镍基催化焦油重整制氢与碳纳米管生长的耦合作用机理研究

The formation of tar reduces the efficiency of biomass gasification, and is prone to cause clogging and fouling of downstream pipes and equipment. Nowadays, tar problem has become a bottleneck in the development of biomass gasification technology. This project combines catalytic tar reforming with catalytic chemical deposition, and proposes a new idea of using biomass tar as a carbon source to prepare co-production of hydrogen-rich gas and carbon nanotube (CNTs) over Ni-based catalysts. While solving the tar problem, high-grade nanocarbon materials are obtained, thereby improving the economy of gasification system and developing a low-cost preparation method of carbon nanotubes. This process includes catalytic tar reforming and CNTs growth. There exist strong coupling effects between these two processes. It is the key to resolve coupling effects for improving the yield and quality of co-products. Thus in this project, the mechanisms of catalytic reforming reaction and CNTs growth are analyzed by in-situ characterization and other advanced testing techniques. Based on the analysis of their coupling effects, kinetic model of coupling process is conduced, and finally propose comprehensive control methods of optimizing reaction conditions and catalyst modification. Through the research of this project, it can provide an important theoretical basis for the development and application of catalytic reforming of tar to prepare co-production of hydrogen-rich gas and CNTs.

焦油生成降低了生物质气化效率，而且容易在后续设备上冷凝导致堵塞和腐蚀等问题，焦油问题已经成为生物质气化技术发展的瓶颈。本项目将催化焦油重整与催化化学沉积法结合，提出利用生物质焦油作为碳源，镍基催化重整制备富氢气体和碳纳米管共产物的新思路。在解决焦油问题的同时，得到高品位纳米碳材料，从而提高气化系统的经济性并开发一种低成本的碳纳米管制备途径。催化焦油重整制备共产物包括催化重整和碳纳米管生长两个过程，两者之间存在强烈耦合作用，且解析该耦合作用是提高共产物产量和品质的关键。基于此，本项目借助原位表征等先进测试技术深入探究镍基催化重整反应过程和碳纳米管生长演化机理，解析两者之间耦合作用过程机理，从而建立共产物制备的动力学耦合模型，最终提出优化反应条件和催化剂改性的综合调控方法。通过本项目研究，能够为镍基催化焦油重整制备共产物技术的发展和应用提供重要理论基础。

本项目致力于镍基催化焦油重整制氢与碳纳米管生长的耦合作用机理研究。首先，探究了催化重整制氢过程中碳纳米管和无定形碳生成演化特性，发现了总积碳量呈现先增加后趋于稳定的趋势，无定形碳要先于碳纳米管生成，随着反应进行部分无定形碳转化为石墨型碳。然后，根据不同载体催化剂上碳纳米管生长特性，发现了催化剂载体与活性金属之间相互作用强弱决定了碳纳米管顶端生长与底部生长过程的规律，揭示了顶端自生长碳纳米管原位促氢效应，阐明了催化重整制氢与碳纳米管生长两过程的耦合作用机理。最后，利用密度泛函理论和过渡态理论，探究了不同活性晶面上催化裂解、积碳及碳纳米管生成过程中关键步骤的活化能和反应热，发现了Fe-Ni合金比Ni单质与Co-Ni合金表现出更高的催化活性和碳原子迁移速率，促进氢气和碳纳米管共产物的生成。基于以上结果，提出了催化剂配方（Fe/Ni为2）、反应温度（600oC）和水碳比（S/C为2）的调控策略，实现共产物产量和品质的最优化。另外，针对所制备碳纳米管实际应用中难分离的问题，开展了利用电极材料基体泡沫镍作为催化剂载体，在催化重整制氢的过程中原位生长碳纳米管，制备碳纳米管包裹泡沫镍的高性能纳米碳电极材料，该方法无需进行碳纳米管的分离。实验结果表明，原位制备的电极材料表现出优异的电化学性能和稳定性，在超级电容器等领域具有重要应用潜力。