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1.
Palladium catalysts supported on mixed oxides (Pd/Al2O3–MOx; M=Co, Cr, Cu, Fe, Mn, and Ni) were investigated for the low-temperature catalytic combustion of methane. Although the surface area decreased with increasing NiO in Pd/mAl2O3–nNiO, Pd/Al2O3–36NiO demonstrated an excellent activity due to the small particle size of palladium. Also, the catalytic activity strongly depended on the composition of the support. Temperature-programmed desorption of oxygen revealed that the catalytic activity in the low-temperature region depends on the adsorption state of oxygen on palladium. The activity was enhanced when the amount of adsorbed oxygen increased. In-situ XRD analysis indicated that the PdO phase was thermally stabilized on Pd/Al2O3–36NiO. 相似文献
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H.L. Tidahy M. Hosseni S. Siffert R. Cousin J.-F. Lamonier A. Aboukaïs B.-L. Su J.-M. Giraudon G. Leclercq 《Catalysis Today》2008,137(2-4):335
Hierarchical bimodal macro-mesoporous zirconia oxide has been synthesized by a simple method in the presence of CTMABr surfactant. The synthesized zirconia having uniform macropores of 300–600 nm in diameter with wormhole-like mesoporous walls and high surface area was calcined at 400 and 600 °C and impregnated with 0.5 wt.% of palladium and compared with classical 0.5 wt.% Pd/ZrO2 catalyst for toluene oxidation. The highest activity of 0.5 wt.%/macro-mesoporous zirconia calcined at 600 °C was mainly explained by a rather high Pd dispersion and by H2-TPR measurements showing a higher quantity of PdO species easily reducible at 0 °C. 相似文献
4.
Superior catalytic behaviour of Pt-doped Pd catalysts in the complete oxidation of methane at low temperature 总被引:1,自引:0,他引:1
G. Lapisardi L. Urfels P. Glin M. Primet A. Kaddouri E. Garbowski S. Toppi E. Tena 《Catalysis Today》2006,117(4):564-568
The catalytic combustion of methane at low temperature under lean conditions was investigated over bimetallic palladium-platinum catalysts supported on alumina. Pd-Pt catalysts with constant 2 wt.% metal loading and varying compositions in Pt and Pd were prepared by successive impregnations of the metal salts. The catalysts were characterised by powder X-ray diffraction, transmission electron microscopy/electron dispersion X-ray spectroscopy (TEM/EDX), volumetry of H2 chemisorption, FTIR study of CO adsorption and temperature-programmed oxidation (TPO). In the absence of water added to the feed, the methane conversion over Pd-rich bimetallic catalysts (Pt/Pt + Pd molar ratios less than 0.3) was found to be the same as that of the reference Pd/Al2O3 catalyst. Interestingly, under wet conditions, these bimetallic catalysts exhibited an improved performance with respect to Pd/Al2O3. This effect was found to be maintained upon mild steam ageing. An interaction between both metals was suggested to explain the enhanced activity of bimetallic catalysts. This was confirmed by TPO experiments indicating that formation and decomposition of PdO is affected upon Pt addition even for very low amounts of Pt. The adsorption of CO on reduced catalysts studied by FTIR revealed new types of adsorbed CO species, suggesting again an interaction between two metals. 相似文献
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Influence of the exchanged cation in Pd/BEA and Pd/FAU zeolites for catalytic oxidation of VOCs 总被引:1,自引:0,他引:1
H.L. Tidahy S. Siffert J.-F. Lamonier R. Cousin E.A. Zhilinskaya A. Aboukaïs B.-L. Su X. Canet G. De Weireld M. Frre J.-M. Giraudon G. Leclercq 《Applied catalysis. B, Environmental》2007,70(1-4):377-383
0.5 wt% palladium supported on exchanged BEA and FAU zeolites were prepared, characterized and tested in the total oxidation of volatile organic compounds (VOCs). The BEA and FAU zeolites were exchanged with different cations to study the influence of alkali metal cations (Na+, Cs+) and H+ in Pd-based catalysts on propene and toluene total oxidation. The exchange with different cations (Na+, Cs+) and H+ led to a decrease of the surface area and the micropore volume. All Pd/BEA and Pd/FAU zeolites were found to be powerful catalysts for the total oxidation of VOCs. They were active at low temperature and totally selective for CO2 and H2O. However, their activity depends significantly on the type of zeolite and on the nature of the charge-compensating cation. The activity order for propene and toluene oxidation on FAU catalysts, Pd/CsFAU > Pd/NaFAU > Pd/HFAU, is the reverse of the activity order on BEA catalysts: Pd/HBEA > Pd/NaBEA > Pd/CsBEA. The catalytic activities can be rationalized in terms of the influence of the electronegativity of the charge-compensating cation on the Pd particles, the Pd dispersion, the PdO reducibility and the adsorption energies for VOCs. 相似文献
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Promoting effect of water vapor on catalytic oxidation of methane over cobalt/manganese mixed oxides
Methane oxidation was conducted in a fixed bed quartz tubular reactor on a series of mixed oxides of cobalt/manganese prepared by a sol–gel method. A unique promoting effect of water vapor on methane conversion was observed for the first time on these cobalt/manganese mixed oxides calcined at 450 or 600 °C. However, these mixed catalysts lost their catalytic activities after being calcined at 850 °C. The catalytic activity of methane oxidation was significantly improved by supporting the cobalt/manganese mixed species onto the high surface area SiO2 or Al2O3–SiO2 materials. It was noteworthy that the water enhancement effect was retained on these supported catalysts. 相似文献
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The influence of the reaction parameters including temperature, oxygen concentration, and of in situ hydrogen reduction on the Pd catalyst activity towards complete methane oxidation is studied experimentally.Zero porosity α-alumina plates are used as a support for Pd catalyst. This lowers the influence of metal–support interaction on the catalyst state as confirmed by UV–visible spectroscopy. A plug flow reactor with a high linear gas velocity is used to measure the reaction rate. Overall conversion is kept low for most of the experiments so that the reaction is in the kinetically limited regime. The oxidation state of the catalyst before and after the reaction is determined using UV–visible reflectance spectroscopy of the plate surface. Changes in the catalyst activity with time are monitored after stepwise changes in the reaction parameters.Activity was found to decrease with time at low temperatures and high oxygen concentrations (condition when PdO phase is stable) and to increase with time at high temperatures and low oxygen concentrations (conditions when Pd is stable). A sharp increase in conversion was observed after the in situ hydrogen reduction of the sample.The experimental data is consistent with the reduced Pd form of the catalyst being more active towards methane oxidation than the oxidized PdO form at high temperatures. Possible particle size and morphology effects are discussed. 相似文献
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J.-M. Giraudon T.B. Nguyen G. Leclercq S. Siffert J.-F. Lamonier A. Aboukaïs A. Vantomme B.-L. Su 《Catalysis Today》2008,137(2-4):379
Two series of supported Pd catalysts were synthesized on new mesoporous–macroporous supports (ZrO2, TiO2) labelled M (Zr and Ti). The deposition of palladium was carried out by wet impregnation on the calcined TiO2 and ZrO2 supports at 400 °C (Pd/Zr4, Pd/Ti4) and 600 °C (Pd/Zr6, Pd/Ti6) and followed by a calcination at 400 °C for 4 h. The pre-reduced Pd/MX catalysts were investigated for the chlorobenzene total oxidation and their catalytic properties where compared to those of a reference catalyst Pd/Ti-Ref (TiO2 from Huntsman Tioxide recalcined at 500 °C) and of a palladium supported on the fresh mesoporous–macroporous TiO2 (Pd/Ti). Based on the activity determined by T50, the Pd/Ti and Pd/Ti4 catalysts have been found to be more active than the reference one. Moreover activity decreased owing to the sequence: Pd/TiX Pd/ZrX and in each series when the temperature of calcination of the support was raised. The overall results clearly showed that the activity was dependant on the nature of the support. The better activity of Pd/TiX compared to Pd/ZrX was likely due to a better reducibility of the TiO2 support (Ti4+ into Ti3+) leading to an enhancement of the oxygen mobility. Production of polychlorinated benzenes PhClx (x = 2–6) and of Cl2 was also observed. Nevertheless at 500 °C the selectivity in HCl was higher than 90% for the best catalysts. 相似文献
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On the role of acidity in catalytic oxidation 总被引:2,自引:0,他引:2
The role of the catalyst surface acid-base properties on the heterogeneously-catalyzed oxidation reaction mechanisms is discussed. Acid-base properties depend on the covalent/ionic character of the metal-oxygen bonds and are involved in some steps of the oxidation reactions, such as the activation of the C---H hydrocarbon bonds, the step associated with the evolution of alkoxide species and the desorption/overoxidation of the partial oxidation products. Thus they participate with the cation redox properties in determining the selective/unselective catalyst behavior. 相似文献
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Complete benzene oxidation over Pt-Pd bimetal catalyst supported on γ-alumina: influence of Pt-Pd ratio on the catalytic activity 总被引:1,自引:0,他引:1
Hyoung Sik Kim Tae Won Kim Hyoung Lim Koh Seo Ho Lee Byoung Ryul Min 《Applied Catalysis A: General》2005,280(2):125-131
Pt-Pd bimetal catalysts were prepared in order to develop and investigate catalysts with excellent activity and stability for benzene destruction. In the reaction results, the addition of Pt to Pd/γ-Al2O3 catalyst brought about the increase of catalytic activity. Moreover, it was effective in preventing the deactivation of the catalysts in benzene combustion. The addition of some amount of Pt made Pd particles available for better benzene combustion. On the contrary, the addition of Pt beyond a certain amount decreases activity because of the Pd active sites overlapped with the Pt active sites. The activity of the catalysts is related to oxidation state of metal, Pd/Al ratio and particle size on γ-Al2O3. These effects of Pt addition to Pd catalysts were studied by XPS, XRD, and TEM analyses. 相似文献
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Properties and performance of Pd based catalysts for catalytic oxidation of volatile organic compounds 总被引:1,自引:0,他引:1
Catalytic oxidations of volatile organic compounds (VOCs) (benzene, toluene and o-xylene) over 1 wt% Pd/γ-Al2O3 catalyst were carried out to assess the properties and performance of the Pd based catalyst. The properties of the prepared catalysts were characterized by the Brunauer Emmett Teller (BET) surface area, H2 chemisorption, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) analyses. The experimental results revealed a significant increase in VOCs conversion with the lapse of the reaction time at certain reaction temperatures. On the other hand, the hydrogen pretreated 1 wt% Pd/γ-Al2O3 catalyst, whose shape of conversion curve is similar to the non pretreated catalyst, led the conversion curves for the total oxidation of VOCs to be shifted to lower temperature. It was also found that such increases in VOCs conversion were highly dependent on the oxidation state of Pd and the growth of Pd particles in the catalyst. In addition, in the case of the catalyst consisting of the same oxidation state (PdO/Pd2+ or Pd0), the particle sizes possibly play a more important role in the catalytic activity. The activity order of 1 wt% Pd/γ-Al2O3 catalyst with respect to the VOC molecule was o-xylene > toluene > benzene. 相似文献
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《Ceramics International》2021,47(22):31485-31496
Mesoporous SmMnO3/CuMnOx catalyst was prepared by a two-step method using flaky CuMnOx with high specific surface and excellent catalytic ability as the carrier, which was further applied to photothermal synergistic degradation of gaseous toluene. Quantitative analysis of O2-TPD and H2-TPR showed that SmMnO3/CuMnOx exhibited abundant of the surface oxygen species and oxygen vacancies content, which enabled it to convert free oxygen to lattice oxygen more quickly during the reaction, and thus improving the reaction process. I-t and photoluminescence experiments demonstrated the improvement of photogenerated electron and hole separation ability of SmMnO3/CuMnOx catalyst. UV–Vis analysis manifested the full spectral range of absorption. XPS analysis verified the unequal positions of valence band of the two materials, which can facilitate the separation of photogenerated electrons from holes and improve the ability of better electron transfer. SmMnO3/CuMnOx catalyst has higher adsorbed oxygen content and light absorption capacity, which is beneficial to the catalytic oxidation. In situ DRIFTs proved that the oxidation reaction on the catalyst followed the Mars-van Krevelen redox cycle. The VOCs test found that SmMnO3/CuMnOx composite catalyst is with lower onset reaction temperature (T90 = 190 °C, T90, corresponding to 90% conversion) and good mineralization (100% at 275 °C). 相似文献
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The catalytic activity of fresh Pd and Pt catalysts supported on γ-alumina in the complete oxidation of CH4 traces under lean-burn conditions was studied in the presence or the absence of water or H2S. Steam-aged catalysts were also studied in order to simulate long-term ageing in real lean-burn natural gas fuelled vehicles (NGVs) exhaust conditions. Without water or H2S added to the feed, Pd catalysts exhibit a superior catalytic activity in methane oxidation compared to Pt ones, whatever the catalysts were fresh or aged. The addition of 10 vol.% water vapour to the feed strongly affects the activity of the fresh Pd catalyst, thus being only slightly more efficient than the fresh Pt one. H2S has a strong poisoning effect on the catalytic activity of Pd catalysts, while Pt catalysts are more resistant. The fresh H2S-poisoned Pd/Al2O3 catalyst was studied by TPD in O2/He. Poisoning species decompose above 873 K as SO2 and O2 in relative concentrations consistent with the decomposition of surface sulphate species. However, a treatment in O2/He at temperatures as high as 923 K does not allow the complete regeneration of the catalytic activity of H2S-poisoned Pd/Al2O3. A mechanism involving the poisoning of PdO by sulphate species is proposed. Different diffusion processes by which these sulphate species can migrate back and forth between PdO and the support, depending on the experimental conditions, are suggested. 相似文献
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Xiaoqiang Li Jie Xu Lipeng Zhou Feng Wang Jin Gao Chen Chen Jianbo Ning Hong Ma 《Catalysis Letters》2006,110(3-4):255-260
Copper manganese oxides (Cu–Mn oxides) were prepared by coprecipitation method and characterized by several techniques, such
as X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and Temperature-programmed reduction (TPR).
Catalytic activities of the Cu–Mn oxides were tested by the oxidation of toluene with molecular oxygen in liquid phase and
solvent-free conditions. The molar ratio of Cu:Mn in catalyst was optimized to be 1:1 and thus the corresponding crystalline
material was designated as Cu1.5Mn1.5O4. 相似文献
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Xiaoqiang Li Jie Xu Lipeng Zhou Feng Wang Jin Gao Chen Chen Jianbo Ning Hong Ma 《Catalysis Letters》2006,110(1-2):149-154
Copper manganese oxides (Cu–Mn oxides) were prepared by coprecipitation method and characterized by several techniques, such
as X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and Temperature-programmed reduction (TPR).
Catalytic activities of the Cu–Mn oxides were tested by the oxidation of toluene with molecular oxygen in liquid phase and
solvent-free conditions. The molar ratio of Cu:Mn in catalyst was optimized to be 1:1 and thus the corresponding crystalline
material was designated as Cu1.5Mn1.5O4. 相似文献
16.
A. Aranzabal 《Chemical engineering science》2006,61(11):3564-3576
The complete catalytic oxidation of 1,2-dichloroethane (DCE) over palladium supported on alumina was evaluated. The effect of temperature, inlet DCE concentration, and the space time on the reaction rate and selectivity was examined with the aim of better understanding of the reaction pathway. DCE oxidation reactions were carried out in a conventional fixed-bed reactor at atmospheric pressure under conditions of lean DCE concentration in air. The outlet composition was analysed by a gas chromatograph equipped with an electron capture detector (ECD) and a thermal conductivity detector (TCD). The reaction scheme resulted in a first dehydrochlorination step of DCE, leading to the formation of vinyl chloride (VC), followed by direct oxidation of VC to CO and CO2. CO is finally oxidized to CO2. The developed kinetic model provided an accurate correlation of the experimental data, determined by a non-linear least-squares regression. 相似文献
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《Ceramics International》2020,46(3):3166-3176
A large number of studies had shown that the morphology of the sample had a significant effect on the microwave absorption properties and catalytic activity of the sample. Manganese dioxide with different morphologies was synthesized by hydrothermal method through different precursors. The effects of sample morphology and microwave absorption properties on the catalytic activity of the sample in conventional thermal and microwave fields were studied. The results indicated that compared with the conventional thermal field, the catalytic activity of the samples in microwave field were obviously improved, and the activation energy of the reaction were decreased. Compared with the conventional thermal field, the conversion of toluene in microwave thermal field of MnO2(Ac), MnO2(S) and MnO2(N) increased by 59%, 42% and 12%, and the mineralization rate increased by 36%,11% and 2%, respectively, when the catalytic temperature was 150 °C. Compared with the traditional thermal field, the activation energy of the sample MnO2(Ac) in the microwave field was reduced by 88.3 KJ. A series of characterization results showed that the sample MnO2(Ac) had good catalytic activity in the microwave field was due to: MnO2(Ac) had proper microwave absorption properties, large amount of surface functional groups, large specific surface area and rich pore structure. The analysis results of electromagnetic parameters showed that: the reason that the sample MnO2(Ac) had good microwave absorption performance was that the MnO2(Ac) had proper impedance matching, high attenuation constant and Debye dipole relaxation effect. 相似文献
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Carlo Resini Federico Catania Silvia Berardinelli Ombretta Paladino Guido Busca 《Applied catalysis. B, Environmental》2008,84(3-4):678-683
The catalytic performances of lanthanum strontium manganite (La0.8Sr0.2)Mn0.98O3, in catalytic wet oxidation (CWO) of a phenol solution under milder conditions of temperature (398–498 K) and pressure (Po2=4 bar), in a batch reactor, have been investigated. Aim of this study is the evaluation of the effect of temperature, catalyst loading, phenol concentration and stirrer speed on phenol conversion. Experimental data obtained from the different test conditions are best-fitted to evaluate the effective reaction order and apparent activation energy. 相似文献
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采用微波催化氧化法对苯胺模拟水的处理进行了初步的探讨分析;考察了微波时间、微波功率、pH值、H2O2浓度、高分子负载型催化荆质量对废水中苯胺降解的影响,确定了最佳工艺条件.在最佳工艺条件下,CODcr的去除率达到98%以上. 相似文献