Facile synthesis of Nb-Al oxides for Levulinic acid production from glucose Available to Purchase

Valued-added levulinic acid can be synthesized from glucose as an abundance feedstock. Solid acid catalysts have been applied for this task due to the high catalytic activity with ease of separation. In this work, Al₂O₃ support was synthesized using solution combustion method and xNb/Al₂O₃ catalysts (x=1, 5, and 10 wt% of Nb₂O₅) were prepared by incipient wetness impregnation. The catalysts were characterized by XRD, N₂ adsorption, SEM, and NH₃-TPD. The XRD results indicated that a mixture of γ- and α-Al₂O₃ was obtained from solution combustion. The specific surface area of Al₂O₃ support was 159 and it decreased to 103, 98, and 79 m2/g with increasing Nb₂O₅ to 1, 5, and 10 wt%, respectively. Moreover, the NH₃−TPD results demonstrated that amount of acid sites also declined from 1.01 to 0.85, 0.53, and 0.44 mmol NH₃/g as Nb₂O₅ contents increased. While one-pot derived 10 wt% Nb₂O₅−Al₂O₃ resulted in γ-Al₂O₃ as majority with surface area of 159 m2/g and acidity of 0.89 mmol NH₃/g. This suggested that incorporation of Nb₂O₅ in Al₂O₃ retarded the phase transformation at high temperature. For a series of Nb-impregnated Al₂O₃, levulinic acid yields were 6.6, 6.5, and 5.5 mol% for 1, 5, and 10 wt% Nb₂O₅/Al₂O₃, respectively. Interestingly, one-pot derived 10 wt% Nb₂O₅-Al₂O₃ produced the highest levulinic acid yield of 18.9 mol%. This study shows the advantage of solution combustion for synthesizing metal-oxide acid catalysts to convert biomass-based feedstock to value-added products.