In this work, Au-Ag based catalysts supported on Al₂O₃ were prepared by a precipitation-deposition method at controlled pH and tested in the selective lactose (LA) oxidation to lactobionic acid (LB) in aqueous phase. Combining XPS and STEM-HAADF, it was found that there is an important surface Ag enrichment of bimetallic nanoparticles for bulk atomic ratios Au/(Au + Ag)>0.5. These bimetallic nanoparticles were active for the selective LA oxidation into LB and the maximum activity was reached with Au/(Au + Ag) = 0.9. In this case, the surface Au/(Au + Ag) atomic ratio was about 0.5, which indicates that there is the same amount of both elements at the active surface of the catalyst. Assuming that LA is chemisorbed on Au sites, and O₂ on Ag ones, this particular surface atomic ratio would favor the interaction and reaction between both reactants. Thus, the synergistic effect between Au and Ag could explain the results of this study. A compensation effect between frequency factor and activation energy supports the existence of such synergy. If the atomic ratio is Au/(Au + Ag)≤0.5, a layer of Ag deposits over the Au nanoparticles (core-shell structure) and the conversion of LA into LB drops to zero.

在这项工作中，通过沉淀-沉积法在控制的pH值下制备了负载在Al ₂ O ₃上的Au-Ag基催化剂，并在水相中将选择性乳糖（LA）氧化为乳糖酸（LB）进行了测试。结合XPS和STEM-HAADF，发现对于体积比Au /（Au + Ag）> 0.5的双金属纳米粒子，存在重要的表面Ag富集。这些双金属纳米粒子对选择性LA氧化为LB具有活性，并且在Au /（Au + Ag）= 0.9时达到了最大活性。在这种情况下，表面Au /（Au + Ag）的原子比约为0.5，这表明在催化剂的活性表面上两种元素的含量相同。假设LA被化学吸附在Au位和O _2上对于银，该特定的表面原子比将有利于两种反应物之间的相互作用和反应。因此，金和银之间的协同作用可以解释本研究的结果。频率因子和激活能之间的补偿效应支持了这种协同作用的存在。如果原子比为Au /（Au + Ag）≤0.5，则在Au纳米颗粒（核-壳结构）上会沉积一层Ag，并且LA到LB的转化率将降至零。