Cu-based catalysts for hydrogenation of 5-hydroxymethylfurfural: Understanding of the coordination between copper and alkali/alkaline earth additives

Abstract

This study investigated impacts of alkali or alkaline earth metals additives (Na, K, Mg, Ca, Sr or Ba) on the physicochemical properties and catalytic behaviors of Cu/Al2O3 catalyst in hydrogenation of 5-hydroxymethylfurfural (HMF). Na or K addition to Cu/Al2O3 led to the decreased specific area via merging of the small pores and the partial transformation of γ-Al2O3 into AlOOH phase. Na, K or Mg addition could drastically increase the activity for hydrogenation of HMF to 2,5-dihydroxy methyl furan (DHMF) at low temperatures (i.e. 60 °C), possibly attributing to the increased weak alkaline sites and the synergetic effects between the additives and copper. In addition, the additives could effectively suppress the hydrogenolysis or the opening of furan ring, retaining DHMF, the major initial product from HMF hydrogenation, in the reaction medium. The in situ DRIFTS of hydrogenation of HMF and in situ DRIFTS-MS of thermal treatment of HMF indicated the presence of the additives significantly impacted the reaction intermediates formed during the hydrogenation of HMF.