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1.
The oxidation of CH4 over Pt–NiO/δ-Al2O3 has been studied in a fluidised bed reactor as part of a major project on an autothermal (combined oxidation–steam reforming) system for CH4 conversion. The kinetic data were collected between 773 and 893 K and 101 kPa total pressure using CH4 and O2 compositions of 10–35% and 8–30%, respectively. Rate–temperature data were also obtained over alumina-supported monometallic catalysts, Pt and NiO. The bimetallic Pt–NiO system has a lower activation energy (80.8 kJ mol−1) than either Pt (86.45 kJ mol−1) and NiO (103.73 kJ mol−1). The superior performance of the bimetallic catalyst was attributed to chemical synergy. The reaction rate over the Pt–NiO catalyst increased monotonically with CH4 partial pressure but was inhibited by O2. At low partial pressures (<30 kPa), H2O has a detrimental effect on CH4 conversion, whilst above 30 kPa, the rate increased dramatically with water content. 相似文献
2.
Kou Sugawara Takeshi Nobukawa Masanori Yoshida Yoshihiro Sato Kazu Okumura Keiichi Tomishige Kimio Kunimori 《Applied catalysis. B, Environmental》2007,69(3-4):154-163
Effect of the loading amount of Fe over ion-exchanged Fe-MFI catalysts on the catalytic performance of N2O reduction with NH3 was investigated, and the results indicated that the turnover frequency (TOF) was almost constant in the Fe/Al range between 0.05 and 0.40. The activity of N2O + NH3 reaction was much lower than that of N2O + CH4 reaction over Fe-MFI (Fe/Al = 0.40), and the preadsorption of NH3 decreased drastically the activity of N2O + CH4 reaction. The temperature-programmed desorption (TPD) of NH3 showed the formation of stronger acid sites on Fe-MFI (Fe/Al = 0.24 and 0.40), and the amount of the acid sites agrees well with the desorption amount O2 in O2-TPD in the low temperature range. The acid sites gave a 3610 cm−1 peak (Brønsted acid) in FTIR observation. These results suggest that the acid sites were formed on the bridge oxide ions in binuclear Fe species. Adsorbed NH3 on the strong acid sites inhibited N2O dissociation, which can be related to the low activity of N2O + NH3 reaction over Fe-MFI with high Fe loading. 相似文献
3.
Xiankuan Zhang Arden B. Walters M. Albert Vannice 《Applied catalysis. B, Environmental》1996,7(3-4):321-336
Both NO decomposition and NO reduction by CH4 over 4%Sr/La2O3 in the absence and presence of O2 were examined between 773 and 973 K, and N2O decomposition was also studied. The presence of CH4 greatly increased the conversion of NO to N2 and this activity was further enhanced by co-fed O2. For example, at 773 K and 15 Torr NO the specific activities of NO decomposition, reduction by CH4 in the absence of O2, and reduction with 1% O2 in the feed were 8.3·10−4, 4.6·10−3, and 1.3·10−2 μmol N2/s m2, 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 N2 formation by decomposition was inhibited by O2 in the feed even though the reaction order in NO remained the same. The rate of NO reduction by CH4 continuously increased with temperature to 973 K with no bend-over in either the absence or the presence of O2 with equal activation energies of 26 kcal/mol. The addition of O2 increased the reaction order in CH4 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 O2 was 0.26 up to 0.5% O2 during which time the CH4 concentration was not decreased significantly. N2O decomposition occurs rapidly on this catalyst with a specific activity of 1.6·10−4 μmol N2/s m2 at 623 K and 1220 ppm N2O and an activation energy of 24 kcal/mol. The addition of CH4 inhibits this decomposition reaction. Finally, the use of either CO or H2 as the reductant (no O2) produced specific activities at 773 K that were almost 5 times greater than that with CH4 and gave activation energies of 21–26 kcal/mol, thus demonstrating the potential of using CO/H2 to reduce NO to N2 over these REO catalysts. 相似文献
4.
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
5.
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
6.
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
7.
S. Surez M. Yates A.L. Petre J.A. Martín P. Avila J. Blanco 《Applied catalysis. B, Environmental》2006,64(3-4):302-311
Monolithic catalysts based on Rh/TiO2–sepiolite were developed and tested in the decomposition of N2O traces. Several effects such as the presence of NO, O2 and NO + O2 in the gas mixture, the catalysts pre-treatment and the metal loading were evaluated. The system was extremely sensitive to the amount of rhodium, passing through a maximum in the catalytic activity at a Rh content of 0.2 wt.%. It has been demonstrated that both NO and O2 compete for the same adsorption sites as N2O; however, this effect was not as severe as for other previously reported Rh systems. For NO + O2 gas mixtures the inhibition effect was stronger than when only NO or O2 was present. Analysis of the pre-reduced sample by XPS showed Rh mainly in the metal state, even after treatment with N2O + O2 mixtures, suggesting that the oxygen consumption observed in the Temperature Programmed Reaction experiments was related to the oxygen uptake by vacancies in the support. The presence of sepiolite in the support preparation and its role as a matrix over which TiO2 particles were distributed, seems to play an important effect in the migration process of oxygen species through the support vacancies. The Rh/TiO2 monolithic system is an attractive alternative for the elimination of N2O traces from stationary sources due to the combination of high catalytic activity with a low pressure drop and optimum textural/mechanical properties. 相似文献
8.
9.
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
10.
Baitao Li Ritsuko Watanabe Kenji Maruyama Mohammad Nurunnabi Kimio Kunimori Keiichi Tomishige 《Applied Catalysis A: General》2005,290(1-2):36-45
During the reactions related to oxidative steam reforming and combustion of methane over -alumina-supported Ni catalysts, the temperature profiles of the catalyst bed were studied using an infrared (IR) thermograph. IR thermographical images revealed an interesting result: that the temperature at the catalyst bed inlet is much higher under CH4/H2O/O2/Ar = 20/10/20/50 than under CH4/H2O/O2/Ar = 10/0/20/70; the former temperature is comparable to that over noble metal catalysts such as Pt and Pd. Based on the temperature-programmed reduction and oxidation measurements over fresh and used catalysts, the metallic Ni is recognized at the catalyst bed inlet under CH4/H2O/O2/Ar = 20/10/20/50, although it is mainly oxidized to NiAl2O4 under CH4/H2O/O2/Ar = 10/0/20/70. This result indicates that the addition of reforming gas (CH4/H2O = 10/10) to the combustion gas (CH4/O2 = 10/20) can stabilize Ni species in the metallic state even under the presence of oxygen in the gas phase. This would account for its extremely high combustion activity. 相似文献
11.
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
12.
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
13.
The catalytic behavior in N2O reduction by propane in the presence of O2, H2O and SO2 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 N2O reduction on the decrease in C3H8 to N2O ratio in the feed and a higher resistance to deactivation by SO2 in accelerated durability tests with high SO2 concentration (500 ppm). This catalyst shows stable catalytic behavior in the presence of SO2 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 Fe3+ species, in this catalyst. On the other hand, Fe2O3 particles are not present in the sample prepared by CVD while mainly isolated Fe3+ ions and iron-oxide nanoclusters are present. 相似文献
14.
Transient isotopic studies in the temporal analysis of products (TAP) reactor evidenced the importance of the lifetime of oxygen species generated upon N2O decomposition on extraframework iron sites of Fe-silicalite for methane oxidation at 723 K. Fe-silicalite effectively activates CH4 when N2O and CH4 are pulsed together in the reactor. However, these oxygen species gradually become inactive for methane oxidation as the time delay between the N2O and CH4 pulses is increased from 0 to 2 s. 相似文献
15.
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
16.
The objective of this work was to study the promotional effect of Pt on Co-zeolite (viz. mordenite, ferrierite, ZSM-5 and Y-zeolite) and Co/Al2O3 on the selective catalytic reduction (SCR) of NOx with CH4 under dry and wet reaction stream. After being reduced in H2 at 350°C, the PtCo bimetallic zeolites showed higher NO to N2 conversion and selectivity than the monometallic samples, as well as a combination of the latter samples such as mechanical mixtures or two-stage catalysts. After the same pretreatment, under wet reaction stream, the bimetallic samples were also more active. Among the other catalysts studied with 5% of water in the feed, (NO = CH4 = 1000 ppm, O2 = 2%), the NO conversion dropped to zero over Co2.0Mor at 500°C and GHSV = 30,000 h−1, whereas it is 20% in Pt0.5Co2.0Mor. In Pt/Co/Al2O3 the NOx conversion dropped below 5% with only 2% of water under the same reaction conditions. The specific activity given as molecules of NO converted per total metal atom per second were 16.5 × 10−4 s−1 for Pt0.5Co2.0Fer, 13 × 10−4 s−1 for Pt0.5Co2.0Mor, 4.33 × 10−4 s−1 for Pt0.5Co2.0ZSM-5 and 0.5 × 10−4 s−1 for Pt/Co/Al2O3. The Y-zeolite-based samples were inactive in both mono and bimetallic samples. The species initially present in the solid were Pt° and Co°, together with Co2+ and Pt2+ at exchange positions. Co° seems not to participate as an active site in the SCR of NOx. Those species remained after the reaction but some reorganization occurred. A synergetic effect among the different species that enhances both the NO to NO2 reaction, the activation of CH4 and also the ability of the catalyst to adsorb NO, could be responsible for the high activity and selectivity of the bimetallic zeolites. 相似文献
17.
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
18.
S. N. Vereshchagin N. P. Kirik N. N. Shishkina S. V. Morozov A. I. Vyalkov A. G. Anshits 《Catalysis Today》2000,61(1-4):129-136
Conversion of CH4, C2H6, C3H8, benzene and their binary mixtures over H-NaZSM-5 catalyst in the presence of N2O was studied. It was found that under experimental conditions methane alkylates benzene to give toluene and xylenes. Acidity of the catalyst had no effect on the reactivity of active oxygen formed from N2O towards methane and benzene, but affected their secondary transformation. Acidic samples favored the reaction of aromatic ring methylation with methane whereas deep oxidation of CH4 prevailed on NaHZSM-5. Based on the relative reactivities and 13C label distribution in the products of 13CH4+C6H6+N2O feed conversion, the scheme of hydrocarbon transformation was proposed. 相似文献
19.
NO removal using CH4 as a reductant in a dual-bed system has been investigated with Co-NaX and Ag-NaX catalysts, which were prepared by Co2+-, 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 Co3O4, which promotes NO oxidation to NO2 by excess O2 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 N2 by CH4 in the presence of excess O2 and H2O, but the NO reduction decreases quickly as time passes. However, the NO reduction to N2 in a deNO bed at 523 K and a deNO2 bed at 423 K, which are relatively lower than the reaction temperatures for common SCR systems, still remained at 67% even in a H2O 10% gas mixture after 160 min. 相似文献
20.
Cu-AlTS-1 catalyst was prepared by solid state ion exchange and studied in the NO and N2O decomposition. Oscillation was observed in a wide range of experimental conditions during the decomposition of N2O. At full N2O conversion, oscillations were observed only in the O2 and NO concentrations the latter being out of phase with respect to O2 and being originated from the decomposition of an excess oxygen containing nitrito–nitrato-like surface complex. Traces of NO extinguished the oscillations and increased the N2O conversion if it was below 100%. The NO also plays a key role in the feed back and synchronisation. 相似文献