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1.
A series of CeO 2 promoted cobalt spinel catalysts were prepared by the co-precipitation method and tested for the decomposition of nitrous oxide (N 2O). Addition of CeO 2 to Co 3O 4 led to an improvement in the catalytic activity for N 2O decomposition. The catalyst was most active when the molar ratio of Ce/Co was around 0.05. Complete N 2O conversion could be attained over the CoCe0.05 catalyst below 400 °C even in the presence of O 2, H 2O or NO. Methods of XRD, FE-SEM, BET, XPS, H 2-TPR and O 2-TPD were used to characterize these catalysts. The analytical results indicated that the addition of CeO 2 could increase the surface area of Co 3O 4, and then improve the reduction of Co 3+ to Co 2+ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step of the N 2O decomposition over cobalt spinel catalyst. We conclude that these effects, caused by the addition of CeO 2, are responsible for the enhancement of catalytic activity of Co 3O 4. 相似文献
2.
通过焙烧猪骨和鸡骨获得羟磷灰石(nHAP)载体,并采用浸渍法制备Co3O4/nHAP催化剂。采用XRD、N2物理吸附-脱附、FT-IR和H2-TPR等对催化剂进行表征,在连续流动微反装置上考察催化剂催化分解N2O的性能。结果表明,相比于鸡骨源Co3O4/nHAP催化剂,以猪骨源HAP为载体的催化剂因其较大的比表面积以及较小的Co3O4粒径尺寸,提供了更多的活性位点。特别是猪骨源Co3O4/nHAP催化剂中适量的K、Na等元素促进了Co^3+到Co^2+的还原,削弱了Co-O键,使催化剂的催化活性显著提高。 相似文献
3.
以Co(NO_3)_2·6H_2O为钴源,K_2CO_3为沉淀剂,采用沉淀法制备Co_3O_4催化剂,用于催化N_2O直接分解反应。利用N_2~-物理吸附、XRD、FT-IR、TEM、TPR和ICP等对其进行表征,考察沉淀方式对Co_3O_4催化剂结构及其催化性能的影响。结果表明,沉淀方式对制备的Co_3O_4催化剂织构性质、物相组成和晶粒尺寸等影响不大,但显著影响其K残留量和还原性能,进而决定催化剂直接催化分解N_2O的催化性能。反加法制得的催化剂中K残留量为1.43%,明显高于正加法,同时催化剂中Co~(3+)较正加法更易还原,因而表现出更高的催化性能。在空速10 000 h~(-1)和N_2O体积分数0.1%的条件下,反加法制备的催化剂可在280℃催化N_2O完全分解,较正加法低20℃。 相似文献
4.
A series of cobalt–cerium mixed oxide catalysts (Co 3O 4–CeO 2) with a Ce/Co molar ratio of 0.05 were prepared by co-precipitation (with K 2CO 3 and KOH as the respective precipitant), impregnation, citrate, and direct evaporation methods and then tested for the catalytic decomposition of N 2O. XRD, BET, XPS, O 2-TPD and H 2-TPR methods were used to characterize the catalysts. Catalysts with a trace amount of residual K exhibited higher catalytic activities than those without. The presence of appropriate amount of K in Co 3O 4–CeO 2 may improve the redox property of Co 3O 4, which is important for the decomposition of N 2O. When the amount of K was constant, the surface area became the most important factor for the reaction. The co-precipitation-prepared catalyst with K 2CO 3 as precipitant exhibited the best catalytic performance because of the presence of ca. 2 mol% residual K and the high surface area. We also discussed the rate-determining step of the N 2O decomposition reaction over these Co 3O 4–CeO 2 catalysts. 相似文献
5.
Catalytic oxidation of Hgo to Hg O is an efficient way to remove Hg 0 from coal-fired flue gas.The catalyst with ordered pore structure can lower mass transfer resistance resulting in higher Hg 0 oxidation efficiency.Therefore,in the present work,wood vessels were used as sacrificial template to obtain Co 3O 4with ordered pore structure.SEM and BET results show that,when the mass concentrations of Co(NO 3) 2·6H 2O wa... 相似文献
6.
The one-step highly selective oxidation of cyclohexane into cyclohexanone and cyclohexanol as the essential intermediates of nylon-6 and nylon-66 is considerably challenging. Therefore, an efficient and low-cost catalyst must be urgently developed to improve the efficiency of this process. In this study, a Co 3O 4–CeO 2 composite oxide catalyst was successfully prepared through ultrasound-assisted co-precipitation. This catalyst exhibited a higher selectivity to KA-oil, which was benefited from the synergistic effects between Co 3+/Co 2+ and Ce 4+/Ce 3+ redox pairs, than bulk CeO 2 and/or Co 3O 4. Under the optimum reaction conditions, 89.6% selectivity to KA-oil with a cyclohexane conversion of 5.8% was achieved over Co 3O 4–CeO 2. Its catalytic performance remained unchanged after five runs. Using the synergistic effects between the redox pairs of different transition metals, this study provides a feasible strategy to design high-performance catalysts for the selective oxidation of alkanes. 相似文献
7.
Co 3O 4/CeO 2 composite oxides with different cobalt loading (5, 15, 30, 50, 70 wt.% as Co 3O 4) were prepared by co-precipitation method and investigated for the oxidation of methane under stoichiometric conditions. Pure oxides, Co 3O 4 and CeO 2 were used as reference. Characterization studies by X-ray diffraction (XRD), BET, temperature programmed reduction/oxidation (TPR/TPO) and X-ray photoelectron spectroscopy (XPS) were carried out. An improvement of the catalytic activity and thermal stability of the composite oxides was observed with respect to pure Co3O4 in correspondence of Co3O4–CeO2 containing 30% by weight of Co3O4. The combined effect of cobalt oxide and ceria, at this composition, strongly influences the morphological and redox properties of the composite oxides, by dispersing the Co3O4 phase and promoting the efficiency of the Co3+–Co2+ redox couple. The presence in the sample Co3O4(30 wt.%)–CeO2 of a high relative amount of Ce3+/(Ce4+ + Ce3+) as detected by XPS confirms the enhanced oxygen mobility. The catalysts stability under reaction conditions was investigated by XRD and XPS analysis of the used samples, paying particular attention to the Co3O4 phase decomposition. Methane oxidation tests were performed over fresh (as prepared) and thermal aged samples (after ageing at 750 °C for 7 h, in furnace). The resistance to water vapour poisoning was evaluated for pure Co3O4 and Co3O4(30 wt.%)–CeO2, performing the tests in the presence of 5 vol.% H2O. A methane oxidation test upon hydrothermal ageing (flowing at 600 °C for 16 h a mixture 5 vol.% H2O + 5 vol.%O2 in He) of the Co3O4(30 wt.%)–CeO2 sample was also performed. All the results confirm the superiority of this composite oxide. 相似文献
8.
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
9.
Both NO decomposition and NO reduction by CH 4 over 4%Sr/La 2O 3 in the absence and presence of O 2 were examined between 773 and 973 K, and N 2O decomposition was also studied. The presence of CH 4 greatly increased the conversion of NO to N 2 and this activity was further enhanced by co-fed O 2. For example, at 773 K and 15 Torr NO the specific activities of NO decomposition, reduction by CH 4 in the absence of O 2, and reduction with 1% O 2 in the feed were 8.3·10 −4, 4.6·10 −3, and 1.3·10 −2 μmol N 2/s m 2, respectively. This oxygen-enhanced activity for NO reduction is attributed to the formation of methyl (and/or methylene) species on the oxide surface. NO decomposition on this catalyst occurred with an activation energy of 28 kcal/mol and the reaction order at 923 K with respect to NO was 1.1. The rate of N 2 formation by decomposition was inhibited by O 2 in the feed even though the reaction order in NO remained the same. The rate of NO reduction by CH 4 continuously increased with temperature to 973 K with no bend-over in either the absence or the presence of O 2 with equal activation energies of 26 kcal/mol. The addition of O 2 increased the reaction order in CH 4 at 923 K from 0.19 to 0.87, while it decreased the reaction order in NO from 0.73 to 0.55. The reaction order in O 2 was 0.26 up to 0.5% O 2 during which time the CH 4 concentration was not decreased significantly. N 2O decomposition occurs rapidly on this catalyst with a specific activity of 1.6·10 −4 μmol N 2/s m 2 at 623 K and 1220 ppm N 2O and an activation energy of 24 kcal/mol. The addition of CH 4 inhibits this decomposition reaction. Finally, the use of either CO or H 2 as the reductant (no O 2) produced specific activities at 773 K that were almost 5 times greater than that with CH 4 and gave activation energies of 21–26 kcal/mol, thus demonstrating the potential of using CO/H 2 to reduce NO to N 2 over these REO catalysts. 相似文献
10.
The utilization of CO2 as rawmaterial for chemical synthesis has the potential for substantial economic and green benefits. Thermal decomposition of hexamethylene-1,6-dicarbamate (HDC) is a promising approach for indirect utilization of CO2 to produce hexamethylene-1,6-diisocyanate (HDI). In this work, a green route was developed for the synthesis of HDI by thermal decomposition of HDC over Co3O4/ZSM-5 catalyst, using chlorobenzene as lowboiling point solvent. Different metal oxide supported catalysts were prepared by incipientwetness impregnation (IWI), PEG-additive (PEG) and deposition precipitation with ammonia evaporation (DP) methods. Their catalytic performances for the thermal decomposition of HDC were tested. The catalyst screening results showed that Co3O4/ZSM-525 catalysts prepared by different methods showed different performances in the order of Co3O4/ZSM-525(PEG) N Co3O4/ZSM-525(IWI) N Co3O4/ZSM-525(DP). The physicochemical properties of Co3O4/ZSM- 525 catalyst were characterized by XRD, FTIR, N2 adsorption-desorption measurements, NH3-TPD and XPS. The superior catalytic performance of Co3O4/ZSM-525(PEG) catalyst was attributed to its relative surface content of Co3+, surface lattice oxygen content and total acidity. Under the optimized reaction conditions: 6.5% HDC concentration in chlorobenzene, 1 wt% Co3O4/ZSM-525(PEG) catalyst, 250 °C temperature, 2.5 h time, 800 ml·min?1 nitrogen flow rate and 1.0 MPa pressure, the HDC conversion and HDI yield could reach 100% and 92.8% respectively. The Co3O4/ZSM-525(PEG) catalyst could be facilely separated from the reaction mixture, and reused without degradation in catalytic performance. Furthermore, a possible reaction mechanism was proposed based on the physicochemical properties of the Co3O4/ZSM-525 catalysts. 相似文献
11.
NO removal using CH 4 as a reductant in a dual-bed system has been investigated with Co-NaX and Ag-NaX catalysts, which were prepared by Co 2+-, Ag +-ion exchange into zeolite NaX, respectively, and activation for 5 h at 500 °C. The experimental result has been compared with that of a Co-NaX-CO catalyst, additionally pre-treated under CO flow for the Co-NaX catalyst. The cobalt crystal structure of a Co-NaX-CO catalyst is Co 3O 4, which promotes NO oxidation to NO 2 by excess O 2 at a low temperature (523 K). The mechanical mixture of Co-NaX-CO and Ag-NaX catalysts shows a synergy effect on NO reduction to N 2 by CH 4 in the presence of excess O 2 and H 2O, but the NO reduction decreases quickly as time passes. However, the NO reduction to N 2 in a deNO bed at 523 K and a deNO 2 bed at 423 K, which are relatively lower than the reaction temperatures for common SCR systems, still remained at 67% even in a H 2O 10% gas mixture after 160 min. 相似文献
12.
The catalytic behavior in N 2O reduction by propane in the presence of O 2, H 2O and SO 2 of Fe/ZSM-5 catalysts prepared by ion exchange and chemical vapour deposition (CVD) is reported. The catalyst prepared by CVD shows a lower dependence of the rate of selective N 2O reduction on the decrease in C 3H 8 to N 2O ratio in the feed and a higher resistance to deactivation by SO 2 in accelerated durability tests with high SO 2 concentration (500 ppm). This catalyst shows stable catalytic behavior in the presence of SO 2 for more than 600 h of time-on-stream. Characterization of the catalysts by UV–VIS–NIR diffuse reflectance indicates that the poor performances of the sample prepared by ion exchange could be related to the presence of highly clustered Fe 3+ species, in this catalyst. On the other hand, Fe 2O 3 particles are not present in the sample prepared by CVD while mainly isolated Fe 3+ ions and iron-oxide nanoclusters are present. 相似文献
13.
Sharp NO and O 2 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 H 2 treatment at 773 K or high-temperature (HT) treatment at 1073 K followed by N 2O treatment. The amounts of O 2 and NO desorption were dependent on the pretreatment pressure of N 2O in the H 2 and N 2O treatment. The adsorbed species could be regenerated by the H 2 and N 2O treatment after TPD, and might be considered to be active oxygen species in selective catalytic reduction (SCR) of N 2O with CH 4. However, the reaction rate of CH 4 activation by the adsorbed species formed after the H 2 and N 2O or the HT and N 2O treatment was not so high as that of the CH 4 + N 2O reaction over the catalyst after O 2 treatment. The simultaneous presence of CH 4 and N 2O is essential for the high activity of the reaction, which suggests that nascent oxygen species formed by N 2O dissociation can activate CH 4 in the SCR of N 2O with CH 4. 相似文献
14.
分别以Cu(NO_3)_2·3H_2O和50%Mn(NO_3)_2水溶液为铜源和锰源,K_2CO_3为沉淀剂,采用沉淀法和共沉淀法制备单一Cu、Mn氧化物催化剂和Cu-Mn-O复合氧化物催化剂,用于催化N_2O直接分解反应,并利用N_2物理吸附-脱附、XRD、FT-IR和TPR等进行表征。结果表明,单一Cu和Mn氧化物分别以体相CuO和Mn2O_3物相形式存在,Cu-Mn-O复合氧化物中除形成CuMn_2O_4尖晶石物相外,还有一定量小晶粒CuO,较单一氧化物具有更加优异的还原性能,表现出较高的催化N_2O直接分解活性。在空速10 000 h~(-1)和N_2O体积分数0.1%条件下,Cu-Mn-O复合氧化物催化剂可在440℃催化N_2O完全分解,分别较单一Cu和Mn氧化物催化剂降低了40℃和60℃。 相似文献
15.
Various spinel-type catalysts AB 2O 4 (where A = Mg, Ca, Mn, Co, Ni, Cu, Cr, Fe, Zn and B = Cr, Fe, Co) were prepared and characterized by XRD, BET, TEM and FESEM-EDS. The performance of these catalysts towards the decomposition of N 2O to N 2 and O 2 was evaluated in a temperature programmed reaction (TPR) apparatus in the absence and the presence of oxygen. Spinel-type oxides containing Co at the B site were found to provide the best activity. The half conversion temperature of nitrous oxide over the MgCo 2O 4 catalyst was 440 °C and 470 °C in the absence and presence of oxygen, respectively (GHSV = 80,000 h −1). On the grounds of temperature programmed oxygen desorption (TPD) analyses as well as of reactive runs, the prevalent activity of the MgCo2O4 catalyst could be explained by its higher concentration of suprafacial, weakly chemisorbed oxygen species, whose related vacancies contribute actively to nitrous oxide catalytic decomposition. This indicates the way for the development of new, more active catalysts, possibly capable of delivering at low temperatures amounts of these oxygen species even higher than those characteristic of MgCo2O4. 相似文献
16.
The catalytic properties of cobalt containing ZSM-5 zeolites prepared by various methods were compared. TPR, XRD, N 2-BET, XPS, FTIR and UV–vis spectroscopy were used for characterizing the samples. Well-dispersed cobalt oxide-like species and isolated Co 2+ ions in charge compensation positions were found in the zeolite. Catalysts prepared using a single step cation exchange method showed high activity for N 2O decomposition in a temperature range 300–550°C, in the presence of 0–5% O 2, and high stability in the presence of 10% H 2O to the feed. UV–vis spectra and TPR experiments indicated the presence of some cobalt oxides, not detected by DRX, in a Co-ZSM-5 catalyst containing 3.76 wt% Co, prepared by a solid-state reaction procedure. The N 2O conversion over this catalyst was strongly affected by addition of both O 2 and H 2O to the feed. 相似文献
17.
CO and CH 4 combined oxidation tests were performed over a Pd (70 g/ft 3)/Co 3O 4 monolithic catalyst in conditions of GHSV = 100,000 h −1 and feed composition close to that of emission from bi-fuel vehicles. The effect of SO 2 (5 ppm) on CO and CH 4 oxidation activity under lean condition ( λ = 2) was investigated. The presence of sulphur strongly deactivated the catalyst towards methane oxidation, while the poisoning effect was less drastic in the oxidation of CO. Saturation of the Pd/Co 3O 4 catalytic sites via chemisorbed SO 3 and/or sulphates occurred upon exposure to SO 2. A treatment of regeneration to remove sulphate species was attempted by performing a heating/cooling cycle up to 900 °C in oxidizing atmosphere. Decomposition of PdO and Co 3O 4 phases at high temperature, above 750 °C, was observed. Moreover, sintering of Pd 0 and PdO particles along with of CoO crystallites takes place. 相似文献
18.
In this study, we examine the interaction of N 2O with TiO 2(1 1 0) in an effort to better understand the conversion of NO x species to N 2 over TiO 2-based catalysts. The TiO 2(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 TiO 2(1 1 0) in vacuum at high temperature (above about 800 K) generates oxygen vacancy sites that are associated with reduced surface cations (Ti 3+ 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 N 2O molecules adsorbed at 90 K on TiO 2(1 1 0) are weakly held and desorb from the surface at 130 K. However, a small fraction of the N 2O molecules exposed to TiO 2(1 1 0) at 90 K decompose to N 2 via one of two channels, both of which are vacancy-mediated. One channel occurs at 90 K, and results in N 2 ejection from the surface and vacancy oxidation. We propose that this channel involves N 2O molecules bound at vacancies with the O-end of the molecule in the vacancy. The second channel results from an adsorbed state of N 2O that decomposes at 170 K to liberate N 2 in the gas phase and deposit oxygen adatoms at non-defect Ti 4+ sites. The presence of these O adatoms is clearly evident in subsequent water TPD measurements. We propose that this channel involves N 2O 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 Ti 4+ site. The partitioning between these two channels is roughly 1:1 for adsorption at 90 K, but neither is observed to occur for moderate N 2O exposures at temperatures above 200 K. EELS data indicate that vacancies readily transfer charge to N 2O at 90 K, and this charge transfer facilitates N 2O decomposition. Based on these results, it appears that the decomposition of N 2O to N 2 requires trapping of the molecule at vacancies and that the lifetime of the N 2O–vacancy interaction may be key to the conversion of N 2O to N 2. 相似文献
19.
The study of catalytic decomposition of nitrous oxide to nitrogen and oxygen over Rh catalysts supported on various supports (USY, NaY, Al 2O 3, ZrO 2, FSM-16, CeO 2, La 2O 3) showed that the activities of Rh/Al 2O 3 and Rh/USY (ultrastable Y zeolite) catalysts were comparable to or higher than the other catalysts reported in the literatures. The catalytic activity of N 2O 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 N 2O experiment over a Rh/USY catalyst suggested that the catalytic N 2O decomposition occurs on oxygen-covered surface and that O 2 may be freed on collision of N 2O molecules with the adsorbed oxygen atoms. 相似文献
20.
Co/ZSM-5 catalysts were prepared by several methods, including wet ion exchange (WIE), its combination with impregnation (IMP), solid state ion exchange (SSI) and sublimation (SUB). FTIR results show that the zeolite protons in H-ZSM-5 are completely removed when CoCl 2 vapor is deposited. TPR shows peaks for Co 2+ ions at 695–705°C and for Co 3O 4 at 385–390°C, but a peak in the 220–250°C region appears to indicate Co 2+ oxo-ions. The catalysts have been tested for the selective reduction of NOx with iso-C4H10 under O2-rich conditions and in the absence of O2, both with dry and wet feeds. A bifunctional mechanism appears to operate at low temperature: oxo-ions or Co3O4 clusters first oxidize NO to NO2, which is chemisorbed as NOy (y≥2) and reduced. In this modus operandi catalyst SUB shows the highest N2 yield 90% near 390°C for dry and wet feeds. It is found to be quite stable in a 52 h run with a wet feed. In contrast, the WIE catalyst, which mainly contains isolated Co2+ ions and has poor activity below 400°C, excels at T>430°C. This and the observation that, at high temperature, NO is reduced in O2-free feeds over Co/MFI catalysts, suggest that NO can be reduced over Co2+ ions without intermediate formation of NO2. The bifunctional mechanism at low temperature is supported by the fact that a strongly enhanced performance is obtained by mixing WIE with Fe/FER, a catalyst known to promote NO2 formation. 相似文献
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