Reactions of cationic iron clusters with ammonia, models of nitrogen hydrogenation and dehydrogenation

Abstract

The gas phase reactivities of small cationic iron clusters, Fen+ (n = 1-20), towards ammonia were investigated using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Sequential addition of ammonia molecules to the clusters was observed to be the dominating process for n > 4. In the case of n = 4 we observed addition of ammonia accompanied by dehydrogenation. This reaction was modelled using hybrid density functional theory. Clusters with n < 4 do not react with ammonia. Clusters Fen+ (n = 1-20) react with neither N2 nor H2 at around 10(-8) mbar. When dinitrogen was seeded into the expanding helium, mixed clusters of the type FenNm+ were observed. These ions react with H2, either by addition, or by substitution of N2. The clusters with m = 1 were isolated in separate experiments and reacted with H2, which showed that mixed clusters with n = 5-13 add up to 5 molecules of dihydrogen in successive slow reactions.

Gas-phase perspective on the thermodynamics and kinetics of heterogeneous catalysis

“…77 The first four of these values are estimated from the enthalpies of formation of bulk compounds and only the latter value has been measured directly. Similar values have been obtained from calorimetry experiments: 78-85 6.3 ± 0.2 eV for Cr, 4.0-5.5 eV for Fe, 4.7-5.1 for Co, and 5.0 and 4.8 eV for Ni (111), 5.0 eV for Ni (110), and 5.4 eV for Ni (100). As a function of cluster size, vanadium behaves somewhat differently than the other metals by reaching a maximum BDE at n = 5, and then declining to a plateau above n = 10.…”

Density functional study on cage and noncage (Fe2O3)n clusters

“…Therefore, B3LYP has been used widely in iron-containing system to give reliable results. [7][8][9][10][27][28][29][49][50][51][52] A benchmark calculation is done on FeO, Fe 2 , and O 2 with B3LYP and BPW91 functionals and results are summarized in Table I. For FeO, similar results are obtained by the two functionals.…”

“…LANL2DZ denotes the Dunning/Huzinaga full double zeta basis set 57 and the corresponding Los Alamos relativistic effective core potential 58 for Fe atoms and Dunning/Huzinaga valence double zeta 57 for O atoms. This basis set combined with B3LYP is successfully used for many iron-containing systems, [50][51][52] and it gives similar results with the all-electron basis sets 59,60 6-311+ G ‫ء‬ in our benchmark calculation, only except for the poor description of O-O bond energy. Thus LANL2DZ is used throughout this work, except that for the Fe 4 O n cluster series ͑n =0-8͒ a combined basis set ͑LANL2DZ for Fe and 6-311+ G ‫ء‬ for O, denoted as LAN6311G͒ is used to give better description for the O-O bond energy.…”

Bimetallic Cobalt/Rhenium Systems: Preferred Position of Rhenium Through an Interdisciplinary Approach

“…Metal clusters have proven to be useful models for surface and bulk phenomena both in theoretical [9] 1 and experimental [11][12][13][14][15][16] investigations. In particular smaller metal clusters are well suited for quantum mechanical studies, as indicated by the amount of literature available on the subject [17][18][19].…”