核壳双金属复合催化剂的界面结构优化及催化机理研究

Development of metallurgy and demand of energy conservation and environment protection have made the carbon-containing refractories to be lower carbon content. However, low carbon content leads to decreasing of oxidation and thermal shock resistance, which has restricted the refractories further development. In order to solve these issues, this project will calculate the surface atomic state and the stable absorption site of metallic catalyst using density functional theory, and the core-shell bimetallic structure with different d orbit electron and surface atomic state will be established. According to these, the core-shell bimetallic catalyst with specified surface atomic state will be synthesized. The effect of core-shell interfacial structure and electron interaction on the selective absorption of carbide like CxHy and CO and catalytic activity of catalyst will determined. It will confirm the determining step of carbon nanotubes growth as well as the growth model of carbon nanotubes. Subsequently, the correlation between core-shell interfacial structure, process parameters of catalyzing and high temperature properties of low carbon refractories will be established. The aim of the project is to regulate and optimize the interfacial structure of core-shell bimetallic catalyst, and to reveal the mechanism of phenolic resin graphitization and carbon nanotubes growth and improve the high temperature properties of low carbon refractories. The results of this research will provide a theoretical basis and technical thought for improving contents of residual carbon and carbon nanotubes.

冶炼新技术和节能环保使含碳耐火材料逐渐向低碳化发展，而碳含量降低引起材料抗氧化性和热震稳定性急剧下降成为制约该材料发展的主要瓶颈。因此，本项目以核壳双金属复合催化剂为研究对象，采用密度泛函理论分析金属催化剂表面原子状态和碳化物最稳定的吸附位置，借此构建不同d轨道电子结构和表面原子状态的核壳双金属结构，研究核-壳界面结构对CxHy和CO等碳化物选择性吸附和催化活性的影响；分析碳纳米管在酚醛树脂中生长的控制步骤，建立碳纳米管生长模型，确定核-壳界面结构、催化工艺与低碳耐火材料高温抗折强度、抗氧化性和热震稳定性等性能之间的内在联系。本项目旨在调控和优化核壳双金属催化剂的界面结构，揭示它对酚醛树脂催化活性和碳纳米管生长的影响机制，提高低碳耐火材料的高温性能。相关研究成果有助于显著提高低碳耐火材料的残碳量和碳纳米管的生成率，为低碳耐火材料中新型催化剂的设计与调控提供理论基础和借鉴意义。

随着冶炼新技术的发展，含碳耐火材料逐渐向低碳化发展。本项目制备了具有核壳结构的Fe基催化剂，研究了制备工艺、显微结构和催化性能等对碳纳米管合成过程和机理的影响；研究了Fe-Mo和Fe-Ni催化剂对于低碳MgO-C耐火材料结构和力学性能的影响。结论如下：.(1) 前驱体Fe-Mo催化剂以钼酸铁的形式存在，当铁钼摩尔比为1:3时催化剂存在MoO3。随着Mo含量的增加，Fe和Mo的相互作用使部分电子从Fe转移到Mo，使Fe处于缺电子状态，改善了Fe对于烃类气体的吸附，提高了掺杂树脂热解后的石墨化程度。.(2) Fe-Mo二元催化剂原位合成CNTs机理为：当热解温度为500~800℃时，Fe-Mo催化剂分解为Fe2O3和MoO3。Fe2O3在还原气氛下生成纳米铁颗粒并吸附烃类气体在其表面形成沉积态碳；而钼氧化物与吸附在催化剂表面沉积态碳反应生成α-MoC1-x，进而转变为石墨C和β-Mo2C，完成碳原子在催化剂中扩散-析出过程，最后形成碳纳米管。当热解温度高于800℃时，沉积态碳原子在β-Mo2C中根据溶解-析出原理生成碳纳米管。.(3) 通过化学镀镍的方式制备了具有核壳结构的铁镍二元催化剂，在铁镍二元催化剂中，随着内核Fe2O3的添加量减少，包覆层Ni的厚度增加。核壳结构中Fe-Ni产生相互作用并使部分电子从Ni转移到Fe，提高了Ni对于烃类气体的吸附性。随着催化剂中Ni相对含量增加，催化合成CNTs的含量以及石墨化程度呈现先增加后减小。碳纳米管的起始形成温度为500~600℃，且碳纳米管的长度随着热解温度的上升而显著增加；当热解温度高于1000℃时，由于烃类气体分压降低导致碳纳米管长径比降低。.(4) 在低碳MgO-C耐火材料的基质中分别引入Fe-Mo和Fe-Ni催化剂，在材料内部均能催化合成碳纳米管及MgAl2O4晶须，且Fe-Ni催化剂具有更好的催化效果。由于材料中碳纳米管及MgAl2O4晶须的生成，使低碳MgO-C耐火材料试样具有更好的力学性能及热震稳定性。