Adsorption of H-2/D-2 on graphene (G), graphene oxide (GO), single walled carbon nanotube (SWCNT), N-doped graphene [(N)G], and a sample of active carbon (C) has led to the detection of HD, indicating dissociative chemisorption of hydrogen on the surface of the material. The amount of HD detected follows the order G > SWCNT > GO similar to (N)G similar to C, G giving about five-fold higher H-2/D-2 adsorption and HD exchange level than SWCNT and about ten-fold larger values than that of the other samples. Quantum-chemistry calculations modeling a carbon atom vacancy on a G cluster estimates an activation barrier for H-2 dissociation of ca. 84 kJ/mol for a mechanism involving under coordinated carbon atoms at the defect site.