Pd@Al-containing mesoporous silica Yolk–Shell-structured nanospheres as high performance nanoreactors for the selective hydrogenolysis of glucose to 1,2-propylene glycol

Abstract

In this work, a series of Pd@Al-MSiO2 yolk–shell-structured nanospheres (YSNSs) with different Al contents were synthesized by a facile one-pot method. The EDX elemental analysis and high-magnification TEM image of Pd@Al-MSiO2 YSNSs confirmed that its well-defined yolk-shell structure with a moving Pd core and mesoporous silica shell rich in Al species. Furthermore, Solid state NMR and Py-FTIR results confirmed that Al species grafting mainly formed 4-coordinated Al (AlO4) in the mesoporous silica framework which led to generating abundant Lewis acid sites. The influence of Al species on the physicochemical properties of Pd@Al-MSiO2 YSNSs, as well as their catalytic performance for the hydrogenolysis of glucose to 1,2-propylene glycol (1,2-PG), was investigated. The mesoporous silica shell with abundant Lewis acid sites is a significant contributor to the isomerization of glucose into fructose, while the Pd core plays a role in promoting the hydrogenation of intermediates. The unique hollow space inside the Pd@Al-MSiO2 YSNSs provides a location for the retro-aldol condensation of fructose and consequently avoids direct hydrogenation of fructose. The as-synthesized Pd@Al3-MSiO2 YSNSs shows superior catalytic activity (1,2-PG selectivity of 47.4%, glucose conversion of 95.4%) in the hydrogenolysis of glucose, and far outperforms the Pd/Al3-MSiO2 catalysts. In addition, owing to the influence of the 4-coordinated Al species on the geometry and chemical properties of the mesoporous silica shell, the nanospheres show good stability and reusability over multiple catalytic cycles without significant loss of activity.