Kinetic Studies on Diacetyl Synthesis over V-Containing Zeolites

The gas-phase oxidation of methyl ethyl ketone (MEK) was studied on V-ZSM-5 zeolite in the presence of molecular oxygen. Two types of competitive partial oxidations, i.e., diacetyl formation and oxidative scission reaction leading to acetaldehyde and acetic acid, took place at 200–350°C. A detailed kinetic study was realized for the oxidation reaction, a linear relationship was observed between the conversion and partial pressure of oxygen, and an activation energy of 16 kcal/mol was encountered. The content of vanadium in the catalyst was also analyzed.     

Isomerization of isobutyraldehyde to methyl ethyl ketone on zeolite catalysts

The isomerization of isobutyraldehyde (IBH) was studied over aluminium-free ZSM-5 zeolite catalysts with different boron content in the framework. The selectivity to methyl ethyl ketone (MEK) is high, ca. 83 wt%. With the increase of boron content, the conversion of IBH increased but the selectivity to MEK decreased. The effects of Na content, cation-exchange, 500°C-steam treatment and temperature on catalyst activity were investigated. It was observed that cation-exchange resulted in the decrease of conversion of IBH and increase of selectivity to MEK, but 500°C-steam treatment resulted in the decrease of selectivity to MEK.     

Partial oxidation of ethane to synthesis gas over Co-loaded catalysts

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.     

Effect of hydrocarbon species on no oxidation over diesel oxidation catalysts

The effect of propylene concentration on NO oxidation as a function of temperature and position over a model Pt-Pd/Al₂O₃ diesel oxidation catalyst was investigated. Propylene had an apparent inhibition effect on NO oxidation. This apparent inhibition is a result of NO₂, as the NO oxidation product, acting as an oxidant in the reaction with propylene. This was verified with experiments that included NO₂, and a resulting significant temperature decrease in the onset of NO₂ reduction when propylene was present. Furthermore, increasing amounts of propylene further decreased the NO₂ reduction temperature. Similar results were observed with m-xylene and dodecane addition as well. The results also demonstrate that NO₂ was consumed preferentially relative to O₂ during hydrocarbon oxidation. With low inlet levels of O₂, the addition of NO₂ apparently inhibited propylene oxidation after the onset of NO₂ reduction. This subsequent inhibition was due to the NO formed, demonstrating that propylene results in reduced NO₂ outlet levels while NO inhibits propylene oxidation.     

Partial oxidation of methane to synthesis gas over Rh-hexaaluminate-based catalysts

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.     

仲丁醇脱氢制甲乙酮的Cu-ZnO催化剂

采用共沉淀法和机械混合法制备了铜锌催化剂,并利用TPR、XRD和N2O吸附分解催化剂表征手段分析了铜锌催化剂中ZnO和Cu在仲丁醇（sec-butanol,SBA）脱氢反应中的作用。研究表明,Cu0是SBA脱氢的活性中心,ZnO具有分散铜物种和抗烧结能力。ZnO能够有效分散铜物种和阻止Cu0烧结的原因是在催化剂制备过程中形成了(CuZn)x(OH)y(CO3)z(x=1,5;y=2,6,z=1,2)前体,经焙烧形成了高分散的CuO-ZnO固溶体。同时,通过SBA催化脱氢反应测试筛选了适宜的Cu/Zn摩尔比,当Cu/Zn为1∶1时,表现出良好的反应活性,常压、240 ℃下质量空速为17.5 h?1时,该催化剂对SBA转化率达到80.54%,甲乙酮（methyl ethyl ketone,MEK）收率达到76.04%。铜锌催化剂的脱氢活性与Cu0比表面积不呈线性关系,SBA脱氢反应是一结构敏感型反应。     

Effect of carbon dioxide on the selectivities obtained during the partial oxidation of methane and ethane over Li+/MgO catalysts

AtT 650 °C carbon dioxide either formed during reaction or added to the system increases the selectivity for the desired hydrocarbon products during the oxidative coupling of methane and the oxidative dehydrogenation of ethane reaction over Li⁺/MgO catalysts. Similarly, CO₂ inhibits secondary reactions of CH₃-radicals with the surface of the Li⁺/MgO. The improved selectivities are attributed to the poisoning effect that CO₂ has on the secondary reactions of alkyl radicals with the surface.     

Chaos and synchronisation in heterogeneous catalytic systems: CO oxidation over Pd zeolite catalysts

The influence of experimental parameters on the structure of global reaction rate oscillations and the coupling of local oscillators on a catalyst bed in a continuous stirred tank reactor is studied for the oxidation of CO on zeolite supported palladium catalysts. Global coupling can be achieved via mass transfer through the gas phase or via heat transfer in the case of a support of high heat conductivity. Characteristic differences in the activity of catalysts as well as in the period and the amplitude of the oscillations are related to the size of the palladium clusters and can be simulated by adding the state of the oxidation of the metal surface as a parameter to a common kinetic model. The analysis of observed chaotic behaviour leads to the conclusion that diffusional chaos characteristic of a distributed system is observed on the level of the zeolite crystallite that supports the palladium clusters.     

Oxidation of primary amines over vanadium silicalite molecular sieve,VS-1

The mild oxidation of various primary amines with diluted hydrogen peroxide has been studied over vanadium silicalite molecular sieve, VS-1. The reaction leads to the corresponding oximes and imines. The nature of solvent was found to have a strong influence on the product selectivity. The use of chloroform favors the formation of nitroalkanes. Under similar conditions primary amines with no -hydrogen, such as aniline, were oxidized mainly to the corresponding azoxy derivatives.     

Low temperature complete combustion of dilute toluene and methyl ethyl ketone over Mn‐doped ZrO2 (cubic) catalysts

Combustion of dilute toluene and methyl ethyl ketone over Mn‐doped ZrO₂ catalysts prepared using different precipitating agents, such as tetra‐alkyl ammonium hydroxides and NH₄OH, having Mn/Zr ratios from 0.05 to 0.67, and calcined at different temperatures has been thoroughly investigated. The Mn‐doped ZrO₂ catalyst shows high toluene or methyl ethyl ketone combustion activity, particularly when its ZrO₂ is in cubic form, when its Mn/Zr ratio is close to 0.2, and when it is prepared using tetra‐methyl ammonium hydroxide as a precipitating agent and calcined at 773 K. Copyright © 2005 Society of Chemical Industry     

CO oxidation over promoted Pt catalysts

A study of CO oxidation by O₂ over Pt catalysts, promoted by MnO_x and CoO_x, is described. The activities of Pt/SiO₂, Pt/MnO_x/SiO₂ and Pt/CoO_x/SiO₂ are compared with commercial Pt/Al₂O₃, Pt/Rh/Al₂O₃ and Pt/CeO_x/Al₂O₃ catalysts. Since these catalysts differ in dispersion and weight loading of platinum, the turnover frequencies are also compared. The following order in activity in CO oxidation after a reductive pretreatment is found: Pt/CoO_x/SiO₂ > Pt/MnO_x/SiO₂, Pt/CeO_x/Al₂O₃ > Pt/Al₂O₃, Pt/Rh/Al₂O₃, Pt/SiO₂. Over Pt/CoO_x/SiO₂ CO is already oxidised at room temperature. Possible models to account for the high activity of Pt/CoO_x/SiO₂ in the CO/O₂ reaction are presented and discussed. Partially reduced metal oxides are necessary to increase the activity of the Pt/CoO_x/SiO₂, Pt/MnO_x/SiO₂ or Pt/CeO_x/Al₂O₃ catalysts. It was shown that mild ageing treatments did not affect the activity of the Pt/CoO_x/SiO₂ catalyst in CO oxidation.     

甲乙酮生产现状及市场需求分析

2004年全球甲乙酮的总消费量约为90万t/a,生产能力约为130万t/a,预计2007年前甲乙酮市场仍将出现产能过剩的状况。我国甲乙酮市场需求增长迅速,主要依靠进口。介绍了国内外甲乙酮的生产和消费现状,并对甲乙酮市场需求情况进行了分析预测。     

甲醇直接氧化合成二甲氧基甲烷催化剂的研究

二甲氧基甲烷是重要的有机化工原料,在溶剂、化工中间体、制氢和燃料添加剂等领域应用广泛,以甲醇为原料一步合成二甲氧基甲烷是C1化工的研究新热点。以TiO₂为载体,通过负载V₂O₅并采用Ti(SO₄)₂改性制备V₂O₅/TiO₂-SO₄^2-催化剂,在温度（135～150） ℃、V（CH₃OH）∶V（O₂）∶V（N₂）=1∶（1.5～4）∶（7～20）和原料气流量(5 000～8 000) mL·(g·h)^-1条件下,将甲醇直接氧化合成二甲氧基甲烷。结果表明,甲醇转化率为48%,二甲氧基甲烷选择性为80%。     

Pd/HZSM-5催化剂催化加氢丙酮合成甲基异丁基酮

以HZSM-5为载体,采用浸渍法制备系列Pd/HZSM-5催化剂,在高压连续流动固定床反应器中考察Pd/HZSM-5催化剂催化加氢丙酮一步法合成甲基异丁基酮性能,并对工艺条件进行优化。结果表明,当HZSM-5载体上Pd负载质量分数为0.5%时,在反应温度140 ℃、氢压1 MPa、空速0.48 h^-1和氢酮物质的量比为1条件下,Pd/HZSM-5催化剂催化活性较高,丙酮转化率为45.91%,甲基异丁基酮选择性为94.33%。采用XRD、H₂-TPD、SEM、EDS和TGA等对催化剂进行表征,结果表明,负载质量分数0.5%的Pd在HZSM-5分子筛表面分散均匀,且0.5%Pd/HZSM-5催化剂具有较高氢吸附能力,失活的主要原因为催化剂表面积炭,采用流化床反应器取代传统的固定床反应器可以很好的解决催化剂积炭问题。     

过氧化甲乙酮合成工艺的探讨

着重介绍了以磷酸做催化剂，用过氧化氢和丁酮为原料，室温下制备过氧化甲乙酮，在获取大量实验数据的前提下，确定生产过氧化酮的最佳工艺条件。     

Selective oxidation of ammonia over copper-silver-based catalysts

A novel catalyst based on copper-silver was developed to solve the contradiction between the high conversion temperature of Cu-based catalyst and low N₂ selectivity of Ag-based catalyst during selective oxidation of ammonium gas. The Cu-Ag-based catalyst (Cu 5 wt.%-Ag 5 wt.%/Al₂O₃) displayed a relatively low complete conversion temperature (<320 °C) with a high N₂ selectivity (>95%). Increasing loading of Cu and Ag decreases N₂ selectivity. The low N₂ selectivity of Ag-based catalyst is possibly related to the formation of Ag₂O crystals. Improvement of N₂ selectivity of Ag-based catalyst was obtained by doping Cu to decrease crystallized Ag₂O phase. The temperature programmed reaction (TPR) data show that N₂O is the main byproduct of oxidation of ammonia at temperature lower than 200 °C. Two bands of nitrate species at 1541 and 1302 cm⁻¹ were observed on Ag 10 wt.%/Al₂O₃ at the temperature higher than 250 °C, which indicates the formation of NO_x during the selective catalytic oxidation of ammonia. No nitrate species was observed on Cu 10 wt.%/Al₂O₃ and Cu 5 wt.%-Ag 5 wt.%/Al₂O₃, while only one nitrate species (1543 cm⁻¹) existed on Cu 10 wt.%-Ag 10 wt.%/Al₂O₃. We proposed that mixing Ag with Cu inhibited the formation of NO_x during the selective catalytic oxidation of ammonia over Cu-Ag/Al₂O₃.     

AlMCM-41介孔分子筛催化合成苯甲酸甲酯的研究

本文以介孔分子筛AlMCM-41为催化剂,采用碳酸二甲酯(DMC)作为酯化试剂与苯甲酸(BA)反应制备苯甲酸甲酯(BA)。反应结果表明,碳酸二甲酯是一种很好的酯化试剂,介孔分子筛AlMCM-41对此酯化反应是高效的催化剂。并且还发现苯甲酸的转化率和苯甲酸甲酯的选择性与催化剂上的Lewis酸位有很大联系。另外本文还讨论了此反应的机理。     

丙酮一步合成甲基异丁基酮催化剂的研究进展

本文介绍了丙酮一步法合成甲基异丁基酮的工艺过程,并系统地阐述了丙酮一步法制备甲基异丁基酮所用催化剂研究进展情况.在对各类催化剂进行分析比较之后,提出了未来的研究方向.     

Partial oxidation of methane to synthesis gas over iridium–nickel bimetallic catalysts

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.