Ab Initio Investigation of CH₄ Dehydrogenation on a (CeO₂)₁₀ Cluster

Abstract

We report a theoretical investigation of the activation and dehydrogenation of CH 4 on a (CeO 2 ) 10 cluster based on density functional theory calculations combined with the unity bond index-quadratic exponential potential approach. As expected, we identified a physisorption interaction mechanism between the CH 4 and (CeO 2 ) 10 systems. Along the dehydrogenation, the interaction CH n −(CeO 2 ) 10 occurs by chemisorption via the formation of C−O and H−O bonds. Due to adsorption effects, the oxidation state of Ce atoms changes from Ce 4+ to Ce 3+ , which results in the elongation of the Ce−O bonds due to the larger radius of the Ce 3+ species, and hence, it affects the formation of the CO and CH 3 OH species. Our combined approach showed that the first dehydrogenation step involves a transition-state formation induced by the molecular hybridization before the CH 3 radical formation. Finally, our results indicate trends for new compound formation, once the energy barrier involved in the first step of dehydrogenation is overcome.

Theoretical Insights into Methane Activation on Transition-Metal Single-Atom Catalysts Supported on the CeO2(111) Surface

“…The methane adsorption energies magnitudes are very similar to each other, −0.21, −0.23, −0.17, −0.21, and −0.23 eV for Fe, Co, Ni, Cu, and bare surface, respectively. Additionally, for the bare surface, CH 4 adsorption is slightly more favored than adsorption on the (CeO 2 ) 10 cluster (−0.18 eV) . The methane adsorption energies on Ni and Co systems agree with the works of Liu et al , , and Lustemberg and co-workers .…”

“…Additionally, for the bare surface, CH 4 adsorption is slightly more favored than adsorption on the (CeO 2 ) 10 cluster (−0.18 eV). 51 The methane adsorption energies on Ni and Co systems agree with the works of Liu et al, 46,48 and Lustemberg and coworkers. 45 The adsorption of methane does not change the geometry of the substrate or affect the environment; in other words, no other surface Ce is reduced.…”

“…Thus, the modified UBI-QEP depends only on the gas-phase bond energy; further information is provided in the Supporting Information. Moreover, the UBI-QEP method has shown success for a range of reactions involving sulfur oxide, carbon monoxide hydrogenation to light olefins, carbon dioxide hydrogenation to methanol, acid-base and redox reactions, methane dehydrogenation, , and ethanol conversion . The adsorption of the CH 3 and H fragments that are accounted for by both methods is shown in Figure .…”

“…The adsorption of molecular species (CH 4 , CH 3 , CH 3 +H, H) has a higher complexity due to the large number of possible orientations on the substrate and different adsorption sites as a consequence of the presence of the TM adatoms. For example, it has been reported that CH 4 adsorbs via umbrella, anti-umbrella, and scissor orientations on substrates. − The number of configurations is higher than for TM adsorbates, in particular for CH 3 +H, which increases the computational cost. Thus, the same calculation protocol described above was used, where the first relaxation was performed for molecules species adsorbed on frozen TM/CeO 2 (111) substrates, which are optimized within the second step.…”