Hydroxyapatite supported gold nanocatalyst for base-free oxidative esterification of 5-hydroxymethyl-2-furfural to 2,5-furan dimethylcarboxylate with air as oxidant

A series of gold (Au) nanocatalysts has been prepared for base-free protocol-oxidative esterification of lignocellulosic biomass derived 5-hydroxymethyl-2-furfural (HMF) to 2,5-furan dimethylcarboxylate (FDMC) in the presence of air. The prepared Au-based nanocatalysts are thoroughly characterized by various analytical techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N-2-physisorption (adsorption-desorption) method, inductive coupled plasma-atomic emission (ICP-AES) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Moreover, the surface properties of Au-based nanocatalysts were investigated by temperature-programmed desorption of carbon dioxide (CO2-TPD) technique. For a comparison point of view, the activity tests of various prepared metal-based nanocatalysts have also been carried out. Among all, hydroxyapatite (HAP) supported Au nanocatalyst (Au/HAP) prepared by homogeneous deposition-precipitation (HDP) method was found to be the best to give 89.3% yield of FDMC from oxidative esterification of HMF in the presence of air. The excellent yield of FDMC could be attributed to stronger basic sites on the surface of the catalyst. Furthermore, Au/HAP nanocatalyst was simply recovered and reused, which retained its original activity even after five consecutive times without significant loss of original activity, supporting its reusability and stability. (C) 2018 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.