导　　师： 申文杰;徐奕德

学科专业： 070304

授予学位： 博士

作　　者： ;

机构地区： 中国科学院研究生院

摘　　要： 甲烷在碳氢化合物中具有最高的H//C比,甲烷直接裂解制氢是其直接利用的有效途径之一。相对于铁基、钴基催化剂来说,镍基催化剂在这个反应中表现出较高的积碳收率,文献中所报道的镍基催化剂大都为负载型催化剂。本论文在考察了Ni//CeO2催化剂甲烷裂解活性的基础上,重点研究了非负载型氧化镍催化剂在甲烷裂解过程中的催化性能。考察了制备条件对氧化镍结构、形貌和粒径大小,及其在甲烷裂解反应中的催化活性的影响。借助In situ XRD和HRTEM技术对所制备的非负载型氧化镍催化剂在还原过程、甲烷裂解反应的初始阶段以及完全失活后金属镍粒径大小的变化进行了详细的研究。发现甲烷裂解的活性依赖于金属镍粒子的大小;当金属镍粒子的大小为11 nm时,甲烷裂解过程中的积碳量最高,碳纳米纤维的收率可以达到492 g C//g Ni.,这一结果与目前文献中所报道的最高积碳收率相近;当金属镍粒子的大小增加到20 nm时,积碳量下降到271 g C//g Ni ;当金属镍粒子的大小增加到24 nm时,积碳量仅有3.4 g C//g Ni ;当金属镍粒子的大小增加到26 nm时,则没有甲烷裂解的活性。甲烷裂解初期的积碳不仅使金属镍粒子逐渐长大,而且改变了金属镍粒子的形貌。4.0 nm的氧化镍经氢气还原后得到11 nm的金属镍,金属镍然后在积碳的作用下迅速长大到17-18 nm;同时纤维状的金属镍的形貌发生了明显变化,在碳纳米纤维的顶端以梨形的形式存在。 对于利用乙二醇溶液所制备的氧化镍催化剂,发现随着培烧温度的升高,氧化镍催化剂的粒径大小变化不大/(3.0-8.1nm/),经氢气还原后得到粒径相差不大的金属镍/(9.0～11.0 nm/),其甲烷裂解反应的活性相差不多/(343-398 g C//g Ni/)。另外,将所制备的非负载型氧化镍催化剂用于不同不饱和有机官能团的加氢,在此过程中也表现出了非常好的加氢活性和稳定性。 Methane decomposition into hydrogen and carbon nanofiber is regarded as an effective way to provide hydrogen. Nickel-based catalysts showed much more higher catalytic activity in methane cracking as compared with iron- and cobalt-based catalysts. However, most of the reported nickel catalysts were supported by oxides, such as SiO2, Al2O3, to stabilize the nickel particles, which played critical roles in determining the catalytic activity. In this works, we focused on development of novel Ni catalysts without the presence of support. Calcination /(573～1073 K/) of theα-Ni/(OH/)2 prepared in the solution of ethylene glycol resulted in the formation of nickel oxides with similar fibrous shapes and crystalline size of 3.0～8.1 nm. Metallic Ni crystalline sizes of about 11 nm and fibrous structures were obtained after reduction with hydrogen at 773 K. The effect of preparation conditions on the structure of nickel hydroxide, the morphology of nickel oxide and metallic nickel, the crystallite size and the catalytic activity of methane cracking are studied by HRTEM, XRD, FT-IR, TG etc. The catalytic activity of the pure Ni catalysts for methane decomposition was strongly related to the crystalline sizes. The metallic Ni with crystalline size of about 11 nm showed the highest carbon and hydrogen yields, and the nickel crystalline of about 20 nm gave relatively lower carbon yields. While increasing the nickel crystalline size to about 24 nm led to extremely low catalytic activity, and further increasing up to 26 nm resulted in totally deactivation towards methane decomposition. Further evolution of the metallic nickel particles during

关 键 词： 甲烷 碳纳米纤维 镍 乙二醇

分 类 号： [O643.32]

领　　域： [理学] [理学]