逆水煤气变换耦合乙烷脱氢反应中助剂对Cr/SiO2催化剂性能的影响

分别制备了以Mn、Ce、Cu、Zn、K等为助剂的Cr/SiO2催化剂,考察了助剂在逆水煤气变换耦合乙烷脱氢制乙烯反应中对Cr/SiO2催化剂反应性能的影响。结果表明,高温下Mn的加入有利于催化活性的提高,Cr-Mn/SiO2催化剂显示了较好的催化活性。在740℃、n(CO2)/n(C2H6)=7的条件下,乙烷转化率为47%,乙烯选择性为99%。XRD、XPS、UV-DRS和TPR技术的表征表明催化剂表面存在Cr3+、Cr6+、Mn4+物种,Mn的加入使得催化剂还原性能增强,有助于反应过程中氧化还原循环的进行,提高了反应活性。     

逆水煤气变换耦合乙烷脱氢高选择性制备乙烯反应的研究进展

综述了近年来国内外有关利用逆水煤气变换耦合乙烷脱氢制备乙烯反应的研究状况,讨论了该反应的历程和机理。文献表明,担载型铬氧化物、含铬分子筛、纳米氧化物粒子等具有较好的催化活性,CO2的主要作用是通过逆水煤气变换来消除乙烷脱氢产物H2,并与表面积炭反应提高乙烷转化率及催化剂稳定性。反应的关键是选择适宜的催化剂。     

乙烷脱氢催化剂研究进展

乙烯是重要的有机化工原料,随着乙烯需求量的不断增加以及石油资源的日益匮乏,乙烷脱氢已成为乙烯增产的重要途径。乙烷脱氢制乙烯受到越来越多的关注,乙烷脱氢催化剂逐步改善。本文首先介绍了近年来国内外乙烷脱氢制乙烯的研究现状,然后从催化剂制备方法、性能以及应用等方面对乙烷催化脱氢催化剂和乙烷氧化脱氢催化剂的研究进行了总结,并对其进行了系统分类。催化脱氢是低碳烷烃转化为烯烃的有效途径,烯烃选择性高,受到热力学平衡限制,能耗较高。氧化脱氢由于氧化剂的引入打破了热力学平衡限制,能够有效抑制焦炭的生成,减少能量消耗。然而,深度氧化反应难于控制,乙烯的选择性低。因此,选取合适的催化脱氢催化剂,尽可能提高乙烷单程转化率、降低能耗是乙烷脱氢的关键。     

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。     

逆水煤气变换催化剂的制备及反应性能

为解决逆水煤气变换反应环境下催化剂抗还原性和稳定性较差的问题,采用浸渍法和共沉淀法制备了Mn基催化剂,对逆水煤气变换反应进行了热力学分析和催化剂初步筛选,初步考察了不同反应温度、反应压力、氢碳体积比和气体空速下的催化活性和反应选择性,并进行了催化剂稳定性评价和物化表征。结果表明,与浸渍法相比,共沉淀法制备的催化剂性能较好。适宜的逆水煤气变换反应条件为550~600℃,常压~0.5 MPa,氢碳体积比1~1.5,空速10 000~15 000 h-1。在入口温度580℃,压力0.5 MPa,氢碳体积比1.5和气体空速6 000 h-1的条件下,CO2转化率达45%,CO选择性为90%。催化剂500 h稳定性良好,这主要是由于形成了稳定的Mn基尖晶石活性相。     

Na-W-Mn-Zr-S-P/SiO_2催化剂上乙烷氧化脱氢反应

研究了甲烷氧化偶联六组分Na-W-Mn-Zr-S-P/SiO_2催化剂对乙烷氧化脱氢反应的催化性能.考察了不同原料气配比、温度和空速等条件下的催化剂活性.讨论了催化剂中S或P组分的含量对催化活性的影响.实验结果表明,S和P元素的加入可以提高催化剂的活性.660℃时六组分催化剂上乙烷的转化率为65.2%,乙烯的选择性为83.2%,此时得到的乙烯收率最高.乙烷与氧气比的增加有利于提高乙烯的选择性.较低反应温度时,空速的增加可以抑制碳氧化物(CO,CO_2)的生成,提高乙烯选择性.     

负载型杂多酸催化乙烷氧化脱氢反应的起燃特性

研究了负载在SiO₂ 上的杂多酸催化剂的乙烷氧化脱氢活性 .发现在乙烷氧化脱氢反应中存在一个活性起燃温度 ,当反应温度高于此温度时 ,反应以气相自由基反应为主 .杂多酸的酸性与乙烷在杂多酸表面的吸附有关 ,酸性越强 ,引发自由基反应的起燃温度越高     

PtSn-Mg(Zn)AlO催化剂应用于乙烷脱氢反应研究

采用阴离子交换法合成了一系列不同Zn和Pt含量的PtSn-Mg(Zn)AlO催化剂用于乙烷脱氢反应。实验结果表明,在水滑石载体中掺杂少量的Zn对乙烷脱氢反应有明显影响。当Zn含量为2%（质量）时Pt基催化剂活性性能最优,在550℃时乙烷初始转化率达到27.1%,2 h平均转化率为21.6%。BET和SEM结果表明PtSn-Mg(Zn)AlO催化剂比PtSn-MgAlO催化剂比表面积更大,TEM结果显示,PtSn-Mg(Zn)AlO催化剂和PtSn-MgAlO催化剂的金属颗粒的平均直径分别为（1.49±0.31）nm 和（2.0±0.23）nm,说明Zn的掺杂在一定程度上改变了催化剂的结构,能减小Pt颗粒的尺寸,更好地分散Pt颗粒,从而改善乙烷催化脱氢反应性能。此外,考察温度对乙烷脱氢反应性能影响,发现温度越高乙烷初始转化率越高,但催化剂越易失活;考察Pt负载量对乙烷脱氢反应性能的影响,发现增加Pt含量并不能使乙烷转化率得到相应倍数的增加,即增加Pt含量反而使Pt的利用率降低了,因此适量降低PtSn-Mg(2-Zn)AlO催化剂中Pt含量对研究乙烷脱氢反应有深远意义。     

乙烷催化氧化脱氢制乙烯催化剂研究进展

介绍了目前几种乙烯的制备技术,认为使用乙烷催化氧化脱氢来制乙烯的方法较好.分析了乙烷催化氧化脱氢制乙烯机理,叙述了此方法反应过程中使用的4类催化剂,即过渡金属氧化混合物类、碱金属及碱土金属类、稀土类和贵金属类,分别介绍了它们的研究进展情况,其中过渡金属氧化催化剂中的氧化镍类在较低的反应温度下有较高的选择性,且原料来源丰...     

乙烷催化氧化脱氢制乙烯反应及其催化剂的研究进展

综述了国内外有关乙烷氧化催化脱氢反应及其催化剂的研究工作     

Cr/SSZ-13催化二氧化碳氧化乙烷脱氢反应的研究

通过脱氢反应将低碳烷烃转化为同碳数的烯烃是烷烃高值化利用和烯烃原料多元化的重要途径。烷烃氧化脱氢制烯烃的反应具有不受反应平衡限制、积炭少、反应温度低等优点,一直是研究的热点。通过利用浸渍法制备不同铬（Cr）负载量的Cr_x/SSZ-13系列催化剂,采用氮气物理吸附、氨程序升温脱附（NH₃-TPD）、二氧化碳程序升温脱附（CO₂-TPD）、氢气程序升温还原（H₂-TPR）、紫外-可见吸收光谱（UV-Vis）以及高角度环形暗场-扫描透射电镜（HAADF-STEM）与耦合能谱分析（EDX-Mapping）等方法对催化剂进行了物性表征,并用微型固定床反应器评价催化剂对乙烷氧化脱氢制乙烯的催化性能,最终建立了Cr/SSZ-13催化剂的构效关系。研究发现,当n（二氧化硅）/n（氧化铝）=10时,Cr_1.5/SSZ-13-10催化剂上含有丰富的Cr³⁺物种,其中配位不饱和Cr³⁺是优异的脱氢活性位,有利于二氧化碳氧化乙烷脱氢反应的进行。因此,Cr_1.5/SSZ-13催化剂在650 ℃时表现出优异的催化性能,即二氧化碳转化率和乙烷转化率分别达到26.41%和53.2%,乙烯产率为38.83%。     

Effect of supports on catalytic activity of chromium oxide-based catalysts in the dehydrogenation of propane with CO2

Dehydrogenation of propane in the presence and absence of CO₂ over CrO_x/SiO₂ and CrO_x/Al₂O₃ catalysts with Cr loading between 0.7–20.4 wt% was discussed. It was found that the nature of support strongly effects on the catalytic performance in the dehydrogenation with CO₂. Over the CrO_x/SiO₂ catalyst CO₂ enhance the propene yield, whereas over the CrO_x/Al₂O₃ catalyst the yield and selectivity of propene in the presence of CO₂ strongly decrease. The effect of steam on catalytic performance of the tested catalysts was also discussed.     

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.     

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.     

Non-oxidative dehydrogenation of ethane to ethylene over chromium catalysts prepared from layered double hydroxide precursors

Non-oxidative dehydrogenation of ethane into ethylene at 700 °C over reductively pretreated Cr–Mg–Al and Cr–Mg mixed oxide catalysts has been studied. The catalysts were prepared from layered double hydroxide (LDH) precursors that contained various species of chromium (i.e., cationic Cr(III), complex of Cr(III) with an anionic chelating agent, and chromate anion). Synthesized materials were characterized with powder X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy techniques. It was shown that the surface area of the LDH-derived mixed oxides, their catalytic performance, coking ability, and susceptibility to sintering were highly dependent on the method used for introducing chromium into the LDH precursors of the catalysts.     

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.     

Promoting effect of carbon dioxide on the dehydrogenation and aromatization of ethane over gallium‐loaded catalysts

Ga₂O₃ and Ga₂O₃/TiO₂ catalysts were found to be effective agents for the dehydrogenation of ethane to ethene in the presence of carbon dioxide at 650 °C. The activity of the Ga₂O₃ and Ga₂O₃/TiO₂ catalysts in the presence of CO₂ was 2–4 times higher than that without CO₂. Ethene yields reached ca. 20–25% and selectivity was ca. 70–90% at 650°C in the 17% ethane and 83% CO₂ feed at an SV of 9,000 ml/(g‐cat h). The presence of CO₂ markedly promoted dehydrogenation of ethane over Ga₂O₃ and Ga₂O₃/TiO₂ catalysts. Furthermore, the promoting effect of CO₂ on the aromatization of ethane and ethene over a Ga₂O₃+H/ZSM‐5 catalyst was also observed above 650 °C. Aromatics yields were higher than those without CO₂. This revised version was published online in July 2006 with corrections to the Cover Date.