CO选择性甲烷化的研究进展

CO选择性甲烷化被认为是适用于低温燃料电池的、最具发展潜力的CO深度去除技术,而该技术大规模应用的关键在于高性能负载型催化剂的开发。本文综述了近些年来CO选择性甲烷化的研究进展,以催化剂的选取和评判标准为起点,着重论述了CO和CO₂甲烷化的反应机理、粒径效应以及载体和助剂对催化剂活性和选择性的影响,最后总结了CO选择性甲烷化的研究并对未来的研究方向进行了展望。分析表明,选取合适的活性组分负载量以及载体和助剂可以大幅度提高催化剂的CO甲烷化活性,而通过氯离子改性以及Ru-Ni双金属的制备来控制金属-载体作用界面则是提高催化剂CO甲烷化选择性的关键。指出对甲烷化反应机理的研究和具有长期稳定性催化剂的开发是未来CO选择性甲烷化研究的重点。     

CO、CO_2及其共存体系的甲烷化反应

介绍了甲烷化的反应体系,CO、CO2甲烷化反应的机理;比较了CO体系、CO2体系和CO、CO2共存体系的甲烷化反应特点以及三种反应体系对催化剂的要求;综述了适用于不同体系催化剂的研究进展,并重点介绍了多种催化剂的载体、助剂与活性组分之间的相互作用方式以及几种催化剂对碳氧化物甲烷化反应的催化机理;甲烷化反应的应用方向逐步从合成氨、合成气制天然气向燃料电池、焦炉煤气等方向扩展,对反应体系的研究也由CO甲烷化体系向CO2甲烷化体系和共存体系方向发展;复合载体负载的多金属催化剂成为现在甲烷化催化剂的主要研究方向,纳米颗粒催化剂、等离子体等技术开始应用于甲烷化催化剂。     

CO_2/CO甲烷化催化剂及其反应机理研究进展

概述了CO2/CO加氢制甲烷过程,重点阐述甲烷化催化剂制备方法、催化剂活性组分、助剂和载体对催化剂结构的影响;分析了甲烷化反应机理及甲烷化反应中催化剂失活现象。针对目前甲烷化催化剂现状,提出深入研究甲烷化反应机理、开发耐硫催化剂是甲烷化今后的研究方向。     

CO甲烷化研究进展

介绍了国内外CO制甲烷的工艺开发及应用现状,分析对比了国内外甲烷化催化剂的研究进展和技术特点,综述了助剂、载体以及制备方法对甲烷化催化剂催化性能的影响。     

CO选择性甲烷化催化剂研究进展

经过重整反应等制备的富氢气体中通常含有微量CO,当其用于质子交换膜燃料电池或合成氨反应时,导致活性组分中毒而失活。采用CO选择性甲烷化反应可将CO去除,具有广阔的应用前景。综述富氢气体中CO选择性甲烷化催化剂研究进展,重点包括Ru基催化剂、Ni基催化剂以及Ru-Ni双金属催化剂。     

CO2催化加氢甲烷化研究进展

介绍了CO2加氢甲烷化反应及其热力学性质。从催化剂和反应机理等角度阐述了CO2加氢甲烷化反应研究进展。认为采取全球CO2循环策略系统是降低大气中CO2含量的一条有效途径。     

前驱体对Ru/CeO_2-ZrO_2-Al_2O_3催化剂CO选择性甲烷化的影响

以CeO_2-ZrO_2-Al_2O_3复合氧化物为载体,采用分步等体积浸渍法制备了不同Ru负载量及不同Ru前驱体的催化剂,并考察了这些因素对催化剂CO选择性甲烷化活性及为燃料电池供氢操作温度窗口的影响。结果表明,Ru负载量为1%的催化剂具有较好的CO选择性甲烷化活性及最宽的操作温度窗口;以Ru(NO)(NO_3)_3为前驱体制备的催化剂,Ru金属分散度较差,低温CO甲烷化活性较低,高温CO甲烷化选择性较差,操作温度窗口仅为15℃;以RuCl_3·xH_2O为前驱体制备的催化剂具有良好的CO选择性、甲烷化活性及60℃操作温度窗口,且水洗除氯操作对催化剂性能影响不明显。     

煤制天然气高CO甲烷化的研究进展

煤制天然气是目前煤化工的热门领域,文章主要介绍国内外煤制天然气的研究、开发及应用进展,对比分析了国内外高CO甲烷化催化剂,尤其是Ni基催化剂的研究进展和技术特点、反应器的设计及原理,及高CO甲烷化技术的研究方向。     

可用于富氢重整气中CO消除的负载型Ni基甲烷化催化剂研究进展

富氢重整气中微量CO会引起燃料电池中Pt电极的永久性中毒而影响燃料电池的性能,通过CO甲烷化反应是消除富氢重整气中微量CO的有效方法。介绍了近年来在CO甲烷化Ni基催化剂组成、制备方法和催化机理等方面的研究进展。阐述了载体的性质、稀土和贵金属助剂以及制备方法对CO甲烷化Ni基催化剂性能的影响。研究重点通过优化载体、组成和制备方法制备新型Ni基催化剂,使其在低温下对CO甲烷化反应有着很好的催化活性、选择性和稳定性,同时抑制高温下CO2甲烷化反应和逆水煤气反应的发生。     

负载型Ni基CO甲烷化催化剂研究进展

负载型Ni基催化剂是应用于CO甲烷化反应的重要催化剂,其金属分散度、活性位结构和化学组成是决定催化剂活性与稳定性的关键因素。综述了金属Ni活性中心结构、载体与助剂对负载型Ni基催化剂甲烷化反应活性和稳定性的影响,在提高催化剂活性的基础上,为开发低成本的负载型Ni基催化剂具有重要意义。     

Porous carbon as support for iron and ruthenium catalysts

Iron and ruthenium catalysts have been supported on a porous carbon prepared by pyrolysis and activation of the copolymer Saran. For comparison, a graphitized carbon black (V3G) has also been used as support for both metals. The catalysts have been characterized by chemisorption of H₂ and CO₂ at 298 K (373 K in some cases) and by X-ray line broadening. The hydrogen chemisorption on iron catalysts was very low and increased with adsorption temperature, whereas the CO chemisorption results indicate the formation of subcarbonyl species. However, H₂ and CO uptakes led to similar dispersion values for the ruthenium catalysts. The X-ray results were in good agreement with the chemisorption results except in the case of highly dispersed Fe catalysts. The results obtained in the hydrogenation of CO indicate that in the case of Fe catalysts the highest selectivity toward hydrocarbons was given by the catalyst supported on V3G, with large metal particle size which, at the same time, exhibited a lower decrease in activity with reaction time than the other Fe catalysts with smaller average particle size. The olefin/paraffin ratio is very large for the catalyst prepared from Fe(CO)₅.The Ru catalysts are essentially of the methanation type.     

非晶态Ni-B/MCM-22催化剂上二氧化碳甲烷化的研究

本文采用固定床反应装置考察了非晶态镍基催化剂CO2甲烷化催化反应活性。研究结果表明:以化学还原法制备的非晶态镍基催化剂的二氧化碳甲烷化活性较高;由XRD及TEM结果可知,非晶态镍基催化剂中镍的分散度较高;以MCM-22分子筛为催化剂载体的非晶态镍基催化剂CO2的转化率高于以γ-Al2O3为载体的非晶态催化剂。     

稀土La改性的非晶态Ni基催化剂CO_2甲烷化催化性能的研究

本文采用固定床反应装置考察了稀土镧改性的非晶态镍基催化剂二氧化碳甲烷化催化反应活性。实验结果表明:氧化镧的添加,提高了非晶态镍的晶化温度,阻止了镍的聚集,提高了镍的分散度,从而提高了二氧化碳甲烷化的活性和稳定性。     

ZrO2-Al2O3复合载体负载Ni基催化剂COx甲烷化性能

采用浸渍和粉末压片的方法制备了两种ZrO₂-Al₂O₃复合载体并用于负载Ni基催化剂，并利用氮气等温物理吸附、X射线粉末衍射（XRD）、H₂程序升温还原（H₂-TPR）、扫描电子显微镜（SEM）和透射电子显微镜（TEM）等分析手段对催化剂物化性质进行表征，考察了ZrO₂-Al₂O₃复合载体制备方法及ZrO₂的引入对Ni基催化剂在CO、CO₂和CO-CO₂共存的3种体系下甲烷化反应活性的影响。材料表征和活性测试结果表明，在CO甲烷化体系中，与单一Al₂O₃载体相比，引入ZrO₂的复合载体能有效提高催化剂中Ni物种的分散度从而增强CO甲烷化过程中催化剂活性，且粉末压片法较浸渍法制备的复合载体能有效提高催化剂的还原度，降低还原温度，但前者会大大降低催化剂的比表面积；在CO₂甲烷化体系中，当载体形貌和制备方法相同时，载体的变化对催化剂活性的影响较小，CO₂转化率主要受到制备方法不同引起的物理性质如比表面积变化的影响；在CO-CO₂共存体系中，由于CO在竞争吸附中比CO₂更容易占据活性位点，所以呈现出优先进行CO甲烷化再进行CO₂甲烷化、CO₂的含量先增多后减少的规律。     

生物质合成气甲烷化机理及催化体系研究进展

天然气的供需矛盾促使人们寻找新的天然气资源,其中利用生物质合成天然气（Bio-SNG）的替代技术受到了全世界的关注。在整个工艺过程中,生物质合成气制取甲烷是关键技术,而甲烷化催化剂是其核心要素。简述了近年来生物质合成气甲烷化机理及其催化体系的研究进展,重点讨论了合成气中CO甲烷化、CO₂甲烷化反应机理,以及甲烷化催化剂中活性金属、助剂和载体对CO甲烷化、CO₂甲烷化以及CO与CO₂共存条件下甲烷化反应性能的影响,分析了目前仍存在的主要问题,并指出了进一步研究的发展方向。     

ZtO2晶相形式对Ni-B/ZrO2催化剂CO选择性甲烷化性能的影响

Amorphous Ni-B/ZrO2 catalysts were prepared by coprecipitation-chemical reduction with KBH4 aqueous solution,and various crystalline phase ZrO2(amorphous-ZrO2,tetragonal-ZrO2 and monoclinic-ZrO2) supported Ni-B catalysts were obtained by thermal treatment in 5%H2-N2 stream at different temperature.The effect of ZrO2 polymorphs and the treatment temperature on the catalytic performance for the CO selective methanation were investigated,and the catalysts were characterized by N2 physisorption,Powder X-ray diffraction(XRD), Temperature-Programmed Desorption(CO-TPD and H2-TPD),and Differential Scanning Calorimeter(DSC).The treatment temperature affected strongly the crystalline structure of ZrO2,and the CO methanation activity and selectivity of the Ni-B/ZrO2 catalysts were significantly influenced by the crystalline phase of ZrO2.Of the three forms of ZrO2 polymorphs(amorphou-ZrO2,tetragonal-ZrO2 and monoclinic-ZrO2),the amorphous-ZrO2 supported nickle catalyst showed highest CO methanation activity,attributing in large part to the largest specific surface area and the optimum CO/H2 absorption intensity of the Ni-B/amorphous-ZrO2 catalyst.     

Transient behaviour of an adiabatic fixed-bed methanator—II: Methanation of mixtures of carbon monoxide and carbon dioxide

The transient behaviour of an adiabatic fixed-bed methanator has been studied using the hydrogenation of mixtures of CO and CO₂ at concentrations up to 2·7 vol.% carbon oxide in hydrogen as the test reactions. Responses to disturbances in feed conditions were studied by measuring the axial temperature profile as a function of time. The results show that the dynamic behaviour of the reactor is complicated by the inhibition by CO of the methanation of CO₂.The agreement between theory and experiment was again quite satisfactory: the quasi-homogeneous plug flow model which applied to experiments using binary mixtures of hydrogen and a carbon oxide applies to the data obtained with mixtures of CO, CO₂ and hydrogen, provided that the successive hydrogenation of CO and CO₂ is taken into account. However, it is improbable that the quasi-homogeneous model can be applied to industrial methanation, when the higher temperatures and consequent faster rates of methanation are likely to cause heat and mass transfer limitations. Nevertheless, there is no doubt that response times of but a few seconds must be expected in industrial methanation.     

基于甲烷化反应的催化剂颗粒设计与过程强化

甲烷化反应过程的主要问题是“烧结”和“积炭”。基于甲烷化反应的强放热、减分子特性和对反应机理的认识,从催化剂与反应器的匹配性角度,论述了当前的主要甲烷化工艺、甲烷化催化剂、甲烷化反应及过程强化方法。流化床技术可有效防止催化剂的积炭和烧结,从与流化床反应器匹配的催化剂结构设计源头出发,制备具有耐磨损、易流化、低密度的高活性甲烷化催化剂,是流化床甲烷化发展的一个重要途径。     

Some effects of carbon monoxide in hydroprocessing of heavy feedstocks

Hydroprocessing routes, when utilized for upgrading bituminous feedstocks and heavy oils, represent versatile means for production of additional liquid fuels. Production of pure hydrogen involves expensive gas purification and shift conversion steps so that by-passing these would be economically beneficial. Experiments undertaken to determine the effect of the presence of carbon monoxide (CO) in the hydrogen stream on the hydrocracking of Athabasca bitumen in a high-pressure continuous-flow system showed that CO content up to 50 mol % in the hydrogen feed would not affect thermal hydrocracking detrimentally. The use of a catalyst with stabilizing capability emphasized the apparent non-interference of CO with thermal cracking. On the other hand, significant performance inhibition of molybdenum-containing multi-functional catalysts indicated surface poisoning by CO adsorption which was partially alleviated in the presence of steam. On the addition of water to the feedstock, the latter catalysts caused substantial water-gas shift reaction to take place, accompanied by less extensive methanation. These reactions were less apparent with the other type of catalysts. Depending upon feedstock characteristics it may be possible to incorporate catalytic components allowing the presence of CO in the feed. In the overall evaluation, other important effects of CO presence would have to be examined in connection with the coking propensity of the feedstock and the reactor temperature control.