Selective Cellulose Hydrogenolysis to 2,5-Hexanedione and 1-Hydroxy-2-hexanone Using Ni@NC Combined with H<sub>3</sub>PO<sub>4</sub>
Yuan Liang, Haiyong Wang, Haosheng Xin, Xiaohong Hu, Long Yan, Qi Zhang, Chenguang Wang, Qiying Liu, Longlong Ma
Abstract
The production of ketones from cellulose is critical but challenging due to the easy hydrogenation of ketone groups. Herein, Ni particles encapsulated in N-doped carbon layers (Ni@NC) were synthesized and used as efficient catalysts for direct cellulose hydrogenolysis to 2,5-hexanedione (HD) and 1-hydroxy-2-hexanone (HHO) in H3PO4 aqueous solution. HD and the first reported HHO in this work could be simultaneously produced with the yields of 34.1% and 24.5%, respectively. It was found that the hydrolyzed glucose was the key intermediate in the formation of these two target products. HD originated from the hydrolysis of 2,5-dimethylfuran (2,5-DMF) that was produced via glucose (from cellulose hydrolysis catalyzed by H3PO4) isomerization to fructose, followed by fructose dehydration to 5-hydroxymethylfurfural (5-HMF) and 5-HMF hydrodeoxgenation. In parallel, HHO was obtained from the selective hydrodeoxygenation of hexoses. The N species of Ni@NC catalysts acted as the basic sites for promoting glucose isomerization to fructose. The production of ketones could be attributed to the tailored hydrogenation ability of Ni@NC, which facilitated the selective preservation of C═O bonds. The synergy between H3PO4 (cellulose hydrolysis and C–O bond splitting by hydrogenolysis), base (aldehyde isomerization to ketone), and metallic Ni (hydrogenation) played an essential role in the formation of ketone-containing products with high yields.