Exploring CO dissociation on Fe nanoparticles by density functional theory-based methods: Fe13 as a case study

Cryo spectroscopy of N2 on cationic iron clusters

Infrared photodissociation (IR-PD) spectra of iron cluster dinitrogen adsorbate complexes [Fe_n(N₂)_m]⁺ for n = 8-20 reveal slightly redshifted IR active bands in the region of 2200-2340 cm^-1. These bands mostly relate to stretching vibrations of end-on coordinated N₂ chromophores, a μ_1,end end-on binding motif. Density Functional Theory (DFT) modeling and detailed analysis of n = 13 complexes are consistent with an icosahedral Fe₁₃ ⁺ core structure. The first adsorbate shell closure at (n,m) = (13,12)-as recognized by the accompanying paper on the kinetics of N₂ uptake by cationic iron clusters-comes with extensive IR-PD band broadening resulting from enhanced couplings among adjacent N₂ adsorbates. DFT modeling predicts spin quenching by N₂ adsorption as evidenced by the shift of the computed spin minima among possible spin states (spin valleys). The IR-PD spectrum of (17,1) surprisingly reveals an absence of any structure but efficient non-resonant fragmentation, which might indicate some weakly bound (roaming) N₂ adsorbate. The multiple and broad bands of (17,m) for all other cases than (17,1) and (17,7) indicate a high degree of variation in N₂ binding motifs and couplings. In contrast, the (17,7) spectrum of six sharp bands suggests pairwise equivalent N₂ adsorbates. The IR-PD spectra of (18,m) reveal additional features in the 2120-2200 cm^-1 region, which we associate with a μ_1,side side-on motif. Some additional features in the (18,m) spectra at high N₂ loads indicate a μ_1,tilt tilted end-on adsorption motif.

Direct versus hydrogen-assisted CO dissociation over stepped Ni and Ni3Fe surfaces: a computational investigation

The adsorption and dissociation of CO over stepped Ni and Ni3Fe surfaces were systematically studied using density functional theory slab calculations. Both (211)-like surface structure terminations (NiNi step and NiFe step, denoted as Ni3Fe(211)-AA and Ni3Fe(211)-AB) are considered for Ni3Fe. Direct scission of the C-O bond in CO is identified as the least likely one among the three proposed dissociation pathways and CO dissociation via a CHO intermediate appears to be most feasible at low CO coverage on pure and alloyed Ni(211) surfaces. The priority of H-assisted CO dissociation might originate from the more activated C-O bond in COH and CHO. Compared to Ni(211), the Ni3Fe(211)-AB surface could facilitate CO activation especially for the most possible CHO intermediate mechanism, whose rate-limiting step is found to be altered. The d-band center theory and Mulliken charge analysis are also employed to explain the activity difference between Ni3Fe(211)-AB and Ni3Fe(211)-AA. The significant structural sensitivity of CO dissociation highlights the importance of Fe locating in the step edge and the high reactivity of Ni3Fe(211)-AB is largely ascribed to the synergistic effect between Ni and Fe at the step edge.

Direct oxidation of methane to methanol on Fe–O modified graphene

The reaction mechanisms of the partial oxidation of methane to methanol over FeO/graphene are unraveled using an advanced DFT approach.