Sulfated complex metal oxides solid acids with dual Bronsted-Lewis acidic property for production of 5-ethoxymethylfurfural from biomass-derived carbohydrates

The transformation of aldose-based carbohydrates into 5-ethoxymethylfurfural (EMF) is very challenging as compared to ketose-based carbohydrates, but the formers are more abundant and cheaper. Here, a series of sulfated complex metal oxides were synthesized for the conversion of aldose-based mono-, di-, and polysaccharides, as well as starchy food waste into EMF. The catalysts were carefully characterized and the results showed that the type and strength of the acid sites were more important than their concentration. It was also shown that the efficiency of these catalysts was significantly affected by the metal species in the catalyst composition and followed the order tetra- > tri- > bi- > mono-component metal oxides based catalyst. Among the prepared catalysts, Zr-Sn-Fe-Al-O-S exhibited superior catalytic activity, with an EMF yield of 33.1% from glucose, and yields ranging from 4.1-26.3% for di-, poly-saccharides and starchy food waste in ethanol/ dimethyl sulfoxide solvent system under glucose/catalyst mass ratio of 4. The role of co-solvent in the reaction pathway was also studied. It was found that the predominant reaction pathway for EMF production was closely related to the co-solvent amount. A kinetic model of glucose conversion to EMF was developed and the thermodynamic analysis was performed, the main features of the experimental observations can be described by the model. Zr-Sn-Fe-Al-O-S was reused for four runs without intermediate regeneration steps, showing a slight decay in activity. After reactivation by calcination before the fifth cycle, the catalyst recovered its activity, indicating good reusability and thermal stability.