【作者】 李凤梅；

【导师】 赵永祥； 王永钊；

【作者基本信息】 山西大学 ， 物理化学， 2012， 硕士

【摘要】 CO甲烷化不但在合成氨、石油化工制氢方面得到广泛应用,而且在其他许多方面也具有重要的应用价值,如燃料电池中氢气纯化；城市煤气中CO解毒以提高其热值；F-T合成中避免甲烷产生的研究等；尤其是近年来利用焦炉煤气甲烷化以及劣质煤经气化、甲烷化合成代用天然气,已成为学术界和产业界共同瞩目的一个研究课题。同时,在理论研究方面,由于该反应体系简单而常被用作研究甲烷化催化剂的探针反应。在CO甲烷化催化剂中,贵金属Ru催化活性最高,但由于价格昂贵,使其应用受到限制；Ni具有较好的活性,且价格相对低廉,大多数富氢气体中少量CO的甲烷化过程都普遍使用镍基催化剂。为了提高催化剂的催化性能,在催化剂中加入适宜助剂可谓一种有效的方法。常用的助剂有碱金属、碱土金属以及稀土金属氧化物,其中Ce02由于具有良好的储放氧能力、氧化还原性以及分散表层活性组分等特性而在催化领域广泛受到青睐。Si02气凝胶具有小粒径、高比表面积、高孔隙率等特性,是一种性能优良的催化剂载体。本课题组前期研究工作表明,Ni/SiO2催化剂具有较好的CO甲烷化催化活性,本文在前期工作的基础上,采用等体积浸渍法制备了一系列Ni/SiO2和Ni-M/SiO2(M=Ce、 Co、 Cu)催化剂,考察了不同助剂对Ni/SiO2催化剂CO甲烷化催化活性影响,同时进一步优化了Ni-Ce/SiO2催化剂的各种制备条件(包括不同Ni/Ce比、Ce含量、浸渍顺序等)。在此基础上,通过N2-physisorption、 XRD、 H2-TPR、 TPD、 TPSR等手段对催化剂的结构和表面性质进行表征,深入探讨了Ce助剂的引入对催化剂上甲烷化反应物与产物分子吸脱附行为的影响。本文最后还考察了反应工艺条件(包括空速、反应温度、原料气中CO含量)对Ni-Ce/SiO2催化剂甲烷化催化活性的影响,以及该催化剂的耐热稳定性和寿命。主要结果如下：1.助剂Ce的添加能有效提高Ni/SiO2催化剂的CO甲烷化活性。其中,7wt%Ni-2wt%Ce/SiO2表现出优于7wt%Ni/SiO2和13wt%Ni/SiO2的催化性能,其催化CO甲烷化反应起燃温度和完全转化温度分别为190℃和230℃。2.对7wt%Ni/SiO2和7wt%Ni-2wt%Ce/SiO2催化剂进行结构和表面性质表征,结果表明,将Ce引入Ni/SiO2催化剂后,NiO、 CeO2和Si02三者之间产生了相互作用,虽对催化剂的织构特征影响不大,但显著促进了催化剂中活性镍物种的分散,减弱了活性组分与载体间的相互作用,增加了活性比表面积,并促使在催化剂表面形成了新的中等强度的CO吸附中心,增强了催化剂对CO的吸附活化能力,显著提高了催化剂的CO甲烷化活性。3.在针对7wt%Ni-2wt%Ce/SiO2催化剂CO甲烷化反应工艺条件、耐热稳定性及寿命考察实验中发现,在空速由3000h1提高到10000h-1的过程中,催化剂上CO转化率略有下降；在考察的反应温度范围内(100-640℃),该催化剂具有宽的反应活性温度区域；在550℃高温下反应后催化剂耐热稳定性良好,在240℃、7000h-1、1%CO的评价条件下,催化剂在近240h的寿命考察实验中活性未见下降。更多还原

【Abstract】 Carbon monoxide methanation not only has been widely used in these aspects such as hydrogen preparation in synthesis of ammonia and petroleum chemicals, but also has important applications in other many fields. For example, hydrogen purification in fuel cells; improvement of the calorific value of city gas and the study on avoiding generation of methane in F-T synthesis and so on. Especially in recent years, the synthesis of the substitute natural gas through the methanation of coke oven gas or the gasification and methanation of the low quality coal has attracted a great deal of attention in aeademia and industry fields. Meanwhile, in the theoretical research aspect, CO methanation is ofen used as a probe reaction to study the methanation catalyst beeause it is a simple reaction system.Among the catalysts for CO methanation, noble-metal Ru catalytic activity is the highest, but its expensive price makes its application limited. However, Ni-based catalyst is widely used for the removal of a small amount of CO in hydrogen-rich gas because of its higher catalytic activity and lower price. In order to improve the catalytic performance of catalyst, adding suitable promoters in catalyst has been considered as an effective way. Alkali metals, alkaline earth metals and rare earth metal oxides are ofen used as catalyst promoters. Specially, CeO2is widely favored in the catalytic field because of its excellent storage and supply oxygen capacity, oxidation-reduction quality and the characteristics of dispersing the surface active component, etc.SiO2aerogel has been used as an excellent catalyst carrier because of its small size, high specific surface area, high porosity and other properties. Our previous studies suggested that the Ni/SiO2catalyst possessed higher catalytic activity for CO methanation. Therefore, in this paper, a series of Ni/SiO2and Ni-M/SiO2(M=Ce、Co、 Cu) catalysts were prepared by incipient-wetness impregnation method, and the catalytic activity was investigated. The effects of preparation conditions (including different Ni/Ce ratios, Ce loading, impregnation orders, etc.) on the CO methanation activity of the Ni-Ce/SiO2catalyst were also studied. On this basis, the structure and surface properties of the catalysts were investigated by N2-physisorption, XRD, H2-TPR, TPD and TPSR techniques and so on, and the effect of the addition of Ce promoter on the absorption and desorption behaviors of the methanation reactants and product was discussed thoroughly. At last, the influence of technological conditions (such as space velocity, reaction temperature, CO content in feed gas) on the catalytic activity of the Ni-Ce/SiO2catalyst, and heat-resistant stability and lifetime were investigated. The main results were as follows:1. The addition of Ce promoter remarkably enhanced the catalytic activity of Ni/SiO2catalyst for CO methanation. The catalytic activity of the7wt%Ni-2wt%Ce/SiO2was higher than that of the7wt%Ni/SiO2and13wt%Ni/SiO2, and its light-off temperature and the lowest complete conversion temperature was190℃and230℃, respectively.2. The structure and surface properties of the7wt%Ni/SiO2and7wt%Ni-2wt%Ce/SiO2were characterized. The results showed that the interaction was generated among NiO, CeO2and SiO2due to the additon of Ce, which did not significantly change the texture characteristics of the catalyst, but markedly promoted the dispersion of the active Ni species, decreased the interaction between the active component and support, increased the active surface areas. Furthermore, new moderate intensity CO adsorption sites were formed on the surface of the7wt%Ni-2wt%Ce/SiO2catalyst. As a result, the catalyst owned higher adsorption and activation capacity toward CO, and exhibited higher catalytic activity for CO methanation.3. In the study of the technological conditions, heat-resistant stability and lifetime on the7wt%Ni-2wt%Ce/SiO2catalyst, we found that in the course of space velocity from3000h-1to10000h-1, CO conversion rate slightly decreased; In the range of100-640℃, the catalyst had wider reaction activity temperature range; The catalyst possessed higher heat-resistant stability after reaction at550℃, and its activity was not declined in about240h lifetime test experiment under the conditions of240℃,7000h-1,1%CO.更多还原