Exploring hierarchical porous γ-Al2O3 modified with MoV metal oxides used as a high-efficiency solid catalyst for sustainable biodiesel production from low-cost acidic oils

Hierarchical porous materials have been considered as promising catalyst carriers due to their large specific surface area and multi-sized pore structure, which can efficiently reduce the mass-transfer resistance of macromolecular reactants as well as improve the exposure of the active sites. In this research, a series of hierarchical porous solid acid catalysts with dual metal oxide active centers, namely Mo/V@H-Al2O3, was prepared by introducing Mo and V into hierarchical porous H-Al2O3 carriers via a successive incipient wetness impregnation approach. The functional species, crystal structures, morphological features, and acidic properties of the synthesized Mo/V@H-Al2O3 catalysts were explored using various characterization techniques. Results showed that this catalyst not only possessed the structural advantages of relatively large surface area and ordered hierarchical porous structure, but also contained dual Brønsted-Lewis acid sites. With the low-cost acidic oils as feedstocks, this catalyst can concurrently catalyze the oil transesterification and free fatty acid (FFA) esterification reaction with the oil conversion rate of 94.3 % and full conversion of FFA under the optimized conditions, achieving one-pot transformation of the acidic oil to biodiesel and thereby simplifying the laborious separation procedure. The synergistic effect between the hierarchical porous structure and the strong acidity was shown to boost the catalytic performance of this Mo/V@H-Al2O3 catalyst for the efficient biodiesel production. The high moisture and FFA-tolerant capacity emerged for this catalyst, and it had good reusability during the biodiesel production process, still with above 80 % of oil conversion even after five cycles of reuse, endowing it to have the great potential for cost-effective and sustainable production of biodiesel in particular with low-cost acidic oils as feedstocks.