Structure-Sensitive Pathway Branching of Reaction Intermediates Drives Catalyst Deactivation in Cycloalkane Dehydrogenation

Abstract

Elucidating how the surface structure alters reaction networks during cycloalkane dehydrogenation remains critical for understanding and mitigating catalyst deactivation. Here, we show that early deactivation of Pt catalysts in cycloalkane dehydrogenation is linked to structure-sensitive pathway branching of a partially dehydrogenated intermediate. Using perhydro-monobenzyltoluene (H12-MBT) as a model system, we identify methylfluorene (H0-MF) as a strongly bound coke precursor. Operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) combined with density functional theory (DFT) reveals a previously unrecognized route in which H0-MF originates from an aromatic-anchored adsorption configuration of the partially dehydrogenated intermediate H6-MBT rather than from the cyclization of the fully dehydrogenated product H0-MBT as commonly assumed. Thermal restructuring and defect-site masking of the Pt surface, together with Pt(211)/Pt(111) DFT calculations, show that low-coordinated Pt ensembles increase access to this cyclization branch, whereas terrace-like surfaces favor continued dehydrogenation. Guided by this mechanism, a series of promotor-modified catalysts spanning varied surface and electronic characteristics reveals that the H0-MF yield within the first 0.5 h quantitatively correlates with initial activity loss. This early H0-MF yield serves as a durability descriptor that distinguishes catalysts undergoing a rapid initial decay from those that transition directly to a more gradual deactivation regime. More broadly, these results define a design principle for structure-sensitive dehydrogenation catalysis by demonstrating surface-structure-dependent pathway branching of partially dehydrogenated intermediates as a mechanistic origin of coke initiation in cycloalkane dehydrogenation.