The core of directed upgrading of low-rank coal pyrolysis volatiles to light aromatics (BTEXN) hinges on the catalyst's selective activation of C-O/C-C bonds in oxygenates. Nb₂O₅ possesses both Brønsted and Lewis acid sites and readily forms oxygen vacancies, making it a promising upgrading catalyst. However, the correlation between its crystal phase and active sites, and how metal modification regulates bifunctional synergy, remain unclear. In this work, Nb₂O₅ crystal phases were tuned via hydrothermal-calcination strategy, and the microstructures and catalytic performances of W-Nb₂O₅, T-Nb₂O₅, and M-Nb₂O₅ were systematically compared. The results reveal that crystal phase is the key factor determining Nb₂O₅ catalytic performances. Both W-Nb₂O₅ and T-Nb₂O₅ exhibited large specific surface areas and abundant dual acid sites, affording BTEXN yields of 18.50 and 18.32 mg/g, respectively. In contrast, M-Nb₂O₅ showed sharply reduced accessible acid sites due to grain sintering and pore collapse, resulting in BTEXN yield of only 9.07 mg/g. On this basis, Ni/Nb₂O₅ bifunctional catalysts were fabricated via impregnation, urea precipitation, and sol-gel methods, with Ni dispersion and metal-support interactions examined. The sol-gel method achieved highly uniform Ni dispersion across the support. Such rich porosity and large surface area ensured ample contact between active sites and pyrolysis intermediates, increasing BTEXN yield to 34.37 mg/g, far exceeding those of other two methods. DFT calculations for p-cresol revealed the bifunctional synergy: Ni sites lowered the barrier of H-H dissociation from 0.48 to 0.07 eV, dominating active hydrogen supply, while Nb₂O₅ oxygen vacancies adsorbed and activated phenolic C-O bonds. This study clarifies how crystal phase and Ni modification regulate catalyst upgrading performance, offering structure-activity insights for designing catalysts for directed conversion of low-rank coal pyrolysis volatiles.
 

Low-rank coal,Catalytic pyrolysis,Nb2O5,Crystal phase,Ni modification