Niobium oxide deposited on high surface area graphite as a stable catalyst in the 1-butanol dehydration reaction

Abstract

Niobium oxide, a promising catalyst for acid-catalyzed reactions in water-rich environments, often faces challenges due to its low specific surface area and performance highly dependent on synthesis conditions. In our study, niobium oxide was dispersed over a high-surface-area graphite support (HSAG), and the resulting composite catalysts were evaluated in the continuous gas-phase dehydration of 1-butanol under mild conditions (275 °C, atmospheric pressure). We systematically investigated the effects of the niobium precursor (chloride vs. oxalate), Nb loading (from 1/6 to 4/3 of the theoretical monolayer), and synthesis method—incipient wetness impregnation (IW) vs. urea-assisted deposition-precipitation (DP). Catalysts prepared by IW showed reduced surface areas and evidence of Nb oxide aggregation or partial reduction (NbO2), while the DP method led to better dispersion, preservation of mesoporosity, and formation of orthorhombic Nb2O5, as revealed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Despite similar acid strength distributions, measured by ammonia temperature-programmed desorption (TPD-NH3), catalytic stability varied markedly across samples. The DP catalyst exhibited outstanding stability and high selectivity toward C4 olefins (≥90%), while IW catalysts experienced progressive deactivation. Post-reaction XRD confirmed structural stability, while thermogravimetric analyses coupled with mass spectroscopy (TGA-MS) revealed greater coke and isobutene retention—key deactivation factors—on deactivated IW samples. These findings demonstrate that the synthesis method governs catalyst dispersion, stability, and resistance to deactivation.