Research progress on the transformation and utilization of nitrogen element based on chemical looping

Under the background of “Carbon Peak and Carbon Neutrality”, nitrogen may become an important element to replace carbon, completing the production of carbon-free fuel ammonia and other compounds. Among them, ammonia, not only an important chemical raw material, but also a good energy carrier, has been widely studied by scholars. However, the existing Haber-Bosch ammonia process is a fossil energy-dependent, energy-intensive and carbon-emitting process. Hence, the development of a new “green” ammonia process driven by renewable energy is an important project for the sustainable development of human society. Chemical looping technology breaks down the process into two or more sub-reactions carried out in different space or time by redesigning the reaction path, and realizes material and energy transfer in a coupled system through the reaction and regeneration of the carrier medium, characterized by easy coupling to renewable energy sources, atmospheric pressure operation, and avoidance of reactants competing for adsorption. In addition to the advantages of intensifying the reaction process, chemical looping technology has a lower carbon emission compared with the traditional technology, which is an effective way in response to “carbon control” strategy and has gained widespread attention in recent years. However, research on chemical looping synthesis and conversion is mostly dominated by carbon-based materials, and for nitrogen-based materials, the only more in-depth chemical looping ammonia synthesis technology still faces the problems of low nitrogen fixation efficiency and low ammonia production rate of nitrogen carriers. Based on this, this paper reviews the research of chemical looping technology in the field of synthesis and conversion of nitrogen-containing compounds, outlines the new development of multiphase catalysis based on the Haber-Bosch process and the chemical looping ammonia synthesis process driven by external field forces, such as light and electricity, and divide the chemical looping ammonia synthesis process into the chemical looping ammonia synthesis process with hydrogen as the hydrogen source and the chemical looping ammonia synthesis process with water as the hydrogen source, according to the hydrogen source are summarized and discussed in this paper. In the synthesis of nitrogen-containing compounds, the chemical looping technology for the oxidation of ammonia to nitric oxide as well as the chemical looping process for the production of alcohols from alkanes with alkyl nitrates as the key intermediates are detailed presented. Among them, the chemical looping ammonia oxidation process has good NO selectivity and avoids N₂O production, which is an efficient and clean advanced technology. Under mild reaction conditions, the light-driven chemical looping synthesizes alcohols to form the key intermediate R-ONO₂. Such a light-assisted pathway can achieve high activity and selectivity at low temperatures, providing a new idea for the preparation of value-added chemicals at low temperatures. Finally, the challenges of nitrogen conversion and utilization are analyzed and discussed, with the expectation to provide a reference for the promotion of non-carbon fuel production and the low-carbon transition of chemicals. The development of superior nitrogen carriers, efficient reactors, novel chemical looping processes, and full life cycle and economic evaluation of scale-up production will help to explore the possibilities of industrialization and commercialization of chemical looping technology in the future.