Arabinose oxidation in a fixed bed of extrudates and solid foams containing gold nanoparticles

Oxidation of arabinose was investigated in a tandem reactor system comprising a fixed bed of gold catalysts supported on extrudates or solid foams and a stirred tank allowing operation under constant pH of 8. Powder catalyst containing 3 wt% Au deposited on γ-alumina was extruded with γ-alumina and attapulgite or sepiolite as a binder or deposited on the solid open-cell aluminum foam after anodic oxidation pretreatment. Alternatively, deposition precipitation of gold with urea from HAuCl4 precursor was done directly on the extruded support or the solid foam.

The presence of gold was essential for catalytic activity which in the applied reactor set-up was strongly limited by mass transfer. Arabinose was rather selectively (ca. 90–95% at full conversion) oxidized to arabinonic acid giving besides arabinolactone other by-products. A mathematical model was developed for the open foam catalyst structures and the extrudates, comprising intrinsic kinetics deduced from batch experiments and the mass transfer within the solid catalyst.