Unraveling Ni Particle Size Effects in Ethanol Steam Reforming Over Ni/CeO ₂ Catalysts

ABSTRACT Ethanol steam reforming (ESR) represents a promising route for sustainable hydrogen production, leveraging the high hydrogen content, renewability, and logistical advantages of ethanol. Although Ni‐based catalysts are leading non‐noble candidates for ESR, their practical deployment is hindered by compromised H 2 production efficiency and rapid deactivation. In this work, we combined catalyst synthesis, kinetic analysis, and mechanistic investigation to elucidate the effects of Ni particle size (3–9 nm) on ESR performance of Ni/CeO 2 catalysts. These Ni/CeO 2 catalysts were prepared via a citric acid‐assisted coprecipitation method, and systematically characterized using complementary techniques, including high‐resolution transmission electron microscopy (HRTEM), in situ X‐ray photoelectron spectroscopy (XPS), hydrogen temperature‐programmed reduction (H 2 ‐TPR), Raman spectroscopy, O 2 /CO chemisorption, and temperature‐programmed surface reaction (TPSR) analyses. Mechanistic study revealed that ethanol dehydrogenation to acetaldehyde is the rate‐determining step, defining the intrinsic activity of Ni sites, whereas C–C bond cleavage governs H 2 selectivity in ESR. At smaller Ni sizes (e.g., 3.1 nm), larger CeO 2 surface was exposed, which promoted acetaldehyde condensation to acetone, and consequently reduced H 2 production efficiency. The Ni/CeO 2 catalyst with ∼5 nm of Ni particles afforded the highest H 2 yield (66.3%) and outstanding stability by balancing dehydrogenation activity, H 2 selectivity, and coking resistance. Conversely, larger Ni particles (> 6 nm) facilitated methanation reaction and catalyst deactivation. This work reconciles prior inconsistencies in the Ni size effects on ESR and provides guidance for the design of efficient and durable Ni‐based catalysts for H 2 production.