Designed synthesis N-doped sulfonated bifunctional catalyst for efficient 5-hydroxymethylfurfural production: A pyridinic N-triggered proton-shift mechanism at basic sites

Abstract

Considering the essential role of acidic/basic sites in efficient 5-hydroxymentylfurfural (5-HMF) production from cellulose, the superiority of acid-base bifunctional catalysts was unfolded. However, the lack of in-depth research on catalytic mechanism of active sites, especially the basic sites, greatly hinders its chemical utilization. Herein, N-doped sulfonated bifunctional catalysts were rationally designed. The synthesized NCS-1H catalyst exhibited outstanding activity and recyclability. Favorable 5-HMF yield of 50.0 % with 62.9 % of selectivity was obtained. Spin polarized density function theory (DFT) analysis revealed a pyridinic N-triggered proton-shift mechanism of glucose isomerization. Catalyzed by pyridinic N, the proton of glucose on C2 was shifted to O5, leading to the cleavage of C1-O1 bond. As a result, an enol intermediate was formed and converted to fructose. Compared to pyrrolic N and graphitic N, pyridinic N significantly reduced the reaction energy barrier of rate-determining step to 0.79 eV, i.e., C1-O1 bond cleavage.