共查询到20条相似文献,搜索用时 15 毫秒
1.
Chunlei Shi Arden B. Walters M. Albert Vannice 《Applied catalysis. B, Environmental》1997,14(3-4):175-188
Dispersing La2O3 on δ- or γ-Al2O3 significantly enhances the rate of NO reduction by CH4 in 1% O2, compared to unsupported La2O3. Typically, no bend-over in activity occurs between 500° and 700°C, and the rate at 700°C is 60% higher than that with a Co/ZSM-5 catalyst. The final activity was dependent upon the La2O3 precursor used, the pretreatment, and the La2O3 loading. The most active family of catalysts consisted of La2O3 on γ-Al2O3 prepared with lanthanum acetate and calcined at 750°C for 10 h. A maximum in rate (mol/s/g) and specific activity (mol/s/m2) occurred between the addition of one and two theoretical monolayers of La2O3 on the γ-Al2O3 surface. The best catalyst, 40% La2O3/γ-Al2O3, had a turnover frequency at 700°C of 0.05 s−1, based on NO chemisorption at 25°C, which was 15 times higher than that for Co/ZSM-5. These La2O3/Al2O3 catalysts exhibited stable activity under high conversion conditions as well as high CH4 selectivity (CH4 + NO vs. CH4 + O2). The addition of Sr to a 20% La2O3/γ-Al2O3 sample increased activity, and a maximum rate enhancement of 45% was obtained at a SrO loading of 5%. In contrast, addition of SO=4 to the latter Sr-promoted La2O3/Al2O3 catalyst decreased activity although sulfate increased the activity of Sr-promoted La2O3. Dispersing La2O3 on SiO2 produced catalysts with extremely low specific activities, and rates were even lower than with pure La2O3. This is presumably due to water sensitivity and silicate formation. The La2O3/Al2O3 catalysts are anticipated to show sufficient hydrothermal stability to allow their use in certain high-temperature applications. 相似文献
2.
The selective catalytic reduction of NO by H2 under strongly oxidizing conditions (H2-SCR) in the low-temperature range of 100–200 °C has been studied over Pt supported on a series of metal oxides (e.g., La2O3, MgO, Y2O3, CaO, CeO2, TiO2, SiO2 and MgO-CeO2). The Pt/MgO and Pt/CeO2 solids showed the best catalytic behavior with respect to N2 yield and the widest temperature window of operation compared with the other single metal oxide-supported Pt solids. An optimum 50 wt% MgO-50wt% CeO2 support composition and 0.3 wt% Pt loading (in the 0.1–2.0 wt% range) were found in terms of specific reaction rate of N2 production (mols N2/gcat s). High NO conversions (70–95%) and N2 selectivities (80–85%) were also obtained in the 100–200 °C range at a GHSV of 80,000 h−1 with the lowest 0.1 wt% Pt loading and using a feed stream of 0.25 vol% NO, 1 vol% H2, 5 vol% O2 and He as balance gas. Addition of 5 vol% H2O in the latter feed stream had a positive influence on the catalytic performance and practically no effect on the stability of the 0.1 wt% Pt/MgO-CeO2 during 24 h on reaction stream. Moreover, the latter catalytic system exhibited a high stability in the presence of 25–40 ppm SO2 in the feed stream following a given support pretreatment. N2 selectivity values in the 80–85% range were obtained over the 0.1 wt% Pt/MgO-CeO2 catalyst in the 100–200 °C range in the presence of water and SO2 in the feed stream. The above-mentioned results led to the obtainment of patents for the commercial exploitation of Pt/MgO-CeO2 catalyst towards a new NOx control technology in the low-temperature range of 100–200 °C using H2 as reducing agent. Temperature-programmed desorption (TPD) of NO, and transient titration of the adsorbed surface intermediate NOx species with H2 experiments, following reaction, have revealed important information towards the understanding of basic mechanistic issues of the present catalytic system (e.g., surface coverage, number and location of active NOx intermediate species, NOx spillover). 相似文献
3.
Jin Xu Robert Clayton Vemuri Balakotaiah Michael P. Harold 《Applied catalysis. B, Environmental》2008,77(3-4):395-408
Experimental results describing the product distribution during the reduction of NO by H2 on Pt/Al2O3 and Pt/BaO/Al2O3 catalysts are presented in the temperature range 30–500 °C and H2/NO feed ratio range of 0.9–2.5. A microkinetic model that describes the kinetics of NO reduction by H2 on Pt/Al2O3 is proposed and most of the kinetic parameters are estimated from either literature data or from thermodynamic constraints. The microkinetic model is combined with the short monolith flow model to simulate the conversions and selectivities corresponding to the experimental conditions. The predicted trends are in excellent qualitative and reasonable quantitative agreement with the experimental results. Both the model and the experiments show that N2O formation is favored at low temperatures and low H2/NO feed ratios, N2 selectivity increases monotonically with temperature for H2/NO feed ratios of 1.2 or less but goes through a maximum at intermediate temperatures (around 100 °C) for H2/NO feed ratios 1.5 or higher. Ammonia formation is favored for H2/NO feed ratios of 1.5 or higher and intermediate temperatures (100–350 °C) buts starts to decompose at a temperature of 400 °C or higher. The microkinetic model is used to determine the surface coverages and explain the trends in the experimentally observed selectivities. 相似文献
4.
Oxidation behaviour and catalytic properties of Pd/Al2O3 catalysts in the total oxidation of methane
A series of Pd/Al2O3 catalysts with a wide range of mean Pd particle sizes (ca. 2–30 nm in diameter) was prepared by using various precursors (H2PdCl4, Pd(NO3)2 and Pd(AcAc)2) and pre-treatments. The mean particle size of reduced samples was determined by H2 chemisorption. The catalytic activity in methane oxidation under lean burn conditions was measured. The oxidation of reduced samples was studied at 300 °C. The extent of oxidation was found to decrease with increasing mean particle size. While small particles (<5 nm) oxidised very rapidly, the oxidation of large particles (ca. >15 nm) proceeded via a two-step process, being first fast and then slow. The decomposition of oxide species was studied by temperature-programmed experiments under vacuum. Two distinct oxidised species with different stability were evidenced depending on the particle size. Oxidised species in larger particles were found of lower stability than in smaller ones. A correlation between the existence of distinct types of oxide species and catalytic properties in methane oxidation was discussed. 相似文献
5.
Zhanggen Huang Zhenyu Liu Xianlong Zhang Qingya Liu 《Applied catalysis. B, Environmental》2006,63(3-4):260-265
The inhibition effect of H2O on V2O5/AC catalyst for NO reduction with NH3 is studied at temperatures up to 250 °C through TPD, elemental analyses, temperature-programmed surface reaction (TPSR) and FT-IR analyses. The results show that H2O does not reduce NO and NH3 adsorption on V2O5/AC catalyst surface, but promotes NH3 adsorption due to increases in Brønsted acid sites. Many kinds of NH3 forms present on the catalyst surface, but only NH4+ on Brønsted acid sites and a small portion of NH3 on Lewis acid sites are reactive with NO at 250 °C or below, and most of the NH3 on Lewis acid sites does not react with NO, regardless the presence of H2O in the feed gas. H2O inhibits the SCR reaction between the NH3 on the Lewis acid sites and NO, and the inhibition effect increases with increasing H2O content. The inhibition effect is reversible and H2O does not poison the V2O5/AC catalyst. 相似文献
6.
Yu Su Karen S. Kabin Michael P. Harold Michael D. Amiridis 《Applied catalysis. B, Environmental》2007,71(3-4):207-215
The reduction of NO under cyclic “lean”/“rich” conditions was examined over two model 1 wt.% Pt/20 wt.% BaO/Al2O3 and 1 wt.% Pd/20 wt.% BaO/Al2O3 NOx storage reduction (NSR) catalysts. At temperatures between 250 and 350 °C, the Pd/BaO/Al2O3 catalyst exhibits higher overall NOx reduction activity. Limited amounts of N2O were formed over both catalysts. Identical cyclic studies conducted with non-BaO-containing 1 wt.% Pt/Al2O3 and Pd/Al2O3 catalysts demonstrate that under these conditions Pd exhibits a higher activity for the oxidation of both propylene and NO. Furthermore, in situ FTIR studies conducted under identical conditions suggest the formation of higher amounts of surface nitrite species on Pd/BaO/Al2O3. The IR results indicate that this species is substantially more active towards reaction with propylene. Moreover, its formation and reduction appear to represent the main pathway for the storage and reduction of NO under the conditions examined. Consequently, the higher activity of Pd can be attributed to its higher oxidation activity, leading both to a higher storage capacity (i.e., higher concentration of surface nitrites under “lean” conditions) and a higher reduction activity (i.e., higher concentration of partially oxidized active propylene species under “rich” conditions). The performance of Pt and Pd is nearly identical at temperatures above 375 °C. 相似文献
7.
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
8.
Haibo Zhao Russell G. Tonkyn Stephan E. Barlow Bruce E. Koel Charles H.F. Peden 《Applied catalysis. B, Environmental》2006,65(3-4):282-290
The adsorption of HCN on, its catalytic oxidation with 6% O2 over 0.5% Pt/Al2O3, and the subsequent oxidation of strongly bound chemisorbed species upon heating were investigated. The observed N-containing products were N2O, NO and NO2, and some residual adsorbed N-containing species were oxidized to NO and NO2 during subsequent temperature programmed oxidation. Because N-atom balance could not be obtained after accounting for the quantities of each of these product species, we propose that N2 and was formed. Both the HCN conversion and the selectivity towards different N-containing products depend strongly on the reaction temperature and the composition of the reactant gas mixture. In particular, total HCN conversion reaches 95% above 250 °C. Furthermore, the temperature of maximum HCN conversion to N2O is located between 200 and 250 °C, while raising the reaction temperature increases the proportion of NOx in the products. The co-feeding of H2O and C3H6 had little, if any effect on the total HCN conversion, but C3H6 addition did increase the conversion to NO and decrease the conversion to NO2, perhaps due to the competing presence of adsorbed fragments of reductive C3H6. Evidence is also presented that introduction of NO and NO2 into the reactant gas mixture resulted in additional reaction pathways between these NOx species and HCN that provide for lean-NOx reduction coincident with HCN oxidation. 相似文献
9.
The phase diagram of the Al2O3–ZrO2–Nd2O3 system was constructed in the temperature range 1250–2800 °C. The liquidus surface of the phase diagram reflects the preferentially eutectic interaction in the system. Two new ternary and one new binary eutectics were found. The minimum melting temperature is 1675 °C and it corresponds to the ternary eutectic Nd2O3·11Al2O3 + F-ZrO2 + NdAlO3. The solidus surface projection and the schematic of the alloy crystallization path confirm the preferentially congruent character of phase interaction in the ternary system. The polythermal sections present the complete phase diagram of the Al2O3–ZrO2–Nd2O3 system. No ternary compounds or regions of remarkable solid solution were found in the components or binaries in this ternary system. 相似文献
10.
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
11.
C.M.L. Scholz V.R. Gangwal M.H.J.M. de Croon J.C. Schouten 《Applied catalysis. B, Environmental》2007,71(3-4):143-150
In this paper, the effect of CO2 and H2O on NOx storage and reduction over a Pt–Ba/γ-Al2O3 (1 wt.% Pt and 30 wt.% Ba) catalyst is shown. The experimental results reveal that in the presence of CO2 and H2O, NOx is stored on BaCO3 sites only. Moreover, H2O inhibits the NO oxidation capability of the catalyst and no NO2 formation is observed. Only 16% of the total barium is utilized in NO storage. The rich phase shows 95% selectivity towards N2 as well as complete regeneration of stored NO. In the presence of CO2, NO is oxidized into NO2 and more NOx is stored as in the presence of H2O, resulting in 30% barium utilization. Bulk barium sites are inactive in NOx trapping in the presence of CO2·NH3 formation is seen in the rich phase and the selectivity towards N2 is 83%. Ba(NO3)2 is always completely regenerated during the subsequent rich phase. In the absence of CO2 and H2O, both surface and bulk barium sites are active in NOx storage. As lean/rich cycling proceeds, the selectivity towards N2 in the rich phase decreases from 82% to 47% and the N balance for successive lean/rich cycles shows incomplete regeneration of the catalyst. This incomplete regeneration along with a 40% decrease in the Pt dispersion and BET surface area, explains the observed decrease in NOx storage. 相似文献
12.
The effect of oxygen concentration on the pulse and steady-state selective catalytic reduction (SCR) of NO with C3H6 over CuO/γ-Al2O3 has been studied by infrared spectroscopy (IR) coupled with mass spectroscopy studies. IR studies revealed that the pulse SCR occurred via (i) the oxidation of Cu0/Cu+ to Cu2+ by NO and O2, (ii) the co-adsorption of NO/NO2/O2 to produce Cu2+(NO3−)2, and (iii) the reaction of Cu2+(NO3−)2 with C3H6 to produce N2, CO2, and H2O. Increasing the O2/NO ratio from 25.0 to 83.4 promotes the formation of NO2 from gas phase oxidation of NO, resulting in a reactant mixture of NO/NO2/O2. This reactant mixture allows the formation of Cu2+(NO3−)2 and its reaction with the C3H6 to occur at a higher rate with a higher selectivity toward N2 than the low O2/NO flow. Both the high and low O2/NO steady-state SCR reactions follow the same pathway, proceeding via adsorbed C3H7---NO2, C3H7---ONO, CH3COO−, Cu0---CN, and Cu+---NCO intermediates toward N2, CO2, and H2O products. High O2 concentration in the high O2/NO SCR accelerates both the formation and destruction of adsorbates, resulting in their intensities similar to the low O2/NO SCR at 523–698 K. High O2 concentration in the reactant mixture resulted in a higher rate of destruction of the intermediates than low O2 concentration at temperatures above 723 K. 相似文献
13.
T. V. Reshetenko L. B. Avdeeva V. A. Ushakov E. M. Moroz A. N. Shmakov V. V. Kriventsov D. I. Kochubey Yu. T. Pavlyukhin A. L. Chuvilin Z. R. Ismagilov 《Applied Catalysis A: General》2004,270(1-2):87-99
Coprecipitated Fe-Al2O3, Fe-Co-Al2O3 and Fe-Ni-Al2O3 catalysts is shown to be very efficient in carbon deposition during methane decomposition at moderate temperatures (600–650 °C). The carbon capacity of the most efficient bimetallic catalysts containing 50–65 wt.% Fe, 5–10 wt.% Co (or Ni) and 25–40 wt.% Al2O3 is found to reach 145 g/gcat. Most likely, their high efficiency is due to specific crystal structures of the metal particles and formation of optimum particle size distribution. According to the TEM data, catalytic filamentous carbon (CFC) is formed on them as multiwall carbon nanotubes (MWNTs). The phase composition of the catalysts during methane decomposition is studied using a complex of physicochemical methods (XRD, REDD, Mössbauer spectroscopy and EXAFS). Possible mechanisms of the catalyst deactivation are discussed. 相似文献
14.
The perovskite-type oxides La0.8Ce0.2Cu0.4Mn0.6O3 and La0.8Ce0.2Ag0.4Mn0.6O3 prepared by reverse microemulsion and sol–gel methods (denoted as R and S, respectively), have been investigated on their catalytic performance for the (NO + CO) reaction, and characterized by means of temperature-programmed desorption (TPD), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). XRD measurements proved the presence of the perovskite phase with a considerable amount of CeO2 phase and the formation of CeO2 phase was restrained with the reverse microemulsion method. TEM investigations revealed that the La0.8Ce0.2Cu0.4Mn0.6O3-R nanoparticles were uniform spheres in shape with diameters ranging from 40 to 50 nm, whereas an aggregation of particles was found for the La0.8Ce0.2Cu0.4Mn0.6O3-S catalyst. The activity of NO reduction with CO decreased in the order of La0.8Ce0.2Cu0.4Mn0.6O3-R > La0.8Ce0.2Cu0.4Mn0.6O3-S > La0.8Ce0.2Ag0.4Mn0.6O3-R > La0.8Ce0.2Ag0.4Mn0.6O3-S. In NO-TPD experiments, the principal desorbed species detected in the effluent was NO with a trace amount of O2 and N2O, suggesting that the non-dissociated adsorption of NO on the surface of the perovskite-type oxides was dominant. The XPS results revealed that Ce4+ and Cu+ was the predominant oxidation state for Ce and Cu components in La0.8Ce0.2Cu0.4Mn0.6O3 and La0.8Ce0.2Ag0.4Mn0.6O3 catalysts. The existence of Cu+ ions and its redox reaction (Cu+ ↔ Cu2+) would benefit the NO adsorption and reduction by CO. 相似文献
15.
Wei Wang Hong-bin Zhang Guo-dong Lin Zhi-tao Xiong 《Applied catalysis. B, Environmental》2000,24(3-4):219-232
Ag-modified La0.6Sr0.4MnO3-based catalysts with the perovskite-type structure were prepared by using a citric acid sol–gel method, and their catalytic performance for complete oxidation of methanol and ethanol was evaluated and compared with that of the γ-Al2O3-supported catalysts, Ag/γ-Al2O3, Pt/γ-Al2O3, and Pd/γ-Al2O3. The results showed that the Ag-modified La0.6Sr0.4MnO3-based catalysts with the perovskite-type structure displayed the activity significantly higher than that of the supported precious metal catalysts, 0.1%Pd/γ-Al2O3 and 0.1%Pt/γ-Al2O3 in the temperature range of 370–573 K. Over a 6%Ag/20%La0.6Sr0.4MnO3/γ-Al2O3 catalyst, the T95 temperature for methanol oxidation can be as low as 413 K. Even at such low reaction temperature, there were little HCHO and CO detected in the reaction exit-gas. However, for the 0.1%Pd/γ-Al2O3 and 0.1%Pt/γ-Al2O3 catalysts, the HCHO content in the reaction exit-gas reached 200 and 630 ppm at their T95 temperatures. Over a 6%Ag/La0.6Sr0.4MnO3 catalyst, the T95 temperature for ethanol oxidation can be as low as 453 K, with a corresponding content of CH3CHO in the exit-gas at 782 ppm; when ethanol oxidation is performed at 493 K, the content of acetaldehyde in the exit-gas can be below 1 ppm. Characterization of the catalysts by X-ray diffraction (XRD), TEM, XPS, laser Raman spectra (LRS), hydrogen temperature-programmed reduction (H2-TPR) and oxygen temperature-programmed desorption (O2-TPD) methods revealed that both the surface and the bulk phase of the perovskite La0.6Sr0.4MnO3 played important roles in the catalytic oxidation of the alcohols, and that γ-Al2O3 as the bottom carrier could be beneficial in creating a large surface area of catalyst. Moreover, a small amount of Ag+ doped onto the surface of La0.6Sr0.4MnO3 was able to partially occupy the positions of La3+ and Sr2+ due to their similar ionic radii, and thus, became stabilized by the perovskite lattice, which would be in favor of preventing the aggregation of the Ag species on the surface and enhancing the stability of the catalyst. On the other hand, modification of the Ag+ to the surface of La0.6Sr0.4MnO3 resulted in an increase in relative content of the surface O22−/O− species highly reactive toward the alcohols and aldehydes as well as CO. Besides, solution of low-valence metal oxides SrO and Ag2O with proper amounts in the lattice of the trivalent metal perovskite-type oxide LaMnO3 would also lead to an increase in the content of the reducible Mnn+ and the formation of anionic vacancies, which would be favorable for the adsorption-activation of oxygen on the functioning catalyst and the transport of the lattice and surface oxygen species. All these factors would contribute to the pronounced improvement of the catalyst performance. 相似文献
16.
Dragos Ciuparu Abdelhamid Bensalem Lisa Pfefferle 《Applied catalysis. B, Environmental》2000,26(4):241-255
We have examined the adsorption of CO and NO on powder Pd/Al2O3, Pd–Ce/Al2O3 and CeO2/Al2O3 catalysts, using temperature-programmed desorption (TPD). For CO adsorption on oxidized and pre-reduced Pd–Ce/Al2O3 TPD profiles are identical to those observed for Pd/Al2O3, suggesting that interactions between ceria and Pd have a negligible effect on the adsorption properties of CO. It does, however, affect the oxidation state of the palladium particles. For NO, there are differences between Pd/Al2O3 and Pd–Ce/Al2O3. On oxidized catalysts, Pd/Al2O3 is more efficient for NO dissociation. However, pre-reduction increases the amount of NO that can adsorb on Pd–Ce/Al2O3 and react to N2O and N2. In comparison with Pd/Al2O3, reduced Pd–Ce/Al2O3catalysts dissociate NO at relatively high temperatures but they are more reactive and favor N2 over N2O. 相似文献
17.
LaxSr2−xMnO4 (0 ≤ x ≤ 0.8) oxides were synthesized and single-phase K2NiF4-type oxides were obtained in the range of 0.1 ≤ x < 0.5. The catalytic activity of LaxSr2−xMnO4 for NO–CO reaction increased with increasing x in the range of solubility limit of La. La0.5Sr1.5MnO4 showed the highest activity among LaxSr2−xMnO4 prepared in this study, but its activity was inferior to perovskite-type La0.5Sr0.5MnO3. Among the Pd-loaded catalysts, however, Pd/La0.8Sr1.2MnO4 showed the higher activity and the selectivity to N2 than Pd/La0.5Sr0.5MnO3 and Pd/γ-Al2O3. The excellent catalytic performance of Pd/La0.2Sr1.2MnO4 could be ascribable to the formation of SrPd3O4 which was detected by XRD in the catalyst but not in the other two catalysts. 相似文献
18.
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
19.
Tae-Won Kim Min-Woo Song Hyoung-Lim Koh Kyung-Lim Kim 《Applied Catalysis A: General》2001,210(1-2):35-44
The influences of calcination temperatures and additives for 10 wt.% Cu/γ-Al2O3 catalysts on the surface properties and reactivity for NO reduction by C3H6 in the presence of excess oxygen were investigated. The results of XRD and XPS show that the 10 wt.% Cu/γ-Al2O3 catalysts calcined below 973 K possess highly dispersed surface and bulk CuO phases. The 10 wt.% Cu/γ-Al2O3 and 10 wt.% Mn–10 wt.% Cu/γ-Al2O3 catalysts calcined at 1073 K possess a CuAl2O4 phase with a spinel-type structure. In addition, the 10 wt.% La–10 wt.% Cu/γ-Al2O3 catalyst calcined at 1073 K possesses a bulk CuO phase. The result of NO reduction by C3H6 shows that the CuAl2O4 is a more active phase than the highly dispersed and bulk CuO phase. However, the 10 wt.% Mn–10 wt.% Cu/γ-Al2O3 catalyst calcined at 1073 K possesses significantly lower reactivity for NO reduction than the 10 wt.% Cu/γ-Al2O3 catalyst calcined at 1073 K, although these catalysts possess the same CuAl2O4 phase. The low reactivity for NO reduction for 10 wt.% Mn–10 wt.% Cu/γ-Al2O3 catalyst calcined at 1073 K is attributed to the formation of less active CuAl2O4 phase with high aggregation and preferential promotion of C3H6 combustion to COx by MnO2. The engine dynamometer test for NO reduction shows that the C3H6 is a more effective reducing agent for NO reduction than the C2H5OH. The maximum reactivity for NO reduction by C3H6 is reached when the NO/C3H6 ratio is one. 相似文献
20.
M. Konsolakis I. V. Yentekakis A. Palermo R. M. Lambert 《Applied catalysis. B, Environmental》2001,33(4):361-302
The reduction of NO by CO over Rb-promoted Pt/γ-Al2O3 catalysts has been investigated over a wide range of temperature (ca. 200–500°C), partial pressures of reactants and promoter loadings. For purposes of comparison, K- and Cs-promoted Pt/γ-Al2O3 catalysts were tested under the same conditions. Rubidium strongly enhanced both catalytic activity and N2-selectivity. Rate increases by factors as high as 110 and 45 for the production of N2 and CO2, respectively, relative to unpromoted Pt were obtained, accompanied by substantial increase in N2-selectivity (e.g. from 24 to 82% at 350°C and [CO]=0.5%, [NO]=1%). Under stoichiometric conditions, Rb-promoted catalysts gave 100% conversion of both reactants with 100% selectivity towards N2 at T350°C and at an effective reactant contact time of only 0.5 s. In contrast, under the same conditions unpromoted Pt delivered <30% conversion and poor N2-selectivity (approximately <40%); even at 480°C the conversion was only 60%. The observed promotional effects are ascribed to alkali-induced changes in the chemisorption bond strengths of CO, NO and NO dissociation products which lead to the observed activity enhancement and dependence of N2-selectivity on promoter loading. The effects of K-promotion mirror those of Rb-promotion, but are significantly less pronounced. Rb is the best alkali promoter. 相似文献