Natural Gas-Assisted NO<sub><i>x</i></sub> Abatement Using Chemical Looping Scheme

In\nthis study, we explore a novel approach to nitrogen oxide (NO<sub><i>x</i></sub>) purification based on the principles of\nthe chemical looping (CL) platform. This technique harnesses the reducing\npower of natural gas (CH<sub>4</sub>), instead of ammonia, to eliminate\nNO<sub><i>x</i></sub> in the flue gas, addressing environmental\nconcerns such as ammonia slip in the state-of-the-art selective catalytic\nreduction process. The CL scheme involves utilizing nickel oxide (NiO)\nas the solid oxygen carrier to facilitate oxygen transfer from NO<sub><i>x</i></sub> to CH<sub>4</sub> in two steps. In the first\nstep (carrier oxidation), NO<sub><i>x</i></sub> in the flue\ngas reacts with reduced nickel (Ni), transferring its [O] to the carrier,\nthereby forming NiO. In the subsequent step (carrier reduction), CH<sub>4</sub> reacts with the lattice oxygen of the oxidized carrier, generating\na pure stream of CO<sub>2</sub> and reducing NiO to Ni. We designed\na high-performance carrier by dispersing NiO on an inert support to\nenhance the carrier’s kinetics and thermal stability. We evaluated\nvarious support materials, and among them, alumina (Al<sub>2</sub>O<sub>3</sub>) and zirconia (ZrO<sub>2</sub>) demonstrated significantly\nsuperior reactivity. Notably, the Al<sub>2</sub>O<sub>3</sub>-supported\ncarrier outperformed the ZrO<sub>2</sub>-supported carrier in NO purification\nand CH<sub>4</sub> reduction and demonstrated stable performance over\n10 redox cycles. Furthermore, fixed-bed experiments revealed 100%\nNO conversion during carrier oxidation, with optimal reaction kinetics\nachieved at lower space velocities, resulting in an overall high carrier\nutilization. Importantly, CO<sub>2</sub> showcased no adverse effects\nduring the NO<sub><i>x</i></sub> purification step. During\nthe carrier reduction, complete combustion was favored, leading to\nCH<sub>4</sub> conversion exceeding 95% and a CO<sub>2</sub> selectivity\nof 90% at 400 °C. The CL NO<sub><i>x</i></sub> purification\napproach represents a promising strategy for mitigating NO<sub><i>x</i></sub> emissions.