A high-efficiency zirconium-based single-atom catalyst for the transformation of biomass-derived 5 hydroxymethylfurfural to 2,5-bis(hydroxymethyl)furan with nearly 100% selectivity

Abstract

Zirconium-organic coordination catalysts (ZOCCs), possessing abundant zirconium–oxygen active species (Zr−O_x), have been widely used for the transformation of biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-bis(hydroxymethyl)furan (BHMF) via transfer hydrogenation (TH). However, most ZOCCs contain a high content of Zr and show low selectivity and turnover frequency (TOF) in primary alcohols, which greatly limit their practical application. In this work, we constructed a high-efficiency Zr-based single-atom catalyst (Zr/NC) with merely 0.58 wt% Zr by directly pyrolyzing Zr-doped ZIF-8. The experimental and theoretical results indicated that the atomically dispersed Zr–N₄ coordination centers were confirmed to be the catalytic sites, and they displayed a fantastic catalytic activity. When isopropanol was used as a typical hydrogen donor, HMF could be completely converted with nearly 100% BHMF selectivity and 124.26 h⁻¹ TOF in 150 min at 130 °C. More gratifyingly, when the hydrogen donor was switched to ethanol or n-butanol, the BHMF yield and selectivity were still more than 95% under appropriate reaction conditions. Such a remarkable performance should be principally attributed to the electron transfer from the pyridinic-N to Zr in Zr–N₄ catalytic sites with high Lewis acid–base strengths, which could change the electron cloud densities of metal and ligand centers and then facilitate the formation of the target product. Additionally, mechanism studies revealed that the direct hydrogen transfer from the α-C of iPrOH to the carbonyl carbon of HMF on Zr–N₄ catalytic sites was the rate-controlling step in the process of TH. Furthermore, Zr/NC could also exhibit excellent substrate applicability. To the best of our knowledge, this is the first work on the synthesis of a Zr-based single-atom catalyst with Zr–N₄ catalytic sites to boost catalytic activity in the TH of biomass-derived carbonyl compounds.