共查询到20条相似文献,搜索用时 15 毫秒
1.
Yanxia Zheng Heng Zhang Lei Wang Suojiang Zhang Shaojun Wang 《Frontiers of Chemical Science and Engineering》2016,10(1):139-146
Heteropoly compounds with the general formula Cs1M0.5x+H3?0.5xP1.2Mo11VO40 (M= Fe, Co, Ni, Cu or Zn) and Cs1CuyH3?2yP1.2Mo11VO40 (y = 0.1, 0.3 or 0.7) were synthesized and then used as catalysts for the selective oxidation of methacrolein to methacrylic acid. The effects of the transition metals on the structure and activity of the catalysts were investigated. FTIR spectra showed that the transition metal-doped catalysts maintained the Keggin structure of the undoped catalysts. X-ray diffraction results indicated that before calcination, the catalysts doped with Fe and Cu had cubic secondary structures, while the catalysts doped with Co, Ni or Zn had both triclinic and cubic phases and the Co-doped catalyst had the highest content of the triclinic form. Thermal treatment can decrease the content of the triclinic phase. NH3 temperature-programmed desorption and H2 temperature-programmed reduction results showed that the transition metals changed the acid and redox properties of the catalysts. The addition of Fe or Cu had positive effects on the activities of the catalyst which is due to the improvement of the electron transfer between the Fe or Cu and the Mo. The effects of the copper content on structure and catalytic activity were also investigated. The Cs1Cu0.3H2P1.2Mo11VO40 catalyst had the best performance for the selective oxidation of methacrolein to methacrylic acid. 相似文献
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The catalytic performances of five lanthanide oxides (La2O3, Sm2O3, CeO2, Pr6O11 and Tb4O7) for the selective oxidation of isobutene to methacrolein are evaluated within the framework of the remote control mechanism. Mechanical mixtures of these oxides with typical donor (Sb2O4) or acceptor (MoO3) phases of spill-over oxygen were prepared and tested for their activity in the isobutene-to-methacrolein oxidation at 400°C. Amongst the five lanthanide oxides tested, only CeO2 and Pr6O11 were found to display significant cooperation effects for the investigated reaction, with enhanced yields and selectivity for partial oxidation and concomitant decrease of CO2 production. The fresh and used catalysts were characterized by X-ray diffractometry, and the occurrence of solid state reactions between the partner oxides outside the reaction conditions was investigated in parallel in the temperature range 400–500°C. No new phase was observed in the case of the mixtures with La2O3, Sm2O3, CeO2 and Tb4O7. Account taken of the absence of any new phase in the CeO2-MoO3 system, it can be concluded that CeO2 is a potential donor of spill-over oxygen. The situation in the MoO3-Pr6O11 mixtures is more complex, owing to the generation of various praseodymium molybdates, together with the oxocarbonate Pr2CO5. The latter phase was shown to have no intrinsic tendency to produce methacrolein, but it seems that some of the praseodymium molybdates present in the working catalysts may exhibit noticeable catalytic properties. 相似文献
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Jose Luis G. Fierro Emilio Salazar Juan A. Legarreta 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1986,36(5):219-229
The adsorption of isobutene (in the temperature range 309–341K) and methacrolein (in the temperature range 296–336 K) on a Mo/(Mo+U)=0.89 catalyst were studied. The equilibrium data were analysed according to Freundlich's model. The high coverages observed at lower temperatures suggest some participation of physical adsorption in the reversible adsorption. Entropy calculations showed that these adsorbed species are best described by a mobile model which assumes bidimensional translation and two rotational degrees of freedom. Isobutene is weakly chemisorbed, producing reversible species which were identified as a π-complex formed by interaction with surface OH groups through π-electrons (infrared bands at 1655, 1615, 1470 and 1375 cm?1), and only a small fraction of isobutene interacts strongly via lattice oxygen forming intermediate species in the oxidation reaction. However, in the presence of oxygen at 523 K a majority of the surface species are strongly held by the surface (infrared bands at 1775, 1723, 1610, 1460 and 1350 cm?1 associated to a methacrylic complex and bands at 1590 and 1538 cm?1 of carbonate-carboxylate species). 相似文献
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开发低温下高催化活性的柴油机碳烟颗粒燃烧催化剂是当前环境催化领域的热点问题。利用共沉淀的方法制备了用于碳烟催化燃烧反应的Ag/Ce0.75Zr0.25O2催化剂。活性评价结果表明,相对于Ce0.75Zr0.25O2催化剂,Ag的引入可显著降低碳烟催化燃烧温度。而且,Ag的负载量存在一个最佳值。以XRD、in-situ XRD、BET、TPR等表征手段探究了该系列催化剂结构性质及其变化产生的影响。结果表明,Ag与Ce物种间的相互作用可显著降低催化剂(特别是CeO2表面氧)的还原温度。该相互作用使Ag/Ce0.75Zr0.25O2催化剂在一定温度下(>200℃)就表现出Ag+的性质。这些性质与该催化剂具有较高的碳烟氧化活性相关。而且,该催化剂也表现出良好的稳定性。 相似文献
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Na-oyoshi Iwasaki Takanori Miyake Eriko Yagasaki Toshimitsu Suzuki 《Catalysis Today》2006,111(3-4):391-397
Attention has been increasingly paid to the partial oxidation of lower alkanes to synthesis gas, due to its intrinsic energy saving process. We studied the partial oxidation of ethane (POE) on Co loaded on various supports. The POE performance varied as follows: Y2O3, CeO2, ZrO2, La2O3 SiO2, Al2O3, TiO2 > MgO. Comparing Y2O3 and CeO2, the carbon deposition during the POE was negligible on CeO2 and therefore CeO2 was the most preferable support. By changing space velocity and O2 partial pressure, reaction mechanism of POE was studied and it was revealed that two-step mechanism was prevailing; combustion of ethane to H2O and CO2 and subsequent reforming of ethane with H2O and CO2 to synthesis gas. Co/CeO2 catalyst exhibited high and stable catalytic activity for 10 h; high ethane conversion of 18% (maximum ethane conversion 20% at O2/C2H6 = 0.2) with H2 and CO selectivities of 93 and 84%, respectively. 相似文献
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《Journal of Industrial and Engineering Chemistry》2014,20(4):1542-1548
In this study, performance of nano-structure Ni over different zeolite supports in partial oxidation of butane was investigated. First, partial oxidation process was performed without catalyst to evaluation of optimal conditions. For in situ reduction of catalysts, H2 produced from homogenous reaction was used. Catalytic partial oxidation was carried out using nano-structure nickel catalysts supported by ZSM5, mordenite and Y. Each catalyst was synthesized through reverse microemulsion method. The catalysts were characterized by BET surface area, XRD, SEM and TGA. Highest butane conversion (≈89%) observed in the presence of Ni/Y catalyst. Also Ni/Y shows the highest overall selectivity to CO and H2 as the most desired partial oxidation products. Results from TGA showed that the minimum quantity of formatted coke was related to Ni/Y, which confirmed the stability of butane conversion versus time for this catalyst. 相似文献
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采用炼厂异丁烷塔顶轻组分作为原料,运用Pt-Sn/Al2O3为脱氢催化剂生产异丁烯。通过制备不同的铂锡催化剂考察影响催化剂性能的各种因素。结果表明,异丁烷的转化率随着Pt含量的增加先增大后减小,在0.40%左右达到最大值,反应8 h后仍然保持在35%以上,同时异丁烯的收率也能保持在22%以上。异丁烷的转化率和异丁烯的选择性均随Pt/Sn原子比的增大呈现先增大后减小的趋势,并且在Pt/Sn原子比为2∶3时,异丁烯的收率达到最大,反应8 h后仍能达到26%以上。通过碱溶电位滴定法分析催化剂中的氯含量,研究了氯含量与催化剂性能的关系。结果表明,随着氯含量增大,异丁烷的转化率不断上升,而异丁烯的选择性不断下降。综合考虑异丁烯的收率和转化率及选择性,催化剂中氯含量为相似文献
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针对甲基丙烯醛氧化酯化浆态床反应过程中颗粒催化剂易破碎、活性组分易流失等缺点,采用浸渍法在电沉积到泡沫镍合金表面的氧化铝-氧化镁涂层上负载活性组分,制备了PdxPby/Al2O3-MgO/泡沫镍合金整体式催化剂。研究分析了铝溶胶含量、Al2O3含量、沉积电压和沉积时间等条件对涂层负载的影响,并对载体和催化剂进行了BET、XRD、SEM、ICP和TEM表征和气-液-固固定床反应性能评价。结果表明,当铝溶胶的体积含量为35%~40%,Al2O3含量为25~30 g·L-1,沉积电压为10~12 V,沉积时间为8~12 min,搅拌速度为200~250 r·min-1时可得到稳定的涂层。在温度为80℃、压力为0.3 MPa、醇醛摩尔比为8:1、液相物料进口流量为0.5 ml·min-1、氧气进口流量为35 ml·min-1、反应时间为2 h条件下,整体式催化剂上甲基丙烯醛转化率最高为76.1%,甲基丙烯酸甲酯选择性为81.2%。研究结果可为甲基丙烯醛氧化酯化制甲基丙烯酸甲酯的生产工艺优化提供科学数据。 相似文献
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Laura Majocchi Gianpiero Groppi Cinzia Cristiani Pio Forzatti Luca Basini Alessandra Guarinoni 《Catalysis Letters》2000,65(1-3):49-56
The partial oxidation of methane to synthesis gas over catalysts consisting of Rh supported on hexaaluminates (BaAl12O19, CaAl12O19 and SrAl12O19) was investigated at atmospheric pressure and high reactant dilution in order to compare their performances within the kinetic-controlling regime. Comparison with the results obtained over a commercial Rh/-Al2O3 system indicates that hexaaluminate catalysts are active and selective in this reaction. Despite of the higher surface area of the support, hexaaluminate-supported catalysts were found less stable, active and selective than an -Al2O3-supported catalyst. 相似文献
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Osami Nakayama Na-oki Ikenaga Takanori Miyake Eriko Yagasaki Toshimitsu Suzuki 《Catalysis Today》2008,138(3-4):141
The gas–solid reaction between methane and the lattice oxygen of Ni, Co, and Fe-oxides loaded on various support materials produced a synthesis gas (hydrogen and carbon monoxide) at 600–800 °C. Metal oxides were reduced to metals or lower valence oxides, and they were re-oxidized to oxides by introducing air after the reaction. Thus, production of hydrogen or synthesis gas free from nitrogen can be achieved alternatively without using pure oxygen. As a metal oxide, Fe2O3 and Rh2O3-loaded on Y2O3 exhibited the highest H2 selectivity of 60.1% with a moderate CH4 conversion of 54% and a high lattice oxygen utilization of 84% at 800 °C. 相似文献
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The partial oxidation of methane (POM) to syngas, i.e. H2 and CO, over supported Rh catalysts was investigated at atmospheric pressure. The influence of support material, Rh loading and the presence of water vapor on the methane conversion efficiency and the product gas composition was studied. The catalysts containing ceria in the support material showed the highest activity and formation of H2 and CO. By increasing the Rh loading, a decrease of the ignition temperature was obtained. The addition of water vapor to the reactant gas mixture was found to increase the ignition temperature and the formation of hydrogen, which is favorable for combustion applications where the catalytic POM stage is followed by H2-stabilized homogeneous combustion. 相似文献
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A series of calcium-modified alumina-supported cobalt catalysts were prepared with a two-step impregnation method, and the effect of calcium on the catalytic performances of the catalysts for the partial oxidation of methane to syngas (CO and H2) was investigated at 750 °C. Also, the catalysts were characterized by XRD, TEM, TPR and (in situ) Raman. At 6 wt.% of cobalt loading, the unmodified alumina-supported cobalt catalyst showed a very low activity and a rapid deactivation, while the calcium-modified catalyst presented a good performance for this process with the CH4 conversion of 88%, CO selectivity of 94% and undetectable carbon deposition during a long-time running. Characterization results showed that the calcium modification can effectively increase the dispersion and reducibility of Co3O4, decrease the Co metal particle size, and suppress the reoxidation of cobalt as well as the phase transformation to form CoAl2O4 spinel phases under the reaction conditions. These could be related to the excellent catalytic performances of Co/Ca/Al2O3 catalysts. 相似文献
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The catalytic partial oxidation of propane in supercritical carbon dioxide has been investigated in a stirred batch reactor. Various metals (oxides) have been used as supported catalysts with respect to their activity and selectivity for the formation of oxygenates. The reactions run with a 1:2.3–2.9:68–108 molar ratio of propane:synthetic air:CO2 at 453–573 K and 80–100 bar. Using a precipitated 2.4 wt.% Co3O4–SiO2 catalyst at 573 K, a total oxygenate (i.e. acetic acid, acetone, acetaldehyde, methanol) selectivity of 59% and a propene selectivity of 21% were obtained at a propane conversion of 12 mol%. The same catalyst has been used to investigate the influence of the supercritical conditions and initial feed composition on the reaction, varying the density of CO2 and the concentration of synthetic air, respectively. 相似文献
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Takafumi Sato Ayako Watanabe Norihito Hiyoshi Masayuki Shirai Naotsugu Itoh 《The Journal of Supercritical Fluids》2007,43(2):295
Partial oxidation of m-hydroxybenzyl alcohol was studied over several supported noble metal catalysts in a temperature range from 373 to 413 K, up to 2 MPa of oxygen pressure and 20 MPa of carbon dioxide pressure. The major product detected was m-hydroxybenzaldehyde. A charcoal supported palladium catalyst gave the highest yield of the aldehyde. For high temperature above 393 K and high oxygen pressure above 0.5 MPa, total oxidation was observed, which caused the selectivity of m-hydroxybenzaldehyde to decrease. Supercritical carbon dioxide medium seemed to improve heat dissipation of the reaction to allow the partial oxidation of m-hydroxybenzyl alcohol to occur under mild conditions. The partial oxidation of benzyl alcohol over a charcoal supported palladium catalyst was also examined for comparison and the major product formed was benzaldehyde. The conversion of benzyl alcohol and the selectivity to benzaldehyde was higher than those for the case of partial oxidation of m-hydroxybenzyl alcohol. 相似文献
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Kiyoharu Nakagawa Naoki Ikenaga Yonghong Teng Tetsuhiko Kobayashi Toshimitsu Suzuki 《Applied Catalysis A: General》1999,180(1-2):183-193
Partial oxidation of methane to synthesis gas was carried out using supported iridium–nickel bimetallic catalysts, in order to reduce loading levels of iridium and nickel, and to avoid carbon deposition on nickel-based catalysts by adding iridium. The performance of supported iridium–nickel bimetallic catalysts in synthesis gas formation depended strongly upon the support materials. La2O3 gave the best performance among the support materials tested. Ir(0.25 wt%)–Ni(0.5 wt%)/La2O3 afforded 36% conversion of methane (CH4/O2=5) to give CO and H2 with the selectivities of above 90% at 800°C, and those at 600°C were 25.3% conversion of methane and CO and H2 selectivities of about 80%, respectively. Reduced monometallic Ir(0.25 wt%)/La2O3 and Ni(0.5 wt%)/La2O3 catalysts did not produce synthesis gas at 600°C. A higher conversion of methane was obtained by synergistic effects. The product concentrations of CO, H2, and CO2, and CH4 conversion were maintained in high values, even increasing the space velocity of feed gas over Ir–Ni/La2O3 catalyst, indicating that rapid reaction takes place. As a by-product, a small amount of carbon deposition was observed, but carbon formation decreased with increasing the space velocity. On the other hand, with reduced monometallic Ni(10 wt%)/La2O3 catalyst, yield of synthesis gas and carbon decreased with increasing the space velocity. 相似文献