MoO3/Nb2O5 Composites Prepared by Wet High-Energy Ball Milling: Structural Evolution, Physicochemical Properties, and Catalytic Performance in Biodiesel Production

The development of heterogeneous catalysts with suitable structural and physicochemical properties is important for catalytic processes involving renewable feedstocks. In this study, Nb2O5 and MoO3/Nb2O5 composite catalysts were prepared by high-energy wet milling, systematically characterized, and subsequently evaluated in the transesterification of waste cottonseed oil. The effect of MoO3 incorporation on the structural, morphological, thermal, and catalytic properties of the resulting materials was investigated. X-ray diffraction revealed the predominantly amorphous character of the hydrated Nb2O5 precursor, whereas increasing MoO3 content promoted the formation and growth of orthorhombic α-MoO3 crystalline domains. FTIR spectroscopy confirmed the presence of Nb-O-Nb vibrations and Mo-O/Mo=O species in the composite catalysts. SEM and SEM-EDS analyses revealed distinct morphologies and a homogeneous distribution of Nb, Mo, and O at the micrometric scale. The particle-size analysis showed changes in the particle-size distribution following MoO3 incorporation. These structural and physicochemical modifications were accompanied by a substantial enhancement in catalytic performance compared with bare Nb2O5. At catalyst loadings of 4 and 6 wt.%, 35Mo/Nb achieved conversions of 88.34 ± 0.08% and 90.21 ± 0.14%, respectively. The 15Mo/Nb reached 69.50 ± 5.07% and 62.17 ± 0.21%. The 35Mo/Nb catalyst was further subjected to five reuse cycles, and XRD, FTIR, and TGA analyses indicated preservation of the oxide framework, along with the presence of adsorbed reaction-derived species after reuse. The results demonstrate that high-energy wet milling provides an effective route for preparing MoO3/Nb2O5 composite catalysts with composition-dependent structural and physicochemical characteristics, whose catalytic applicability was demonstrated in biodiesel production.