An ONIOM study of amines adsorption in H-[Ga]MOR

The adsorption of amines (NH3, MeNH2, Me2NH and Me3N) in two stable bridging oxygen sites (O10H and O2H) in H-[Ga]MOR clusters is investigated by using the ONIOM2 method. All amines are protonated and the formed [HNR3]+ are stabilized by the H-bonds between the negatively charged zeolite oxygen atoms and the hydrogen atoms of the NH and CH bonds in the adsorbates. On the basis of the calculated adsorption energies, it is concluded that the relative basicity of amines follows the order of Me2NH > Me3N > MeNH2 > NH3. Due to the effect of introduced methyl groups and their different basicity and structures, NH3 prefers to adsorb at the O2H Brønsted site (Fig. a), while Me2NH and Me3N prefer to adsorb at the O10H site (Fig. b), and MeNH2 can be in equilibrium between O2H and O10H.