A Kinetic Modeling of the Liquid-Phase Oxidation of Lactose Over Pt- and Au-Supported Catalysts

• Published in: Topics in catalysis 2016-02, Vol.59 (2-4), p.168-177
• Main Authors: Meyer, C. I., Regenhardt, S. A., Zelin, J., Sebastian, V., Marchi, A. J., Garetto, T. F.
• Format: Article
• Language: English
• Subjects: Catalysis; Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Industrial Chemistry/Chemical Engineering; Original Paper; Pharmacy; Physical Chemistry
• ISSN: 1022-5528; 1572-9028
• DOI: 10.1007/s11244-015-0427-4

Pt and Au catalysts, 2 wt% metal loading, supported on SiO 2 and Al 2 O 3 were used to study the effect of metal and support on the liquid-phase oxidation of lactose. Pt-based catalysts were prepared by incipient wetness impregnation while Au-based catalysts were obtained by the precipitation-deposition method. Catalytic tests were carried out in aqueous phase at 65 °C, using O 2 as oxidizing agent and keeping pH constant at 9 by controlled addition of NaOH aqueous solution. In all of the cases, the only product of reaction detected and quantified was lactobionic acid. It was found that Pt supported on Al 2 O 3 was more active than Pt supported on SiO 2 . This was explained on the basis that metal Pt dispersion on Al 2 O 3 was three times higher than on SiO 2 . At the same time, Au/Al 2 O 3 catalyst was more active than Pt/Al 2 O 3 catalysts. The higher activity of Au/Al 2 O 3 was attributed to Au nanoparticles interacting with the support, as determined by transmission electron microscopy. It was also verified that Au/Al 2 O 3 activity was almost the same after two consecutive runs, indicating a good stability of the Au active phase. Kinetic studies were carried out by varying the initial concentration of lactose in the reaction mixture. A negative order respect to the reactant, determined applying a pseudo-homogeneous model, was estimated, which indicates that lactose molecules are strongly adsorbed on the surface of metal Au nanoparticles. A LHHW model, assuming that oxygen chemisorption was the controlling step, allowed to explain the negative order respect to lactose.