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.