Mechanistic Insights into Radical-Mediated Cracking of n -Butylbenzene over CeO ₂ (111) toward Selective Light Olefin Formation

The direct catalytic cracking of long-chain alkyl aromatics into light olefins is a key strategy for efficient oil-to-chemicals conversion. While current research has primarily focused on solid acid catalysts, investigations of solid bases, particularly rare-earth metal oxides, remain scarce, and their mechanistic roles are poorly understood. Here, density functional theory (DFT) calculations followed by experimental validation were conducted to elucidate the cracking mechanism of n-butylbenzene on the CeO₂(111) surface. The CeO₂(111) facet provides bifunctional active sites: Lewis-basic surface oxygen (O²⁻) and redox-active Ce⁴⁺/Ce³⁺ centers cooperatively mediate hydrogen-atom and electron transfer processes to drive radical-based C-H and C-C bond activation. Compared with the carbanion pathway, C-H activation preferentially proceeds via a hydrogen atom transfer (HAT) mechanism, forming carbon-centered radicals that undergo β-scission to yield light olefins. Among the competing routes, C3-H activation followed by C1-C2 bond cleavage exhibits a relatively low energy barrier (1.75 eV), preferentially yielding propylene. In contrast, the ethylene-forming route is kinetically hindered by a higher barrier (2.25 eV), resulting from the dehydrogenation of surface-bound C₂H₅* species and surface electronic reorganization. The synergistic interplay between Ce 4f redox flexibility and surface basicity thus governs selective C-H/C-C bond activation and product distribution. This study provides fundamental insight into radical-mediated, nonacidic hydrocarbon cracking on rare-earth oxides and a mechanistic basis for designing a selective base-type oil-to-chemicals catalysts.