Abstract:

The chemisorption of NH_3 on Ni(111) surface has been studied by X_a-DV method. Total energies, ground states, charges transfer and total densities of states are calculated for ontop and three-fold sites respectively, The results show that NH_3 tends to adsorb on on-top site and not to adsorb on three-fold site. The interaction between NH_3 and Ni(111)is mainly due to the mixture of the lone-pair orbital 3a_1 of NH_3 and the 4s orbital of Ni. Charge transfer from bonding orbitals to anti-bonding orbitals causes the activation of NH_3. The interaction between intermediate NH and Ni(111) surface inccluded in our calculations shows that the NH adsorbed on Ni(111) is much stronger than that of NH_3. So that the step NH_(ad)+2H_(ad)→NH_(3ad) needs much more energy on Ni(111) surface than that of on Fe surface. The difficulty of the NH_3 formation on Ni(111) surface is another possibel reason of why Ni is not a good catalyst for NH_3 synthese.