Development of sustainable catalysts from ornamental rock waste and Nb2O5 for biodiesel production

This work reports a strategy for valorizing granite and marble waste as supports for Nb2O5-based catalysts in biodiesel production. Composites containing 15, 45, and 60 wt% Nb2O5 were prepared by high-energy grinding and characterized by X-ray diffraction (XRD), particle size analysis, scanning electron microscopy (SEM), and catalytic tests. The results indicate that the residues provide suitable structural properties for catalyst support. Although higher Nb2O5 contents increased surface area and porosity, the 15% catalyst showed the best performance, reaching 55% conversion to methyl esters from waste oil.