(426e) Selective Lactose Conversion to Lactobionic Acid Via Aerobic Oxidation Over Gold-Based Mesostructured Catalysts

Lactobionic acid (LBA) (4-O-ß-D-galactopyranosyl-D-gluconic acid), is a high-value derivative of lactose oxidation. Presently, LBA is available for pharmaceutical use in small quantities at a high cost. LBA is also used in calcium supplementation, and represents a new ingredient in skin care products featuring potent antioxidant and humectant properties. In the food industry, LBA can be used as acidulant with a sweet taste; as filler in cheese production; as firming agent, and to fortify functional drinks with essential minerals. Catalytic oxidation approach can be advantageous from industrial stand point to produce LBA at reasonable costs. Carbon supported catalyst system consisting of palladium, and bismuth as oxidation promoter, has been used for the conversion of sugars. However this system does not maintain continuous dehydrogenation of sugars and he reaction stops as the catalyst surface is saturated with aldonic acid and suffers from deactivation by overoxidation. The aim of this work is to selectively produce LBA for use in therapeutic, pharmaceutical and food applications by partial oxidation of lactose over a novel Au-based catalyst using nanostructred silica materials with improved activity, selectivity and stability. Highly active gold catalysts supported on mesoporous silica were successfully synthesized, and their catalytic activity was evaluated for the oxidation of lactose to lactobionic acid (LBA) in an agitated semi-batch reactor. The catalysts were characterized by BET surface, XRD, XPS and TEM. The XPS measurements indicated that gold particles were present in the catalysts as both metallic (Au⁰) and oxidized (Au⁺ and Au³⁺) species. The influence of the reaction conditions, i.e., temperature, pH value, metal loading and catalyst/lactose ratio on lactose conversion were also investigated. After a reaction time of 2h, the catalyst containing 0.7%Au showed the highest catalytic activity (>99% lactose conversion) and a total selectivity towards LBA, when it was used at 0.2 w/w catalyst/lactose ratio under alkaline (pH 9.0) mild reaction temperature (65^ºC).