Au负载SBA-15分子筛上葡萄糖氧化反应

探讨了金与铝改性的SBA-15分子筛催化剂(Au-Al/SBA-15)上活性中心与葡萄糖氧化制葡萄酸反应性能的关系.通过固体核磁共振波谱(ss NMR)、X射线光电子能谱(XPS)、紫外-可见光谱(UV-Vis)和透射电子显微镜(TEM)等手段对不同Au及Al含量的Au-Al/SBA-15催化剂进行了结构表征.发现Al改性能够在SBA-15载体上产生四配位Al物种,Au主要以单质的形式存在; SBA-15上的四配位Al物种具有稳定Au颗粒大小的作用.通过对比发现,催化剂上的Au和骨架四配位Al物种间的相互协作促进了对葡萄糖氧化的活性,而非骨架Al物种会导致副反应的发生,降低葡萄糖酸产物的选择性.通过固体13C NMR揭示了反应体系中的NaOH能够将强吸附的产物葡萄糖酸分子从催化剂表面解离,保持活性位不被覆盖进而促进反应持续进行.

Glucose Oxidation on Au-supported SBA-15 Molecular Sieve †

Conversion of glucose to high-valued chemicals is one of the important routes for biomass utilization. Gold and aluminum modified SBA-15 molecular sieve catalysts(Au-Al/SBA-15) were prepared for aerobic oxidation of glucose. The active site-catalytic performance relationship was investigated. The structures of Au-Al/SBA-15 catalysts with different Au and Al contents were characterized by means of solid-state nuclear magnetic resonance(NMR) in combination with other techniques. It was found that four-coordinated Al is generated on SAB-15 and Au mainly exists in form of metallic state. The supported Au can be stabilized by four-coordinated Al, resulting in smaller Au particles on SBA-15. The interaction between Au and Al species promotes glucose oxidation, while the extra-framework Al species causes the side reaction and lower selectivity to gluconic acid. The role of NaOH in the reaction was revealed by ¹³C solid-state NMR experiments, it benefits desorption of gluconic acid molecules from the catalyst surface, keeping the active sites uncovered and promoting the reaction.