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.