Reactivity of the Fe₂O₃(0001) Surface for Methane Oxidation: A GGA + U Study

Abstract

CH4 oxidation by an oxygen carrier, such as iron oxide, continues to be involved in many important valuable industrial catalytic processes, including chemical looping combustion. In this paper, reaction pathways of complete and partial oxidations of CH4 on thermodynamically stable hematite (α-Fe2O3) (0001) facets are investigated with periodic GGA + U calculations. Upon Fe–O3–Fe-termination, initial CH4 decomposition proceeds via C–H bond activation on the Fe site, with an energy barrier of 1.04 eV. Subsequent decomposition and oxidation of the CH x species (x = 1, 2, 3) exploit the lattice O species according to the Mars–van Krevelan mechanism, forming CH x O in more thermodynamically and kinetically favorable pathways. The reduced iron oxide can be reoxidized with O2 as the oxidant, allowing VO to greatly facilitate O2 dissociation, i.e., dramatically lowering the O2 dissociation barrier by 2.83 eV, for active site regeneration. Furthermore, CH4 oxidation chemistry involving the ferryl O (i.e., oxygen species adsorbed on the Fe site) is also investigated. The ferryl O species are highly energetic and able to activate the C–H bond via direct oxygen insertion, thereby producing methanol with an energy barrier of 0.37 eV. However, the role of surface ferryl O in iron oxide is limited due to its high reactivity and low concentration indicated by the high surface energy of the O–Fe–O3-terminated surface.

Density functional theory study on the effect of OH and Cl adsorption on the surface structure of α-Fe2O3

“…Table 1 shows that the average relative energies are all greater than or equal to zero, meaning that the AFM + + --is the most energetically favorable magnetic configuration for α-Fe2O3. This is consistent with previous computational [45,47] and experimental studies [48]. The magnetic moments for all four magnetic configurations are comparable and close to the experimental value of 4.9 μB [49].…”

Metal oxide decorated porous carbons from controlled calcination of a metal–organic framework

“…In this work, we have focused on a typical iron-containing MOF, PCN-250 (PCN ¼ porous coordination network) 28 3 . This iron-based MOF was of particular interest for carbonization due to the catalytic applications of iron oxide particles, 30,31 as well as the ease of separation afforded by the magnetic behavior of iron oxide. 18 PCN-250 has been well studied for gas storage and separation applications due to its accessible open metal sites.…”

Adsorption-based membranes for air separation using transition metal oxides

“…† A good agreement with previous experimental as well as computational work is obtained. 57,[69][70][71][72][73][74][75][76][77] We performed adsorption calculations on the relaxed structure obtained. While many adatom adsorption congurations exist, only a handful of them are stable.…”