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1.
Selective Catalytic Reduction of NO by C3H6 over Co/Al2O3 Catalyst with Extremely Low Cobalt Loading 总被引:1,自引:0,他引:1
Tatsuro Horiuchi Takamichi Fujiwara Laiyuan Chen Kenzi Suzuki Toshiaki Mori 《Catalysis Letters》2002,78(1-4):319-323
In order to reveal the optimum Co loading, the selective catalytic reduction of NO with C3H6 over Co/Al2O3 catalyst was studied in a systematic fashion by varying the amount of cobalt oxide. It was found that upon loading a small amount of cobalt oxide (namely 0.5 wt% on a Co metal basis), the combination between Co(II) acetate salt and a high-purity alumina provided an active catalyst in the presence of excess oxygen and water. TPR measurement showed the presence of Co species other than CoAl2O4 spinel in the most excellent performance catalyst, from which the active sites should be produced. 相似文献
2.
Selective catalytic reduction of NO with propene was investigated over In2O3/Al2O3 catalysts prepared by three methods, namely, a single sol-gel (SG), impregnation (IM), and co-precipitation method (CP). The catalysts were characterized by means of BET, XRD, XPS, and TPD. The maximum NO conversion over In2O3/Al2 O3 prepared by sol-gel method was 95% at 400 °C in the absence of H2O, and the activity decreased slightly in the presence of H2O, and it was still 76% even in the presence of H2O and SO2. Although the retarding effect of SO2 on the activity was observed for the three catalysts, In2O3/Al2O3 (SG) showed relatively high activity. It is found that the high surface area and low average pore diameter are important to the catalytic activity, and the strong interaction between indium and alumina for In2O3/Al2O3 catalyst prepared by sol-gel method may be the reason of high activity for NO reduction. The reaction and surface studies showed that NO3− and partially oxidized hydrocarbons (RCOO− species) are mainly intermediates, and the oxidation C3H6 to RCOO− species maybe the key reaction process in the SCR of NO with C3H6. 相似文献
3.
The selective catalytic reduction (SCR) of NO by decane under an oxidising atmosphere has been carried out on Cu/ZrO2 and Cu/ZrO2(SO
4
2–
). Zirconia-supported Cu catalysts were prepared by ligand exchange with Cu acetylacetonate followed by calcination at 773 K. The solids obtained were characterised by temperature programmed reduction (TPR) by hydrogen and temperature programmed desorption (TPD) of NO. Cu/ZrO2 is active and selective in the reduction of NO by decane at low temperature (< 600 K) but oxidises NO to NO2 between 640 and 770 K. By contrast, whatever the temperature, a total selectivity to nitrogen is obtained with Cu/ZrO2(SO
4
2–
). About 40% NO conversion to N2 is observed with GHSV of 70 000 h–1. The promoting effect of sulfate is attributed to the large increase of acidity and the strong interaction between copper and sulfur species which is evidenced by TPD of NO and TPR by H2. 相似文献
4.
A 10%Co/ZrO2 catalyst prepared by impregnation was tested for its activity for the oxidation of CO to CO2 in excess oxygen. Activity tests showed that conversion could be obtained at temperatures as low as 20 °C. Time-on-stream
studies showed no loss of activity in these experiments, indicating that this catalyst is stable in the experimental oxidizing
conditions. The activation energy for the CO to CO2 oxidation reaction was calculated as Ea = 54 kJ/mol over this catalyst. Characterization of the material by thermogravimetric analysis, temperature-programmed techniques,
X-ray photoelectron spectroscopy, and laser Raman spectroscopy indicate that Co3O4 is present on monoclinic ZrO2 after the calcination of the catalyst. 相似文献
5.
Catalytic performance of Co/ZSM-5 with different metal loadings and of HZSM-5 was compared in the NO + O2, C3H8 + O2, and NO + C3H8 + O2 reactions. It was found that Co/ZSM-5 catalysts containing only isolated cobalt ions in cationic positions are inactive in NO2 formation. To achieve appreciable NO conversion in the SCR process over these catalysts higher reaction temperatures are required. These results make it possible to suggest that NO2 formation is not a prerequisite for the SCR of NO with hydrocarbons over Co/ZSM-5. With increasing Co loading, however, Co/ZSM-5 begins to exhibit activity in NO2 formation. This is explained by the formation of cobalt oxide particles on the zeolite carrier, which are active in the NO2 formation. Increase in NO2 formation strongly enhances catalytic activity in SCR of NO at lower reaction temperatures. Comparison of the C3H8 conversion in the C3H8 + O2 and C3H8 + O2 + NO reactions provides evidence that NO2 activates hydrocarbon molecules resulting in the formation of the reaction intermediates of the SCR process.On leave from N.D. Zelinskii Institute of Organic Chemistry, Leninskii Pr. 47, Moscow, Russia. 相似文献
6.
Takashi Ohno Eiji Tanaka Fumikazu Hatayama Yoshio Toda Hisashi Miyata 《Catalysis Letters》2001,77(4):183-187
The effect of Pt addition to a V2O5/ZrO2 catalyst on the reduction of NO by C3H6 has been studied by FTIR spectroscopy as well as by analysis of the reaction products. Pt loading promoted the catalytic activity remarkably. FTIR spectra of NO adsorbed on the catalysts doped with Pt show the presence of two different types of Pt sites, Pt oxide and Pt cluster, on the surface. The amount of these sites depends on Pt contents and the catalyst state. Pt atoms highly disperse on the surface as Pt oxide at low Pt content, being aggregated into Pt metal clusters by increasing Pt amount or reducing the catalysts. The spectral behavior of V=O bands on the surface also supports the formation of Pt clusters. It is concluded that Pt promotes the NO–C3H6 reaction through a reduction–oxidation cycle between its oxide and cluster form. 相似文献
7.
Novel catalysts, SnxZr1-xO2 solid solutions, for NO selective catalytic reduction:NO SCR) are reported. They have much higher activity and selectivity than SnO2 and ZrO2. Sn4+ is the main reductive sites as proved by TPR. The dilution of Sn sites by the coexisting Zr causes a suppression of propene combustion and consequently promoted the selective reduction of NO. The rutile structure might be beneficial to NO SCR. 相似文献
8.
In/HZSM-5/In2O3 catalyst that contained two different kinds of In induced by the impregnating and the physical mixing method respectively has shown remarkable activity for the CH4-SCR of NO
x
comparing with In/HZSM-5. The addition of In2O3 into In/HZSM-5 improved the NO conversion through enhancing the adsorption of NO
x
over In/HZSM-5. 相似文献
9.
The Ce modified In/W–ZrO2 catalysts were prepared by impregnation and mechanical mix method. Their activities for SCR of NO
x
with methane were investigated. The activity of the In/W–ZrO2 catalyst was enhanced by addition of Ce with both methods, while the promotional effect was more pronounced for catalyst
prepared by mechanical mix method compared to impregnation method. The function of Ce was to improve the oxidation of NO to
NO2. The maximum NO
x
conversion over the mechanical mixed catalyst can be stabilized at 74% at 450 °C in a dry gas flow and 37% at 500 °C in wet
flow (24,000 h−1). For the impregnated catalysts, Ce was found to compete with In to adsorb on strong acid site over W–ZrO2 support and inhibited the formation of InO+, which resulted in the lower activity of these catalysts than mechanical mixed catalysts. 相似文献
10.
Activity and selectivity of selective CO oxidation in an H2-rich gas stream over Co3O4/CeO2/ZrO2, Ag/CeO2/ZrO2, and MnO2/CeO2/ZrO2 catalysts were studied. Effects of the metaloxide types and metaloxide molar ratios were investigated. XRD, SEM, and N2 physisorption techniques were used to characterize the catalysts. All catalysts showed mesoporous structure. The best activity was obtained from 80/10/10 Co3O4/CeO2/ZrO2 catalyst, which resulted in 90% CO conversion at 200°C and selectivity greater than 80% at 125°C. Activity of the Co3O4/CeO2/ZrO2 catalyst increased with increase in Co3O4 molar ratio. 相似文献
11.
Structural, textural and surface properties of sulfated and non-sulfated titanium-pillared clay were correlated with catalytic tests in the reduction of NO by NH3 in the presence of oxygen. Lower specific surface areas and basal spacings but stronger acid sites were observed on sulfated Ti-pillared clay than on Ti-pillared clay. Sulfated Ti-pillared clays were more active than Ti-pillared clay. Accordingly, it is suggested that the strong Brønsted acidity generated by sulfate is responsible for the high reactivity of sulfated Ti-pillared clay at high temperature. 相似文献
12.
A series of catalysts, NiSO4/TiO2–ZrO2 having different TiO2–ZrO2 composition, for acid catalysis was prepared by the impregnation method using an aqueous solution of nickel sulfate. The
addition of TiO2 to ZrO2 improved the surface area of the catalyst and enhanced its acidity remarkably because of the formation of new acid sites
through the charge imbalance of Ti–O–Zr bonding. The binary oxide, TiO2–ZrO2 calcined above 600 °C resulted in the formation of crystalline orthorhombic phase of ZrTiO4. Therefore, NiSO4/TiO2–ZrO2 calcined at 500 °C exhibited a maximum catalytic activity for acid catalysis, and then the catalytic activity decreased with
the calcination temperature. The correlation between catalytic activity and acidity held for both reaction, 2-propanol dehydration
and cumene dealkylation. NiSO4 supported on 50TiO2–50ZrO2 (TiO2/ZrO2 ratio = 1) among TiO2–ZrO2 binary oxides exhibited the highest catalytic activity for acid catalysis. 相似文献
13.
F.B. Noronha A. Shamsi C. Taylor E.C. Fendley S. Stagg-Williams D.E. Resasco 《Catalysis Letters》2003,90(1-2):13-21
CO2 reforming of methane was performed on Pt/ZrO2 and Pt/Ce-ZrO2 catalysts at 1073K under different reactions conditions: (i) atmospheric pressure and CH4:CO2 ratio of 1:1 and 2:1; (ii) in the presence of water and CH4:CO2 ratio of 2:1; (iii) under pressure (105 and 190 psig) and CH4:CO2 ratio of 2:1. The Pt supported on ceria-promoted ZrO2 catalyst was more stable than the Pt/ZrO2 catalyst under all reaction conditions. We ascribe this higher stability to the higher density of oxygen vacancies on the promoted support, which favors the cleaning mechanism of the metal particle. The increase of either the CH4:CO2 ratio or total pressure causes a decrease in activity for both catalysts, because under either case the rate of methane decomposition becomes higher than the rate of oxygen transfer. The Pt/Ce-ZrO2 catalyst was always more stable than the Pt/ZrO2 catalyst, demonstrating the important role of the support on this reaction. 相似文献
14.
Effect of additives, Ce and Mn, on the catalytic performance of Sn/Al2O3 catalyst prepared by sol–gel method for the selective reduction of NOx with propene under lean conditions was studied. Sn–Ce/Al2O3 catalysts exhibited higher activity than Sn/Al2O3 catalyst and the optimum Ce loading is 0.5–1%. The promoting effect of Ce is to enhance the oxidation of NO to NO2 and facilitate the activation of propene, both of which are important steps for the NOx reduction. The presence of oxygen contributes to the oxidation of NO and shows a promoting effect. 相似文献
15.
J.D.A. Bellido 《Fuel》2009,88(9):1673-1034
ZrO2, γ-Al2O3 and ZrO2/γ-Al2O3-supported copper catalysts have been prepared, each with three different copper loads (1, 2 and 5 wt%), by the impregnation method. The catalysts were characterized by nitrogen adsorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR) with H2, Raman spectroscopy and electronic paramagnetic resonance (EPR). The reduction of NO by CO was studied in a fixed-bed reactor packed with these catalysts and fed with a mixture of 1% CO and 1% NO in helium. The catalyst with 5 wt% copper supported on the ZrO2/γ-Al2O3 matrix achieved 80% reduction of NO. Approximately the same rate of conversion was obtained on the catalyst with 2 wt% copper on ZrO2. Characterization of these catalysts indicated that the active copper species for the reduction of NO are those in direct contact with the oxygen vacancies found in ZrO2. 相似文献
16.
Selective catalytic oxidation of hydrogen in the presence of hydrocarbons was studied in a fixed bed quartz reactor, over
3 wt%Au/TiO2 and 5 wt%Au/TiO2 catalysts. This reaction can be utilised in the production of light alkenes via catalytic dehydrogenation, providing in situ heat to the endothermic dehydrogenation reaction and simultaneously removing a fraction of the produced hydrogen. It is important
to avoid the non-selective combustion of the hydrocarbons in the mixture. Both 3 wt%Au/TiO2 and 5 wt%Au/TiO2 are active for the combustion of hydrogen, but in a gas mixture with propane and oxygen the selectivity is dependent upon
the feed ratio of hydrogen and oxygen. At 550 °C, with propane present, no carbon oxides are formed when the H2:O2 ratio is four, but at lower ratios some CO2 and some CO is formed. 相似文献
17.
A novel process for the direct ammoxidation of propane over steam-activated Fe-silicalite at 723–823 K is reported. Yields
of acrylonitrile (ACN) and acetonitrile (AcCN) below 5% were obtained using N2O or O2 as the oxidant. Co-feeding N2O and O2 boosts the performance of Fe-silicalite compared to the individual oxidants, leading to AcCN yields of 14% and ACN yields
of 11% (propane conversions of 40% and products selectivity of 25–30%). The beneficial effect of O2 on the propane ammoxidation with N2O contrasts with other N2O-mediated selective oxidations over iron-containing zeolites (e.g. hydroxylation of benzene and oxidative dehydrogenation
of propane), where a small amount of O2 in the feed dramatically reduces the selectivity to the desired product. It is shown that the productivity of ACN and especially
AcCN, expressed as mol product h−1 kgcat−1, is significantly higher over Fe-silicalite than over active propane ammoxidation catalysts reported in the literature. Our
results open new perspectives to improve the performance of alkane ammoxidation catalysts. 相似文献
18.
Choowong Chaisuk Pornpoj Boonpitak Joongjai Panpranot Okorn Mekasuwandumrong 《Catalysis communications》2011,12(10):917-922
The Co/ZrO2 catalysts with various Co loadings (5–10 wt.%) were prepared by one-step flame spray pyrolysis (FSP) under different flame conditions. As revealed by XRD and TEM, all the resulting Co/ZrO2 nanoparticles were composed of single-crystalline particles exhibiting the characteristic tetragonal structure of ZrO2. Varying the amount of Co dopants during FSP synthesis did not alter the primary particle size of ZrO2 which was determined to be ca. 14 nm. On the other hand, increasing precursor feed rate from 3 to 8 ml/min resulted in an increase of ZrO2 crystallite size from 10 to 19 nm. The higher precursor feed rate produced higher enthalpy of flame and longer residence times, which increased coalescence and sintering of the particles. Compared to the Co/ZrO2 prepared by conventional impregnation method, the catalytic activities of the FSP-made catalysts were much higher. Moreover, the hydrogenation rates of the FSP-made Co/ZrO2 catalysts were increased with increasing Co loading and precursor feed rate. According to H2 chemisorption and H2 temperature program reduction results, the improvement of catalytic activity and C2–C6 selectivities of the FSP-made catalysts in the CO hydrogenation was attributed to the higher number of Co metal active sites and lower interaction between Co/CoO and ZrO2 support obtained via the FSP synthesis. 相似文献
19.
D. A. Storm 《Topics in Catalysis》1995,2(1-4):91-101
The optimized compositions K(4.9)/Co(2.7)/Mo(6.4)/A1203(gamma) and K(1.2)/ Rh(1.1)/Co(0.6)/Mo(5.7)/A1203(gamma) are both productive catalysts for higher alcohols. The incorporation of rhodium into the K/Co/Mo/A1203-system allows the space-time-yield for alcohols to be increased from 0.37 g alcohols (g catalyst)–1 h–1 to 1.1 g alcohols (g catalyst)–1 h–1. In addition, the higher productivity can be achieved with the rhodium-type catalyst at a lower reaction temperature (45°C lower), and so a higher selectivity to alcohols is observed. Potassium is a key promoter in both catalyst systems, and shifts the distribution of oxygenates towards higher alcohols. In IR measurements it is found that potassium stimulates bands for adsorbed CO around 1885 cm–. These bands are small for the K/Co/Mo/A1203 system, but are greatly stimulated by the incorporation of rhodium. It is suggested that these bands are indicative of the sites used to catalyze higher alcohols, thereby explaining the promotional effect of rhodium in the K/Co/Mo/A1203 catalyst system. Previous workers have suggested that the less-electron-rich sites (ionic) are important for methanol synthesis, while the more electron-rich sites (metallic) are important for higher alcohols and hydrocarbons synthesis. The IR measurements and reactivity data support these suggestions. 相似文献
20.
The ammonia method has been successfully used for preparing thermostable and well dispersed alumina‐supported catalysts with
a surface average size of cobalt particle D
s= 5.7 nm. The disproportionation reaction of CO over this Co/Al2O3 catalyst and a similar Co/SiO2 catalyst leads to the formation of carbon nanotubes demonstrating the same morphology. The amount of nanotubes over Co/Al2O3, however, is much larger than that obtained over Co/SiO2, because of a faster ageing in the latter solid. Similar support effects have already been reported for other catalytic reactions
involving carbon oxides.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献