In-situ catalytic decomposition of emitted ammonia from municipal solid waste gasification by Ni–M bimetallic catalysts supported on sewage sludge-derived biochar

Gasification technology can effectively realize energy recovery from municipal solid waste (MSW) to reduce its negative impact on the environment. However, ammonia, as a pollutant derived from MSW gasification, needs to be treated because its emission is considered harmful to mankind. This work aims to decompose the NH₃ pollutant from MSW gasification by an in-situ catalytic method. The MSW sample is composed of rice, paper, polystyrene granules, rubber gloves, textile and wood chips. Ni–M (M=Co, Fe, Zn) bimetallic catalysts supported on sewage sludge-derived biochar (SSC) were prepared by co-impregnation method and further characterized by X-ray diffraction, N₂ isothermal adsorption, scanning electron microscopy, transmission electron microscopy and NH₃ temperature programmed desorption. Prior to the experiments, the catalysts were first homogeneously mixed with the MSW sample, and then in-situ catalytic tests were conducted in a horizontal fixed-bed reactor. The effect of the second metal (Co, Fe, Zn) on the catalytic performance was compared to screen the best Ni-M dual. It was found that the Ni–Co/SSC catalyst had the best activity toward NH₃ decomposition, whose decomposition rate reached 40.21% at 650 °C. The best catalytic performance of Ni–Co/SSC can be explained by its smaller Ni particle size that facilitates the dispersion of active sites as well as the addition of Co reducing the energy barrier for the associative decomposition of NH species during the NH₃ decomposition process. Besides, the activity of Ni–Co/SSC increased from 450 °C to 700 °C as the NH₃ decomposition reaction was endothermic.