Simply Assembly of Acidic Nanospheres for Efficient Production of 5-Ethoxymethylfurfural from 5-Hydromethylfurfural and Fructose

A series of organic–inorganic acidic hybrids in uniform nanospheres were prepared by self-assembly of phosphotungstic acid (HPW) and pyridine (PY) or triethylamine (TEA) without using a template and surfactant. The prepared samples were characterized by XRD, TEM, FTIR, and N 2 adsorption–desorption isotherms, and their surface acidity was determined by titration. Particularly, PY-PW-1 showed a predominant catalytic performance in the near complete etherification of 5-hydromethylfurfural (HMF) to 5-ethoxymethylfurfural (EMF) with a high yield of 90 % at 80 °C in 24 h, which might be ascribed to its relatively high acidity and smaller particle size. This kinetic study elucidated the superior activity of PY-PW-1 in the HMF-to-EMF conversion. Fructose could also be directly converted to EMF in a moderate yield of 55 % at an elevated temperature of 120 °C by a cascade reaction process. In addition, PY-PW-1 could be reused five times with no evident loss of its catalytic activity. Importantly, the downstream product of EMF (i.e., ethyl levulinate) in an excellent yield of 93 % could also be achieved from HMF by further increasing the reaction temperature to 140 °C.