Partial Oxidation of Methanol on the Fe₃O₄(111) Surface Studied by Density Functional Theory

Abstract

To understand recent temperature-programmed desorption (TPD) experiments carried out for methanol adsorbed on a Fe 3 O 4 (111) single crystal surface by Batista and co-workers, we accomplished a systematic density functional theory study on the various dehydrogenation pathways of methoxy species on that surface. For a mass/charge ratio of 30, these experiments detected two desorption peaks, one centered at about 330 and the second one at about 630 K, indicating that methoxide is partially oxidized to formaldehyde. Yet the origin of these two peaks has not been fully understood. Based on computed activation barriers for the H-transfer from methoxy species to the symmetrically distinct surface oxygen ions using the PBE+U approach and the HSE hybrid functional corrected for dispersion effects, we simulated the corresponding TPD peaks by numerical solution of a Polanyi−Wigner rate equation of first order. The simulated spectra using HSE suggest that the observed peaks are caused by the two inequivalent oxygen ions in the Fe 3 O 4 (111) surface. They have comparable activities in the protonation step upon adsorption of methanol but feature distinct reactivities toward the redox or H-transfer step causing significantly different activation barriers.

Machine Learning in Computational Surface Science and Catalysis: Case Studies on Water and Metal–Oxide Interfaces

“…PBE+U predicts that upon dissociation of one H 2 O molecule per unit cell, protonation of O a is slightly more favorable than protonation of O b . We find an energy difference of 0.08 eV only, which is small but comparable in magnitude as obtained for the dissociative adsorption of methanol (CH 3 OH) in a p(2 × 1)-Fe 3 O 4 (111) surface unit cell (Li and Paier, 2019). As discussed in Li and Paier (2019), this energy difference is small and depends on the electronic structure method.…”

“…We find an energy difference of 0.08 eV only, which is small but comparable in magnitude as obtained for the dissociative adsorption of methanol (CH 3 OH) in a p(2 × 1)-Fe 3 O 4 (111) surface unit cell (Li and Paier, 2019). As discussed in Li and Paier (2019), this energy difference is small and depends on the electronic structure method. For the dissociative adsorption of water on the p(1 × 1) -Fe 3 O 4 (111) surface employing the HSE hybrid functional, we find that protonation of the O b oxygen ion is by ca.…”

Facile Decomposition of Organophosphonates by Dual Lewis Sites on a Fe3O4(111) Film

“…This test yields a dissociative adsorption energy of methanol of -2.82 eV, which agrees well to previous published literature. 50 Subsequent investigation of possible adsorption modes of MMP in the presence of a single methoxy bonded on tetrahedral Fe yielded three possible adsorption conformations ( Fig. S4 and Table S3).…”

Dual Lewis site creation for activation of methanol on Fe3O4(111) thin films

“…The Lewis acidity of Fe tet1 is theoretically predicted to accommodate methoxy species. 71 Further oxidation with C–D cleavage occurs at 700 K, leading to the formation of formaldehyde and water.…”