Solid superacid SO42−/TiO2/Al2O3 with unique “Ecological Infiltration System” for efficient catalytic synthesis of cellulose triacetate

Abstract

Cellulose triacetate is a vital derivative of cellulose, which normally adopts H₂SO₄ as catalysts, facing huge challenges associated with cellulose degradation and acid wastewater disposal. SO₄²⁻/M_xO_y has been proven to have higher catalytic performance in cellulose acetylation. However, the obvious loss of sulfur species can induce serious catalyst deactivation. Herein, an innovative solid superacid SO₄²⁻/TiO₂/Al₂O₃ successfully fabricated by carrier-supporting strategy can realize the effective synthesis of cellulose triacetate (CTA). Research displayed that compared with SO₄²⁻/TiO₂, SO₄²⁻/TiO₂/Al₂O₃ presented loose and small irregular nanoparticles with much rough surface morphology. Meanwhile, the incorporation of Al₂O₃ enhanced the overall acidic content by forming new Al-O = S bonds and providing empty places for accepting electrons acting as Lewis acids. The highly exposed active surface area along with copious and stable total acid sites may accelerate solution penetration and provide lasting high catalytic efficiency. When used for CTA production, SO₄²⁻/TiO₂/Al₂O₃ acquired a maximum degree of substitution (DS) of 2.97. Notably, it exhibited superior cyclic stability and only displayed a 1.7% DS drop after 5 CTA synthesis. Moreover, the resultant CTAs indicated splendid homogeneity, showing huge practical application potential. The finding depicts that sustainable SO₄²⁻/TiO₂/Al₂O₃ may enable the use of alternative cellulose sources for the production of high-quality CTA.