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1.
Micro-channel plates with dimension of 1 mm × 0.3 mm × 48 mm were prepared by chemical etching of stainless steel plates followed by wash coating of CeO 2 and Al 2O 3 on the channels. After coating the support on the plate, Pt, Co, and Cu were added to the plate by incipient wetness method. Reaction experiments of a single reactor showed that the micro-channel reactor coated with CuO/CeO 2 catalyst was highly selective for CO oxidation while the one coated with Pt-Co/Al 2O 3 catalyst was highly active for CO oxidation. The 7-layered reactors coated with two different catalysts were prepared by laser welding and the performances of each reactor were tested in large scale of PROX conditions. The multi-layered reactor coated with Pt-Co/Al 2O 3 catalyst was highly active for PROX and the outlet concentration of CO gradually increased with the O 2/CO ratio due to the oxidation of H 2 which maintained the reactor temperature. The multi-layered reactor coated with CuO/CeO 2 showed lower catalytic activity than that coated with Pt catalyst, but its selectivity was not changed with the increase of O 2/CO ratios due to the high selectivity. In order to combine advantages (high activity and high selectivity) of the two individual catalysts (Pt-Co/Al 2O 3, CuO/CeO 2), a serial reactor was prepared by connecting the two multi-layered micro-channel reactors with different catalysts. The prepared serial reactor exhibited excellent performance for PROX. 相似文献
2.
Residual chlorine ions on a Pt/Al 2O 3 catalyst surface prepared from chlorine-containing precursors appear to inhibit the total oxidation of methane. At 450°C, as chlorine is eliminated with time on stream, the reaction rate increases despite the sintering of the platinum particles. The steady state reaction rate which is reached after 60 h is identical to that obtained with a catalyst prepared from a precursor containing no chlorine. Whether chlorine is present or not in the initial state of the catalyst does not appear to have an influence on the evolution of the platinum particle size. 相似文献
3.
A series of Pd/Al 2O 3 catalysts with a wide range of mean Pd particle sizes (ca. 2–30 nm in diameter) was prepared by using various precursors (H 2PdCl 4, Pd(NO 3) 2 and Pd(AcAc) 2) and pre-treatments. The mean particle size of reduced samples was determined by H 2 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
4.
The role of vanadium oxide and palladium on the benzene oxidation reaction over Pd/V 2O 5/Al 2O 3 catalysts was investigated. The Pd/V 2O 5/Al 2O 3 catalysts were more active than V 2O 5/Al 2O 3 and Pd/Al 2O 3 catalysts. The increase of vanadium oxide content decreased the Pd dispersion and increased the benzene conversion. A strong Pd particle size effect on benzene oxidation reaction was observed. Although the catalysts containing high amount of V 4+ species were more active, the Pd particle size effect was responsible for the higher activity. 相似文献
5.
The influence of the addition of 5 vol.% of carbon monoxide, hydrogen, carbon dioxide or water to the feed of partial oxidation of methane was investigated over Ni/γ-Al 2O 3 and Rh/γ-Al 2O 3 catalysts. In addition to catalytic tests, thermodynamic calculations were performed to predict the effect of these gas co-feeds. Compared to the thermodynamic trends, differences in the influence of the co-feeding on catalytic performances were observed between both catalysts. Co-feeding of CO, H 2, CO 2 or H 2O can modify the oxidation state and dispersion of the metal component of the catalysts during reaction, and as a consequence, their performances. Changes in catalysts can be due to dynamic processes occurring during reaction. It is suggested to take these processes into account in a more complex kinetic equation for the reactions involved. 相似文献
6.
The catalytic activity of a mixed phase of copper–cobalt and copper–manganese oxides supported on magnesium fluorine or alumina has been studied in low temperature CO oxidation at 30 °C. During calcination, the oxides studied partially react to form different type spinels depending on the calcination temperature. These spinels have different effect on the catalytic activity. In low temperature CO oxidation the copper–manganese catalysts are more active than the copper–cobalt ones. 相似文献
7.
Surface-phase ZrO 2 on SiO 2 (SZrOs) and surface-phase La 2O 3 on Al 2O 3 (SLaOs) were prepared with various loadings of ZrO 2 and La 2O 3, characterized and used as supports for preparing Pt/SZrOs and Pt/SLaOs catalysts. CH 4/CO 2 reforming over the Pt/SZrOs and Pt/SLaOs catalysts was examined and compared with Pt/Al 2O 3 and Pt/SiO 2 catalysts. CO 2 or CH 4 pulse reaction/adsorption analysis was employed to elucidate the effects of these surface-phase oxides. The zirconia can be homogeneously dispersed on SiO2 to form a stable surface-phase oxide. The lanthana cannot be spread well on Al2O3, but it forms a stable amorphous oxide with Al2O3. The Pt/SZrOs and Pt/SLaOs catalysts showed higher steady activity than did Pt/SiO2 and Pt/Al2O3 by a factor of three to four. The Pt/SZrOs and Pt/SLaOs catalysts were also much more stable than the Pt/SiO2 and Pt/Al2O3 catalysts for long stream time and for reforming temperatures above 700 °C. These findings were attributed to the activation of CO2 adsorbed on the basic sites of SZrOs and SLaOs. 相似文献
8.
The importance of the hydrodearomatisation (HDA) is increasing together with tightening legislation of fuel quality and exhaust emissions. The present study focuses on hydrogenation (HYD) kinetics of the model aromatic compound naphthalene, found in typical diesel fraction, in n-hexadecane over a NiMo (nickel molybdenum), Ni (nickel) and Ru (ruthenium) supported on trilobe alumina (Al 2O 3) catalysts. Kinetic reaction expressions based on the mechanistic Langmuir–Hinshelwood (L–H) model were derived and tested by regressing the experimental data that translated the effect of both naphthalene and hydrogen concentration at a constant temperature (523.15 and 573.15 K over the NiMo catalyst and at 373.15 K over the Ni and Ru/Al 2O 3 catalysts) on the initial reaction rate. The L–H equation, giving an adequate fit to the experimental data with physically meaningful parameters, suggested a competitive adsorption between hydrogen and naphthalene over the presulphided NiMo catalyst and a non-competitive adsorption between these two reactants over the prereduced Ni and Ru/Al 2O 3 catalysts. In addition, the adsorption constant values indicated that the prereduced Ru catalyst was a much more active catalyst towards naphthalene HYD than the prereduced Ni/Al 2O 3 or the presulphided NiMo/Al 2O 3 catalyst. 相似文献
9.
Carbon black oxidation in the presence of CeO 2, Al 2O 3 and manganese oxide catalysts has been studied in tight contact conditions. In the presence of manganese based catalysts, the temperature gain is about 275 °C compared to the non-catalysed carbon black oxidation. The contribution of the manganese species to enhance the reactivity of carbon black oxidation has been evaluated by EPR technique. For Mn/Ce + CB mixtures the Mn 2+ content considerably increases consequently to tight milled treatment indicating the reduction of some manganese species with higher oxidation states into Mn 2+ ions. This phenomenon can be considered as the first step in the carbon black oxidation mechanism in the presence of Mn/Ce catalysts. 相似文献
10.
A series of CuO–ZnO/Al 2O 3 solids were prepared by wet impregnation using Al(OH) 3 solid and zinc and copper nitrate solutions. The amounts of copper and zinc oxides were varied between 10.3 and 16.0 wt% CuO and between 0.83 and 7.71 wt% ZnO. The prepared solids were subjected to thermal treatment at 400–1000°C. The solid–solid interactions between the different constituents of the prepared solids were studied using XRD analysis of different calcined solids. The surface characteristics of various calcined adsorbents were investigated using nitrogen adsorption at −196°C and their catalytic activities were determined using CO-oxidation by O 2 at temperatures ranged between 125°C and 200°C. The results showed that CuO interacts with Al2O3 to produce copper aluminate at ≥600°C and the completion of this reaction requires heating at 1000°C. ZnO hinders the formation of CuAl2O4 at 600°C while stimulates its production at 800°C. The treatment of CuO/Al2O3 solids with different amounts of ZnO increases their specific surface area and total pore volume and hinders their sintering (the activation energy of sintering increases from 30 to 58 kJ mol−1 in presence of 7.71 wt% ZnO). This treatment resulted in a progressive decrease in the catalytic activities of the investigated solids but increased their catalytic durability. Zinc and copper oxides present did not modify the mechanism of the catalyzed reaction but changed the concentration of catalytically active constituents (surface CuO crystallites) without changing their energetic nature. 相似文献
11.
Zirconia supported on alumina was prepared and characterized by BET surface area, X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), temperature programmed desorption (TPD), and pulse reaction. 0.2% Pd/ZrO 2/Al 2O 3 catalyst were prepared by incipient wetness impregnation of supports with aqueous solution of Pd(NO 3) 2. The effects of support properties on catalytic activity for methane combustion and CO oxidation were investigated. The results show that ZrO 2 is highly dispersed on the surface of Al 2O 3 up to 10 wt.% ZrO 2, beyond this value tetragonal ZrO 2 is formed. The presence of a small amount of ZrO 2 can increase the surface area, pore volume and acidity of support. CO–TPD results show that the increase of CO adsorption capacity and the activation of CO bond after the presence of ZrO 2 lead to the increase of catalytic activity of Pd catalyst for CO oxidation. CO pulse reaction results indicate that the lattice oxygen of support can be activated at lower temperature following the presence of ZrO 2, but it does not accelerate the activity of 0.2% Pd/ZrO 2/Al 2O 3 for methane combustion. 0.2% Pd/ZrO 2/Al 2O 3 dried at 120 °C shows highest activity for CH 4 combustion, and the activity can be further enhanced following the repeat run. The increase of treatment temperature and pre-reduction can decrease the activity of catalyst for CH 4 combustion. 相似文献
12.
Catalytic performance for partial oxidation of methane (POM) to synthesis gas was studied over the Rh/Al 2O 3 catalysts with Rh loadings between 0.1 and 3 wt%. It was found that the ignition temperature of POM reaction increased with the decreasing of the Rh loadings in the catalysts. For the POM reaction over the catalysts with high (≥1 wt%) Rh loadings, steady-state reactivity was observed. For the reaction over the catalysts with low (≤0.25 wt%) Rh loadings, however, oscillations in CH 4 and reaction products (CO, H 2, and CO 2) were observed. Comparative studies using H 2-TPR, O 2-TPD and high temperature in situ Raman spectroscopy techniques were carried out in order to elucidate the relation between the redox property of the Rh species in the Rh/Al 2O 3 with different Rh loadings and the performance of the catalysts for the reaction. Three kinds of oxidized rhodium species, i.e. the rhodium oxide species insignificantly affected by the support (RhO x), that intimately interacting with the Al 2O 3 surface (Rh iO x) and the Rh(AlO 2) y species formed by diffusion of rhodium oxides in to sublayers of Al 2O 3 [C.P. Hwang, C.T. Yeh, Q.M. Zhu, Catal. Today, 51 (1999) 93.], were identified by H 2-TPR and O 2-TPD experiments. Among them, the first two species can be easily reduced by H 2 at temperature below 350 °C, while the last one can only be reduced by H 2 at temperature above 500 °C. The ignition temperatures of POM reaction over the catalysts are closely related to the temperature at which most of the RhO x and Rh iO x species can be reduced by CH 4 in the reaction mixture. Compared to the Rh/Al 2O 3 with high Rh loadings, the catalysts with low Rh loadings contain more Rh iO x species which possess stronger RhO bond strength and are more difficult to be reduced than RhO x by the reaction mixture. Higher temperature is therefore required to ignite the POM reaction over the catalysts with lower Rh loadings. The oscillation during the POM reaction over the Rh/Al 2O 3 with low Rh loadings can be related to the behaviour of Rh(AlO 2) y species in the catalyst switching cyclically from the oxidized state to the reduced state during the reaction. 相似文献
14.
Dispersing La 2O 3 on δ- or γ-Al 2O 3 significantly enhances the rate of NO reduction by CH 4 in 1% O 2, compared to unsupported La 2O 3. 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 La 2O 3 precursor used, the pretreatment, and the La 2O 3 loading. The most active family of catalysts consisted of La 2O 3 on γ-Al 2O 3 prepared with lanthanum acetate and calcined at 750°C for 10 h. A maximum in rate (mol/s/g) and specific activity (mol/s/m 2) occurred between the addition of one and two theoretical monolayers of La 2O 3 on the γ-Al 2O 3 surface. The best catalyst, 40% La 2O 3/γ-Al 2O 3, 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 La 2O 3/Al 2O 3 catalysts exhibited stable activity under high conversion conditions as well as high CH 4 selectivity (CH 4 + NO vs. CH 4 + O 2). The addition of Sr to a 20% La 2O 3/γ-Al 2O 3 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 La 2O 3/Al 2O 3 catalyst decreased activity although sulfate increased the activity of Sr-promoted La 2O 3. Dispersing La 2O 3 on SiO 2 produced catalysts with extremely low specific activities, and rates were even lower than with pure La 2O 3. This is presumably due to water sensitivity and silicate formation. The La 2O 3/Al 2O 3 catalysts are anticipated to show sufficient hydrothermal stability to allow their use in certain high-temperature applications. 相似文献
15.
The effect of Al 2O 3 on mechanical properties of Ti 3SiC 2/Al 2O 3 composite fabricated by SPS was studied systematically. The results show that the hardness of the Ti 3SiC 2/Al 2O 3 composite can reach 10.28 GPa, 50% higher than that of pure Ti 3SiC 2. However, slight decrease in the other mechanical properties was observed with Al 2O 3 addition higher than 5–10 vol.%, which is believed to be due to the agglomeration of Al 2O 3 in the composite. 相似文献
16.
Ni/Al_2O_3催化剂是甲烷二氧化碳重整反应制取合成气研究最多、最具应用潜力的一种催化剂。通过对催化剂进行CO_2-TPD研究,考察还原态Ni/Al_2O_3催化剂的CO_2脱附特性。结果表明,浸渍法制备的Ni/Al_2O_3催化剂CO_2脱附曲线呈现双峰,分别在(60~65)℃和(350~380)℃出现高低温两个活性位;高温CO_2吸附量为3.0 cm~3·g~(-1),低温CO_2吸附量为24.0 cm~3·g~(-1)。催化剂的CO_2吸附量与其Ni含量无关。考察选用不同载体的CO_2脱附行为,发现以Al_2O_3为载体的催化剂CO_2吸附量是MgO和SiO_2为载体催化剂的2~4倍,以TiO_2为载体的催化剂几乎不吸附CO_2。 相似文献
17.
An In 2O 3/Al 2O 3 catalyst shows high activity for the selective catalytic reduction of NO with propene in the presence of oxygen. The presence of SO 2 in feed gas suppressed the catalytic activity dramatically at high temperatures; however it was enhanced in the low temperature range of 473–573 K. In TPD and FT-IR studies, the formation of sulfate species on the surface of the catalyst caused an inhibition of NO X adsorption sites, and the absorbance ability of NO was suppressed by the presence of SO 2, and the amount of ad-NO 3− species decreased obviously. This leads to a decrease of catalytic activity at higher temperatures. However, addition of SO 2 enhanced the formation of carboxylate and formate species, which can explain the promotional effect of SO 2 at low temperature, because active C 3H 6 (partially oxidized C 3H 6) is crucial at low temperature. 相似文献
18.
Ag/Al 2O 3 catalysts prepared from boehmite needles (ca. 10 nm×100 nm), which were formed by a hydrolysis of aluminium tri-isopropoxide (AIP), showed good performances for selective catalytic reduction of NO x compared with the previously reported catalysts [N. Aoyama, K. Yoshida, A. Abe, T. Miyadera, Catal. Lett. 43 (1997) 249], especially when ethanol is employed as a reducing agent in the presence of water. Temperature programmed reduction (TPR) study revealed that the Ag species are attractively interacted with the alumina surface and the oxidized Ag species contribute positively for the improvement of the catalytic activity at the temperatures above 750 K. It is concluded that the boehmite needles as a precursor of alumina support are useful to create the catalytically active sites for NO x reduction. 相似文献
19.
The oxidative dehydrogenation (OXDH) of n-butane and 1-butene on undoped and K-doped alumina-supported vanadia catalysts has been studied. The low selectivity to OXDH products on alumina-supported vanadia catalysts is a consequence of the isomerization of olefins (low temperatures) and the formation of carbon oxides (high temperatures) on acid sites. The presence of potassium results in a decrease of the number of acid sites and a higher selectivity to OXDH products from both n-butane and 1-butene. Infrared spectroscopy data of 1-butene adsorbed on the catalysts suggest the presence of different adsorbed species: (i) O-containing species on the undoped catalyst, or (ii) adsorbed butadiene on K-doped catalyst. A reaction network including parallel and consecutive reactions is proposed. 相似文献
20.
由丙烷直接催化脱氢制取丙烯已经成为增产丙烯的重要手段之一。以水热法制备Al_2O_3载体,采用等体积浸渍法制备不同PtSn负载量的PtSn/Al_2O_3催化剂。通过XRD、N2-吸附、拉曼光谱和H2-TPR等对其进行表征,并考察不同PtSn负载量对催化剂催化丙烷脱氢性能的影响。结果表明,在制备的催化剂中,Pt1.5Sn3/Al_2O_3具有最高的催化丙烷脱氢活性和稳定性,丙烷初始转化率高达55.6%,丙烯选择性98.1%。反应330 min后,丙烷转化率仅降约10%,选择性保持不变。 相似文献
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