Effect of the support and added oxides on the bistability observed in the oxidative dehydrogenation of 2-propanol over copper-supported catalysts

A bistability phenomenon has been observed in the oxidative dehydrogenation of 2-propanol over supported copper catalysts. Cu/Al₂O₃ and Cu/CeO₂ have been prepared by room temperature adsorption of the copper amino complex on the supports. The comparison of the hysteresis observed when the partial pressure of oxygen is varied, indicates that there is an important effect of the support. This effect is explained by the variation in specific surface areas of the supports and in their reducibilities. The possible influence of a second phase (-Sb₂O₄, SnO₂, Bi₂O₃ and NiO) added to the copper catalysts has also been studied.     

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.     

CO2气氛下乙烷氧化脱氢制乙烯催化剂研究进展

CO2是导致全球变暖的主要温室气体，又是宝贵的可再生C1资源，将其转化为有价值的化学品，在环境保护和碳资源合理利用方面具有双重意义。作为页岩气的重要组成部分，乙烷高效催化转化制乙烯不仅具有重要的理论研究意义，而且具有广阔的工业应用前景。在CO2气氛下乙烷氧化脱氢制乙烯（CO2-ODHE）已成为增产乙烯的有效手段之一。该文重点阐述了在CO2-ODHE反应中不同类型的催化剂及影响该反应催化活性和稳定性的主要因素和关键问题，并对比介绍了乙烷直接氧化脱氢（O2-ODHE）和乙烷化学链氧化脱氢（CL-ODHE）。最后，结合反应机制提出了构筑高效催化剂可能的方向和发展前景。     

Effect of chromium promoter on copper catalysts in ethanol dehydrogenation

A series of chromium-promoted copper catalysts with various Cr to Cu molar ratios were prepared with the co-precipitation method. The promotional effects of chromium on copper catalysts were examined by X-ray powder diffraction (XRD), nitrous oxide decomposition, and the dehydrogenation reaction of ethanol. The dehydrogenation reaction was carried out in a continuous-flow microreactor between 523 and 583 K under atmospheric pressure. The results indicated that the promotional effect was dependent on the Cr/Cu molar ratio, and the predominant decay of catalysts in this study was caused by sintering. The catalyst with the Cr/Cu molar ratio of 4/40 has the highest activity and stability. The surrounded well-dispersed chromia strongly influenced the catalytic properties of copper metal. It also showed that the over-promotation of a catalyst has a disastrous effect on the total make of product. The ethanol dehydrogenation reaction follows a first-order reaction, and the kinetics for deactivation can be described by a second-order expression.     

碳基硼基催化体系丙烷氧化脱氢催化剂的研究进展

以碳基硼基为代表的非金属催化剂氧化能力不如金属氧化物,这使得非金属催化体系如碳基和硼基催化剂对于丙烷氧化脱氢反应具有独特的优势。本文综述了应用廉价环保型改性碳基和硼基的非金属丙烷脱氢催化剂将丙烷转化为丙烯的技术前沿,阐述了有序介孔炭材料,纳米碳材料（纳米纤维、石墨烯、碳纳米金刚石等）和六方氮化硼材料各自的丙烷氧化脱氢机理以及通过杂原子改性后提高其催化活性的情况。并对其未来的发展方向以及丙烷氧化脱氢新材料领域的发展做了展望。     

Oxidative coupling of methane and oxidative dehydrogenation of ethane over strontium-promoted rare earth oxide catalysts

Sr-promoted rare earth (viz. La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er and Yb) oxide catalysts (Sr/rare earth ratio = 0·1) are compared for their performance in the oxidative coupling of methane (OCM) to C₂ hydrocarbons and oxidative dehydrogenation of ethane (ODE) to ethylene at different temperatures (700 and 800°C) and CH₄ (or C₂H₆)/O₂ ratios (4–8), at low contact time (space velocity = 102000 cm³ g⁻¹ h⁻¹). For the OCM process, the Sr–La₂O₃ catalyst shows the best performance. The Sr-promoted Nd₂O₃, Sm₂O₃, Eu₂O₃ and Er₂O₃ catalysts also show good methane conversion and selectivity for C₂ hydrocarbons but the Sr–CeO₂ and Sr–Dy₂O₃ catalysts show very poor performance. However, for the ODE process, the best performance is shown by the Sr–Nd₂O₃ catalyst. The other catalysts also show good ethane conversion and selectivity for ethylene; their performance is comparable at higher temperatures (≥800°C), but at lower temperature (700°C) the Sr–CeO₂ and Sr–Pr₆O₁₁ catalysts show poor selectivity. © 1998 SCI.     

Oxidative dehydrogenation of ethane over alkali‐metal doped sulfated zirconia catalysts

Alkali‐metal doped sulfated zirconia catalysts were tested for the oxidative dehydrogenation of ethane into ethene. The effects of metal precursor compounds and acidic anion promoters on the catalytic activity in this reaction were studied. It was found that sulfation of zirconia increases the selectivity of ethane towards ethene. Lithium‐, sodium‐, and potassium‐doped sulfated zirconia catalysts showed quite different activities in this reaction. Sulfated zirconia doped with lithium catalysts were found to be effective for the oxidative dehydrogenation of ethane, giving over 90% selectivity to ethene and 25% ethene yield at 650 °C. © 1999 Society of Chemical Industry     

CeO2‐CrOy/γ‐Al2O3 redox catalyst for the oxidative dehydrogenation of propane to propylene

CeO₂‐CrO_y loaded on γ‐Al₂O₃ was investigated in this work for the oxidative dehydrogenation (ODH) of propane under oxygen‐free conditions. The ODH experiments of propane were conducted in a fluidized bed at 500°C‐600°C under 0.1 Mpa. The prepared catalyst was characterized by N₂ adsorption‐desorption measurements, H₂‐temperature‐programmed reduction, O₂‐temperature‐programmed desorption, NH₃‐temperature‐programmed desorption, x‐ray photoelectron spectroscopy, and x‐ray diffraction. The change in the selectivity of propylene resulted from the thermal cracking of the propane and the competition for lattice oxygen in the catalyst between propylene formation and propane and propylene combustion. Therefore, to achieve higher propylene yield in the industry, the reaction temperature should be 550°C‐575°C for the 17.5Cr‐2Ce/Al catalyst. The results of H₂‐TPR (from 0.2218 mmol/g‐0.3208 mmol/g) revealed that the addition of CeO₂ can enhance the oxygen capacity of CrO_y. Compared with that for 17.5Cr/Al, the conversion can be enhanced from 22.4% to 28.5% and the selectivity of propylene can be improved from 72.2% to 75.9% for the 17.5Cr‐2Ce/Al catalyst. In addition, CeO₂ can inhibit the evolution of lattice oxygen (O^2?) to electrophilic oxygen species (O₂^?), causing the average CO_x (CO and CO₂) selectivity to decrease from 9.64% to 6.31%.     

PtSn负载量对PtSn/Al2O3催化剂上丙烷脱氢性能的影响

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。     

柱撑型钒基催化剂的制备及其丙烷氧化脱氢催化性能

以人工合成的3种不同层板组成的层状双羟基金属氢氧化物MgAl-CO₃-LDHs、CoAl-CO₃-LDHs和NiCr-CO₃-LDHs为载体,以偏钒酸钠NaVO₃为柱撑剂和钒前体,采用离子交换法制备了钒柱撑的催化剂样品（MgAlVO、CoAlVO和NiCrVO）,通过XRD、FTIR、XPS和Raman等手段表征了样品的物相、钒物种的存在形态以及钒的价态,以丙烷氧化脱氢制丙烯为模型反应,表征了所制备的催化剂样品的催化性能,着重探讨了LDHs载体的层板组成以及钒的含量对催化剂样品中的钒氧物种存在形态及其丙烷氧化脱氢催化性能的影响。结果表明：以20%理论含量的钒柱撑MgAl-CO₃-LDHs所制备的催化剂样品20%MgAlVO对丙烷氧化脱氢反应的催化性能较好,当反应温度为560℃时,丙烯收率可以达到11.3%,Raman光谱显示该催化剂样品中的钒以Mg₃V₂O₈和α-Mg₂V₂O₇两种形式共存,且晶格氧O^2-和吸附氧O^-所占的比例较为均衡,有利于获得较好的丙烷氧化脱氢催化性能,而在同样条件下制备的催化剂样品20%CoAlVO和20%NiCrVO中的钒物种只观察到分别以Co₃V₂O₈和Ni₃V₂O₈存在的正钒酸盐,前者对丙烯的收率不到8%,后者甚至完全得不到丙烯。     

xCeO_2/高岭土催化剂上丙烷氧化脱氢制丙烯

采用浸渍法制备不同CeO_2负载量的xCeO_2/高岭土催化剂,采用XRD、N_2吸附-脱附、H_2-TPR和XPS等对催化剂物化性质进行表征。将xCeO_2/高岭土催化剂应用于丙烷氧化脱氢反应中,考察CeO_2负载量对丙烷氧化脱氢反应的影响,同时对催化剂进行原位电导测试。结果表明,CeO_2负载质量分数8%时,CeO2/高岭土催化剂的催化性能最好,500℃时,丙烷转化率为17.92%。在氧-丙烷-氧+丙烷连续变化的不同气氛下均显示了氧化还原可逆性。     

MoO3/ZrO2催化剂的丙烷氧化脱氢制丙烯催化性能

以十六烷基三甲基溴化铵为表面活性剂,采用溶剂热法制备系列MoO_3/ZrO_2催化剂,采用H2-TPR、N_2吸附-脱附、X射线衍射等对其进行表征,并评价MoO_3/ZrO_2催化剂的丙烷氧化脱氢制丙烯催化性能。结果表明,MoO_3负载于ZrO_2载体上制备的催化剂催化活性增加,MoO_3负载质量分数为20%的MoO_3/ZrO_2催化剂,在反应温度为600℃时,丙烷转化率27.45%,丙烯选择性44.78%,丙稀收率12.29%。     

过渡金属氧化物催化剂对丙酮氧化的催化性能

以氧氯化锆和过渡金属硝酸盐为原料,溶胶-凝胶法制备氧化锆载体,采用溶液浸渍法制备出负载型纳米复合氧化物催化剂。对过渡金属氧化物(Mn、Ni、Cu、Fe和Co)催化剂进行初步筛选,其中Mn₂O₃/ZrO₂催化活性最佳。考察了活性组分含量、焙烧温度和焙烧时间等对催化剂催化活性的影响。催化剂的最佳制备条件：锰负载量为6%,450 ℃焙烧6 h。丙酮的转化率达62%。通过TEM、SEM、XRD和TG-DTA对催化剂结构进行了表征。结果显示,催化剂颗粒均匀,大小约为20 nm;无定形的Mn2O3是催化剂的活性中心。     

The oxidative dehydrogenation of ethane with CO2 over Mo2C/SiO2 catalyst

Mo₂C prepared on SiO₂ was found to be an effective catalyst for the dehydrogenation of ethane to produce ethylene in the presence of CO₂. The selectivity to ethylene at 850–923 K was 90–95% at an ethane conversion of 8–30%. With the increase of the temperature the dry reforming of ethane became also a significant process. It is assumed that the Mo oxycarbide formed in the reaction between CO₂ and Mo₂C plays an important role in the activation of ethane. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of alkali metals additives to V2O5/TiO2 catalyst on physicochemical properties and catalytic performance in oxidative dehydrogenation of propane

The effect of alkali metal additives Li, K, and Rb to V₂O₅/TiO₂ catalyst on the rate of catalyst reduction with propane and reoxidation with oxygen, sorption of propene, and the electron work function has been examined. The results have been correlated with the catalytic performance in oxidative dehydrogenation, ODH, of propane. It has been found that the rates of reduction, reoxidation and the ODH of propane decrease in the order: VTi>LiVTi>KVTi>RbVTi. The activation energies of the reduction and reoxidation are not, however, affected by the presence of the alkali metals. The same sequence has been observed for the work function values of the catalysts. It is argued that alkali metal poisons the centres of the hydrocarbon activation. The yield and selectivity to propene in the ODH of propane increase, however, for the promoted catalysts, following the above sequence. This effect is ascribed to the decrease in the heat of the propene adsorption, which is due to the increase in the basicity and decrease in acidity on the promoted catalysts.     

Role of chromia in copper catalysts for dehydrogenation of ethanol

During direct vapour phase dehydrogenation of ethanol, a copper-on-silica catalyst lost much of its activity in 100 h. Analysis with X-ray diffraction, scanning electron microscopy and X-ray photoemission showed that both sintering and carbon deposition accompanied the drop in activity. In catalysts in which chromia was also present copper was found to be in a more highly dispersed form which was more resistant to sintering. The chromia catalyst accumulated carbon comparably to those containing copper only.     

Oxidative dehydrogenation of n-butane on V/MgO catalysts. Influence of the type of contactor

A comparative study of the catalytic performance of a selective V-Mg-O catalyst in the oxidative dehydrogenation of n-butane is presented using three different types of reactor: (i) an adiabatic fixed-bed reactor; (ii) a fluidized-bed reactor; and (iii) an in situ redox fluidized-bed reactor. The results obtained indicate that the in situ redox fluidized-bed reactor outperforms the conventional fixed- and fluidized-bed reactors, especially at high n-butane conversions. Thus, a selectivity to C₄ olefins of 54% at n-butane conversions of 60% was achieved at 550°C using an in situ redox fluidized-bed reactor while selectivities to C₄-olefins lower than 43% were obtained on the other reactor types under the same reaction conditions (isoconversion and reaction temperature). This revised version was published online in July 2006 with corrections to the Cover Date.