The goal of our research is developing an efficient and cost-effective carbonaceous CO2 sorbent. Using petroleum coke as the precursor, porous nitrogen-doped carbons were prepared by combining ammoxidation with KOH activation. The as synthesized samples possess highly developed microporosities and large nitrogen loadings. High CO2 adsorption capacities of 3.76-4.57 mmol/g at 25 degrees C and 5.80-6.62 mmol/g at 0 degrees C under atmospheric pressure were achieved. Specifically, the sample prepared under mild temperature (650 degrees C) and low KOH/precursor ratio (KOH/precursor = 2) shows a CO2 uptake of 4.57 mmol/g at 25 degrees C, among the highest achieved for nitrogen-doped porous carbons. This high CO2 capture capacity can be attributed to the synergistic effect of nitrogen doping and high narrow microporosity of the sorbent. However, experimental evidence suggests that nitrogen doping contributes less than narrow microporosity. Additionally, the CO2/N-2 selectivity and CO2 heats of adsorption of the sorbent are as high as 22 and 37 kJ/mol, respectively. The sorbent also shows high cyclic stability, fast kinetics, and superior dynamic CO2 capture capacity under simulated flue gas conditions, thereby demonstrating that it is an excellent candidate for CO2 capture.