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。为了解决持续的环境问题，已将极大的努力放在绿色能源的开发上。在所有其他物质中，氢已被证明是一个有希望的候选者。这不仅是因为它的高质量能量，而且因为燃烧的唯一产物是水。然而，氢的商业化仍面临一些挑战。由于氢是最小的分子，储存起来非常困难，更不用说运输了。这导致了氢经济中的一个重要瓶颈，即氢的储存和运输。氨（NH3）被认为是解决上述问题的有效解决方案。一方面，氨含有相对高的氢含量。另一方面，氨本身有一个标准的合成和储存过程。氨合成是通过一种称为哈伯-博世工艺的复杂技术实现的，在该工艺中，氮气和氢气反应生成氨。然后，所产生的氨可以被加压并以相对低的成本在温和的条件下以液体形式安全地储存。这使得氨分解回氮气和氢气成为通过氨的氢气系统的最后一个难题。因此，开发高效的氨分解催化剂已成为当务之急。在这个项目中，有效的氨分解是研究在氮掺杂的碳材料嵌入金属。有证据表明，在层状碳材料上掺杂氮可以促进氨分解的催化活性。然而，其潜在的机制仍然是未知的。我们小组先前发表的一篇论文已经提出，在氨分解过程中，来自N-石墨烯的氮可能有助于通过H-N-M-N-H类刘易斯对过渡态破坏氨中的N-H键。此外，氮以不同的形式存在于碳层上，即吡咯、吡啶、季铵和末端。它们中的每一种具有不同的化学性质，这将对总体反应动力学产生不同的影响。因此，氮环境对整体催化作用的影响有待进一步研究。该基础研究为今后新型催化剂的设计提供了机理上的认识。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，该石英管置于垂直固定床流动反应器中。氨流过装置，在反应中发生氨分解，同时用原位气相色谱法分析残余气体。基于氮、氢和未反应的氨的峰的强度计算转化率。在表征方面，采用了非原位BET、XRD、TEM、TPD和TGA等手段对催化剂的结构和化学性质进行了研究。将进行XPS以揭示氮含量和环境，将进行原位IR以了解反应期间的键形成和断裂。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。我的项目将与牛津大学的衍生公司Oxford绿色Innotech（OXGRIN）合作，该公司旨在建立一个世界级的一站式催化剂平台，包括研究，制造和与最终用户应用程序的集成。该项目属于EPSRC能源和脱碳研究领域的福尔斯。

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.