Shuo Zhao

Synthesis of immobilized heteropolyanion-based ionic liquids on mesoporous silica SBA-15 as a heterogeneous catalyst for alkylation

Phosphotungstic acid (H3PW12O40) has been successfully loaded onto sulfonate-functionalized ionic liquid-modified mesoporous silica SBA-15 by total anion-exchange. The immobilized catalysts were characterized by XRD, N2 adsorption, TEM, and FTIR spectroscopy. Characterization results show that the mesopore structure of SBA-15 was maintained well even after surface modification and the subsequent anion-exchange step of [PW12O40]3− (PW). In comparison with the task-specific basic ionic liquid (1-(propyl-3-sulfonate) 3-methyl-imidazolium phosphotungstate), the obtained catalyst showed much higher efficiency in alkylation of o-xylene with styrene. More importantly, such an immobilized task-specific basic ionic liquid could be reused without significant loss of catalytic activity even after recycling six times.

In-situ formation of supported Au nanoparticles in hierarchical yolk-shell CeO2/mSiO2 structures as highly reactive and sinter-resistant catalysts

A novel strategy was described to construct Au-based yolk-shell SCVmS-Au nanocomposites (NCs), which combined the sol-gel template-assisted process for the assembly of hierarchical SCVmS NCs with modified CeO2/mSiO2 as yolks/shells, and the unique deposition-precipitation (DP) process mediated with Au(en)2Cl3 compounds for the synthesis of extremely stable supported Au nanoparticles (NPs). Characterization results indicated that the obtained SCVmS-Au NCs featured mesoporous silica shells, tunable interlayer voids, movable CeO2-modified cores and numerous sub-5nm Au NPs. Notably, the Au(en)2Cl3 was employed as gold precursors to chemically modify into the modulated yolk-shell structure through the DP process and the subsequent low-temperature hydrogen reduction induced the in-situ formation of abundant supported Au NPs, bestowing these metal NPs with ultrafine grain size and outstanding sinter-resistant properties that endured harsh thermal conditions up to 750°C. Benefiting from the structural advantages and enhanced synergy of CeO2-Au/mSiO2-Au yolks/shells, the SCVmS-Au was demonstrated as markedly efficient catalysts with superior activity and reusability in catalyzing the reduction of 4-nitrophenol to 4-aminophenol, and its pristine morphology still maintained after eight recycling tests.

Synthesis and characterization of hollow ZrO2–TiO2/Au spheres as a highly thermal stability nanocatalyst

A novel binary-metal-oxide-coated hollow microspheres-titanium dioxide-zirconium dioxide-coated Au nanocatalyst was prepared via a facile hydrothermal synthesis method. SEM, TEM, EDX, FTIR, XRD, UV-vis and XPS analyses were employed to characterize the composition, structure, and morphology of ZrO2-TiO2 hollow spheres. The size of Au nanoparticles was found to be 3-5nm in diameter before being immobilized on the aforementioned mesoporous ZrO2-TiO2 layer and used as catalysts in the reduction of 4-nitrophenol to 4-aminophenol by NaBH4. Compared with TiO2/Au and ZrO2/Au, ZrO2-TiO2/Au NPs showed a higher catalytic activity because of due to mixed oxide synergistic effect. Besides, the sample gets the highest thermal stability and reactivity at 550°C, after calcining the hollow ZT/Au NPs at 550°C, 300°C and room temperature, respectively. Finally, a possible reaction mechanism was also proposed to explain the reduction of 4-nitrophenol to 4-aminophenol over ZrO2-TiO2/Au catalyst.

Fabrication of Ellipsoidal Silica Yolk–Shell Magnetic Structures with Extremely Stable Au Nanoparticles as Highly Reactive and Recoverable Catalysts

A novel strategy was reported for the fabrication of yolk-shell magnetic MFSVmS-Au nanocomposites (NCs) consisting of double-layered ellipsoidal mesoporous silica shells, numerous sub-4 nm Au nanoparticles (NPs), and magnetic Fe central cores. The hierarchical FSVmS NCs with ellipsoidal α-Fe2O3@mSiO2/mSiO2 as yolks/shells were first prepared through the facile sol-gel template-assisted method, and plenty of extremely stable ultrafine Au NPs were postencapsulated within interlayer cavities through the unique deposition-precipitation method mediated with Au(en)2Cl3 compounds. Notably, ethylenediamine ligands were used to synthesize the stable cationic complexes, [Au(en)2]3+, that readily underwent the deprotonation reaction to chemically modify negatively charged mesoporous silica under alkaline conditions. The subsequent two-stage programmed hydrogen annealing initiated the in situ formation of Au NPs and the reduction of α-Fe2O3 to magnetic Fe, where the synthesized Au NPs were highly resistant to harsh thermal sintering even at 700 °C. Given its structural superiority and magnetic nature, the MFSVmS-Au was demonstrated to be a highly efficient and recoverable nanocatalyst with superior activity and reusability toward the reduction of 4-nitrophenol to 4-aminophenol, and the pristine morphology was retained after six recycling tests.

Synthesis of ordered mesoporous La2O3-ZrO2 composites with encapsulated Pt NPs and the effect of La-dopping on catalytic activity

In this work, we report a feasible approach to synthesize a ternary nanocomposites, Pt/lanthanum doped mesoporous zirconium oxide (Pt/La2O3-ZrO2), via an effective two-step method. Ordered mesoporous La2O3-ZrO2 composites were firstly fabricated with mesoporous silica KIT-6 as a hard template. Subsequently, uniform Pt nanoparticles encapsulated by 4 hydroxyl-terminated poly (amidoamine) (G4-OH PAMAM) dendrimers were deposited on the La2O3-ZrO2 composites. The as-prepared samples were characterized by transmission electron microscope (TEM), N2 adsorption-desorption isotherm analysis, energy dispersion X-ray analysis (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and temperature programmed reduction (H2-TPR). The average size of PtDENs was found to be 1.48nm in diameter. Furthermore, the introduction of La could improve the structure of the supports which was confirmed by XRD and H2-TPR analysis. The reduction of p-nitrophenol to p-aminophenol by NaBH4 was utilized to evaluate the catalytic performances of catalysts. Results indicated that the Pt/La2O3-ZrO2 catalyst calcined in nitrogen at 550°C exhibited the highest catalytic performance and still kept the high catalytic activity even after six cycles. This phenomenon suggests that synergistic effect among Pt-Zr-La could enhance the catalytic efficiency. Finally, reaction mechanism was proposed for the reduction of p-nitrophenol.

Double-Shelled TiO2 Hollow Spheres Assembled with TiO2 Nanosheets

High-quality double-shelled TiO2 hollow spheres (DHS-Ti) assembled with TiO2 nanosheets have been synthesized for the first time through a simple hydrothermal treatment of sSiO2 @TiO2 (TiO2 -coated solid SiO2 spheres). The double-shelled structure shows a high BET surface area up to 417.6 m2  g-1 . Anatase DHS-Ti of high crystallinity can be obtained without structural collapse by calcination treatment. The effects of cetyl trimethylammonium bromide (CTAB) concentration, pH, and hydrothermal reaction temperature have also been investigated with a series of contrast experiments. A formation mechanism involving the in situ growth of amorphous TiO2 nanosheets followed by the redeposition of dissolved silica species is proposed. Lastly, the DHS-Ti forming strategy can be extended as a general strategy to fabricate various morphological hollow nanostructures and double-shelled Pt nanocatalysts by rationally selecting functional sSiO2 nanoparticles as core materials. This work could open up a new strategy for controllable synthesis of complex hollow structures and other functional materials.

In situ doping of Pt active sites via Sn in double-shelled TiO2 hollow nanospheres with enhanced photocatalytic H2 production efficiency

A Sn4+-doped double-shelled Pt/TiO2 hollow nanocatalyst (DHS-SnPt) with excellent photocatalytic H2 production efficiency was prepared successfully via a facile hydrothermal method. In the catalytic system, Pt active sites were in situ reduced by Sn2+ and showed an enhanced interaction with Sn species. The enhanced SnO2/Pt interface could accelerate the migration rate of e− from SnO2 to Pt, improving the charge separation efficiency of h+ and e−. The as prepared DHS-SnPt contained a very low Pt content (0.24 wt%) and showed the highest photocatalytic H2 production efficiency (ca. 18 496 μmol g−1 within 3 h), nearly 5.8 and 1.678 times as high as that of a pure double-shelled Pt/TiO2 hollow nanocatalyst and the traditional Sn4+ doped counterpart, respectively, demonstrating the significantly improved Pt atom utilization of DHS-SnPt in photocatalytic H2 evolution activity. On the basis of experimental results, a possible photocatalytic H2 production mechanism was proposed to explain the excellent H2 production efficiency of DHS-SnPt.

Synthesis of micro/mesoporous silica material by dual-template method as a heterogeneous catalyst support for alkylation

A series of micro/mesoporous composites were synthesized using non-ionic block copolymer Pluronic P123 and protic ionic liquid (triethylamine acetate) as the co-templates. The structures of all the composites were characterized by using small angle X-ray scattering, N2 gas sorption, dynamic laser light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results reflected that the structure of the final silica materials changes along with the content of protic ionic liquid (PIL) and hydrothermal temperature. It was found that the sample whose mass ratio of PIL to (P123 + PIL) was 40% had a t-plot micropore area of 404 m2 g−1 at the hydrothermal temperature of 373 K, without destroying the ordered mesoporous structure. The formation mechanism of the micro/mesoporous silica which is based on the interaction between PIL and P123 is tentatively elucidated. 12-Tungstophosphoric acid (HPW) catalysts supported on these micro/mesoporous materials were prepared by impregnation, and their catalytic performances were investigated in the alkylation of o-xylene with styrene. Alkylation results showed that all the catalysts showed high catalytic performance in terms of propane conversion and selectivity to propene.

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.