Selective ketones production from holocellulose pyrolysis vapors by oxygen-vacancy and grain-size regulation in Ca-doped CeO2

Selective production of ketone-rich bio-oil from biomass pyrolysis vapors remains challenging because catalyst acidity/basicity, redox properties, and defect chemistry must be precisely balanced. In this work, a series of CaO–CeO 2 composite oxides with a Ca/(Ca+Ce) molar ratio of 0.3 were synthesized by co-precipitation and calcined at different temperatures for the ex-situ catalytic pyrolysis of corn stover holocellulose. Catalytic performance was evaluated by Py-GC/MS and a two-stage fixed-bed reactor, while the catalysts were characterized by XRD, BET, XPS, TEM, and EDS. The results showed that calcination temperature significantly affected crystallite size, surface area, and defect density, thereby governing ketone selectivity. Among the catalysts, Ca 0.3 Ce 0.7 O 2-δ -600 exhibited the highest ketone content of 47.50% in Py-GC/MS, which was associated with its small crystallite size (15.7 nm), relatively high specific surface area (40.59 m 2 /g), and abundant surface oxygen vacancies. In fixed-bed experiments, lowering the catalytic-bed temperature from 600 to 450 °C reduced the gas yield from 62.00% to 51.63% and increased the liquid yield from 19.56% to 29.76%. Meanwhile, the relative ketone content in bio-oil reached a maximum of 33.19%, while the acid fraction decreased to 4.6%. After three consecutive cycles, the catalyst still maintained high ketone contents, and regeneration restored more than 95% of the initial performance. These results demonstrate that defect-engineered Ca–Ce composite oxides are effective and stable catalysts for producing ketone-rich bio-oil under relatively mild catalytic conditions.