Coupling dehydrogenation of isobutane in the presence of carbon dioxide over chromium oxide supported on active carbon

The dehydrogenation of isobutane （IB） to produce isobutene coupled with reverse water gas shift in the presence of carbon dioxide was investigated over the catalyst Cr2O3 supported on active carbon （Cr2O3/AC）. The results illustrated that isobutane conversion and isobutene yield can be enhanced through the reaction coupling in the presence of carbon dioxide. Moreover, carbon dioxide can partially eliminate carbonaceous deposition on the catalyst and keep the active phase （Cr2O3）, which are then helpful to alleviate the catalyst deactivation.     

Kinetics of the Oxidative Dehydrogenation of Propane over a VMgO Catalyst

The reaction kinetics of the oxidative dehydrogenation of propane was studied at 475-550℃ over a VMgO catalyst. Vanadium-magnesium-oxides are among the most selective and active catalysts for the dehydrogenation of propane to propylene. Selectivity to propylene up to about 60% was obtained at 10% conversion, but the selectivity decreased with increasing conversion. No oxygenates were detected, the only by-products were CO and CO2. The reaction rate of propane was found to be first order in propane and close to zero order in oxygen, which is in agreement with a Mars van Krevelen mechanism with the activation of the hydrocarbon as the rate determining step. The activation energy of the conversion of propane was found to be 122±6 kJ/mol.     

Formaldehyde intermediate participating in the conversion of methanol to aromatics over zinc modified H-ZSM-5

Metal-modified H-ZSM-5 has a high selectivity of aromatics in methanol to aromatics(MTA)reaction,which is often attributed to the metal promoting the aromatization of intermediate olefins.However,the effect of methanol dehydrogenation on aromatics formation over these catalysts is rarely studied.Here,we report that HCHO,which is formed by methanol dehydrogenation over Zn/H-ZSM-5 prepared by Zn impregnation,can participate in the synthesis of aromatics.Methanol conversion can produce more aromatics than olefins(propylene or ethylene)conversion over Zn/H-ZSM-5,indicating the conventional MTA pathway including methanol-to-olefins and olefins-to-aromatics is not complete.Moreover,an MTA mechanism including the conventional pathway and the methanol and HCHO coupling pathway is systematically proposed.     

Molecular catalysis for the steam reforming of ethanol

In this paper,the application of molecular catalysis for steam reforming of ethanol(SRE)is reviewed.Eight metals(Ni,Co,Cu,Pt,Rh,Pd,Ir and Ru)have shown high catalytic activity for SRE.Among them Ni and Rh are very promising because of high d character in the metal bond and low metal-oxygen bonding(vs.metal-carbon).They can effectively promote C–C bond cleavage in the rate-determining process during SRE.However,Rh is weak in water-gas-shift so that CH4 and CO become the main by-products at low reaction temperatures,while Ni catalysts suffer from rapid deactivation due to coking and sintering.Two low-temperature CO-free catalysts have been developed in our lab,namely Rh-Fe/Ca-Al2O3 and carbonyl-derived Rh-Co/Ce O2,in which the presence of iron oxide or Co can promote water-gas-shift reaction and significantly improve the SRE performance.On the other hand,adding 3 wt%Ca O to Ni/Al2O3 can greatly improve the catalyst stability because the Ca modification not only increases Ni concentration on the Ni/Ca-Al2O3 surface and 3d valence electron density,but also facilitates the water adsorption and coke gasification via water-gas-shift.The availability of abundant surface OH groups helps the formation and conversion of adsorbed formate intermediate.Hence,ethanol reaction on Ca-Al2O3-supported Ni,Pt,Pd and Rh catalysts are found to follow the formate-intermediated pathway,a new reaction pathway alternative to the traditional acetate-intermediated pathway.     

Effect of MgO promoter on Ni-based SBA-15 catalysts for combined steam and carbon dioxide reforming of methane

A series of Ni/SBA-15 catalysts with Ni contents ranging from 5 wt% to 15 wt%, as well as another series of 10%Ni/MgO/SBA-15 catalysts, in which the range of the MgO content was from 1 wt% to 7 wt%, were prepared, and their catalytic performances for the reaction of combined steam and carbon dioxide reforming of methane were investigated in a continuous flow microreactor. The structures of the catalysts were characterized using the XRD, H2-TPR and CO2-TPD techniques. The results indicated that the CO selectivity for this reaction was very close to 100%, and the H2/CO ratio of the product gas could be controlled by changing the H2O/CO2 molar ratio of the feed gas. The simultaneous and plentiful existing of steam and CO2 had a significant influence on the catalytic performance of the 10%Ni/SBA-15 catalyst without modification. After reacting at 850 °C for 120 h over this catalyst, the CH4 conversion dropped from 98% to 85%, and the CO2 conversion decreased from 86% to 53%. However, the 10%Ni/3%MgO/SBA-15 catalyst exhibited a much better catalytic performance, and after reacting for 620 h, the CO2 conversion over this catalyst dropped from 92% to around 77%, while the CH4 conversion was not decreased. Oxidation of the Ni0 species as well as carbon deposition during the reaction were the main reasons for the deactivation of the catalyst without modification. On the other hand, modification by the MgO promoter improved the dispersion of the Ni0 species, and enhanced the CO2 adsorption affinity which in turn depressed the occurring of carbon deposition, and thus retarded the deactivation process.     

多相催化体系的反应机理和失活模式(英文)

Solving the problem of catalyst deactivation is essential in process design. To do this, various aspects of the kinetics of processes with catalyst deactivation, and their different mechanisms, are discussed. Catalyst deactivation often cannot be avoided, but more knowledge on its mechanism can help to find kinetic means to reduce its harmful consequences. When deactivation is caused by coke, the generation of coke precursors is the determining step in the deactivation kinetics. Different types of deactivation were distinguished that lead to different evolution of the process. The phenomenon of non-uniform coking can be linked to catalyst surface non-uniformity. For the class of catalysts with more than one type of active sites, an explanation was suggested for the observed trends in the deactivation modes. For catalytic proc-esses using catalyst particles of industrial size, the influence of intraparticle diffusion resistance is important. The analysis showed that for a number of processes, the decrease of the reaction rate due to deactivation is less under diffusion control. For certain reaction mechanisms, there exist operation conditions where the rate of the process under diffusion control exceeds the rate in the kinetic control regime. A signifi-cant problem is the change of selectivity in the course of catalyst deactivation. The selectivity may either decrease or increase, and depends on the reaction mechanism during deactivation. The changes are larger when there is no diffusion resistance. The intentional poisoning of catalysts and its influence on catalyst activity and selectivity for the process of ethylene oxide production was discussed.     

Direct conversion of natural gas to higher hydrocarbons:A review

Direct conversion of methane to higher hydrocarbons is an effective process to solve the problem of natural gas utilization. Although remarkable progress has been achieved on the dehydro-aromatization of methane (DAM), low conversion caused by severe thermodynamic limitations,coke formation, and catalysis deactivation remain important drawbacks to the direct conversion process. Molybdenum catalysts supported on HZSM-5 type zeolite support are among the most promising catalysts. This review focuses on the aspects of direct methane conversion, in terms of catalysts containing metal and support, reaction conditions, and conversion in different types of reactors. The reaction mechanism for this catalytic process is also discussed.     

Kinetic study of propane dehydrogenation and catalyst deactivation over Pt-Sn/Al2O3 catalyst

The kinetics of propane dehydrogenation and catalyst deactivation over Pt-Sn/Al2O3 catalyst were studied.Performance test runs were carried out in a fixed-bed integral reactor.Using a power-law rate expression for the surface reaction kinetics and independent law for deactivation kinetics,the experimental data were analyzed both by integral and a novel differential method of analysis and the results were compared.To avoid fluctuation of time-derivatives of conversion required for differential analysis,the conversion-time data were first fitted with appropriate functions.While the time-zero and rate constant of reaction were largely insensitive to the function employed,the rate constant of deactivation was much more sensitive to the function form.The advantage of the proposed differential method,however,is that the integration of the rate expression is not necessary which otherwise could be complicated or impossible.It was also found that the reaction is not limited by external and internal mass transfer limitations,implying that the employed kinetics could be considered as intrinsic ones.     

Microcalorimetric Adsorption of Alumina Oxide Catalysts for Combination of Ethylbenzene dehydrogenation and carbon Dioxide Shift-reaction

Styrene (STY) is now produced industrially in fairly large quantities by the dehydrogenation of ethylbenzene (EB) using promoted iron oxide catalyst with superheated steam. In this case, small amount of carbon dioxide formed as a by-product was known to inhibit the catalytic activity of commercial catalyst. Recently, there have been some reports which carbon dioxide showed positive effects to promote catalytic activities on the reaction over several catalysts. In this study, we attempted to …     

Effects of Temperature and Catalyst to Oil Weight Ratio on the Catalytic Conversion of Heavy Oil to Propylene Using ZSM-5 and USY Catalysts

It is useful for practical operation to study the rules of production of propylene by the catalytic conversion of heavy oil in FCC (fluid catalytic cracking). The effects of temperature and C/O ratio (catalyst to oil weight ratio) on the distribution of the product and the yield of propylene were investigated on a micro reactor unit with two model catalysts, namely ZSM-5/Al2O3 and USY/Al2O3, and Fushun vacuum gas oil (VGO) was used as the feedstock. The conversion of heavy oil over ZSM-5 catalyst can be comparable to that of USY catalyst at high temperature and high C/O ratio. The rate of conversion of heavy oil using the ZSM-5 equilibrium catalyst is lower compared with the USY equilibrium catalyst under the general FCC conditions and this can be attributed to the poor steam ability of the ZSM-5 equilibrium catalyst. The difference in pore topologies of USY and ZSM-5 is the reason why the principal products for the above two catalysts is different, namely gasoline and liquid petroleum gas (LPG), repspectively. So the LPG selectivity, especially the propylene selectivity, may decline if USY is added into the FCC catalyst for maximizing the production of propylene. Increasing the C/O ratio is the most economical method for the increase of LPG yield than the increase of the temperature of the two model catalysts, because the loss of light oil is less in the former case. There is an inverse correlation between HTC (hydrogen transfer coefficient) and the yield of propylene, and restricting the hydrogen transfer reaction is the more important measure in increasing the yield of propylene of the ZSM-5 catalyst. The ethylene yield of ZSM-5/Al2O3 is higher, but the gaseous side products with low value are not enhanced when ZSM-5 catalyst is used. Moreover, for LPG and the end products, dry gas and coke, their ranges of reaction conditions to which their yields are dependent are different, and that of end products is more severe than that of LPG. So it is clear that maximizing LPG and propylene and restricting dry gas and coke can be both achieved via increasing the severity of reaction conditions among the range of reaction conditions which LPG yield is sensitive to.     

CO2选择性氧化乙苯制苯乙烯

本文评述了近年来国内外利用温室气体CO₂选择性氧化乙苯制苯乙烯的研究进展.和乙苯直接脱氢法相比,新工艺不仅能降低反应温度,大幅度降低能耗,还能在一定程度上抑制催化剂的失活.氧化铝负载的Fe系催化剂和活性炭负载的La等过渡金属改性的V系催化剂具有较好的催化活性.CO₂对乙苯脱氢的显著促进作用要归因于金属氧化物催化剂的氧化还原机制以及乙苯脱氢和逆水煤气变换反应耦合的协同作用.尽管新工艺显示了良好的应用前景,但在将来的研究工作中还要强化催化剂失活机理的研究,开发新型高效催化剂并对新工艺的成本进行详细的评估。     

Microcalorimetric Adsorption of Alumina Oxide Catalysts for Combination of Ethylbenzene dehydrogenation and carbon Dioxide Shift-reaction

Styrene (STY) is now produced industrially in fairly large quantities by the dehydrogenation of ethylbenzene (EB) using promoted iron oxide catalyst with superheated steam.In this case, small amount of carbon dioxide formed as a by-product was known to inhibit the catalytic activity of commercial catalyst. Recently, there have been some reports which carbon dioxide showed positive effects to promote catalytic activities on the reaction over several catalysts.In this study, we attempted to combine the dehydrogenation of EB to STY with the carbon dioxide shift-reaction. The combine reaction (EB + CO2 → STY + H2O + CO) can be considered as one of the ways of using CO2 resources and can yield simultaneously STY and Carbon oxide.Alumina oxide catalysts such as Al2O3, Na2O/Al2O3 and K2O/Al2O3 were prepared by the usual impregnation method with an aqueous solution of NaNO3 and KNO3, and then calcined at 650℃ for 5 h in a stream of air. The reaction condition is 600℃, flow of CO2 38ml/mon and space velocity (EB) 1.28h-1.     

CO偶联临氢反应Pd-Fe/Al2O3催化剂的XPS研究

 利用XPS及氩离子溅射等技术对CO偶联和临氢反应中所用催化剂\r\n表面活性组分和助剂的含量及其化学状态进行了分析，并通过测定氢在\r\n催化剂表面的化学吸附，以及氢浓度对催化剂活性的影响，探讨了CO偶\r\n联反应中催化剂临氢失活的主要原因．XPS表征结果表明，CO偶联反应\r\n中催化剂活性组分以Pd0和Pd2＋形式共存；而临氢反应后仅以Pd0形式\r\n存在，助剂FeO从催化剂的内部向表面迁移且有少量Fe2＋转变为Fe3＋\r\n．催化剂临氢失活的主要原因是H2在活性组分Pd及助剂Fe（主要是FeO\r\n）表面均可形成解离吸附，形成的金属氢化物可在低活化能条件下发生\r\n迁移．这种迁移有利于副产物乙醇的生成，从而削弱了CO偶联主反应，\r\n催化剂表面活性组分Pd的相对含量减少，并几乎处于钝化状态，导致临\r\n氢反应中CO转化率、草酸二乙酯选择性及空时收率均下降．停止通入H\r\n2后，催化剂的活性可恢复至正常状态．     

CO2 气氛下 MCF 负载氧化钒催化剂上乙苯脱氢反应

 以介孔氧化硅泡沫 MCF 为载体合成了一系列负载型氧化钒催化剂 (V 含量为 2%?10%). 采用 N2 吸附、X 射线衍射和 H2 程序升温还原对 V/MCF 催化剂的结构和织构性质进行了表征, 并评价了催化剂在 CO2 气氛下的乙苯脱氢性能. V/MCF 催化剂具有较高的乙苯脱氢活性, 其中 V 含量为 6% 的催化剂具有最高的反应活性. V/MCF 催化剂的乙苯脱氢活性显著高于 V/MCM-41, 这是由于前者具有较高的可还原性以及较好的扩散性能. CO2 气氛下的乙苯转化率明显高于 N2 气氛下的, 这归因于 CO2 与乙苯发生氧化脱氢, 并通过逆水煤气变换反应在线除去脱氢反应生成的氢.     

纳米Cr2O3系列催化剂上CO2氧化乙烷脱氢制乙烯反应

 采用溶胶－凝胶法和共沸蒸馏法耦合技术制备了纳米Cr2O3催化剂，并采用共沉淀法和共沸蒸馏法耦合技术制备了纳米Cr2O3／Al2O3，Cr2O3／ZrO2和Cr2O3／MgO复合催化剂．应用BET，XRD，XPS，TPR和TEM等物理化学方法对催化剂的结构和物化性质进行了表征，并考察了该系列催化剂上CO2氧化乙烷脱氢制乙烯的反应性能．结果表明，纳米Cr2O3催化剂上乙烷和CO2的转化率均明显高于常规Cr2O3催化剂，但乙烯的选择性低于常规Cr2O3催化剂；纳米复合催化剂中的复合成分显著影响催化剂的催化性能．其中，10％Cr2O3／MgO纳米复合催化剂在温度为973K时，乙烷转化率和乙烯选择性分别可达到61．54％和94．79％．纳米催化剂表面Cr的还原性以及Cr6＋／Cr3＋比值是影响乙烷转化率和乙烯选择性的重要因素．     

Role of carbon dioxide in the ethylbenzene dehydrogenation coupled with reverse water–gas shift

The dehydrogenation of ethylbenzene (EB) to styrene (ST) in the presence of carbon dioxide instead of steam is believed to be an energy-saving and environmentally friendly process. However, the reaction mechanism for this coupling system still remains unclear. Therefore, the role of carbon dioxide was investigated by means of catalytic reactions and temperature-programmed desorption (TPD) of carbon dioxide over a series of Fe and V supported catalysts as well as thermodynamic analysis. The results showed that the ethylbenzene conversion is associated with the conversion of carbon dioxide, and that there exists a synergistic effect between the ethylbenzene dehydrogenation and the reverse water–gas shift. However, the difference in the behaviour of the catalysts between the single reverse water–gas shift and the coupled ethylbenzene dehydrogenation may suggest that the catalysts are different in the reaction mechanisms for the coupled ethylbenzene dehydrogenation. Carbon dioxide can be activated through either basic sites or redox sites on the catalyst. Based on these results, the role of carbon dioxide and reaction mechanisms are proposed.     

Molecular-level understanding of the catalytic cycle of dehydrogenation of ethylbenzene to styrene over iron oxide-based catalyst

Dehydrogenation of ethylbenzene (EB) to styrene over iron oxide-based catalyst is an important industrial catalytic process. A great deal of insight into this reaction has been accomplished by surface science studies of the model catalysts. However, molecular understanding still lacks in the removal of the resultant hydrogen from the oxide surface. Employing gas-phase atomic hydrogen, we successfully prepared hydroxyls on an alpha-Fe2O3(0001) film with biphase surface structure under ultrahigh-vacuum conditions. Upon heating, hydroxyls react to form hydrogen and water, the latter of which results in the partial reduction of Fe2O3. These results add important insight into the complete understanding of the catalytic cycle of dehydrogenation of ethylbenzene to styrene over iron oxide-based catalyst.     

水蒸汽对PtSn／Al2O3催化剂结构及反应性能的影响

比较研究了Ａｌ２Ｏ３负载的铂及ＰｔＳｎ催化剂在氮气及水蒸汽稀释条件下的丙烷脱氢性能,并利用ＸＰＳ及氢脉冲吸附对催化剂进行了表征。结果表明,水蒸汽可促使Ｐｔ／Ａｌ２Ｏ３催化剂的铂晶粒烧结。与在氮气氛中相比,在水蒸汽存在下反应显著提高了Ｐｔ／Ａｌ２Ｏ３的丙烷转化率,却降低了丙烯的选择性。另一方面,水蒸汽可调变ＰｔＳｎ／Ａｌ２Ｏ３催化剂的结构,破坏了ＰｔＳｎ／Ａｌ２Ｏ３中与锡相互作用的铂簇团结构。从而导     

Effect of Re and Al 2 O 3 Promotion on the Working Stability of Cobalt Catalysts for the Fischer–Tropsch Synthesis

The results of the working stability studies of cobalt catalysts based on SiO2 and Al2O3 promoted with Re and Al2O3 in the synthesis of hydrocarbons from CO and H2 in continuous tests for 200–300 h are presented. The prepared catalysts were characterized by transmission electron spectroscopy, temperature-programmed reduction with hydrogen, temperature-programmed desorption of CO, and X-ray fluorescence spectroscopy and tested at a temperature 200°C, a pressure of 0.1 MPa, and a GHSV of 100 h–1. It was determined that a cobalt–silica catalyst promoted with Al2O3 had the highest activity. It was established that the addition of Al2O3 to a cobalt–silica catalyst increased the conversion of CO and selectivity for C5+ hydrocarbons and inhibited the agglomeration of Co particles under the action of a reaction atmosphere in the Fischer–Tropsch synthesis. It was found that the initial conversion of CO increased by a factor of 2 upon the introduction of 0.1 wt % rhenium into the Co/γ-Al2O3 catalyst; however, the rate of its deactivation increased in this case due to an almost twofold increase in the size of cobalt particles in the course of synthesis after operation for 300 h.