Aqueous-phase oxidation of 5-hydroxymethylfurfural over Pt/ZrO2 catalysts: Exploiting the alkalinity of the reaction medium and catalyst basicity

Abstract

The basicity required for the aqueous-phase selective oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid (FDCA) is explored through different approaches. Homogeneous hydroxides were tested along with a Pt/ZrO2 catalyst to establish a benchmark with widespread literature. Insoluble hydroxides were then taken to evaluate the behavior of dual metal/base heterogeneous catalytic systems. Finally, an attempt to bring such alkalinity to a bifunctional catalyst was investigated by using ZrO2-based solid solutions as supports. Mg, Ca, Y, and Ti were used as dopants. It was seen that a moderate alkali solution leads to 70% yield to FDCA. Equivalent yields are achieved by replacing homogeneous alkali by poorly soluble Mg(OH)2 in a heterogeneous system. Performing aqueous-phase oxidation under base-free conditions on ZrO2-doped supported catalysts indicated that the production of FDCA is associated with the reaction pH imposed by the bifunctional catalyst itself. Among the studied dopants, Mg-containing catalysts were the ones capable of promoting selective oxidation. However, it is shown that hosting Mg into the ZrO2 crystalline structure does not prevent leaching upon reaction in an aqueous medium.