NH_3/Ir(100): Electronic structure and dehydrogenation

摘要

Density functional theory was employed to compute the geometric and electronic structures and the stepwise dehydrogenation of NH_3 on Ir(100). The NH_3, NH_2 and NH were found to bind predominately on top, bridge and four-fold hollow sites with adsorption energies to be 0.82 eV, 3.26 eV and 4.85 eV respectively. The mixings of 3α_1(NH_3)~5d_z~2/6s(Ir), 3α_1/lb_1(NHz) ~ 5d_(yz)(Ir) and 3α_1 + la_2(NH) ~ 5d_(xz)(Jr) and 2α_1(NH)~5d_z~ 2(Ir) are responsible for the adsorption of NH_3, NH_2 and NH respectively. The reaction barriers are 0.88 eV, 0.97 eV, 0.94 eV and 0.63 eV for the first, second, third N-H bond breakings and N_2 formation respectively. The competition between decomposition and desorption for NH_3 was demonstrated, NH_2 was found to be the most stable surface species, its accumulation in practice would suppress the first N-H bond scission and thus make it to be the rate-determining step.