One-step flame-synthesized catalysts enable high-value sugar production from cellulose fast pyrolysis

• Flame spray pyrolysis enables effective synthesis of nano-alumina and metal-loaded alumina catalysts with smaller particle sizes and larger specific surface areas. • Fe 2 O 3 -Al 2 O 3 catalyst achieves 46.3% selectivity for D-allose from cellulose pyrolysis at 550℃ • Optimized utilization of cellulose through pyrolysis, resulting in a high selectivity of D-allose. D-allose is a novel, low-calorie monosaccharide with strong potential as a substitute for traditional high-calorie sweeteners, offering wide-ranging applications in both the food and pharmaceutical industries. However, producing D-allose from renewable biomass remains challenging, and there is an urgent need for a simple, scalable method to enable industrial production. In this study, we present a straightforward approach for producing D-allose using alumina-based catalysts prepared via flame spray pyrolysis (FSP). This one-step method allows precise control over catalyst morphology by adjusting the precursor solution concentration and injection flow rate. To enhance catalytic performance, the alumina was doped with metal oxides Fe 2 O 3 , NiO, and MgO. Catalysts produced under 0.5 M precursor concentration and 1000 mL/h flow rate exhibited high specific surface areas of up to 188.5 m²/g. Among the various formulations tested, the Fe 2 O 3 -doped alumina catalyst delivered the highest selectivity for D-allose (up to 46.3%). This improvement is attributed to the synergistic interaction between γ-Al₂O₃ and Fe₂O₃ acid sites, which promoted selective isomerization of C 6 sugars while minimizing unwanted degradation. Characterization using pore structure and NH₃-TPD analysis showed that both the number and strength of acid sites—closely linked to surface area and composition—play a crucial role in the catalytic conversion process. This method avoids the need for biomass pretreatment and complex catalyst fabrication, highlighting its potential as a scalable, sustainable solution for producing high-value sugars from lignocellulosic biomass.