Methane Dissociation on the Ceria (111) Surface

Abstract

The complete oxidation of methane into water and carbon dioxide on the (111) surface of ceria is considered within a DFT + U framework in order to gain insight into the coke-free operation of solid oxide fuel cells with ceria-containing anodes. Preferred adsorption sites and energies are determined for CH x (x ) 0, ..., 3), H, and CO, together with transition states and kinetic barriers along the complete pathway from CH 4 to H 2 O and CO 2 . The results presented are in excellent agreement with existing theoretical and experimental work suggesting that ceria is more easily reduced by CO than by H 2 and offer an explanation for the apparently inconsistent observations of carbon coke formation in Ni-ceria anodes and the stable, coke-free oxidation of methane in Cu-ceria anodes.

Alkane reforming on partially sulfided CeO2 (1 1 1) surfaces

“…This correction effectively penalizes the delocalization of Ce f electrons. We utilized a U-value of 5 eV on the f orbitals of cerium which is consistent with previous DFT studies of ceria [9][10][11][12][13][16][17][18][19]21,[47][48][49]. The oxygen vacancy formation and methane activation energies depend on the value of U chosen for the f-states of Ce in CeO 2 and M x Ce 1Àx O 2 .…”

“…A single material capable of performing both cleanup steps at gasifier effluent temperatures would aid process integration [1,2]. MO x -CeO 2 materials can be used to adsorb sulfur [3][4][5][6][7][8] as well as reform hydrocarbons [8][9][10][11][12][13]. These two processes have mostly been studied independently from one another on oxides, though reforming in the presence of sulfur species has been examined on metal catalysts [14,15].…”

“…These two processes have mostly been studied independently from one another on oxides, though reforming in the presence of sulfur species has been examined on metal catalysts [14,15]. There are several studies (both experimental and computational) examining hydrocarbon reforming over ceria, with most of them focused on methane [9][10][11][12][13][16][17][18]. The overall mechanism to reform methane over a ceria surface is established [4,11,19].…”

“…There are several studies (both experimental and computational) examining hydrocarbon reforming over ceria, with most of them focused on methane [9][10][11][12][13][16][17][18]. The overall mechanism to reform methane over a ceria surface is established [4,11,19]. The adsorption of sulfur using M-doped ceria has also been examined using both experimental and computational techniques [3][4][5][6][7].…”

“…In gasifier effluent cleanup, the adsorption step is typically performed at temperatures lower than those coming off the gasifier and subsequent catalytic steps, leading to process energy inefficiencies [1]. M-doped ceria has shown promise as a high temperature sulfur sorbent [3][4][5][6][7] as well as a hydrocarbon reforming catalyst [3,[9][10][11][12][13][16][17][18]. Few studies have examined hydrocarbon reforming on CeO 2 -based oxides in the presence of S-containing molecules.…”