Fully catalytic upgrading synthesis of 5-Ethoxymethylfurfural from biomass-derived 5-Hydroxymethylfurfural over recyclable layered-niobium-molybdate solid acid

Biomass-derived resources exploited in depth toward the synthesis of high value-added chemicals is very promising, but still limited by the applicable catalyst. In this paper, we report regulated robust multilayer-like polyoxometalates(Niobium molybdate) specific to the catalytic synthesis of promising 5-Ethoxymethylfurfural (EMF). The present solid acid catalysts resulted from precisely-tuned compositions of Nb and Mo toward acquiring controlled Brønsted acid amounts and interlayer space coupling with specific Lewis acid sites are demonstrated to be the determining factors for tuning conversion and selectivity in the synthesis of EMF, respectively. The characterization results indicate that the increment in Nb moiety is beneficial to produce more accessible acid sites and the enlarged interlayer space in the catalyst, thereby promoting the acid-catalyzed conversion. As a result, the full conversion(Conv. 100%) of 5-hydroxymethylfurfural into the 5-Ethoxymethylfurfural (Select. >99%) by etherification with ethanol within only 60 min was realized as the record-high yield under the solvent-free condition, far outperforming several traditional catalysts. In addition, the rational 67% yield of EMF was received when using fructose as an initial reactant. Ulteriorly, the resultant catalyst inherits the superior catalytic activity in the substrate expansion experiments in the presence of different alcohols. More importantly, the resulted catalyst shows durable catalytic activity without any activity-loss during the eight recycling, which reveals the huge potential industrial application prospect.