text: In thermodynamic equilibrium [27], the coverage of the ac- 
  tive sites follows from 
  
  K[X]C[X] 
  Θ[X] =  ,  (4) 
  1 + (cid:80) 
  Y K[Y ]C[Y ] 
  
  where K = k+/k− is the ratio of forward and backward rate 
  constants for the adsorption reaction, 
  
  (cid:20)  (cid:21) 
  
  Eads[X] + T S[X] 
  kBT 
  
  The adsorption energies for N2, O2, H2O, CO, NH3, and 
  H2S on the metallic site of the doped (6,6) CNTs are shown in 
  Fig. 2(a). The adsorption energy of a molecule X is deﬁned 
  by 
  
  K[X] = exp  −  .  (5) 
  
  In these expressions C[X] is the concentration of species X, 
  S[X] is its gas phase entropy and T is the temperature. Ex- 
  perimental values for the gas phase entropies have been taken 
  from Ref. [28].  Eads[X@M@VC] = E[X@M@VC] − E[X] − E[M@VC], 
  (3) 