Effective gold catalyst supported on mesoporous silica decorated by ceria for the synthesis of high value lactobionic acid
Gold supported on mesoporous SBA-15 and SBA-15-CeO2 with Ce/Si molar ratios of 0.1, 0.2, 0.4 and 0.6 were synthesized via wet chemical process using a gold cationic complex precursor [Au(en)2]3+ (en = ethylenediamine), and investigated as catalysts for the partial oxidation of lactose to selectively synthesize lactobionic acid (LBA) for therapeutic, pharmaceutical and food grad applications.These catalysts were characterized by N2 physisorption, XRD, FT-IR, TEM and XPS. N2 physisorption and XRD analysis revealed that SBA-15-CeO2 with the investigated Ce/Si molar ratios support possess ordered hexagonal mesoporous structure, characterized with a high surface area and large pore volume, similar to SBA-15, whereas BET surface area and pore volume of catalyst were significantly decreased upon impregnation. XPS analysis revealed the coexistence of metallic and oxidized gold species (Au0, Au+ and Au3+) in all prepared catalysts and the presence of both Ce3+ and Ce4+ oxidation states for gold supported on mesoporous SBA-15-CeO2 catalysts.The influence of the pH value on lactose conversion was also investigated. After 60 min of reaction, the 0.7%Au/SBA-15-CeO2 (Ce/Si = 0.1 and 0.2) catalysts showed high catalytic activity (100% lactose conversion) and a 100% selectivity towards LBA, when they were used at a catalyst/lactose ratio of 0.2, under alkaline (pH 9.0) and mild reaction temperature (65 °C). At the optimized conditions, 0.7% Au/SBA-15-CeO2 catalysts with Ce/Si of 0.1, 0.2 and 0.4 were more active than 0.7% Au/SBA-15 catalyst. A maximum of activity is reached at Ce/Si of 0.2. The experimental catalytic tests and characterizations show clearly the role of Ce in the enhancement in the catalyst activity was the coordination and agglomeration states of Ce atoms could have an important effect.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (135 K)Download as PowerPoint slideHighlights► Rapid and simple synthesis method of very active Au catalyst for the aerobic oxidation of lactose. ► The catalyst presents a regular array of mesopores and well dispersed spherical AuNPs. ► Lactose is almost depleted after 60 min of reaction using the 0.7%Au/SBA-15-CeO2 catalyst. ► The 0.7%Au/SBA-15-CeO2 is 100% selective towards LBA production.
Journal: Applied Catalysis A: General - Volumes 425–426, 28 May 2012, Pages 213–223