Nitrogen doping in porous biochar from cotton stalk with H3PO4 activation for reduction of NOx with NH3-SCR at low temperatures: Characteristics and catalytic activity analysis

This study aimed to prepare a series of nitrogen-doped modified biochar using the cotton stalk as the raw ma-terial and examine the effect of different nitrogen-containing groups on the NH3-selective catalytic reduction (SCR) reaction. The X-ray photoelectron spectroscopy results and denitration activity analysis revealed that the pyridine nitrogen (N-5) and pyrrole nitrogen (N-6) were the main nitrogen-containing groups determining the denitration activity of the biochar. The NO-temperature-programmed desorption results showed that the surface basicity of the biochar after nitrogen doping increased, and its adsorption capacity for NO improved. The results of the NO oxidation test indicated that the SCR reaction on the biochar existed as both a "fast-SCR" reaction and a "standard-SCR" reaction. That is, the NH3-SCR reaction mainly depended on the "fast-SCR" reaction at low temperatures (50-150 degrees C). The main reaction at high temperatures (150-260 degrees C) was the "standard-SCR" reac-tion. The O2-TPD results showed that the biochar doped with nitrogen produced a large number of oxygen holes, increasing the O2 activation ability of the biochar. Both E-R and L-H mechanisms existed in the denitrification process of the nitrogen-doped cotton stalk-based biochar, and both gaseous and adsorbed NO were obtained by center dot NH2 reduction.