The effect of bismuth on the selective oxidation of lactose on supported palladium catalysts.

The selective oxidation of lactose by molecular oxygen has been studied in a batch reactor containing an aqueous slurry of 0.5 kmol m-1 reactant and 1.0 kg m-3 catalyst. The in situ Bi promotion of a commercial Pd-C catalyst resulted in 100% selectivity to sodium lactobionate up to conversions of 95% in the pH range 7-10 and at temperatures up to 333 K. Performing the reaction under such conditions that the oxygen transfer to the liquid phase was rate-controlling allowed the production of sodium lactobionate in high yields in approximately 1 h. A maximum initial reaction-rate of 0.47 mol kg-1 s-1 was found at a molar Bi to Pd ratio of 0.50-0.67. Fifteen batches of lactose were oxidized with the same charge of catalyst without significant loss in initial activity or selectivity. Such other aldoses as maltose, glucose, and galactose could be oxidized analogously with similar selectivities.