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Tuning Methane Activation Chemistry on Alkaline Earth Metal Oxides by Doping
journal contribution
posted on 2018-09-07, 00:00 authored by Hassan Aljama, Jens K. Nørskov, Frank Abild-PedersenWe
study oxidative coupling of methane (OCM) on alkaline earth
metal oxides (AEMOs) doped with either a transition metal (TM) or
an alkaline earth metal (AEM) different from that of the host oxide.
We assess whether doping can lead to new materials that are better
than the pure oxides or deviate from the limitations of the scaling
relations. Density functional theory (DFT) calculations show that
doped AEMO surfaces follow similar linear scaling relations as observed
on pure AEMO; however, doped surfaces bind the adsorbates, hydrogen,
and methyl more strongly. Both TM- and AEM-doped AEMOs show that methane
activation mostly occurs through a surface-mediated pathway, where
at the transition state the methane C–H bond is stretched,
and the methyl interacts mostly with the dopant atom and the hydrogen
with the lattice oxygen. The stronger hydrogen binding in the doped
surfaces leads to a lower methane activation barrier; however, in
some cases, the catalyst surface binds the hydrogen too strongly,
poisoning the active site and making the catalyst inactive. The doped
systems are largely constrained by the scaling relations, but sites
closer to the optimum of the volcano plot exist, suggesting room for
improvement.
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host oxideOCMAlkaline Earth Metal Oxidesstudy oxidativeearth metalearth metal oxidesAEM-doped AEMOs showlattice oxygenmethane activation barrierTuning Methane Activation Chemistrysurfaces bindvolcano plotTMcalculations showtransition statetransition metalhydrogen bindingAEMO surfacesmethylDFTsitecatalyst surfacemethane activationsurface-mediated pathwaydopant atom
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