Catalytic oxidative coupling of methane over hydroxyapatite modified with lead

Hydroxyapatite modified with lead catalyzes the oxidative dehydrogenation of methane with high selectivity to C₂ compounds at reaction temperatures as low as 700 °C. The activity is stabilized after reduction in the surface area of the catalyst during the reaction.     

The low-temperature oxidative coupling of methane over zirconium oxide

Zirconium oxide is shown to be capable of catalyzing the conversion of methane to ethane at temperatures as low as 530 °C. The lowest temperature at which ethane is produced is found to be dependent upon the method employed for the preparation of the catalyst. The presence of surface hydroxyl groups appears to be necessary for the production of ethane at these low temperatures.     

Cation effects in the oxidative coupling of methane on phosphate catalysts

The conversion of methane and the selectivities to the various products have been measured at 700 and 775 °C on a variety of phosphates of La(III), Zr(IV), V(V), Cr(III), Mn(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Al(III), B(III), Pb(II), Bi(III) and Sm(III) in the presence and absence of carbon tetrachloride. The conversions reach as high as 30 and 49% at 700 and 775 °C, respectively, with methane and oxygen at partial pressures of 200 and 25 Torr, respectively. The highest C₂₊ selectivities (61 and 82%, respectively) were obtained for lead(II) phosphate at 700 and 775 °C, respectively. In general the conversions and C₂₊ selectivities are enhanced on addition of carbon tetrachloride (1.1 Torr) to the feedstream, although there are notable exceptions. Significantly high selectivities to formaldehyde are observed with a number of the catalysts, in particular 32% with boron(III)phosphate.     

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.     

Catalytic properties of bismuth vanadates based catalysts in oxidative coupling of methane and oxidative dehydrogenation of propane

The oxidative coupling of methane (OCM) and the oxidative dehydrogenation of propane (ODHP) have been performed on new mixed Bi-V oxides having a --Bi₂MoO₆-like structure. The results yield a correlation between the methane conversion and the oxygen diffusivity. The introduction of metals (Fe, Cu, Sr with 10 mol%) improves the C₂ selectivity. The use of an oxide with a scheelite structure (BiVO₄) shows that, under catalytic conditions, this oxide has the same behaviour as the above solids.     

丙烷氧化脱氢制丙烯的钒基介孔催化材料研究进展

介绍了近年来丙烷氧化脱氢催化技术的最新研究进展,针对其中应用最广泛的钒基介孔催化剂,对其反应机理、载体性能和制备方法进行了综述,并比较了不同催化体系的丙烷氧化脱氢性能,提出了改善钒基介孔催化剂催化活性与选择性的途径。通过比较已经报道的同类研究结果,着重阐述了载体的孔结构对于氧化脱氢过程的影响,比表面积和孔径的优化对于提高催化剂的活性组分分散度以及活性位的数量效果明显。今后研究应着重提高催化剂孔道结构在高温下的稳定性以及使用寿命。     

Lithium-chloride-promoted sulfated zirconia catalysts for the oxidative dehydrogenation of ethane

The oxidative dehydrogenation of ethane over sulfated-zirconia-supported lithium chloride catalysts has been systematically investigated. The optimal experimental parameters were obtained. It is found that sulfation of zirconia increases the catalytic activity. 2–3.5 wt% lithium chloride on sulfated zirconia catalysts exhibit high catalytic activity for oxidative dehydrogenation of ethane, with particularly high activity for ethene production. 70% selectivity to ethene at 98% ethane conversion, giving 68% ethene yield, is achieved over 3.5 wt% LiCl/SZ at 650°C.     

The selective oxidative dehydrogenation of propane on vanadium aluminophosphate catalysts

VAPO-5 and V/ ALPO-5 catalysts have been tested for the oxidative dehydrogenation of propane. Depending on the vanadium contents and the preparation procedure, different vanadium species and different catalytic behavior are observed. The catalyst containing V⁵⁺ species with a tetrahedral coordination presents the higher yield of propene in the oxidative dehydrogenation of propane. The same yields of CO₂ are observed on all vanadium aluminophosphate catalysts, while the higher the yield of propene the lower the yield of CO is.     

Kinetic modelling of the gas phase ethane and propane oxidative dehydrogenation

Gas phase thermal and oxidative dehydrogenation of ethane and propane are explored experimentally and mikrokinetically. Kinetic data for the elementary reactions postulated were adopted from the literature. The results show that oxygen plays a dominating role in the primary activation of the alkanes by producing an HO₂ and a hydrocarbon radical. The kinetic sequences developed predict satisfactorily conversion and products yields for ethane and propane oxidative dehydrogenation.     

Propane oxidative dehydrogenation on silica based oxide catalysts

The oxidative dehydrogenation of propane to propylene with molecular O₂ (PPD) has been investigated on commercial bare SiO₂ and medium loaded V₂O₅ and MoO₃ catalysts at 450–525°C. The direct relationship between the density of reduced sites (, 10¹⁶ s_r g _cat– ¹ ), evaluated in steady-state conditions by O₂ chemisorption, and the POD reaction rate proves the occurrence of a concerted reaction mechanism involving the activation of gas-phase O₂ on the reduced sites of the catalyst surface. A straight-line correlation between the activity of such silica based catalysts in POD and methane partial oxidation to formaldehyde (MPO) at 525°C has been disclosed.     

The formation of active species for oxidative dehydrogenation of propane on magnesium molybdates

Pure and mixed magnesium molybdate phases (MoO₃, MgMoO₄, and MgMo₂O₇) have been examined for the oxidative dehydrogenation reaction of propane. The results are very sensitive to the stoichiometry and method of preparation. The catalysts exhibiting superior activity and selectivity are characterized by a unique temperature-programmed reduction peak that is not present for the poorly active or selective catalysts. Mixtures of MgMoO₄ and MoO₃ or MgMoO₄ and MgMo₂O₇, materials that perform poorly by themselves, show significant improvements in performance upon heating. The solid-state interactions leading to these improvements correspond to the appearance of the characteristic reduction peak. The results suggest that the beneficial synergistic effects seen with mixtures of inactive phases are due to formation of a new phase or species, rather than remote communication between phases (e.g., oxygen spillover). This revised version was published online in November 2006 with corrections to the Cover Date.     

丙烷氧化脱氢制丙烯研究进展

开发新型丙烯制备工艺对于满足人们日益增长的丙烯需求具有重要意义。由于商业化无氧脱氢技术存在热力学平衡限制、反应温度高、催化剂易积炭等不足,近年来,人们将研究重心转向了丙烷氧化脱氢技术。本文简述了丙烷氧化脱氢制丙烯的发展现状,综述了近年来文献报道的丙烷氧化脱氢催化剂体系（V基、Cr基、Co基、Ni基、Mo基、Pt基、Ce基和非金属基催化剂）、机理研究和不同氧化剂选择,并对各自的优势和不足进行了简单分析。分析发现,虽然目前丙烷氧化脱氢催化剂的种类非常广泛,但产物丙烯的收率仍有待提高,机理研究也需要更加系统和深入。最后指出,系统研究丙烷氧化脱氢机理,并在此基础上开发先进催化剂,进一步提高丙烯的选择性和收率是未来丙烷氧化脱氢研究的重要方向。     

Catalytic behavior of vanadium-containing mesoporous silicas in the oxidative dehydrogenation of propane

Three series of vanadium-containing silica catalysts (2–7.6 wt% V) have been prepared by varying the synthesis method. In all cases, conversion values in the oxidative dehydrogenation of propane increase with the temperature, vanadium loading and reducibility. For impregnated and anchored catalysts, a relationship between the selectivity towards propene and the effective acidity, as determined in the dehydration of 2-propanol, can be established. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Catalytic contribution of reactor wall materials on oxidative coupling of methane

Gas-phase oxidative coupling of methane (OCM) was investigated with empty tubular-flow reactors made of various materials (quartz, ceramic and stainless steel tubes). When the temperature is higher than 680°C, the CH₄ conversions in three kinds of empty reactors are measurable, and the gas-phase OCM becomes noticeable at 750°C or higher. High temperature is beneficial to the activation of CH₄ and the dehydrogenation of C₂H₆ to C₂H₄. Residence time of reactants in the heated volume plays an important role in the gas-phase OCM. Experiments indicated that the gas-phase OCM can be minimized by increasing reactant gas velocity or filling the free volume of the reactor with inert materials. Reactor surface also has an effect on the reaction and may participate in some surface reactions. Based on the kinetic results and the SEM investigation on the surfaces of reactors, a gas-phase reaction mechanism of OCM is proposed.     

BiOCl催化剂的丙烷氧化脱氢催化性能

以_L-赖氨酸为模板剂,采用沉淀法制备了BiOCl催化剂,对催化剂进行了X射线衍射、N₂吸附-脱附和H₂-TPR等表征,并测试了BiOCl催化剂对丙烷氧化脱氢制丙烯反应的催化性能。结果表明,制备的BiOCl催化剂为四面体结构,500 ℃焙烧3 h后,催化剂比表面积为11.2 m²·g^-1,未完全还原氧物种的含量较多。随着反应温度升高,丙烷转化率和丙烯选择性增加,丙烷转化率为20%时,丙烯选择性达64.5%。     

Deactivation of alkane oxidative dehydrogenation catalyst by deep reduction in periodic flow reactor

The activity loss of β‐NiMoO₄ catalyst has been studied in the oxidative dehydrogenation of propane with an operating periodic flow reactor. Under severe operating conditions (i.e., high temperature and long periods of the pulses), the lattice oxygen depletion is faster than the reoxidation one. After an induction period, carbon whiskers on the catalyst surface were detected together with noticeable amounts of cracking products in the gas phase as CH₄, C₂ hydrocarbons and H₂. Deep reduction dramatically changes the reaction path and irreversibly modifies the catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

Vanadium supported on hexagonal mesoporous silica: active and stable catalysts in the oxidative dehydrogenation of alkanes

Hexagonal mesoporous silica (HMS) catalysts post-synthetically doped with vanadia oxo-species were characterized by means of XRD, UV-Vis spectroscopy, H₂-TPR and studied in oxidative dehydrogenation of propane (ODH). The relationship between catalytic activity in ODH and the presence of different vanadia-oxo species (monomeric, oligomeric and oxide-like species) was suggested. Monomeric VOx species are responsible for high catalytic activity and selectivity, oligomeric species containing V-O-V bond are active but non-selective to propene and oxide-like VOx particles are significantly less active and selective.     

Studies on oxidative dehydrogenation of n-butane on bismuth molybdate on alumina

Oslefins and diolefins are important intermediates in the petrochemical industry and the future promises a further substantial increase in demand. While several catalysts have been formulated in the past for the abstraction of hydrogen from butenes and propylene, these catalysts are inefficient in the abstraction of first hydrogen from butane. Bismuth molybdates (β and γ-phases) containing iron oxide and supported on alumina are used as catalysts in the present investigation on the oxidative dehydrogenation of n-butane. Effects of catalyst content, temperature and oxygen: n-butane ratio on conversion and selectivity to butadiene and (C₄H₈ + C₄H₆) are studied in the following ranges of experimental conditions: β-bismuth molybdate/100 mol support I(K), 3–9; γ-bismuth molybdate/100 mol support I(K), 5-20; temperature, 400–500°C; O₂: butane ratio, 0.6:1.7.     

The oxidative dehydrogenation of ethane over alkali-doped lanthanum-calcium oxide catalysts

The oxidative dehydrogenation of ethane has been investigated over Li-, Na- and K-doped La/CaO catalysts at temperatures of 550–650°C. The addition of alkali metals to La/CaO increases the ethylene selectivity. For Li- and Na-doped La/CaO catalysts, the ethane conversion remains almost unaltered. The increase of ethylene selectivity over the two catalysts is believed to be mainly caused by coordinative action of lithium and lanthanum or sodium and lanthanum. However, the Li-doped La/CaO catalyst exhibits stronger coordinative action than the Na-doped La/CaO catalyst. Catalyst characterization reveals that the strong coordinative action of components in Li/La/CaO is probably related to the chemical and crystal structure of the catalyst which is favorable for oxidative dehydrogenation of ethane. The results also show that addition of potassium, being a poor dopant, to La/CaO results in a sharp decrease in catalytic activity.