Catalytic Ammonia Decomposition in Green Energy Supply

人口增长导致化石燃料的能源消耗增加，从而引发严重的环境危机，如全球变暖，海平面上升，酸雨等。为了解决持续存在的环境问题，人们大力发展绿色能源。氢，在所有其他元素中，已经被证明是一个很有希望的候选者。不仅因为它的质能高，而且因为它燃烧的唯一产物是水。然而，氢的商业化仍然面临着一些挑战。由于氢是最小的分子，它极难储存，更不用说运输了。这导致了氢经济的一个重要瓶颈，氢的储存和运输。氨（NH3）被认为是解决上述问题的有效方法。一方面，氨含有较高的氢含量。另一方面，氨本身有一个标准的合成和储存过程。氨的合成是通过一种叫做哈伯-博世法的复杂技术来实现的，在这种技术中，氮和氢反应产生氨。然后可以对产生的氨加压，并以相对较低的成本在温和的条件下以液体形式安全地储存。这使得氨的分解回到氮和氢是通过氨的氢系统的最后一个难题。因此，开发有效的氨分解催化剂已成为当务之急。在本项目中，研究了氮掺杂碳材料上嵌入金属的有效氨分解。有证据表明，氮掺杂层状碳材料可以提高氨分解的催化活性。然而，其潜在机制尚不清楚。我们小组之前发表的一篇论文已经提出，在氨分解过程中，n -石墨烯中的氮可能通过H-N-M-N-H类刘易斯对过渡态帮助打破氨中的N-H键。此外，氮以不同的形式存在于碳层上，即吡啶、吡啶、季氮和端氮。它们每一种都有不同的化学性质这对整个反应动力学有不同的影响。因此，氮环境对整体催化的作用有待进一步研究。该基础研究将为今后新型催化剂的设计提供机理上的认识。该项目将结合催化剂活性测试和必要的原位和非原位表征进行。催化剂将在石英管中进行测试，石英管被固定在垂直固定床流动反应器中。氨通过装置，在反应中进行氨分解，同时用原位气相色谱法分析残留气体。转化率是根据氮、氢和未反应氨的峰强度计算的。表征方面，采用非原位BET、XRD、TEM、TPD和TGA等方法了解催化剂的结构和化学性质。用XPS分析氮含量和反应环境，用原位IR分析反应过程中键的形成和断裂。结合进一步的计算，可以提出在该催化剂上反应的基本机理。我的项目将与牛津绿色创新科技公司（OXGRIN）合作，这是一家从牛津大学分拆出来的公司，旨在建立一个世界级的一站式催化剂平台，包括研究、制造和最终用户应用的集成。该项目属于EPSRC能源和脱碳研究领域。

Rising population has led to higher energy consumption of fossil fuel and thus trigger severe environmental crisis like global warming, sea level rise, acid rains etc. To address the ongoing environmental problem, extreme effort has been placed on the development of green energy source. Hydrogen, amongst all the others, has shown to be a promising candidate. Not only due to its high energy by mass, but also as the only product of combustion is water. However, commercializing hydrogen still faces some challenges. As hydrogen is the smallest molecule, it is extremely hard to store, not to mention its transportation. This leads to one essential bottleneck within the hydrogen economy, hydrogen storage and transportation. Ammonia (NH3) is considered as an effective solution to tackle down the above question. On one hand, ammonia contains relatively high hydrogen content. On the other hand, ammonia itself has a standard process for synthesis and storage. Ammonia synthesis is achieved through a sophisticated technique called the Haber-Bosch process, where nitrogen and hydrogen react to give ammonia. The produced ammonia can then be pressurized and safely stored as liquid form under mild condition at a relative low cost. This leaves the decomposition of ammonia back to nitrogen and hydrogen being the last puzzle for the hydrogen system via ammonia. Hence, development of effective catalyst for ammonia decomposition has become an essential task with high priority. In this project, effective ammonia decomposition is studied over a metal embedded on nitrogen doped carbon material. Evidence has shown that nitrogen doping on a layered carbon material can promote the catalytic activity of ammonia decomposition. However, the underlying mechanism is still unknown. It has been suggested by one previous paper published in our group that, during ammonia decomposition, the nitrogen from the N-Graphene might help to break the N-H bond in ammonia, via a H-N-M-N-H like Lewis pair transition state. Furthermore, nitrogen exists in different forms on the carbon layer, namely pyrrolic, pyridinic, quaternary and terminal. Each of them has different chemical properties which would have different impact on the overall reaction kinetics. Thus, further investigation would be carried out on the function of nitrogen environments towards the overall catalysis. The fundamental study would provide mechanistic understanding for future novel catalyst design. The project would be carried out with a combination of catalyst activity testing and essential in-situ and ex-situ characterisations. Catalyst will be tested in a quartz tube which is held in the vertical fixed-bed flow reactor. Ammonia is flown through the set-up with ammonia decomposition taking place in the reaction while the residue gas is analysed with an in-situ Gas chromatography. The conversion rate is calculated based on the intensity of the peaks of nitrogen, hydrogen and unreacted ammonia. As for characterisation, ex-situ BET, XRD, TEM TPD and TGA are used to understand the structure and chemical property of the catalyst. XPS will be carried out the reveal the nitrogen content and environment, in-situ IR will be performed to understand the bond formation and breakage during the reaction. Together with further computational calculation, a fundamental mechanism can be proposed for the reaction over this catalyst. My project would collaborate with Oxford Green Innotech (OXGRIN), a spin-out company from the University of Oxford, which is aiming for building a world-class One-Stop Catalyst Platform that comprises research, manufacture and integration with end user applications. This project falls within the EPSRC Energy and decarbonisation research area.