Facet-selective ethanol dehydrogenation/dehydration on CeO2 nanocrystals explored through modulation excitation DRIFT spectroscopy

Abstract

This work explores the facet-dependent mechanisms governing ethanol dehydrogenation and dehydration oncerium oxide (CeO2) nanocrystals. Shape-controlled CeO2 nanocubes ({1 0 0} facets) and nanosheets ({1 1 1}facets) were synthesized and evaluated under steady-state conditions. Catalytic performance was significantlyinfluenced by surface structure: nanosheets exhibited markedly higher ethanol conversion (90 % at 400 ◦C)compared to nanocubes (18 %), with selectivity transitioning from acetaldehyde to ethylene as temperatureincreased. Operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), combined withmodulation excitation spectroscopy and phase-sensitive detection (MES-PSD), enabled the identification of keysurface intermediates. Bidentate ethoxy species predominated on {1 0 0} facets, while monodentate ethoxyspecies were favored on {1 1 1} facets. Phase-resolved spectra revealed that acetaldehyde forms rapidly via αC–H bond cleavage, whereas ethylene formation proceeds through slower β C–H activation involving enolatetypeintermediates. The enhanced reactivity of {1 1 1} facets was attributed to their ability to orient ethoxyspecies favorably for C–O and C–H bond activation, while the accumulation of thermally stable acetates limitedreactivity on {1 0 0} surfaces. These findings establish a direct correlation between CeO2 morphology, surfacechemistry, and product distribution, providing mechanistic insight relevant to the rational design of selectiveoxidation catalysts.1.