Influence of Local Defects on the Dynamics of O–H Bond Breaking and Formation on a Magnetite Surface

Abstract

The transport of H adatoms across oxide supports plays an important role in many catalytic reactions. We investigate the dynamics of H/Fe3O4(001) between 295 and 382 K. By scanning tunneling microscopy at frame rates of up to 19.6 fps, we observe the thermally activated switching of H between two O atoms on neighboring Fe rows. This switching rate changes in proximity to a defect, explained by density functional theory as a distortion in the Fe-O lattice shortening the diffusion path. Quantitative analysis yields an apparent activation barrier of .9 ± . eV on a pristine surface. The present work highlights the importance of local techniques in the study of atomic-scale dynamics at defective surfaces such as oxide supports.

Quantitative structure determination of adsorbed formate and surface hydroxyls on Fe3O4(001)

“…[48][49][50] Within this work we have determined the O OH to occupy an int site. This is consistent with DFT calculations performed by Arndt et al 23 and was also the site predicted by Bourgund et al 51 for native surface hydroxyls on the Fe 3 O 4 (001) surface due to the adsorption of background gas phase hydrogen. Moreover, DFT calculations into the formation of water monolayers on the Fe 3 O 4 (001) surface indicate that these monolayers are initiated by the formation of surface hydroxyls which occupy the int site.…”

“…We have also determined experimentally, for the first time, the adsorption site of the surface hydroxyl as the int site corroborating several DFT calculations and STM measurements into the site of the hydroxyl species. 23,51,52 Through determining experimentally the surface hydroxyl adsorption site we have reinforced the pivotal role that hydroxyl plays in the lifting of the SCV reconstruction. The preference of the surface hydroxyl to be situated in a bulk-like int site likely drives the Fe int cation into the first subsurface cation vacancy, initiating the destabilisation of the SCV reconstruction to cation diffusion from the bulk.…”

Atomic‐Scale Studies of Fe3O4(001) and TiO2(110) Surfaces Following Immersion in CO2‐Acidified Water

“…Following their arguments, we propose that both H + and the HCO 3 À ions in solution at pH 3.9 play a similar role as organic ligands in the dissolution. First, the adsorption of protons would polarize the neighbour FeÀ O bond [41,28] and reduce surface Fe 3 + to Fe 2 + . The now available Fe(II) is complexated by the bicarbonate ions, which act as ligands and form iron bicarbonate surface species (Fe(HCO 3 ) 2 ), [33,35,41] according to the equation Fe 2þ þ 2HCO À 3 !…”

Effect of Surface Functionalization on the Magnetization of Fe3O4 Nanoparticles by Hybrid Density Functional Theory Calculations

“…Note that one of the two dissociated protons goes on the extremely reactive O atom at the O-corner, causing some Fe−O bond breaking and corner reconstruction, whereas the other is adsorbed on an O atom of the flat surface that is generally recognized in the literature as the most easily protonated. 40,41 If we increase the local density of MPA molecules at the O-corner, in the proximity of the Fe Oct 3+ 6c-(3) site (Figure 2), using the three undercoordinated octahedral Fe ions around the O at the vertex, the additional two MPA molecule are found to preferentially adsorb as monodissociated bidentate, which is one of the most common adsorption modes on metal oxide surfaces. 42 that with the largest adsorption energy (−3.91 eV) at the Ocorner site (see Table 2, Figure S3, and Figure S5), if compared to undissociated bidentate, bidissociated bidentate, undissociated chelate, dissociated chelate, and bidissociated chelate, which are at least 1 eV higher in energy if not unstable.…”