Highly Selective Production of p-Xylene from 2,5-Dimethylfuran over Hierarchical NbOx-Based Catalyst

A hierarchical NbOx-based catalyst with both Bronsted acid and Lewis acid sites was synthesized in the absence of corrosive hydrofluoric acid, exhibiting high catalytic activity for biobased p-xylene (PX) production from 2,5-dimethylfuran (DMF). The as-prepared composite was composed of Nb2O5 and NbOPO4 crystals, and the densities of Bronsted acid and Lewis acid were determined to be 232.9 and 80.4 mu mol/g, respectively. The well-balanced Bronsted/Lewis acidity and the hierarchical structure with small mesopores (3 nm) and large mesopores (48 nm) contributed to the high activity and stability: a conversion of 87.2% with the PX selectivity of 92.7%, and a carbon balance of 94.6% was achieved after 6 h of reaction at 523 K. In comparison with Sn-Beta, NbOx-based catalyst prepared in this work showed obvious advantages in suppressing carbon deposition: 90.9 and 54.7 mmol of PX were obtained over the NbOx-based catalyst and the Sn-Beta, respectively, after 24 h. Spent catalysts were regenerated through calcination at high temperature and they proved to be recyclable: a decrease of 3.7% in DMF conversion and no loss in PX selectivity could be evidenced over five consecutive runs. Overall, NbOx-based catalyst which is synthesized through the green and sustainable approach is sufficiently stable, active, and regenerable, and provides an alternative candidate for efficient PX production.