Institute of Physical Chemistry, Polish Academy of Sciences, Warsaw, 01-224, Poland.
Institute of Chemical Technology, Leipzig University, Leipzig, 04103, Germany.
ChemSusChem. 2021 Mar 5;14(5):1351-1362. doi: 10.1002/cssc.202002687. Epub 2021 Jan 21.
Solar energy-driven processes for biomass valorization are priority for the growing industrialized society. To address this challenge, efficient visible light-active photocatalyst for the selective oxidation of biomass-derived platform chemical is highly desirable. Herein, selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) was achieved by visible light-driven photocatalysis over titania. Pristine titania is photocatalytically inactive under visible light, so an unconventional approach was employed for the visible light (λ=515 nm) sensitization of titania via a formation of a visible light-absorbing complex of HMF (substrate) on the titania surface. Surface-complexation of HMF on titania mediated ligand-to-metal charge transfer (LMCT) under visible light, which efficiently catalyzed the oxidation of HMF to DFF. A high DFF selectivity of 87 % was achieved with 59 % HMF conversion after 4 h of illumination. The apparent quantum yield obtained for DFF production was calculated to be 6.3 %. It was proposed that the dissociative interaction of hydroxyl groups of HMF and the titania surface is responsible for the surface-complex formation. When the hydroxyl groups of titania were modified via surface-fluorination or calcination the oxidation of HMF was inhibited under visible light, signifying that hydroxyl groups are decisive for photocatalytic activity.
太阳能驱动的生物质增值过程是日益发展的工业化社会的首要任务。为了解决这一挑战，高效可见光活性光催化剂对于生物质衍生平台化学品的选择性氧化是非常理想的。在此，通过二氧化钛的可见光驱动光催化，实现了 5-羟甲基糠醛（HMF）向 2,5-二糠醛（DFF）的选择性氧化。在可见光下，纯二氧化钛没有光催化活性，因此采用了一种非传统的方法，通过在二氧化钛表面形成 HMF（底物）的可见光吸收络合物，使二氧化钛在可见光（λ=515nm）下敏化。在可见光下，HMF 在二氧化钛上的表面络合介导配体到金属电荷转移（LMCT），有效地催化了 HMF 向 DFF 的氧化。在光照 4 小时后，HMF 的转化率为 59%，DFF 的选择性达到 87%。计算得出 DFF 生成的表观量子产率为 6.3%。据推测，HMF 的羟基与二氧化钛表面的解离相互作用是导致表面络合物形成的原因。当通过表面氟化或煅烧修饰二氧化钛的羟基时，HMF 的氧化在可见光下受到抑制，这表明羟基对于光催化活性是决定性的。
