Kinetic studies of adsorbed CO electrochemical oxidation on Pt(335) at full and sub-saturation coverages

Electrochemical measurements were performed to characterize the kinetics of adsorbed CO oxidation on the surface of the stepped Pt(s)-[4(111)x(100)][triple bond, length half m-dash]Pt(335) single crystal electrode. For CO adsorbed to full coverage at 0.1 V (versus the reversible hydrogen electrode, RHE) in 0.5 M H(2)SO(4) at ambient temperature (23 degrees C), oxidation of the layer gave 7.6 x 10(14) +/- 0.3 CO/cm(2) as the saturation CO coverage, just below the average value reported for CO on Pt(335) in ultra high vacuum (8.3 x 10(14) +/- 0.6 CO/cm(2)). In potential step measurements carried out between 0.75 and 0.9 V, the peak region in the current-time transient was consistent with the surface reaction between adsorbed CO and adsorbed oxide as rate limiting. Plotting the log of the rate constant for the surface reaction versus potential gave a Tafel slope of 79 mV per decade, consistent with responses for CO electrochemical oxidation on structurally related stepped Pt electrodes. For CO coverages below saturation, current-time transients were more stable in 0.05 M H(2)SO(4) than in the higher concentration electrolyte. Numerically solving the rate equations to the Langmuir-Hinshelwood model of adsorbed CO electrochemical oxidation reproduced the main features in current-time transients measured at 0.7 V in 0.05 M H(2)SO(4) for sub-saturation CO coverages. The results provide new insights into CO oxidation on Pt at sub-saturation coverage and confirm that anions play a role in CO surface chemistry.     

First identification and thermodynamic characterization of the ternary U(VI) species, UO2(O2)(CO3)2(4-), in UO2-H2O2-K2CO3 solutions

In alkaline carbonate solutions, hydrogen peroxide can selectively replace one of the carbonate ligands in UO2(CO3)3(4-) to form the ternary mixed U(VI) peroxo-carbonato species UO2(O2)(CO3)2(4-). Orange rectangular plates of K4[UO2(CO3)2(O2)].H2O were isolated and characterized by single crystal X-ray diffraction studies. Crystallographic data: monoclinic, space group P2(1)/ n, a = 6.9670(14) A, b = 9.2158(10) A, c = 18.052(4) A, Z = 4. Spectrophotometric titrations with H 2O 2 were performed in 0.5 M K 2CO 3, with UO2(O2)(CO3)2(4-) concentrations ranging from 0.1 to 0.55 mM. The molar absorptivities (M(-1) cm(-1)) for UO2(CO3)3(4-) and UO2(O2)(CO3)2(4-) were determined to be 23.3 +/- 0.3 at 448.5 nm and 1022.7 +/- 19.0 at 347.5 nm, respectively. Stoichiometric analyses coupled with spectroscopic comparisons between solution and solid state indicate that the stable solution species is UO2(O2)(CO3)2(4-), which has an apparent formation constant of log K' = 4.70 +/- 0.02 relative to the tris-carbonato complex.     

钙改性的Pd/CeO2-ZrO2-Al2O3催化剂催化甲醇裂解反应

采用共沉淀法制备了未改性的和Ca掺杂的CeO2-ZrO2-Al2O3样品,进一步用浸渍法制备了Pd/CeO2-ZrO2-Al2O3(Pd/CZA)和Pd/CeO2-ZrO2-Al2O3-CaO (Pd/CZACa)催化剂.运用X射线衍射、N2吸附-脱附、储氧量测定、CO化学吸附、NH3程序升温脱附、CO2程序升温脱附、...     

SiO2—Al2O3和MgO催化剂上吸附CH3NO2的TPD和IR研究

用TPD和IR方法研究了CH_3NO_2在典型固体酸SiO_2-Al_2O_3和固体碱MgO催化剂上的吸附分解。结果表明,在SiO_2-Al_2O_3表面CH_3NO_2吸附转化为表面甲酰胺物种,后者在高温下分解为CO_2和NH_3。在MgO表面CH_3NO_2吸附形成多种表面化学物种,它们在升温过程中脱附,并通过表面亚硝基甲烷物种分解为NO、C_2H_4、C_2H_6和N_2O.讨论了CH_3NO_2分解过程中表面酸、碱中心的作用。     

改性Ag/α-Al_2O_3催化丙烯气相环氧化反应

制备了以分子氧为氧化剂,对丙烯气相环氧化具有较好催化性能的改性负载银催化剂,并利用氧气程序升温脱附(O2-TPD)技术研究了氧在其表面上的脱附行为.实验结果表明:Ag/α-Al2O3催化剂只能使丙烯完全氧化成二氧化碳和水;当该催化剂用K2O改性后,可获得少量的环氧丙烷;Y2O3改性的Ag/α-Al2O3催化剂,可获得极少量的丙醛和丙酮;将0.1%(w)Y2O3添加到Ag-K2O/α-Al2O3后,可以显著提高催化剂的丙烯环氧化性能.在0.1MPa、245℃、20%C3H6/8%O2/72%N2和气体空速2000h-1的反应条件下,通过20%(w)Ag-0.1%Y2O3-0.1%K2O/α-Al2O3催化剂时,丙烯转化率为4.0%,环氧丙烷的选择性为46.8%.O2-TPD研究表明,少量的Y2O3、K2O或Y2O3-K2O作为助剂添加到20%Ag/α-Al2O3催化剂中时,减少了高温区与丙烯完全氧化有关的吸附氧物种的量,低温区余下的吸附氧物种量不变,有利于丙烯环氧化反应,提高了环氧丙烷的选择性.     

具有低SO_2氧化活性的Pt/Zr_xTi_(1-x)O_2柴油车氧化催化剂的制备及性能

采用共沉淀法制备了一系列ZrxTi1-xO2(x=0.0,0.1,0.5,0.9,1.0)复合氧化物,并以此为载体,用等孔体积浸渍H2PtCl6制得Pt/ZrxTi1-xO2柴油车氧化催化剂.运用N2吸附-脱附,X射线多晶粉末衍射,X射线光电子能谱,H2程序升温还原和NH3程序升温脱附等手段对催化剂进行了表征.结果表明,在系列催化剂样品中,Zr0.1Ti0.9O2复合氧化物主要以锐钛矿形式存在,具有较好的织构性能,样品的比表面积达94m2/g,孔体积为0.33cm3/g.相应地,Pt/Zr0.1Ti0.9O2催化剂表现出优异的催化氧化性能,HC和CO的起燃温度(T50)分别为185和174oC,完全转化温度(T90)分别为197和201oC;且具有较低的SO2氧化活性,350oC时SO2仅转化25.5%.     

Uptake of CO2, SO2, HNO3 and HCl on calcite (CaCO3) at 300 K: mechanism and the role of adsorbed water

All experimental observations of the uptake of the four title compounds on calcite are consistent with the presence of a reactive bifunctional surface intermediate Ca(OH)(HCO3) that has been proposed in the literature. The uptake of CO2 and SO2 occurs on specific adsorption sites of crystalline CaCO3(s) rather than by dissolution in adsorbed water, H2O(ads). SO2 primarily interacts with the bicarbonate moiety whereas CO2, HNO3 and HCl all react first with the hydroxyl group of the surface intermediate. Subsequently, the latter two react with the bicarbonate group to presumably form Ca(NO3)2 and CaCl2.2H2O. The effective equilibrium constant of the interaction of CO2 with calcite in the presence of H2O(ads) is kappa = deltaCO2/(H2O(ads)[CO2]) = 1.62 x 10(3) bar(-1), where CO2 is the quantity of CO2 adsorbed on CaCO3. The reaction mechanism involves a weakly bound precursor species that is reversibly adsorbed and undergoes rate-controlling concurrent reactions with both functionalities of the surface intermediate. The initial uptake coefficients gamma0 on calcite powder depend on the abundance of H2O(ads) under the present experimental conditions and are on the order of 10(-4) for CO2 and 0.1 for SO2, HNO3 and HCl, with gamma(ss) being significantly smaller than gamma0 for HNO3 and HCl, thus indicating partial saturation of the uptake. At 33% relative humidity and 300 K there are 3.5 layers of H2O adsorbed on calcite that reduce to a fraction of a monolayer of weakly and strongly bound water upon pumping and/or heating.     

Vertical and lateral order in adsorbed water layers on anatase TiO2(101)

The structure and energetics of thin water overlayers on the (101) surface of TiO(2)-anatase have been studied through first-principles molecular dynamics simulations at T = 160 K. At one monolayer coverage, H(2)O molecules are adsorbed at the 5-fold Ti sites (Ti(5c)), forming an ordered crystal-like 2D layer with no significant water-water interactions. For an adsorbed bilayer, H(2)O molecules at both Ti(5c) and bridging oxygen (O(2c)) sites form a partially ordered structure, where the water oxygens occupy regular sites but the orientation of the molecules is disordered; in addition, stress-relieving defects are usually present. When a third layer is adsorbed, very limited parallel and perpendicular order is observed above the first bilayer. The calculated energetics of multilayer adsorption is in good agreement with recent temperature-programmed desorption data.     

Identification of defect sites on MgO(100) thin films by decoration with Pd atoms and studying CO adsorption properties.

CO adsorption on Pd atoms deposited on MgO(100) thin films has been studied by means of thermal desorption (TDS) and Fourier transform infrared (FTIR) spectroscopies. CO desorbs from the adsorbed Pd atoms at a temperature of about 250 K, which corresponds to a binding energy, E(b), of about 0.7 +/- 0.1 eV. FTIR spectra suggest that at saturation two different sites for CO adsorption exist on a single Pd atom. The vibrational frequency of the most stable, singly adsorbed CO molecule is 2055 cm(-)(1). Density functional cluster model calculations have been used to model possible defect sites at the MgO surface where the Pd atoms are likely to be adsorbed. CO/Pd complexes located at regular or low-coordinated O anions of the surface exhibit considerably stronger binding energies, E(b) = 2-2.5 eV, and larger vibrational shifts than were observed in the experiment. CO/Pd complexes located at oxygen vacancies (F or F(+) centers) are characterized by much smaller binding energies, E(b) = 0.5 +/- 0.2 or 0.7 +/- 0.2 eV, which are in agreement with the experimental value. CO/Pd complexes located at the paramagnetic F(+) centers show vibrational frequencies in closest agreement with the experimental data. These comparisons therefore suggest that the Pd atoms are mainly adsorbed at oxygen vacancies.     

Synthesis, structure, chemical stability, and electrical properties of Nb-, Zr-, and Nb-codoped BaCeO3 perovskites

We report the effect of donor-doped perovskite-type BaCeO(3) on the chemical stability in CO(2) and boiling H(2)O and electrical transport properties in various gas atmospheres that include ambient air, N(2), H(2), and wet and dry H(2). Formation of perovskite-like BaCe(1-x)Nb(x)O(3±δ) and BaCe(0.9-x)Zr(x)Nb(0.1)O(3±δ) (x = 0.1; 0.2) was confirmed using powder X-ray diffraction (XRD) and electron diffraction (ED). The lattice constant was found to decrease with increasing Nb in BaCe(1-x)Nb(x)O(3±δ), which is consistent with Shannon's ionic radius trend. Like BaCeO(3), BaCe(1-x)Nb(x)O(3±δ) was found to be chemically unstable in 50% CO(2) at 700 °C, while Zr doping for Ce improves the structural stability of BaCe(1-x)Nb(x)O(3±δ). AC impedance spectroscopy was used to estimate electrical conductivity, and it was found to vary with the atmospheric conditions and showed mixed ionic and electronic conduction in H(2)-containing atmosphere. Arrhenius-like behavior was observed for BaCe(0.9-x)Zr(x)Nb(0.1)O(3±δ) at 400-700 °C, while Zr-free BaCe(1-x)Nb(x)O(3±δ) exhibits non-Arrhenius behavior at the same temperature range. Among the perovskite-type oxides investigated in the present work, BaCe(0.8)Zr(0.1)Nb(0.1)O(3±δ) showed the highest bulk electrical conductivity of 1.3 × 10(-3) S cm(-1) in wet H(2) at 500 °C, which is comparable to CO(2) and H(2)O unstable high-temperature Y-doped BaCeO(3) proton conductors.     

Ethanol adsorption, decomposition and oxidation on Ir(111): a high resolution XPS study.

Ethanol (C(2)H(5)OH) adsorption, decomposition and oxidation is studied on Ir(111) using high-energy resolution, fast XPS and temperature-programmed desorption. During heating of an adsorbed ethanol layer a part of the C(2)H(5)OH(ad) desorbs molecularly, and another part remains on the surface and decomposes around 200 K; these two decomposition pathways are identified, as via acetyl (H(3)C--C=O) and via CO(ad)+CH(3ad), respectively. Acetyl and CH(3ad) decompose around 300 K into CH(ad) (and CO(ad)). CH(ad) decomposes forming C(x) and H(2) around 520 K. In the presence of O(ad) an acetate intermediate is formed around 180 K, as well as a small amount of CH(3ad) and CO(ad). Acetate decomposes between 400-480 K into CO(2), H(2)(/H(2)O) and CH(ad).     

Physisorption of N2, O2, and CO on fully oxidized TiO2(110)

Physisorption of N(2), O(2), and CO was studied on fully oxidized TiO(2)(110) using beam reflection and temperature-programmed desorption (TPD) techniques. Sticking coefficients for all three molecules are nearly equal (0.75 +/- 0.05) and approximately independent of coverage suggesting that adsorption occurs via a precursor-mediated mechanism. Excluding multilayer coverages, the TPD spectra for all three adsorbates exhibit three distinct coverage regimes that can be interpreted in accord with previous theoretical studies of N(2) adsorption. At low coverages (0-0.5 N(2)/Ti(4+)), N(2) molecules bind head-on to five-coordinated Ti(4+) ions. The adsorption occurs preferentially on the Ti(4+) sites that do not have neighboring adsorbates. This arrangement minimizes the repulsive interactions between the adsorbed molecules along the Ti(4+) rows resulting in a relatively small shift of the TPD peak (105 --> 90 K) with increasing coverage. At higher N(2) coverages (0.5-1.0 N(2)/Ti(4+)) the nearest-neighbor Ti(4+) sites become occupied. The close proximity of the adsorbates results in strong repulsion thus giving rise to a significant shift of the TPD leading edges (90 --> 45 K) with increasing coverage. For N(2)/Ti(4+) > 1, an additional low-temperature peak (approximately 43 K) is present and is ascribed to N(2) adsorption on bridge-bonded oxygen rows. The results for O(2) and CO are qualitatively similar. The repulsive adsorbate-adsorbate interactions are largest for CO, most likely due to alignment of CO dipole moments. The coverage-dependent binding energies of O(2), N(2), and CO are determined by inverting TPD profiles.     

EXAFS studies on adsorption-desorption reversibility at manganese oxide-water interfaces. II. Reversible adsorption of zinc on delta-MnO2

Microscopic structures of Zn(II) adsorbed at delta-MnO(2)-water interfaces were studied using extended X-ray absorption fine structure (EXAFS) spectroscopy. In a 0.1 M NaNO(3) solution of pH 5.50, hydrous Zn(II) was adsorbed onto the solid surface in the form of octahedral coordination. Adsorbed octahedral Zn(II) was located above and below the vacancy sites of delta-MnO(2). Each Zn was coordinated on one side to H(2)O molecules forming an H(2)O sheet and on the other side to oxygen atoms shared with layer MnO(6) octahedra forming a corner-sharing octahedral interlayer complex. The average Zn-O and Zn-Mn distances were 2.07+/-0.01 and 3.52+/-0.01 A, respectively. Macroscopic adsorption-desorption isotherms showed that, in contrast to that of the Zn-gamma-MnOOH system, adsorption of Zn(II) on delta-MnO(2) was highly reversible. EXAFS results indicated that the highly reversible adsorption was due to the weak adsorption mode of the corner-sharing linkage between the adsorbate and adsorbent polyhedra.     

Structures and energies of coadsorbed CO and H2 on Fe5C2(001), Fe5C2(110), and Fe5C2(100)

Density functional theory calculations have been carried out on the CO/H2 coadsorption on the (001), (110), and (100) surfaces of Fe5C2 for the understanding of the Fischer-Tropsch synthesis (FTS) mechanism. The stable surface species changes with the variation of the H2 and CO coverage. Along with dissociated hydrogen and adsorbed CO in 2-, 3-, and 4-fold configurations, methylidyne (C(s)H) (C(s), surface carbon), ketenylidene (C(s)CO), ketenyl (C(s)HCO), ketene (C(s)H2CO), and carbon suboxide (C(s)C2O2) are computed as thermodynamically stable surface species on Fe5C2(001) and Fe5C2(110) containing both surface iron and carbon atoms. These surface carbon species can be considered as the preliminary stages for FTS. On Fe5C2(100) with only iron atoms on the surface layer, the stable surface species is dissociated hydrogen and CO with top and 2-fold configurations. The bonding nature of these adsorbed carbon species has been analyzed.     

Kinetics of electron-induced decomposition of CF2Cl2 coadsorbed with water (ice): a comparison with CCl4

The kinetics of decomposition and subsequent chemistry of adsorbed CF(2)Cl(2), activated by low-energy electron irradiation, have been examined and compared with CCl(4). These molecules have been adsorbed alone and coadsorbed with water ice films of different thicknesses on metal surfaces (Ru; Au) at low temperatures (25 K; 100 K). The studies have been performed with temperature programmed desorption (TPD), reflection absorption infrared spectroscopy (RAIRS), and x-ray photoelectron spectroscopy (XPS). TPD data reveal the efficient decomposition of both halocarbon molecules under electron bombardment, which proceeds via dissociative electron attachment (DEA) of low-energy secondary electrons. The rates of CF(2)Cl(2) and CCl(4) dissociation increase in an H(2)O (D(2)O) environment (2-3x), but the increase is smaller than that reported in recent literature. The highest initial cross sections for halocarbon decomposition coadsorbed with H(2)O, using 180 eV incident electrons, are measured (using TPD) to be 1.0+/-0.2 x 10(-15) cm(2) for CF(2)Cl(2) and 2.5+/-0.2 x 10(-15) cm(2) for CCl(4). RAIRS and XPS studies confirm the decomposition of halocarbon molecules codeposited with water molecules, and provide insights into the irradiation products. Electron-induced generation of Cl(-) and F(-) anions in the halocarbon/water films and production of H(3)O(+), CO(2), and intermediate compounds COF(2) (for CF(2)Cl(2)) and COCl(2), C(2)Cl(4) (for CCl(4)) under electron irradiation have been detected using XPS, TPD, and RAIRS. The products and the decomposition kinetics are similar to those observed in our recent experiments involving x-ray photons as the source of ionizing irradiation.     

Site-dependent electron-stimulated reactions in water films on TiO2(110)

Electron-stimulated reactions in thin [<3 ML (monolayer)] water films adsorbed on TiO(2)(110) are investigated. Irradiation with 100 eV electrons results in electron-stimulated dissociation and electron-stimulated desorption (ESD) of adsorbed water molecules. The molecular water ESD yield increases linearly with water coverage theta for 0< or =theta< or =1 ML and 11 ML, the water ESD yield per additional water molecule adsorbed (i.e., the slope of the ESD yield versus coverage) is 3.5 times larger than for theta<1 ML. In contrast, the number of water molecules dissociated per incident electron increases linearly for theta< or =2 ML without changing slope at theta=1 ML. The total electron-stimulated sputtering rate, as measured by postirradiation temperature programmed desorption of the remaining water, is larger for theta>1 ML due to the increased water ESD for those coverages. The water ESD yields versus electron energy (for 5-50 eV) are qualitatively similar for 1, 2, and 40 ML water films. In each case, the observed ESD threshold is at approximately 10 eV and the yield increases monotonically with increasing electron energy. The results indicate that excitations in the adsorbed water layer are primarily responsible for the ESD in thin water films on TiO(2)(110). Experiments on "isotopically layered" films with D(2)O adsorbed on the Ti(4+) sites (D(2)O(Ti)) and H(2)O adsorbed on the bridging oxygen atoms (H(2)O(BBO)) demonstrate that increasing the water coverage above 1 ML rapidly suppresses the electron-stimulated desorption of D(2)O(Ti) and D atoms, despite the fact that the total water ESD and atomic hydrogen ESD yields increase with increasing coverage. The coverage dependence of the electron-stimulated reactions is probably related to the different bonding geometries for H(2)O(Ti) and H(2)O(BBO) and its influence on the desorption probability of the reaction products.     

Ba0.9Sr0.1Ce0.9Nd0.1O3-α陶瓷的离子导电性

用高温固相反应法制备了质子导电性陶瓷Ba0.9Sr0.1Ce0.9Nd0.1O3-α。用粉末X-射线衍射(XRD)和扫描电子显微镜(SEM)对该陶瓷材料进行了表征;用交流阻抗谱技术和气体浓差电池方法研究了材料在500~900℃温度范围内、不同气体气氛中的离子导电性,并与BaCe0.9Nd0.1O3-α和Ba0.9Ca0.1Ce0.9Nd0.1O3-α材料的导电性进行了比较。结果表明,该陶瓷材料为单一钙钛矿型BaCeO3斜方晶结构,具有良好的致密性,在高温下、CO2或水蒸气气氛中具有较高的稳定性。在湿润氢气气氛中、500~800℃温度范围内,材料的质子迁移数为1,是一个纯的质子导体;在900℃下,质子迁移数为0.964,是一个质子与电子的混合导体,质子迁移数高于BaCe0.9Nd0.1O3-α(在700~900℃温度范围内,质子迁移数为0.95)。在湿润空气气氛中,材料的质子迁移数为0.019~0.032,氧离子迁移数为0.093~0.209,是一个质子、氧离子和电子空穴的混合导体,总电导率高于Ba0.9Ca0.1Ce0.9Nd0.1O3-α。在氢-空气燃料电池条件下,材料的离子迁移数为0.957~0.903,是一个质子、氧离子和电子的混合导体,离子电导率高于Ba0.9Ca0.1Ce0.9Nd0.1O3-α。     

The Adsorption and Thermal Decomposition of CH2CO (CD2CO) on Si(111)-7 × 7

The adsorption and thermal decomposition of ketene on Si(l 11)-7 × 7 were investigated using various surface analysis techniques. When the surface was exposed to ketene at 120 K, two CO stretching modes at 220 and 273 meV appeared in HREELS, corresponding to two adsorbed ketene states. After the sample was annealed at ?250 K, the 273 and the 80 meV peaks vanished, indicating the disappearance of one of the adsorption states by partial desorption of the adsorbate. In a corresponding TPD measurement, a desorption peak for ketene species was noted at 220 K. Annealing the sample at 450 K caused the decomposition of the adsorbate, producing CH_x and O adspecies. Further annealing of the surface at higher temperatures resulted in the breaking of the CH bond, the desorption of H and O species and the formation of Si carbide. The desorption of H at 800 K was confirmed by the appearance of the D₂ (m/e = 4) TPD peak at that temperature when CD₂CO was used instead of CH₂CO.     

Doping of calcium in C(60) fullerene for enhancing CO(2) capture and N(2)O transformation: a theoretical study

Recently, capturing or transforming greenhouse gases, such as CO(2) and N(2)O, have attracted considerable interest from the perspective of environmental protection. In the present work, by studying CO(2) and N(2)O adsorption on pristine and calcium (Ca)-decorated fullerenes (C(60)) with density functional theory (DFT) methods, we have evaluated the potential application of this C(60)-based complex for the capture of CO(2) and transformation of N(2)O. The results indicate that the adsorptions of CO(2) and N(2)O molecules on the pristine C(60) are considerably weak accompanied by neglectable charge transfer. When C(60) is decorated with Ca atoms, however, it is found that CO(2) and N(2)O adsorptions on the C(60) are greatly enhanced. Up to five CO(2) molecules can be adsorbed on the CaC(60) system due to the electrostatic interaction. For N(2)O molecule, it is first molecularly adsorbed on the Ca atom with the adsorption energy of -0.534 eV, followed by the N(2) formation with a low barrier and high exothermicity. Moreover, when four Ca atoms are decorated on the surface of C(60), the maximum number of the adsorbed CO(2) molecules is 16. Our results might be useful not only to widen the potential applications of fullerene but also to provide an effective method to capture or transform greenhouse gases.     

CuO/TiO2/γ-Al2O3催化剂表征及对NO+CO反应性能研究

采用色谱-微反流动法反应装置考察了w%CuO/15%TiO₂/γ-Al₂O₃催化剂对NO+CO的反应活性;催化剂经空气氛或氢气氛预处理后,NO转化率达100%的反应温度分别是325和275 ℃;XRD仅能检测到γ-Al₂O₃晶相,负载15%CuO后可以检测到微弱的CuO晶相;H₂-TPR能检测到2个CuO的还原峰(α和β峰),将其归属于高度分散的CuO分别在裸露的γ-Al₂O₃和TiO₂/γ-Al₂O₃载体上的还原;原位红外分析结果表明催化剂经空气氛或氢气氛预处理后,吸附NO+CO反应气后,反应的中间产物N₂O出现的温度分别为200和150 ℃。