Gold based on SBA-15 supports – Promising catalysts in base-free glucose oxidation

Abstract

SBA-15, NbSBA-15, Ca/SBA-15 and Ca/NbSBA-15 were tested as supports for gold in order to obtain effective catalysts for environmentally friendly base-free aerobic selective oxidation of glucose to gluconic acid. Detailed characterization of all catalysts and analyses of their activity allowed to determine the most important features conducive to high efficiency of gold catalysts in this reaction. These features include relatively large/medium sized gold particles endowed with negative charge and the support composition which ensures that negatively charged gold species are exclusively present in a fresh catalyst. Metal-support and reagent-support interactions are attributed to chemical composition of the supports. The most active catalyst was Au/SBA-15 in whose negatively charged gold particles were active in both glucose chemisorption and oxygen adsorption in the form of superoxo species. According to our knowledge the role of negatively charged gold particles in glucose oxidation is considered for the first time. Au/SBA-15 catalyst has been found promising because of its very high activity in glucose oxidation, easy preparation procedure and relatively high stability. Calcium dopant in Au/Ca/SBA-15 enhanced dispersion of gold, stabilized the catalyst but only in four initial reaction cycles and decreased the activity by lowering of zeta potential.