Jun Yan,Longlong Shan,Xiaoli Gu,Xingguang Zhang,Junmeng Cai
Three series of catalysts consisting of gold (Au), platinum (Pt), or gold-platinum bimetallic nanoparticles (NPs) with controlled sizes (Au NPs 10 ± 2 nm, Pt NPs 6 ± 2 nm) anchored on hierarchical micro-/meso-/macroporous silica were successfully developed and systematically evaluated for the selective oxidation of aromatic alcohols to their corresponding aldehydes. The catalysts were prepared by the sol-immobilization method using as-made Au NPs and/or Pt NPs colloids; the silica supports were prepared with controlled pore structures and the hierarchical porous structures of catalysts were created by controllable desilication via the alkaline solution of the metal colloids. The catalysts were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), and these results showed no synergistic effect between Au and Pt on boosting the catalytic performance, whereas they demonstrated a clear dependence of catalytic conversions and reaction rates on the structural porosity of Au-Pt bimetallic catalysts. Our findings could potentially inspire peer researchers and scientists to develop designer porous catalysts and processes in the selective organic conversions.Keywords:steric effect;Au-Pt catalysts;alcohol oxidation;hierarchical porous silica
The specific structure of the support and the interactions between the catalyst components can lead to electron transfer, which in turn could affect the catalytic performance in heterogeneous catalytic reactions. In this paper, we have successfully prepared MnxOyCz composite materials from the calcination of the Mn-organic framework. Then bimetallic Au–Pt nanoparticles (NPs) were supported onto MnxOyCz via the colloidal-deposition method. These catalysts were tested in the selective oxidation of glycerol to glyceric acid under basic conditions. The results demonstrated that the catalytic activity of the bimetallic Au–Pt/MnxOyCz catalyst is considerably superior to those of the monometallic (Au and Pt) supported catalysts. Under the optimized conditions, 100% of glycerol can convert with 57.3% selectivity of glyceric acid. Multicharacterizations showed that the strong interaction between Au and Pt in the Au–Pt/MnxOyCz catalyst can enhance the dispersion of Au–Pt alloy NPs, promoting the electronic coupling effect on the metal surface. At the same time, the rich oxygen vacancies in this catalyst can facilitate the activation of oxygen, which causes the Au–Pt/MnxOyCz catalyst to show better catalytic activity. Specifically, the interaction between Au and Pt not only decreases the particle size of the Au–Pt alloy NPs but also promotes the reduction of Mn-based oxides and the mobility of oxygen. The absence of Au leads to a decrease in Pt 4f7/2 binding energy, resulting in an enrichment of electrons at the Pt active site and enhancing the oxidation ability of the primary hydroxyl group. In addition, the Au–Pt/MnxOyCz catalyst showed excellent stability without substantial loss of activity after being recycled five times. The insights and methodology may provide some new guidance for the reasonable design of bimetallic catalysts for the catalytic oxidation of biopolyols under mild conditions.
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