Catalytic conversion of eucalyptus pre-hydrolysis liquor-derived xylo-oligosaccharides to furfural using dual-acidic functionalized covalent organic frameworks

The application of biorefinery technologies to convert xylo-oligosaccharide (XOS) from pulping process into biofuels or high-value chemicals holds significant potential for extending the value chain of the pulp and paper industry, while simultaneously promoting sustainability. In this study, a series of dual-acid functionalized covalent organic frameworks (COFs) were synthesized to catalyze the one-step liquid-phase conversion of XOS into furfural. The results indicated that TAPT-DHPA exhibited exceptional catalytic activity, achieving a furfural yield of 78.6 % at 180 °C for 3 h with 0.16 wt% catalyst. Furthermore, TAPT-DHPA demonstrated excellent stability, maintaining a furfural yield above 77 % after six reuse cycles. Bader charge analysis via VASP software revealed the presence of both Brønsted and Lewis acid active sites in TAPT-DHPA, arising from the ionization of hydrogen in phenolic hydroxyl groups and the strong electron-withdrawing nature of the triazine ring, respectively. These characteristics are key factors in TAPT-DHPA's superior catalytic performance. Density functional theory calculations confirmed that the most favorable pathway for furfural production involves a cyclic anhydride intermediate, with the rate-limiting step being the initial dehydration of D-xylose triggered by proton attack on the 2-OH group. The addition of TAPT-DHPA reduced the activation energy of this rate-limiting step by 54.43 %.