Plasmonic silver nanoparticles promoted sugar conversion to 5-hydroxymethylfurfural over catalysts of immobilised metal ions

Visible light excites the complexes of immobilized metal ions and glucose, promoting the sugar conversion to 5-hydroxymethylfurfural. The silver nanoparticles concentrate incident light to high intensities and significantly enhance the catalytic conversion at the metal ions. It is a new strategy to develop green processes for acid catalysed transformations. [Display omitted] •Metal ions and Ag particles were immobilised on Al2O3 nanofibres for acid catalysis.•Catalytic glucose conversion achieved 68 % HMF yield under visible light at 70 °C.•Light promotes conversion of several sugars; several metal ions act as active sites.•AgNPs concentrate incident light to high intensities, enhancing the photocatalysis.•The presence of AgNPs increased the glucose turnover number by 13.4 times. Plasmonic photocatalysis has attracted significant attention but not been applied to acid-catalysed reactions. Here we report that visible-light irradiation of silver nanoparticles (AgNPs) significantly promotes Lewis acid-catalysis by several immobilised metal ions to dehydrate sugars, producing 5-hydroxymethylfurfural (HMF) in good yields at moderate temperatures. In one example, we achieved a 68 % yield of HMF for the conversion of d-glucose using immobilised Cr3+ ions and AgNPs under visible-light irradiation. The turnover number achieved in the presence of AgNPs is 13.4 times higher than in the absence of AgNPs. We propose a mechanism whereby sugar molecules coordinate to the metal ions, and light absorption by these metal complexes causes electron density distribution shift to the ions, thereby boosting the catalytic activity. Surface plasmon resonance by the AgNPs amplifies incident light to high intensities, considerably promoting catalytic activity. This plasmon-enhanced acid catalysis performance defines a new paradigm and expands photocatalysis applications.