Converting CO2 to valuable materials is attractive. Herein, we report using simple metallothermic reactions to reduce atmospheric CO2 to dense nanoporous graphene. By using a Zn/Mg mixture as a reductant, the resulted nanoporous graphene exhibits highly desirable properties: high specific surface area of 1900 m2/g, a great conductivity of 1050 S/m and a tap density of 0.63 g/cm3, comparable to activated carbon. The nanoporous graphene contains a fine mesoporous structure constructed by curved few-layer graphene nanosheets. The unique property ensemble enables one of the best high-rate performances reported for electrochemical capacitors: a specific capacitance of ~170 F/g obtained at 2000 mV/s and 40 F/g at a frequency of 120 Hz. This simple fabricating strategy conceptually provides opportunities for materials scientists to design and prepare novel carbon materials with metallothermic reactions.