Impact of surface-active site heterogeneity and surface hydroxylation in Ni doped ceria catalysts on oxidative dehydrogenation of propane

• Published in: Journal of catalysis 2022-09, Vol.413, p.681-691
• Main Authors: Pushkar, Anoop P, Varghese, Jithin John
• Format: Article
• Language: English
• Subjects: Ab-initio thermodynamics; Cerium oxide; Computational Raman spectroscopy; Density Functional Theory; Lewis Base addition; Nickel doping; Propane oxidative dehydrogenation; Surface heterogeneity
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2022.07.019

[Display omitted] •Partially reduced Ce0.83Ni0.17O1.83(110) surface likely under propane ODH environment.•Less than a third of active sites selective for propene formation.•Monolayer hydroxyl coverage on Ce0.83Ni0.17O1.83(110) surface is stable under propane ODH environment.•Surface hydroxylation enhanced propene desorption and improved propene selectivity.•Promotional effects of hydroxyls partly due to hyperconjugation in adsorbates. Using periodic Density Functional Theory calculations, propane oxidative dehydrogenation (ODH) and overoxidation over bare and hydroxylated Ni-doped CeO2 nanorods with predominantly exposed (110) facets were studied. Ab-initio thermodynamics-based surface phase analysis and computational Raman spectroscopic analysis predicted an 8.3 % surface oxygen vacancy concentration (Ce0.83Ni0.17O1.83) at typical ODH conditions. Only one-third of the surface oxygens, adjacent to the dopant, were selective for propene formation. Moreover, activated oxygen (O22–*) favored the formation of overoxidation products over propene. A monolayer hydroxyl coverage from water dissociation was stable at typical ODH conditions. This reduced the activation energy barrier for propene formation by 0.38 eV, increased the barrier for undesired acetone formation by 0.54 eV, and increased the barrier for propene activation by 0.6 eV. These promotional effects were due to the destabilization and induced hyperconjugation effects in the C3 adsorbates due to surface hydroxylation. Hence, surface hydroxylation (Lewis Base addition) is a potential strategy to improve propene selectivity.