Porous carbons with large surface areas, abundant mesopores and weak base sites are promising materials for the capture and conversion of CO2. However, it is still challenging to obtain such porous carbons in a facile and template-free way. Herein, nitrogen-decorated micro-mesoporous carbons were synthesized by direct carbonization of porous organic polymers, which were developed through alkylation-induced hyper-crosslink of rigid organic bases without the use of any templates. The synthesized carbons have ultrahigh surface areas of 2366-3580 m(2)/g, total pore volumes of 1.74-3.38 cm(3)/g and N contents of 1.50-3.24 wt%. As a consequence, the synthesized carbons enable highly efficient and selective adsorption of CO2 from CO2/N-2 mixed gas, with the CO2 capacities of 1.50-2.03 mmol/g at 0 degrees C and 15 kPa, and IAST selectivities of 69-78 for CO2/N-2 (0.15/0.85 vol) mixed gas at 0 degrees C and 100 kPa. After loaded with metal salts, the synthesized carbons also exhibit high activities for the catalytic conversion of CO2, with the TOFs of>600 h(-1) for cycloaddition of CO2 with propylene oxide at 100 degrees C and 1.0 MPa. [GRAPHICS] .