化学链合成氨研究进展与展望

Progress and prospects in the chemical looping ammonia synthesis

氨主要被用作生产氮肥的原料,近年来被认为是一种具有重要应用前景的能源载体。目前工业合成氨主要采用Haber-Bosch工艺,该过程严重依赖化石能源,是高能耗、高碳排放过程,为生态环境带来巨大压力。因此,开发温和条件下可再生能源驱动的绿色合成氨过程具有重要的实用意义和社会价值。化学链合成氨过程是将合成氨反应解耦为两步或多步反应,具有规避催化中普遍存在的Scaling relations关系、避免氮气和氢气竞争吸附、可常压操作等特点,被认为是一种具有应用前景的合成氨技术。此外,该过程适合于分布式、小型化的生产模式,便于与可再生能源利用过程相耦合。因此,近年来化学链合成氨受到广泛关注。本综述首先简述了化学链过程的定义及其在化石能源转化领域的研究概况,随后重点介绍化学链合成氨的发展历史、载氮体分类及近期研究进展,最后对载氮体材料的设计思路及化学链合成氨过程的前景进行展望。根据载氮体不同,分别介绍了二元金属氮化物、多元金属氮化物、亚氨基化物及氮氧化物等载氮体材料在分别以N_(2)-H_(2)和N_(2)-H_(2)O为原料的化学链合成氨过程中材料种类、反应热力学及动力学、合成氨速率等方面研究成果。此外,由于近期外场驱动合成氨取得了较好进展,根据外场驱动力不同,分别介绍了以电、光、等离子体、微波等为外加能量形式的化学链合成氨过程。并从热力学及动力学两方面分别介绍了载氮体材料的改进策略。最后,对化学链合成氨技术存在的问题及外来研究方向进行展望。

Ammonia is mainly used as a raw material for the production of nitrogen fertilizers.In recent years,it also has been seen as a promising energy carrier.Industrial ammonia synthesis is mainly based on the Haber-Bosch(H-B)process requiring a significant energy input,so it relies severely on fossil energy and leads high CO 2 emissions.Therefore,there is an urgent need to develop"Green ammonia synthesis"process driven by renewable energy operating under mild conditions.Chemical looping ammonia synthesis(CLAS)is a process that decouples the ammonia synthesis reaction into multiple sub-reactions mediated by an intermediate N carrier material.It has the advantages of circumventing the ubiquity scaling relationships,avoiding the competitive adsorption between N 2 and H 2(or H 2 O),and being able to operate at atmospheric pressure.In addition,this process is suitable to distributed and small-scale ammonia synthesis and is easy to couple with the utilize of renewable energy.Therefore,CLAS has received widely attention in recent years.This review was initiated by briefly defining chemical looping processes and summarizing the research of chemical looping in the area of fossil fuel conversion.The history of CLAS,the development of nitrogen carrier materials,and some recent progresses were then reviewed.The discussion was concluded with future perspectives on the design of nitrogen carrier materials and the prospective advancements in CLAS.The binary metal nitrides,multi-metallic nitrides,metal imides,and metal nitrides,which were used as nitrogen carrier materials in N_(2)-H_(2)and/or N_(2)-H_(2)O CLAS,were presented.Additionally,the CLAS process assisted by external energy such as electricity,light,plasma,and microwaves was discussed.Strategies to enhance the thermodynamic and kinetic performance of nitrogen carrier materials were also detailed.Finally,the review addressed current challenges and emerging research directions in chemical looping ammonia synthesis.