A new insight into the promotional effect of nitrogen-doping in activated carbon for selective catalytic reduction of NOX with NH3

Abstract

A series of N-doped carbons were prepared to investigate the effect of different N-containing groups on selective catalytic reduction (SCR) of NOx with NH3. Combined the SCR activity with the results of porosity analysis and X-ray photoelectron spectroscopy, it's deduced that the pyridinic N (N-6) rather than the surface area or doped total N was mainly responsible for the promoted SCR activity. The electron paramagnetic resonance and O2-temperature programmed desorption (O2-TPD) experiments indicated that N-6 created numerous of oxygen vacancy. The NO+O2-TPD and transient response of NH3 further demonstrated that the increased oxygen vacancy enhanced the absorbability and reactivity of NOx, therefore the SCR reaction was elevated by accelerating the reaction in the Langmuir-Hinshelwood (L-H) mechanism. Furthermore, the NH3-TPD suggested that N-6 was conductive to the NH3 adsorption. In situ DRIFTs of NH3 adsorption and reaction illustrated that the increased NH3 mainly existed as NH2 species, which were quickly consumed by NO+O2, further elevated the reaction between gaseous NO and adsorbed NH3 in the Eley-Rideal (E-R) mechanism. The N-6 groups doped in the activated carbons facilitated the L-H and E-R reactions and thus promoted the SCR activity.