Mingyu Zhang

Synthesis and characterization of a multifunctional nanocatalyst based on a novel type of binary-metal-oxide-coated Fe3O4–Au nanoparticle

A novel type of binary-metal-oxide-coated Au nanocatalyst, including a mixed oxide layer, a moveable magnetic Fe3O4 core and some Au NPs of 2–5 nm, has been synthesized successfully by a facile hydrothermal synthesis method. SEM, TEM, EDX, FTIR, XRD, and TGA were employed to characterize the prepared samples. The results showed the mSiO2–TiO2 layer could increase the thermal stability and reactivity of metal nanocatalysts compared to a pure TiO2 or SiO2 layer. The reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) was employed as a model reaction to test catalytic performance in this work. The results showed that the binary-metal-oxide-coated nanocatalyst (550 °C) exhibited significantly enhanced catalytic performance compared with the pure SiO2 (550 °C) or TiO2 (550 °C). In particular, the mSiO2–TiO2/Au/C/Fe3O4 particles calcined at 550 °C showed the highest catalytic activity, compared to the samples calcined at 700 °C, 300 °C and RT. Meanwhile, because of C layer burning, the sample presented a few white spots between the Fe3O4 microsphere and the oxide layer, suggesting that the specific surface area was increased by calcination. The sample (550 °C) still has a certain degree of magnetism, suggesting the desired samples could be separated by magnet. Finally, to explain the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), a possible reaction mechanism was also proposed.

Self-assembly of hollow spherical nanocatalysts with encapsulated Pt NPs and the effect of Ce-dipping on catalytic activity

This article reports a facile and controllable one-step method to construct Pt@hollow mesoporous SiO2 (Pt@HMSiO2) nanoparticles (NPs). To enhance the catalytic activity, cerium species were impregnated into Pt@HMSiO2 NPs, fabricating highly reactive Pt–CeO2@HMSiO2 NPs. To verify the successful synthesis of the Pt@HMSiO2 and Pt–CeO2@HMSiO2 NPs, and study the influence of CeO2 species on the catalytic performance, the as-prepared NPs were characterized by several techniques, including SEM, TEM, EDX, FTIR, XRD, BET and UV-vis analyses. In this work, the reduction of 4-NP was employed as a model reaction to test the catalytic performance. Compared to Pt@HMSiO2, the Pt–CeO2@HMSiO2 NPs show higher catalytic activity, because of the co-catalysis of CeO2 NPs. However, the excess amount of CeO2 NPs would lead to a lower catalytic activity, due to the blocking of the catalyst pore. In addition, the Pt–CeO2@HMSiO2 NPs show a high thermal stability due to the protection of the SiO2 shell. Meanwhile, we have also used the reaction of propane dehydrogenation to further verify the excellent catalytic stability of Pt–CeO2@HMSiO2 NPs. This strategy is novel, albeit efficient, and can be extended to the preparation of other nanocatalysts.

Self-assembly structural transition of protic ionic liquids and P123 for inducing hierarchical porous materials

Hierarchical micro–mesoporous silica–zirconium has been obtained by adjusting the interaction between protic ionic liquids (NTA) and Pluronic 123 surfactant through changing the content of NTA and the pH of the solutions. This has resulted in modification of the packing of NTA micelles and P123 micelles, leading to silica–zirconium with different textural and structure characteristics. The structure, crystalline state and textural properties of the materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) analyses and nitrogen adsorption/desorption techniques. The results revealed that NTA displayed notable synergic interaction with P123 by changing the pH of the solution. Two kinds of pore channels could be observed from the materials when the pH was 2. When increasing the pH, a mesocelluar foam, branch-like structure and sphere structure were synthesized, indicating NTA and P123 can exhibit different forms in water at different pH values, which strongly influences the interaction between the NTA and P123, and sequentially changes the self-assembly structure of the mixed micelles in water. Moreover, the formation mechanism of the hierarchical porous silica–zirconium which is based on the interaction between NTA and P123 is tentatively elucidated by studying the size of the NTA/P123 micelles at different compositions. The catalytic behaviors of the materials were investigated in the alkylation of o-xylene with styrene.

Dispersed gold nanoparticles supported in the pores of flower-like macrocellular siliceous foams based on an ionic liquid as catalysts for reduction

A facile method has been developed for the synthesis of a flower-like macrocellular siliceous foam with a large and uniform pore size, using P123 and protic ionic liquid as the co-templates under acidic conditions. The influence of the protic ionic liquid concentration and the hydrothermal temperature on the synthesis of the macrocellular siliceous foam is systematically investigated. The structures of all the composites were characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), X-ray powder diffraction (XRD), UV-vis diffuse reflection spectroscopy, and N2 gas sorption. The results showed that the flower-like macrocellular siliceous foam possessed about 100 nm sized large pores, which was appropriate for it to be applied in catalytic reactions. Moreover, Au NPs were immobilized in the pores of the flower-like macrocellular siliceous foam through a self-assembly procedure. The obtained NH2-S-6-393/Au sample exhibited a remarkably higher catalytic activity in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by NaBH4. The macrocellular siliceous foams are suitable supports for catalytic reactions on account of their special structure and can be highly beneficial for a wide range of applications.