Ethanol Reforming on Co(0001) Surfaces: A Density Functional Theory Study

Abstract

A computational study using density functional theory is carried out to investigate the reaction mechanism of ethanol steam reforming on Co(0001) surfaces. The adsorption properties of the reactant, possible intermediates, and products are carefully examined. The reaction pathway and related transition states are also analyzed. According to our calculations, the reforming mechanism primarily consisting of dehydrogenation steps of ethanol, ethoxy, methanol, methoxy, and formic acid, is feasible on Co(0001) surfaces. It is also found that the reaction of formaldehyde yielding formic acid and hydrogen may not be an elementary reaction. The dehydrogenation of ethoxy possesses the highest barrier and is accordingly identified as the rate-determining step.

Morphology Evolution of Hcp Cobalt Nanoparticles Induced by Ru Promoter

“…Bulk hcp Co was optimized in a (1×1) unit cell of the P63/mmc crystallographic symmetry, with a 9×9×7 Monkhorst‐Pack k‐point grid. The optimized lattice constants for the bulk hcp Co are a=b=2.507 Å and c=4.069 Å, in good agreement with experimental measurement (a=b=2.497 Å, c=4.078 Å) and theoretical values (a=b=2.494 Å, c=4.031 Å) . According to the space group symmetry, the stable exposed index facets of the hcp Co include the (0001), (10‐10), (10‐11), (10‐12), (11‐20), and (11‐21) surfaces.…”

“…The optimized lattice constants for the bulk hcp Co are a = b = 2.507 Å and c = 4.069 Å, in good agreement with experimental measurement (a = b = 2.497 Å, c = 4.078 Å) [35] and theoretical values (a = b = 2.494 Å, c = 4.031 Å). [36] According to the space group symmetry, the stable exposed index facets of the hcp Co include the (0001), (10-10), (10-11), (10)(11)(12), (11)(12)(13)(14)(15)(16)(17)(18)(19)(20), and (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21) surfaces. Their starting geometries were obtained by cleaving the relaxed structure of bulk hcp Co along the appropriate normal directions.…”

Theoretical Insight into the Reaction Mechanism of Ethanol Steam Reforming on Co(0001)

“…This step possesses an energy barrier of 0.64 eV with a reaction energy of 0.29 eV. Our calculated barrier (0.82 eV without ZPE correction) is somewhat lower than that (0.99 eV) reported by Ma et al 25 In the transition state, the breaking C−H bond length is found to be 1.59 Å, about 0.49 Å longer than that in the reactant. After reaction, the acetaldehyde (CH 3 CHO*) is located at an hcp hollow site with its methyl pointing away from the surface and a hydrogen atom at C α goes to an fcc hollow site.…”

“…25,32 This is in contrast to other metal surfaces such as Cu and Ni, where the process has a higher barrier and is endothermic. 51, 52 The subsequent dissociation of OH* to atomic oxygen and hydrogen species is favored thermodynamically on Co(0001), and the reaction barrier (0.89 eV) for this step is not particularly high.…”

“…This result agrees well with the previous experimental observations 19,48 and theoretical data. 25 As shown in Figure 3, there are four possible decomposition pathways for the resulting ethoxyl (CH 3 CH 2 O*) species, which is strongly bound to the surface. The cleavage of its C−C bond is unlikely as the energy barrier is exceedingly large (2.40 eV).…”