Effect of iron on heterogeneous reduction reaction of NO by char: A combined experimental and theoretical study

NOx production during coal combustion can be minimized by using the heterogeneous reduction reaction of NO on char. Here, coal-derived char was loaded with different amounts of Fe for heterogeneous reduction of NO at 1300°C in a one-dimensional tube furnace. The effects of Fe loading on the reaction was investigated for the first time. Meanwhile, theoretical calculations based on the wave function theory and density functional theory were carried out to explore the reaction steps at the molecular level. Two reaction pathways were identified involving different chemisorption sites. The catalytic mechanism of Fe in the entire NO reduction process was revealed, and thermodynamic and kinetic analyses were carried out based on the theoretical results. Overall, the NO reduction rate was greatly enhanced when the char contained Fe. At a FeCl3 loading of 0.4 wt%, the NO reduction rate reached the maximum and was 18.8% higher than that of the demineralized char. The catalytic mechanism of Fe could be attributed to the following aspects: creation of more new active sites for the chemisorption of NO by the destruction of conjugated π-bonds, reduction in the energy barrier of the rate-determining step, and facilitation of N–N bond formation and N2 desorption from the char surface. According to the thermodynamic and kinetic calculations, the introduction of Fe increased the upper limit and rate of the heterogeneous reduction reaction of NO.