O2 treatment. The simultaneous presence of CH4 and N2O is essential for the high activity of the reaction, which suggests that nascent oxygen species formed by N2O dissociation can activate CH4 in the SCR of N2O with CH4. 相似文献
13.
A. Obuchi A. Ogata H. Takahashi J. Oi G. R. Bamwenda K. Mizuno 《Catalysis Today》1996,29(1-4):103-107
Performances of Pt and Rh catalysts for the selective reduction of NO were investigated using various reducing agents under high gas hourly space velocity (GHSV). Higher activities were attained when olefins were used for both Pt and Rh catalysts, and when oxygen containing substances such as methyl tert.-butyl ether (MTBE) were used in the case of Rh catalysts. Selectivity toward N2 for the NO converted was from 7% to 38% for Pt catalysts and from 45% to 67% for Rh catalysts. A comparison of N2O decomposition rates on these catalysts has shown that gaseous N2O is not a principal intermediate in the pathway for N2 formation. The high selectivity toward N2 for Rh/Al2O3 at low GHSV conditions is attributed to an additional catalytic effect of A12O3, which can reduce NO2 with propylene at temperatures as low as 350°C. 相似文献
14.
Catalytic partial oxidation of methane to synthesis gas over ZrO2 and yttrium-stabilized zirconia (YSZ) is studied using O2 and N2O as oxidants. ZrO2 is much more active than YSZ in oxidation of methane with N2O. In contrast, YSZ is significantly more active than ZrO2 when O2 is used as an oxidant. The presence of O2 does not influence the rate of N2O decomposition over ZrO2 and YSZ, while the presence of H2O in the system decreases N2O conversion significantly. O2 and N2O are activated at different active sites. Y-induced oxygen vacancies are active for O2 activation, whereas oxygen co-ordinatively unsaturated Zr cations (Zr-CUS) located at corners, edges, steps and kinks are responsible for N2O activation. These sites are also capable of dissociating H2O, resulting in competition between H2O and N2O. As compared with N2O, molecular O2 is easier to be activated over YSZ and ZrO2. 相似文献
15.
Li Xue Changbin Zhang Hong He Yasutake Teraoka 《Applied catalysis. B, Environmental》2007,75(3-4):167-174
A series of CeO2 promoted cobalt spinel catalysts were prepared by the co-precipitation method and tested for the decomposition of nitrous oxide (N2O). Addition of CeO2 to Co3O4 led to an improvement in the catalytic activity for N2O decomposition. The catalyst was most active when the molar ratio of Ce/Co was around 0.05. Complete N2O conversion could be attained over the CoCe0.05 catalyst below 400 °C even in the presence of O2, H2O or NO. Methods of XRD, FE-SEM, BET, XPS, H2-TPR and O2-TPD were used to characterize these catalysts. The analytical results indicated that the addition of CeO2 could increase the surface area of Co3O4, and then improve the reduction of Co3+ to Co2+ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step of the N2O decomposition over cobalt spinel catalyst. We conclude that these effects, caused by the addition of CeO2, are responsible for the enhancement of catalytic activity of Co3O4. 相似文献
16.
K. Krishna A. Bueno-Lpez M. Makkee J.A. Moulijn 《Applied catalysis. B, Environmental》2007,75(3-4):210-220
CeO2 and CeReOx_y catalysts are prepared by the calcination at different temperatures (y = 500–1000 °C) and having a different composition (Re = La3+ or Pr3+/4+, 0–90 wt.%). The catalysts are characterised by XRD, H2-TPR, Raman, and BET surface area. The soot oxidation is studied with O2 and NO + O2 in the tight and loose contact conditions, respectively. CeO2 sinters between 800–900 °C due to a grain growth, leading to an increased crystallite size and a decreased BET surface area. La3+ or Pr3+/4+ hinders the grain growth of CeO2 and, thereby, improving the surface catalytic properties. Using O2 as an oxidant, an improved soot oxidation is observed over CeLaOx_y and CePrOx_y in the whole dopant weight loading and calcination temperature range studied, compared with CeO2. Using NO + O2, the soot conversion decreased over CeLaOx_y catalysts calcined below 800 °C compared with the soot oxidation over CeO2_y. CePrOx_y, on the other hand, showed a superior soot oxidation activity in the whole composition and calcination temperature range using NO + O2. The improvement in the soot oxidation activity over the various catalysts with O2 can be explained based on an improvement in the external surface area. The superior soot oxidation activity of CePrOx_y with NO + O2 is explained by the changes in the redox properties of the catalyst as well as surface area. CePrOx_y, having 50 wt.% of dopant, is found to be the best catalyst due to synergism between cerium and praseodymium compared to pure components. NO into NO2 oxidation activity, that determines soot oxidation activity, is improved over all CePrOx catalysts. 相似文献
17.
Runduo Zhang Adrian Villanueva Houshang Alamdari Serge Kaliaguine 《Applied catalysis. B, Environmental》2006,64(3-4):220-233
One series of LaCo1−xCuxO3 perovskites with high specific surface area was prepared by the new method designated as reactive grinding. These solids were characterized by N2 adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), H2-temperature programmed reduction (TPR), O2-temperature programmed desorption (TPD), NO + O2-TPD, C3H6-TPD, NO + O2-temperature programmed surface reaction (TPSR) under C3H6/He flow as well as catalytic reduction of NO activity tests. The catalytic performance of unsubstituted sample is poor with a maximum conversion to N2 of 19% at 500 °C at a space velocity of 55,000 h−1 (3000 ppm NO, 3000 ppm C3H6, 1% O2 in helium) but it is improved by incorporation of Cu into the lattice. A maximal N2 yield of 46% was observed over LaCo0.8Cu0.2O3 under the same conditions. Not only the abundance of -oxygen but also the mobility of β-oxygen of lanthanum cobaltite was remarkably enhanced by Cu substitution according to O2-TPD and H2-TPR studies. The better performance of Cu-substituted samples is likely to correspond to the essential nature of Cu and facility to form nitrate species in NO transformation conditions. In the absence of O2, the reduction of NO by C3H6 was performed over LaCo0.8Cu0.2O3, leading to a maximal conversion to N2 of 73% accompanied with the appearance of some organo nitrogen compounds (identified as mainly C3H7NO2). Subsequently, a mechanism involving the formation of an organic nitro intermediate, which further converts into N2, CO2 and H2O via isocyanate, was proposed. Gaseous oxygen acts rather as an inhibitor in the reaction of NO and C3H6 over highly oxidative LaCo0.8Cu0.2O3 due to the heavily unselective combustion of C3H6 by O2. 相似文献
18.
Conversion of NOx with reducing agents H2, CO and CH4, with and without O2, H2O, and CO2 were studied with catalysts based on MOR zeolite loaded with palladium and cerium. The catalysts reached high NOx to N2 conversion with H2 and CO (>90% conversion and N2 selectivity) range under lean conditions. The formation of N2O is absent in the presence of both H2 and CO together with oxygen in the feed, which will be the case in lean engine exhaust. PdMOR shows synergic co-operation between H2 and CO at 450–500 K. The positive effect of cerium is significant in the case of H2 and CH4 reducing agent but is less obvious with H2/CO mixture and under lean conditions. Cerium lowers the reducibility of Pd species in the zeolite micropores. The catalysts showed excellent stability at temperatures up to 673 K in a feed with 2500 ppm CH4, 500 ppm NO, 5% O2, 10% H2O (0–1% H2), N2 balance but deactivation is noticed at higher temperatures. Combining results of the present study with those of previous studies it shows that the PdMOR-based catalysts are good catalysts for NOx reduction with H2, CO, hydrocarbons, alcohols and aldehydes under lean conditions at temperatures up to 673 K. 相似文献
19.
Supporting Pt and Pd catalysts have been examined for the reduction of NO with H2 in the presence of oxygen and moisture. All catalysts showed a conversion maximum in the NO reduction at around 373 K. An additional conversion maximum was found to appear at around 573 K over several metal oxides supporting Pd, and Pd/TiO2 gave the highest conversion at around 573 K among the catalysts tested. In the reaction at 373 K, NO might be reduced directly by H2 both on Pt and Pd catalysts to give N2 and N2O. At the conversion maximum of the Pd/TiO2 catalyst at 575 K, however, in situ generated NO2 seems to react with H2. 相似文献
20.
Catalytic reduction of NO by CO over NiO/CeO2 catalyst in stoichiometric NO/CO and NO/CO/O2 reaction
Yong Wang Aimin Zhu Yuzhuo Zhang C.T. Au Xuefeng Yang Chuan Shi 《Applied catalysis. B, Environmental》2008,81(1-2):141-149
A new catalyst composed of nickel oxide and cerium oxide was studied with respect to its activity for NO reduction by CO under stoichiometric conditions in the absence as well as the presence of oxygen. Activity measurements of the NO/CO reaction were also conducted over NiO/γ-Al2O3, NiO/TiO2, and NiO/CeO2 catalysts for comparison purposes. The results showed that the conversion of NO and CO are dependent on the nature of supports, and the catalysts decreased in activity in the order of NiO/CeO2 > NiO/γ-Al2O3 > NiO/TiO2. Three kinds of CeO2 were prepared and used as support for NiO. They are the CeO2 prepared by (i) homogeneous precipitation (HP), (ii) precipitation (PC), and (iii) direct decomposition (DP) method. We found that the NiO/CeO2(HP) catalyst was the most active, and complete conversion of NO and CO occurred at 210 °C at a space velocity of 120,000 h−1. Based on the results of surface analysis, a reaction model for NO/CO interaction over NiO/CeO2 has been proposed: (i) CO reduces surface oxygen to create vacant sites; (ii) on the vacant sites, NO dissociates to produce N2; and (iii) the oxygen originated from NO dissociation is removed by CO. 相似文献