The catalytic activity of carbon nanotubes (CNTs) for the removal of greenhouse gases, like nitrous oxide (N2O), can be fine-tuned by metal doping. We modify the inert surfaces of CNTs with Sc, Ti and V transition metals in order to investigate their capability of converting N2O to N2. The stable composite catalysts of Sc-, Ti- and V-doped (5,5)single-walled carbon nanotubes (SWCNTs), along with the unmodified one were investigated by periodic DFT calculations. Without metal doping, the N2O decomposition on the bare tube proceeds over a high energy barrier (54.3 kcal mol−1) which in the presence of active metals is reduced to 3.6, 8.0 and 10.2 kcal mol−1 for V-, Ti- and Sc-doped (5,5)SWCNTs, respectively. The superior reactivity is a result of the facilitated electron transfer between the tube and N2O caused by the overlap between the d orbitals of the metal and the p orbitals of N2O.