High selective oxidation of 5-hydroxymethyl furfural to 5-hydroxymethyl-2-furan carboxylic acid using Ag-TiO2

Production of 5-hydroxymethyl-2-furan carboxylic acid (HMFCA) from 5-hydroxymethylfurfural (HMF) selective oxidation using Ag-TiO2 were investigated under oxygen atmosphere. The novel catalyst was prepared by a simple sol-gel method, different characterizations were performed, which included N2 adsorption and desorption measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), NH3/CO2 temperature-programmed desorption (NH3/CO2-TPD), scanning electron microscope (SEM), and high revolution transmission electron microscope (HR-TEM). Reaction parameters, such as temperature, base content, oxygen pressure, catalyst loading and reaction time were investigated. 99% HMF conversion, 96% HMFCA yield, and 97% HMFCA selectivity obtained under optimum condition (25 mg Ag-TiO2, 4 eq. Na2CO3, 1 MPa O2, 80 °C, 32 h). Catalyst stability experiment revealed negligible deactivation (90% HMF conversion and 85% HMFCA yield in fourth time). The appropriate proportion of acidic/basic sites, large surface areas, and strong synergistic interaction between Ag+, metallic Ag and TiO2 for oxygen activation attributed to high catalytic activation.