Behaviors of V-doped Titanium Mixed Oxides in the Catalytic Dehydrogenation of Ethylbenzene

By an acid-catalyzed sol–gel method the V-doped titanium oxides (VxDTOs, x _mol% of V/(V + Ti) molar ratio) were prepared and systematically characterized by the techniques of XRD, TEM, H₂-TPR, XPS and TGA, indicating that most of the vanadium in the catalyst was highly dispersed on the surface of and in the bulk phase of TiO₂. The effect of V⁵⁺ doping level (1–9 mol% V⁵⁺) on the surface of TiO₂ and VxDTOs catalytic performance was analyzed. From the catalytic activity evaluation of VxDTOs in the dehydrogenation of ethylbenzene to styrene in the presence of CO₂ (CO₂-EBDH) at 450 °C, V6DTOs catalyst had the highest activity. Its higher activity in CO₂ than in N₂ clearly shows that CO₂ markedly enhanced the dehydrogenation of ethylbenzene. The activity of V6DTOs catalyst could almost be resumed after regeneration by air while partly resumed after regeneration by CO₂.     

锂对二氧化碳气氛下乙苯脱氢催化剂铁(Fe)/活性炭(AC)的促进作用

研究了助剂Li对CO2气氛下活性炭负载的Fe氧化物(Fe/AC)催化剂上的乙苯脱氢性能的影响和CO2的作用。助剂Li的添加提高了Fe/AC催化剂在CO2气氛下的乙苯脱氢活性和稳定性;CO2气氛下的苯乙烯收率明显高于N2气氛下,表明CO2显著促进了乙苯脱氢反应。     

The Oxidative Dehydrogenation of Ethylbenzene. Cobalt Molybdate Catalysts

The role of the catalyst and feed composition in the conversion and product distribution in the oxidative dehydrogenation of ethylbenzene, using a series of cobalt molybdate catalysts, was investigated.     

CO2选择氧化乙苯制苯乙烯催化剂研究进展

介绍了CO2选择氧化乙苯制苯乙烯的作用机制及其催化剂的研究进展;对CO2选择氧化乙苯制苯乙烯的前景进行了展望,认为在仍需加强作用机制、反应动力学和催化剂作用机理等问题的研究,并通过优化催化剂的组成（活性组分、载体和助剂）、制备条件和制备方法来改进催化剂的性能。     

乙苯氧化脱氢制苯乙烯催化机理及催化过程分析

采用乙苯氧化脱氢过程不仅可以突破热力学平衡的限制, 并且降低了生产过程的能耗。该过程的关键是开发出高活性及高选择性的催化剂。以V-Mg-O为代表的金属氧化物型催化剂遵循典型的Redox机理。影响催化剂性能的主要因素有催化剂的晶相组成、表面电子特性和表面酸行, 同时工艺条件诸如反应温度、O₂浓度、EB空速及水蒸汽用量等也影响着催化剂的性能, 其中催化剂的晶相组成起着决定性作用。     

Hydrogenation of Carbon Oxides over Perovskite-Type Oxides

Transition metals, metal oxides and metal-containing mixed oxides have been extensively used for Fischer-Tropsch hydrocarbon synthesis (1-9) and their ability to yield oxygenated compounds. During the last two decades, an extensive search has been carried out in examining the mechanism of catalytic hydrogenation of co and CO, which produced hydrocarbons and oxygenate compounds. The catalytic models for hydrocarbon synthesis have already been reviewed by Vannice (lo), which gives detailed information and discusses the data which were obtained during their development. As a broad product distribution is obtained during the FT synthesis, the mechanisms are extremely complicated and not clearly understood: therefore this topic is beyond the objective of this chapter and hence no further attention will be paid.     

Hydrogenation of Carbon Oxides over Perovskite-Type Oxides

Transition metals, metal oxides and metal-containing mixed oxides have been extensively used for Fischer-Tropsch hydrocarbon synthesis (1–9) and their ability to yield oxygenated compounds. During the last two decades, an extensive search has been carried out in examining the mechanism of catalytic hydrogenation of co and CO, which produced hydrocarbons and oxygenate compounds. The catalytic models for hydrocarbon synthesis have already been reviewed by Vannice (lo), which gives detailed information and discusses the data which were obtained during their development. As a broad product distribution is obtained during the FT synthesis, the mechanisms are extremely complicated and not clearly understood: therefore this topic is beyond the objective of this chapter and hence no further attention will be paid.     

Separation of m-Xylene and Ethylbenzene in Gaseous Carbon Dioxide

Abstract

The separation of an equal amount of ethylbenzene (EB) and m-xylene on silicalite using carbon dioxide as the carrier was studied. The experimental results indicated that operations in gaseous carbon dioxide provide a better separation efficiency than those at supercritical conditions. The effects of temperature, pressure, and flow rate on separation were also examined. It was found that the most appropriate conditions for obtaining purities of EB and m-xylene over 98% were a temperature around 353 K, a pressure of 40.8 atm, and a flow rate about 15 cm³/min. Comparison of the response curves for single- and two-component injection systems indicated that the model proposed by Gu et al. might be employed to interpret the data.     

Propane Oxidative Dehydrogenation over Metal Pyrophosphates Catalysts

Metal pyrophosphates (M–P₂O₇, where M is V, Zr, Cr, Mg, Mn, Ni or Ce) have been found to catalyze the oxidative dehydrogenation of propane to propene. The reaction was conducted at 1 atm, 450–550°C and feed flowrate of 75 cm³/min (20 cm³/min propane, 5 cm³/min oxygen and the balance is helium). All catalysts showed increase in degrees of conversion and decrease in olefins selectivity with increase in reaction temperature. At 550°C, MnP₂O₇ exhibited the highest activity (40.7% conversion) and total olefins (C₃H₆ and C₂H₄) yield (29.3%). The other catalysts, indicated by their respective metals, may be ranked (based on olefins yield) as V (16.9%) < Cr (17.5%) < Ce (25.1%) < Zr (26.2%) < Ni (26.8%) < Mg (27.9%). The reactivity of the lattice oxygen was estimated from energy of formation of the corresponding metal oxides. Correlation between the selectivity to propene and the standard energy of formation was attempted. Although there was no clear correlation, the result suggested that the lattice oxygen play a key role in the selectivity-determining step.     

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。     

Catalysis of Methane Coupling with Carbon Dioxide Over Binary Oxides

Binary oxides of Ca-Ce, Ca-Cr, and Ca-Mn exhibit good performance and similar kinetic behavior in the conversion of CH₄ to C₂ hydrocarbons with CO₂, whereas the corresponding Sr- and Ba-containing catalysts show lower activity in C₂ formation except for Sr-Mn and Ba-Mn oxides. The Sr-Mn oxide provides even higher C₂ yield than the Ca-containing catalysts. Characterization reveals that solid solution and composite oxides comprising Ca²⁺ species and the redox component (Ce, Cr, or Mn) exist at a steady state of reaction and probably account for the synergy in C₂ formation over the Ca-containing catalysts. On the other hand, Sr and Ba carbonates are formed along with Ce, Cr, or Mn oxides during the reactions over Sr- and Ba-containing oxides. The carbonates, however, can react with MnO to form SrMnO_2.5 and BaMnO_2.5, the probable active species for CH₄ activation over the Sr-Mn and Ba-Mn catalysts.     

Thermodynamic Equilibrium Analysis of Propane Dehydrogenation with Carbon Dioxide and Side Reactions

A thermodynamic analysis of propane dehydrogenation with carbon dioxide was performed using constrained Gibbs free energy minimization method. Different reaction networks corresponding to different catalytic systems, including non-redox and redox oxide catalysts, were simulated. The influences of CO₂/C₃H₈ molar ratio (1–10), temperature (700–1000 K), and pressure (0.5–5 bar) on equilibrium conversion and product composition were studied. In the presence of CO₂ with a molar ratio of CO₂/C₃H₈ = 1, the temperature of dehydrogenation can be 30 K lower than that of dehydrogenation in the presence of steam (H₂O/C₃H₈ = 1) and about 50 K lower than that of simple dehydrogenation without dilution to achieve 60% propane conversion. It was found that the occurrence of dry reforming of propane and coke-forming side reactions could strongly impact the equilibrium product composition of the multireaction system and, therefore, these reactions should be kinetically controlled. Comparison of the simulated reactant conversions with those reported in the literatures revealed that the experimental conversion levels of propane are far below the corresponding equilibrium values due to rapid catalyst deactivation by coke, implying that research efforts should be directed toward formulation of more active and selective catalysts.     

类水滑石型催化剂用于二氧化碳气氛下乙苯脱氢

通过焙烧类水滑石前驱体制备催化剂载体,采用浸渍法制备了铁系列催化剂.实验结果表明,这种结构对于乙苯脱氢有促进作用,而且活性组分Fe附载在载体上时的活性比直接作为结构中的离子时的活性更好.此外,脱氢反应随着CO2分压增加,乙苯的转化率先升高后降低,最后保持在39%左右.