Fe/K催化剂特性及其催化煤热解制碳纳米管机理研究

By using the self-developed Fe/K catalyst, a great amount of carbon nanotubes with smooth wall and uniform diameter were successfully prepared by catalyzed pyrolysis of various types of coals. However, some relative scientific problems have not been recognized systematically and clearly, such as the Fe/K composition, structure, size and its catalytic properties,; the key factors which had influence on the Fe/K catalyzed coal pyrolysis for carbon nanotubes preparation; as well as the mechanism of carbon nanotubes growth . . In order to solve these problems, the following research contents will be carried out in this research: 1. The composition, size and structure properties of Fe/K and its catalytic properties for coal pyrolysis to synthesis carbon nanotubes, the formation mechanism and preparation of high reactivity Fe/K catalyst. 2. The significant factors and essential reasons of Fe/K to catalyze the coal pyrolysis for sythesising the carbon nanotubes 3. The catalytic effect of Fe/K on the coal pyrolysis, the formation mechanism of the precursors of carbon nanotubes and the formation and growth mechanism of the carbon nanotubes during the pyrolysis process.

采用自主研发的Fe/K催化煤热解新方法成功制备出大量管壁光滑、管径均一的碳纳米管。然而，对Fe/K催化剂组成、结构、尺度及其催化特性，影响Fe/K催化煤热解制备碳纳米管关键因素，以及碳纳米管生成生长机理等问题认识不清楚、不系统。针对这些问题，本课题系统开展如下研究：①Fe/K组成、尺度和结构特性及其催化煤热解制碳纳米管的催化特性，高活性Fe/K催化剂的生成规律和制备；②Fe/K催化煤热解制备碳纳米管的关键因素和本质原因；③Fe/K催化剂对煤热解的催化作用，热解过程中中间碳源的生成机理和碳纳米管生成生长的机理。

针对Fe/K催化煤热解制备碳纳米管过程中Fe/K催化剂的组成与碳纳米管生长的构效关系、煤热解高效宏量制碳纳米管的关键因素、Fe/K催化煤热解制碳纳米管碳源形成及碳纳米管的生长机理等科学问题不明确等问题，利用SEM、TG-DTG、XRD、Raman和TEM等分析方法，系统地开展了Fe/K催化剂特性及其催化煤热解制碳纳米管机理研究，主要结论如下：（1）阐明了Fe/K催化煤热解生成碳纳米管的过程规律。Fe/K催化相较于Fe、K单独催化热解产物中碳纳米管的含量显著增大，Fe/K在煤基碳纳米管生长的过程中存在协同作用：Fe原子与C原子在热解时形成Fe-C固溶体，与此同时碳酸钾通过刻蚀无定形碳为其提供了丰富的可用碳原子或碳簇，最终形成大量煤基碳纳米管。（2）提出了“催化剂催化”和“碳纳米管自催化”的共催化作用机制，建立了碳纳米管的“阶梯式生长”模型。在碳纳米管生长过程中，催化剂颗粒表面的石墨烯层由内至外依次生长，沿着碳纳米管生长的方向石墨烯层数逐渐减少，碳纳米管的生长过程符合“阶梯式生长”模型。（3）认识了煤催化热解过程中原生Fe矿物质变迁及其对碳纳米管生长的作用。煤中菱铁矿在KOH催化煤热解过程中的变迁及其催化碳纳米管生长符合FeCO3 → α-Fe → Fe3C + Graphite→ CNTs机制。（4）明确了Fe/K催化煤热解制碳纳米管的关键因素和本质原因。热解温度（A）、升温速率（B）和恒温时间（C）对碳纳米管含量影响的主次顺序是ACB，并提出了K催化剂具有催化甲烷裂解生成碳纳米管和刻蚀煤中固体碳结构为碳纳米管的生长提供碳源的作用。（5）建立了Fe/K催化煤中固相碳结构转化为碳纳米管的机制。在K催化富含菱铁矿的烟煤热解过程中，碳纳米管生成机制为：煤中的芳香C-C、C-H结构将K2CO3、K2O等K组分转化为单质K，然后单质K将醚键C-O-C结构中的碳原子转化为碳原子或碳簇，这些碳原子或碳簇在煤中的催化剂粒子的作用下生成碳纳米管。