NO_<i>x</i> Adsorption Mechanism of Coal-Based Activated Carbon Modified with Trace Potassium: In Situ DRIFTS and DFT Study

A series of coal-based materials were prepared using a hydrothermal method combined with high-temperature CO2 activation. During sample preparation, K modification was performed to optimize the surface functional groups and pore structure. The NOx adsorption volume of each sample was evaluated in a simulated flue gas atmosphere. The physical and chemical parameters of the samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and temperature-programmed desorption of NOx and NO. In addition, the NOx adsorption mechanism of representative samples was explored by in situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory calculations. The adsorption capacity of NOx and SO2 with NOx was also systematically investigated using cyclic adsorption and co-adsorption experiments, respectively. The results showed that the optimized KOH concentration is 0.4 g KOH/30 mL H2O. At this concentration, the material had a relatively good pore structure and abundant surface functional groups. The investigation of the mechanism revealed that pore structure optimization is important for increasing the NOx adsorption capacity on the surface of the coal-based materials, followed by functional group and then surface metal optimization. In addition, oxygen-containing active functional groups with moderately high C–O and R2C═O contents can enhance the adsorption of NO to some extent. Optimizing the ratio of C–O to R2C═O is critical for NOx adsorption. This study is significant for NOx adsorption removal technology.