【作者】 王晓琳；

【导师】 栾涛；

【作者基本信息】 山东大学 ， 工程热物理， 2015， 硕士

【摘要】 由温室效应带来的剧烈的气候变化已经引起了广泛的关注,如何减少温室气体的排放吸引了大众视线,甲烷二氧化碳重整反应能将这两种温室气体同时转化为氢气一氧化碳合成气,有利于下一步的工业合成。该反应不仅减弱了温室效应的影响,还能提供大量化工产品,具有相当可观的环境和经济效益。鉴于催化剂积碳所造成的失活,该过程在工业上广泛应用有一定的困难,开发抗积碳的稳定催化剂引起了广泛的关注。本文以自主研制的镍钴双金属催化剂作为研究对象,对制备条件、还原条件以及反应条件对催化剂催化甲烷二氧化碳重整合成气反应的影响进行了分析研究。本实验采用沉淀法制备了不同煅烧温度下的Ni-Co/AlMgOx催化剂,使用XRD、TPR等表征技术分析催化剂的结构及还原能力,发现煅烧温度对催化剂的结构有显著的影响,随着煅烧温度的增加,金属组分和载体之间的相互作用增强,由镍钴氧化物开始转变为尖晶石结构,但同时其颗粒度也会有所增加,适宜的煅烧温度既能使更多的活性组分被还原,也能维持稳定的甲烷转化反应,实验结果表明煅烧温度为800℃时催化剂具有良好的特性。为了研究还原条件对催化剂性能的影响,分别改变还原时间、还原温度、还原方式等,开展了催化剂活性实验研究。实验研究发现,程序升温还原相比于等温还原,催化剂更稳定、活性更好；还原温度会影响催化剂活性组分和载体的性质,进一步影响两者之间的相互作用,还原温度低,部分活性组分未还原,活性低,而还原温度过高会引起活性组分的聚集,使分散度降低,活性减弱。还原时间同样会影响催化剂的还原效果,一个适宜的还原时间不仅能提高活性组分的分散度,还能增加活性组分的稳定性。为了进一步提高甲烷、二氧化碳的转化活性和稳定性,考察了反应条件变化与重整反应性能之间的相关关系,包括催化剂粒径、空速、反应温度、原料气比例、稳定性及再生性等。实验结果显示,催化剂粒径的分布在一定程度上会影响催化剂表面活性物种的扩散,进而影响催化反应的转化率和产物的选择性；当催化剂固定时,进口流速越大,意味着单位时间流过催化剂的反应物越多,在床层的停留时间越短,反应越不充分,所以在一定程度上降低空速有利于提高转化率,但当空速过低时,要达到相同的处理量就要增加催化剂的用量,对于固定的反应装置,有一定的体积局限性,所以需要根据设备和所要达到的转化率合理的选择空速。甲烷二氧化碳重整反应为强吸热反应,温度越高,越有利于反应的进行,但是温度升高,同样会引起副反应的增加,因此,在增加转化率的基础上要控制副反应的发生,需要选择一个合适的反应温度；增加反应物浓度时,反应有利于向减小该反应物浓度的方向发展,所以当增加甲烷的浓度时,反应会向正反应方向进行,二氧化碳消耗增加,转化率升高,但对于甲烷来讲,浓度是在升高的,反应平衡的移动不能很好地削弱这种影响,与旧体系相比,浓度还是增加的,所以甲烷的转化率会降低,反之亦然。本研究还初步探究了还原性气氛对催化剂再生的可行性,实验证明,经还原气氛处理后,催化剂活性得到一定程度的改善。该催化剂在长期的活性测试实验中有卓越的表现,长达180h内没有观察到明显的失活现象,仍保持高活性和良好的稳定性。更多还原

【Abstract】 The dramatic climate change caused by the greenhouse effect has brought about wide attention, as a consequence, the way of decreasing the emissions of greenhouse gas has attracted the public. It is probable to transform two gases (CH4 and CO2) into hydrogen and carbon monoxide syngas at the same time by the method of methane reforming carbon dioxide reaction, in this situation, it is conducive to the industrial production. This reaction not only reduce the influence of the greenhouse effect, also can provide a large amount of chemical products. Furthermore, it brings considerable environmental and economic benefits. However, the process has not found wide industrial application due to severe catalyst deactivation, basically caused by carbon formation. Therefore, it is of great interest to develop stable catalysts without severe deactivation. This work is primarily focused on nickel-based catalysts to investigate the influence of preparation conditions、reduction conditions and reaction conditions on catalysts performance.The designed catalysts are prepared under different calcination temperature using co-precipitation method,the Ni-Co/AlMgOx catalysts are characterized using various techniques such as XRD, TPR to analyse the structure and reduction ability of catalysts, the result shows:calcination temperature has important impacts on the performance of Ni-Co/AlMgOx catalysts, along with the calcination temperature increasing, the interaction between metal component and support enhances, spinel structures appear, but the particle size also increases,a suitable calcination temperature not only make more reduction of active component, also can maintain stable reaction, so a calcination temperature of 800℃ is recommended.In order to research reduction condition on catalysts performance, we change the reduction time、temperature and methods. The research finds, compared with isothermal reduction, temperature programmed reduction is better; reduction temperature influences the active component and support properties, then affects the interaction between the two, when temperature is low, part of the active component can not be reduced, reactivity is low, on the contrary, high temperature can rise accumulation of active component and reduce the dispersion; reduction time also influences the performance, a right time can increase the metal dispersion and the stability.Further investigation on Ni-Co/AlMgOx catalysts shows that reaction conditions can significantly affect catalyst performance, including particle size、space velocity、 reaction temperature、feed gas ratio、stability and regeneration.The result indicates:to a certain extent,catalyst particle size distribution affects the spread of catalyst surface active species, thus affects catalytic reaction conversion rate and product selectivity; when the catalyst is fixed, the greater the import flow velocity, that means more gases per unit time through the catalyst, the shorter time on the bed, the reaction is inadequate, so reducing space velocity can improve conversion, but when the velocity is too low, in order to achieve the same capacity,the amount of catalyst needed is more, for the fixed device,the volume limitations are certain, so we should choose the suitable speed based on the equipment and wished conversion; methane reforming carbon dioxide reaction is highly endothermic, the higher the temperature is, the better performances are, but the chance of side reactions increases at higher temperatures, such as carbon formation reaction, so we should choose a better temperature to increase the conversion and control side reactions; when the reactants are increased, the reaction is tend to the direction of reducing the reactants, the conversion of CO2 improves with CH4 concentration increasing, but for CH4,concentration is high, reaction equilibrium motion can’t weaken the effect well, so the conversion of CH4 drops, and vice versa; a preliminary exploration on the feasibility of catalyst regeneration with reducing atmosphere carried out, after reducing atmosphere treatment, the catalyst activity has been improved to a certain degree, in order to achieve better results, however, it still need further detailed inspection.This catalyst has superior performance in terms of activity and stability in long-term research,no significant inactivation phenomenon is observed within 180h,it also remains high activity and good stability.更多还原