The invention relates to a method for reducing the CO2 content of a gas by contacting the gaseous effluent to be treated with an absorbent that contains a CO2 trapping agent in the impregnated state on a substrate made of a solid composite material (M) containing a polymer (P) and a compound (C) selected from mineral oxides, silico-aluminates, and activated carbon, wherein said material (M) has an average particle size (D50) higher than or equal to 100 μm, and a pore space (Vd1) defined by pores having a diameter of between 3.6 and 1000 nm and which is at least 0.2 cm3/g. The invention also relates to specific absorbents used in said method.