特定结构和形貌的Fe-C合金纳米催化剂的可控制备及其催化氨分解反应行为

Controlled synthesis of non-noble metal nanocatalysts with tailored structures and morphologies for targeted catalytic performance is one of the main topics in current catalysis research. In this proposal, a catalytic chemical vapor deposition (CCVD) method is proposed to synthesize Fe-C alloy nanocatalysts with tailored structures and morphologies by controlling the growth of carbon nanofibers (CNFs). The influences of the operating conditions of CCVD on the stable surface structures and the surface morphologies of Fe-C alloy nanocatalysts will be studied by combining ab initio atomistic thermodynamics simulation and experiments. The Fe-C alloy nanocatalysts will be used for ammonia decomposition and its activity at low temperatures and stability at high temperatures will be evaluated. DFT calculations will be employed to understand how carbon atoms influence the structures and electronic properties of Fe for increased activity and inhibit the nitridation of Fe for prolonged stability. Microkinetic analysis will be conducted and used to establish LHHW kinetics to understand the kinetic behaviors of Fe-C alloy nanocatalysts with different structures and morphologies. The CCVD method proposed for Fe-based nanocatalysts and the approaches used to understand the structure-performance relationship can also be extended to other non-noble metal catalysts, such as Ni and Co. This research is valuable not only for rational design of Fe-based catalysts with excellent performances, but also for in-depth understanding of the role of C in structural and morphological manipulation of metal catalysts.

特定结构和形貌的非贵金属纳米催化剂的可控制备及其形貌效应是当前催化领域中的热点课题之一。 本申请提出采用CCVD法通过调控纳米碳纤维的生长制备具有特定结构和形貌的Fe-C合金纳米催化剂的新思路。结合从头计算原子级热力学模拟和实验研究，建立反应条件与Fe-C合金稳定结构以及表面形貌的对应关系，以实现特定结构和形貌的Fe-C合金纳米催化剂的可控制备。以氨分解为模型反应体系，考察催化剂的活性和高温稳定性，并结合DFT计算，阐明C原子对催化剂结构特性、电子特性以及氮化过程的影响。通过对氨分解Fe-C合金纳米催化剂的微观反应动力学分析，建立LHHW动力学模型，阐明催化剂结构以及形貌对其动力学行为的影响。 上述调控催化剂结构和形貌的方法也适用于制备可生长纳米碳纤维的Ni、Co等非贵金属催化剂。本项目研究成果不仅可用于指导高效Fe基催化剂的理性设计，还有助于深入理解C对金属催化剂结构和形貌的调控机制。

特定结构和形貌的过渡金属纳米催化剂的可控制备及其形貌效应是当前催化领域中的热点课题之一。目前，国内外对纳米催化剂形貌效应的研究主要针对贵金属，很少针对非贵金属。本项目提出“采用催化化学气相沉积（CCVD）法实现特定结构和形貌的Fe-C合金纳米催化剂的可控制备”的新思路，并从实验和理论上证实了其可行性，同时探究了该方法的普适性，发现CCVD法也适用于制备特定结构和形貌的Ni-C合金纳米催化剂；系统研究了CCVD技术参数对Fe-C、Ni-C合金纳米催化剂形貌与晶相结构的影响，并结合理论计算，揭示了C原子吸附诱导以及石墨烯单元与金属晶面的匹配性是非贵金属纳米催化剂结构与形貌可控合成的内因；比较研究了该类新型催化剂与传统负载型催化剂之间的氨分解活性、高温稳定性以及动力学特征，发现CCVD法制备的催化剂尽管粒径较大，但是其活性以及稳定性明显优于传统等量浸渍法制备的催化剂，同时两种方法制备的催化剂活性趋势相反：传统负载型Ni纳米催化剂氨分解活性高于Fe纳米催化剂，但形貌可控Fe-C合金纳米催化剂的氨分解活性反而高于Ni-C合金纳米催化剂；进一步结合理论计算，揭示了表面C以及次表面C对Fe、Ni催化剂上氨分解性能的影响机制，发现其影响规律呈现出相反的趋势；最终，建立了明确的催化剂结构与氨分解性能之间的构-效关系，为基于CCVD技术制备出高效氨分解非贵金属Fe、Ni纳米催化剂提供了理论基础和实践指导。