Assessment of Different Niobium-Based Catalytic Systems for 5-Hydroxymethylfurfural Production from Glucose and Microcrystalline Cellulose

powder remained active for seven consecutive cycles, whereas the pellet formed partially deactivated after four cycles. Together with the use of relatively green solvents, short reaction times, and noncorrosive conditions, these results support the development of efficient, reusable, and environmentally friendly catalytic systems for carbohydrate valorization. Overall, the combination of competitive productivity at short residence times in a low-hazard solvent system positions these niobium-based catalysts favorably relative to many reported heterogeneous HMF routes that rely on longer reaction times and less sustainable solvents. Moreover, the pelletized catalyst format is directly compatible with fixed-bed continuous-flow reactors, facilitating catalyst handling, separation, and regeneration.