Removal of Nitrogen Pollutants in the Chemical Looping Process: A Review

In the process of fuel utilization, traditional combustion technologies result in the conversion of nitrogen elements in fuels into nitrogen oxides, which are released into the atmosphere, posing serious threats to the environment and human health. The chemical looping process (CLP) is an effective technology for reducing nitrogen-containing (N-containing) pollutants during fuel utilization. During the CLP, the oxygen carrier (OC) can oxidize nitrogen oxide precursors (NH3 and HCN) released from the fuel to N2, while the reduced OC can reduce nitrogen oxides to N2. The achievement of efficient nitrogen pollutant removal relies on the development of highly active oxygen carriers (OCs). This review summarizes the recent progress in the removal of nitrogen pollutants within chemical looping processes (CLPs). It delineates the formation pathways of N-containing pollutants (NH3, HCN, NO, NO2 and N2O) and highlights the performance of various OCs. The influence of reaction conditions and feedstock characteristics is also discussed. Ni-based OCs have demonstrated superior performance in the removal of N-containing pollutants, exhibiting strong oxidation capabilities and excellent catalytic properties. Moreover, iron ore, as a cost-effective and environmentally friendly feedstock, holds promise for wide-scale application. Future research should focus on further optimizing OCs strategies and refining reaction conditions to achieve more efficient and economical N-containing pollutant removal, thereby fostering the widespread application of chemical looping technology in the energy sector.