VxTi复合氧化物催化剂用于二氧化碳气氛乙苯脱氢的研究

采用溶胶-凝胶法制备了以TiO₂为基体的VxTi复合氧化物催化剂,该催化剂用于乙苯二氧化碳低温氧化脱氢制苯乙烯反应。考察了活性组分含量和焙烧温度对催化剂活性的影响。结果表明,活性金属钒的添加有助于提高脱氢反应性能,但存在一适量值,摩尔分数超过5%,催化脱氢活性下降。通过XRD分析发现,不同焙烧温度制备的VxTi催化剂中TiO₂的晶相不同,随着温度的升高,TiO₂的晶相将由锐钛矿型转变为金红石晶相。TiO₂锐钛矿型晶相有利于苯乙烯选择性的提高,而金红石晶相则不利于催化剂的脱氢反应。     

Amorphous porous MxTi mixed oxides as catalysts for the oxidative dehydrogenation of ethylbenzene

The properties of different metal‐oxide‐doped porous titanium oxides as catalysts for the oxidative dehydrogenation of ethylbenzene were investigated. Amorphous porous mixed oxides based on the amorphous titania matrix with selected metal ion centers as active sites have been prepared by an acid‐catalyzed sol–gel method. The dehydrogenation of ethylbenzene was studied in a continuous gas phase flow reactor under different reaction temperatures at ambient pressure. Among the 23 catalysts studied the amorphous porous AM‐Cr₅Ti mixed oxide is the most promising catalyst. At 350 °C a 75% selectivity to styrene at a 29% conversion of ethylbenzene was obtained. BET, HRTEM, XRD, GC, MS, TGA and optical microscopy were employed to characterize the fresh and used AM‐Cr₅Ti catalyst. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mesostructured CeO2 as an Effective Catalyst for Styrene Synthesis by Oxidative Dehydrogenation of Ethylbenzene

A new type of mesostructured ceria material was synthesized via template-assisted precipitation method and tested for the oxidative dehydrogenation (ODH) of ethylbenzene to styrene by molecular oxygen. The effect of calcination temperature on the catalytic performances of the ceria catalysts has been investigated. Among the catalysts tested, the CeO₂-450 sample derived by calcination at 450 °C exhibited the highest ethylbenzene conversion (34%) and styrene selectivity (87%). Comparing the reaction rates for ODH of ethylbenzene (ca. 6.1 mmol ST g _cat ^?1 h^?1 at 450 °C) with the highly active nanostructured carbon-based catalysts in the current literature confirmed the very high activity of these new materials. The superior catalytic performance of the CeO₂-450 sample can be attributed to its high specific surface area and enhanced redox properties as revealed by H₂-TPR measurements.     

Oxidative Dehydrogenation of Ethylbenzene with Carbon Dioxide over Metal-Doped Titanium Oxides

Various metal-doped (Fe, V, Zr, Mg) titanium oxides were prepared by an acid-catalyzed sol–gel method and their properties as catalysts were investigated for oxidative dehydrogenation of ethylbenzene in the presence of carbon dioxide. The characterization techniques, XRD, BET, TGA were employed to analyze the features of catalyst. Fe₃Ti catalyst was found to be quite effective among the catalysts tested at 823 K, 39.8% ethylbenzene conversion and 98% styrene selectivity were acquired.     

Iron Oxide Catalysts for Dehydrogenation of Ethylbenzene in the Presence of Steam

Catalyst research for ethylbenzene (EB) dehydrogenation has been interest to many chemical manufacturers because styrene monomer is such a large-volume chemical and a steady growth of styrene markets is predicted. EB is relatively easy to dehydrogenate and the reaction may be effected by a simple thermal gas-phase process as observed by Berthelot in 1869 [l]. However, a much higher selectivity to styrene is obtained by contact catalysts. The historical evolution of EB dehydrogenation processes has been summarized by Kearby [21 and others [3].     

Reaction Coupling of Ethylbenzene Dehydrogenation with Nitrobenzene Hydrogenation

The chemical equilibrium for the coupling of ethylbenzene dehydrogenation with nitrobenzene hydrogenation, to produce styrene and aniline simultaneously, has been calculated on the basis of the Soave–Redlich–Kwong equation of state. The dehydrogenation of ethylbenzene in the presence of nitrobenzene over the catalysts -Al₂O₃, ZSM-5, activated carbon and platinum supported on activated carbon has been carried out at 400 °C. The effects of Pt loading and the pretreatment of the catalysts have been investigated. It has been revealed that the conversion of ethylbenzene can be greatly improved by the reaction coupling due to the elimination of the hydrogen produced in the reaction by the hydrogenation of nitrobenzene. Platinum supported on the activated carbon has been suggested as a suitable catalyst. The best results with ethylbenzene conversion of 33.8% and styrene selectivity of 99.2% were obtained over Pt(0.02 wt%)/AC at 400 °C. Moreover, such process is also energetically favored since the necessary process heat to drive the ethylbenzene dehydrogenation can be provided by the coupling with the exothermic nitrobenzene hydrogenation reaction.     

掺杂炭纤维对乙苯脱氢催化剂性能的影响

在氮气保护及程序控温条件下,制备了具有一定孔隙的炭纤维掺杂的乙苯脱氢催化剂。通过对比表面积、孔隙度的测定,发现微孔数量随炭纤维加入量的增加而增加,炭纤维催化剂得到了活化。催化剂的扫描电镜分析、侧压强度及抗拉强度测试证明,炭纤维使催化剂的机械强度明显提高。乙苯脱氢实验表明,苯乙烯选择性随炭纤维的加量增大;乙苯的转化率则存在最大值。考虑机械强度与催化活性,加入6%炭纤维的催化剂最佳。     

SO2/O2 dehydrogenation of ethylbenzene

In the SO₂ dehydrogenation of ethylbenzene to styrene using alkalized alumina or titania catalysts, addition of small amounts of oxygen results in (1) higher styrene yields at equivalent SO₂ concentrations, or (2) equivalent styrene yields with lower SO₂ requirements. By staging the oxygen additions, styrene yields of greater than 80% are achieved at SO₂ levels as low as 0.15 mole/mole ethylbenzene when 0.45 mole O₂ is added in increments of 0.15 mole. The low SO₂ concentration and staging of the oxygen result in a high selectivity (94%) for the reaction to styrene by minimizing both byproduct formation and combustion.     

乙苯脱氢制取苯乙烯反应条件的研究

使用氧化铁系催化剂,研究了乙苯脱氢制取苯乙烯中乙苯转化率和苯乙烯的选择性与温度、进料比的关系.实验证明,乙苯的转化率受温度和进料比的共同影响,在所研究的范围内,苯乙烯的选择性主要受温度影响,选择合适的进料比对提高转化率和选择性至关重要.     

高收率乙苯脱氢催化剂GS-12的工艺条件研究

介绍了高收率乙苯脱氢催化剂GS-12的特性,研究了乙苯脱氢反应温度、水蒸汽与乙苯物质的量比、空速与转化率和选择性的关系,确定了乙苯脱氢催化剂GS-12在实际生产中适宜的工艺条件。工业应用表明,GS-12催化剂活性较高,能够适应较低水蒸汽与乙苯物质的量比,机械强度高,抗粉化性能好,床层阻力降小,使用寿命预期在30个月以上,综合性能达到国际先进水平。     

The influence of dopants on the catalytic activity of hematite in the ethylbenzene dehydrogenation

The effect of neodymium, lanthanum, aluminum and zirconium on the textural and catalytic properties of hematite was studied in this work, which aimed to develop catalysts to ethylbenzene dehydrogenation, in the presence of steam, the main commercial route to obtain styrene. Hematite and magnetite were found in fresh and spent catalysts, respectively. All dopants increased the specific surface area of the fresh and spent catalysts and made them more resistant against reduction, but only aluminum avoided sintering during reaction. The dopants increased the catalytic activity per area of hematite, except aluminum which acted only as a textural promoter. The selectivity was decreased due to zirconium and lanthanum while the other dopants did not change this parameter. The neodymium-containing catalyst showed high levels of activity and selectivity and was able to work up to 530 °C, without deactivation, being the most promising with regard to styrene production.     

Ethylbenzene into styrene with carbon dioxide over modified vanadia–alumina catalysts

Dehydrogenation of ethylbenzene to styrene with carbon dioxide has been investigated using various vanadia–alumina catalysts to exhibit high activity and selectivity. Redox behavior of vanadium oxide played a key role in the dehydrogenation. Among several additives, antimony oxide has been found for improving catalyst stability as well as catalytic activity to produce styrene, revealing that the addition of the antimony oxide leads to the easier redox cycle between fully oxidized and reduced vanadium species.     

Iron oxide-based honeycomb catalysts for the dehydrogenation of ethylbenzene to styrene

Corning has recently developed a novel extrusion method to make bulk transition metal oxide honeycomb catalysts. One area of effort has been iron oxide-based catalysts for the dehydrogenation of ethylbenzene to styrene, a major chemical process that yields worldwide 20 MM tons/yr. In industry, the monomer is synthesized mostly in radial-flow fixed-bed reactors. Because of the high cross-sectional area for flow and shallow depth of the catalyst bed in these reactors, low reactor pressure gradients are maintained that favors the yield and selectivity for styrene formation. However, the radial-flow design has inherent detractions, including inefficient use of reactor volume and large temperature gradients that decrease catalyst service life. The overall economics of the process can be improved with parallel-channel honeycomb catalysts and axial flow reactors. The simple axial flow design of honeycomb catalysts provides low-pressure drop, while making more efficient use of reactor volume, with better heat and mass transfer characteristics compared to a conventional radial packed bed. An important part of this concept is the ability to fabricate a wide family of dehydrogenation catalyst compositions into honeycombs with the requisite chemical, physical, mechanical, and catalytic properties for industrial use. The ethylbenzene dehydrogenation (EBD) honeycomb catalysts developed by Corning have compositions similar to those commonly used in industry and are prepared with the same catalyst and promoter precursors and with similar treatments.

However, to enable extrusion of catalyst precursors into honeycomb shapes, especially at cell densities above 100 cell/in.², Corning’s process compensates for the high salt concentrations and the high pH of the batch material that would otherwise prevent or impede honeycomb extrusion. The improved rheological characteristics provide the necessary plasticity, lubricity, and resiliency for honeycomb extrusion with sufficient binder strength needed before calcination to the final product. Iron oxide-based honeycombs after calcination are strong and possess macroporosity and high surface area. In bench-scale testing, particular honeycomb catalyst compositions exhibited 60–76% ethylbenzene conversion with styrene selectivity of 95–91%, respectively, under conventional reaction conditions without apparent deactivation or loss of mechanical integrity.     

Gas-phase oxydehydrogenation of ethylbenzene with nitrobenzene by hydrogen transfer catalyzed reaction to produce styrene and aniline

Gas-phase catalytic hydrogen transfer reaction between ethylbenzene and nitrobenzene, to produce styrene and aniline, has been carried out at 360–460°C on amorphous AlPO₄, SiO₂, Al₂O₃, and on a natural sepiolite, as well as on the corresponding 20 wt% supported nickel catalysts. The influence of Cu as a second metal was also studied. Reactions were also carried out without nitrobenzene, under nonoxidative conditions. Catalytic activity under oxidative conditions was always comparatively higher than in nonoxidative conditions. In both cases, styrene yield and selectivity values obtained with support materials directly used as catalysts were better than those obtained with the corresponding Ni or Ni–Cu supported metal catalysts, with the only exception of SiO₂. The best results were obtained when amorphous AlPO₄ was used as the catalyst. The catalytic activity obtained in both oxidative and nonoxidative conditions, was closely associated to acid–base properties of the catalysts studied. Furthermore, a very similar linear correlation between A and E _a known as “compensation effect” was obtained and a common dehydrogenation mechanism was considered for oxidative and nonoxidative conditions. However, without considering the catalyst, nitrobenzene plays an important role as hydrogen acceptor, not only shifting the ethylbenzene dehydrogenation equilibrium but also avoiding secondary reactions by lowering the level of available hydrogen, especially when supported metals are being used as catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Oxidative dehydrogenation of ethylbenzene to styrene with CO2 over SnO2–ZrO2 mixed oxide nanocomposite catalysts

SnO₂–ZrO₂ nanocomposite catalysts with different compositions ranging from 0 to 100% of SnO₂ were prepared at room temperature by co-precipitation method using aqueous ammonia as a hydrolyzing agent. X-ray diffraction, transmission electron microscopic characterization revealed the SnO₂–ZrO₂ nanocomposite behavior. Acid–base properties of these catalysts were ascertained by temperature-programmed desorption (TPD) of NH₃ and CO₂. Both acidic and basic sites distribution of the nanocomposite catalysts is quite different from those of respective single oxides (SnO₂ or ZrO₂). Catalytic activity of these nanocomposite catalysts for ethylbenzene dehydrogenation (EBD) to styrene in the presence of excess CO₂ was evaluated. The change in the acid–base bi-functionality of the nanocomposite catalysts in comparison with single oxides had profound positive influence in enhancing the catalytic activity.     

沸石膜反应器苯脱氢反应性能

采用管式沸石膜反应器,研究了乙苯脱氢反应生成苯乙烯的性能。考察了不同渗透分离性能的沸石膜对乙苯脱氢反应的影响和不同沸石膜反应器上乙苯脱氢反应的规律。结果表明,与固定床操作条件下相比,沸石膜反应器乙苯转化率可提高近10％－16％,苯乙烯选择性可提高3％－5％。渗透分离性能是决定沸石膜提高脱氢反应性能的最重要因素,H2渗透量越大、H2／C3H8分离系数越高,对反应越有利。渗透分离性能相近但类型不同的沸石膜对乙苯脱氢反应性能有差异,其中Fe-ZSM-5沸石膜反应性能较好,这是杂原子Fe进入沸石骨架后引起的。反应后膜的渗透分离性能略有变化。     

Screening of amorphous metal–phosphate catalysts for the oxidative dehydrogenation of ethylbenzene to styrene

The gas-phase oxidative dehydrogenation of ethylbenzene to styrene was carried out by using as catalyst a series of metal phosphates (Al, Fe, Ni, Ca and Mn) and stoichiometric (Al/Fe = Al/Ca = 1) mixed systems: FeAl(PO₄)₂ and Ca₃Al₃(PO₄)₅, that were prepared by an ammonia gelation method. Their amorphous character was determined through several physical methods: nitrogen adsorption, DRIFT and XRD patterns. These results were compared to those obtained with 24 commercial inorganic solids (several metal oxides, sulfates and phosphates). Reactions were also carried out without oxygen, under non-oxidative conditions, where the catalytic activity was always appreciably lower than under oxidative conditions. Experimental results indicated that the oxidative gas-phase dehydrogenation of ethylbenzene to styrene could be related to the total number of acid and basic sites of catalysts, so that this reaction probably needs selected acid–basic pairs for coke formation, where the oxidative dehydrogenation process is developed.

The main practical conclusion of the catalyst screening was that the best results were obtained with the synthesized amorphous AlPO₄, where 43% ethylbenzene conversion and 99.7% styrene selectivity were achieved. A very reduced number of commercial inorganic solids like Al₂(SO₄)₃, Cr₂(SO₄)₃, Fe₂(SO₄)₃, NiSO₄, Al₂O₃ and Fe₂O₃ were also able to obtain an acceptable catalytic behavior, with conversions ranging between 18 and 23% and selectivity in the 95–100% range. Among the other synthesized solids, Ni₃(PO₄)₂-A-450 was the only metal phosphate exhibiting results in such a range. All the other catalysts studied were rather inactive and/or selective. Additional experiments carried out at longer times on stream (3.5 h) and longer contact times (W/F 0.254 and 0.654) confirmed the superior catalytic behavior of amorphous AlPO₄. Consequently, this solid could be a good candidate for application as a catalyst in the industrial oxydehydrogenation of ethylbenzene to styrene.     

丙烷脱氢制丙烯催化剂的研究进展

丙烷脱氢产业的迅猛发展亟需研发新一代高性能催化剂。本综述阐述了近年来新型负载型Pt纳米簇、金属氧化物和碳材料在丙烷脱氢反应中的研究进展。文章指出：Pt纳米簇的分散性和稳定性是决定其脱氢性能的关键因素;通过发展新合成技术和调节载体性质能改进其催化活性。金属氧化物中不饱和金属阳离子是脱氢反应的活性位点;调节载体的性质、优化制备方法以及结构掺杂都可显著提高其催化活性。碳材料中的含氧官能团被认为是丙烷脱氢反应的活性中心;对碳材料的比表面积、孔道性质及含氧官能团的数量等参数进行合理调控,能改善其催化性能。最后,文章提出未来的研究将重点解决Pt纳米簇的抗烧结性能弱、氧化物的本征活性低、碳材料高温稳定性差的问题,实现该领域的重大突破。     

Optimum ratio of K2O to CeO2 in a wet-chemical method prepared catalysts for ethylbenzene dehydrogenation

Fe₂O₃–K₂O–CeO₂ catalysts with various ratios of K₂O to CeO₂ were prepared by the wet-chemical method. Their phase compositions, reducibility, valence states of elements and catalytic activities for ethylbenzene dehydrogenation were studied. The results demonstrated that when the weight ratio of K₂O: CeO₂ was 1.40, the catalyst had highest ethylbenzene conversion and styrene selectivity, which were attributed to the optimization of active phase content and electron transfer ability, etc. Further, higher CeO₂ content not only enhanced styrene selectivity, but also prolonged the life cycle of catalysts.     

SO2 promoted oxidative dehydrogenation of ethylbenzene

It has been demonstrated that SO₂ acts as an efficient dehydrogenation agent in the conversion of ethylbenzene to styrene in the presence of alkali and alkaline earth metal oxide doped alumina and titania catalysts. Development of these catalysts, which give styrene yields of greater than 80% per pass, is described in the paper. The catalysts allow the use of close to stoichiometric amounts of sulphur dioxide, are active in the presence of steam diluent and show low deactivation with time. The effect of varying process conditions such as temperature, reactant concentration and diluent amount is also described.