Shenghu Zhou

Size Effect of Gold Nanoparticles in Catalytic Reduction of p-Nitrophenol with NaBH4

Gold nanoparticles (Au NPs) were prepared by reducing HAuCl4 with NaBH4. Their average particle sizes could be tuned in the range of 1.7 and 8.2 nm, by adjusting the amount of NaBH4 used during synthesis. The obtained Au NPs (colloids) were then loaded onto a commercial Al2O3 support to prepare Au/Al2O3 catalysts with tunable Au particle sizes. An optimal pH value (5.9) of the Au colloid solution was found to be essential for loading Au NPs onto Al2O3 while avoiding the growth of Au NPs. Au NPs and Au/Al2O3 catalysts were tested in the reduction of p-nitrophenol with NaBH4. Interestingly, the catalytic activity depended on the size of Au NPs, being the highest when the average size was 3.4 nm. Relevant characterization by UV-Vis, TEM, and XRD was conducted.

In situ phase separation of NiAu alloy nanoparticles for preparing highly active Au/NiO CO oxidation catalysts.

In this communication, we report the synthesis of NiAu alloy nanoparticles (NPs) and their use in preparing Au/NiO CO oxidation catalysts. Because of the large differences in Ni and Au reduction potentials and the immiscibility of the two metals at low temperatures,1, 2 NiAu alloy NP colloids are inherently difficult to prepare by reducing metal salts with common reducing agents. This study describes the first solution-based synthesis of NiAu alloy NPs by way of a fast butyllithium reduction method. By supporting the particles on SiO2 and subsequent conditioning, one obtains a NiO-stabilized Au NP catalyst that exhibits remarkable resistance to sintering and is highly active for CO oxidation. The active NiO-stabilized Au NP catalyst is prepared by in situ phase transformation of NiAu alloy NPs through an Au@Ni core-shell like NP intermediate. In contrast, the corresponding NiO-free Au NPs prepared by an analogous method show negligible low-temperature catalytic activity and a high propensity for coalescence.

A soft-templated method to synthesize sintering-resistant Au–mesoporous-silica core–shell nanocatalysts with sub-5 nm single-cores

Nano-gold (sub-5 nm)@mesoporous-silica (m-SiO2) core-shell nanospheres with controlled size and core number were prepared via a soft-templated method. The single-core Au@m-SiO2 particles showed great sintering-resistance at 750 °C and kept high catalytic activity for CO oxidation after the treatment.

Enhanced catalytic performance of molybdenum-doped mesoporous SBA-15 for metathesis of 1-butene and ethene to propene

Molybdenum-doped mesoporous SBA-15, mesoporous SBA-15-supported MoO3/SBA-15, and traditional silica-supported MoO3/SiO2 were successfully synthesized. Various techniques, such as XRD, TEM, BET, UV-DRS, Raman, XPS and IR, were used to characterize the above obtained materials. The studies of TEM, XRD and BET confirmed that the highly ordered mesoporous structure of SBA-15 was maintained in the doped Mo-SBA-15 whereas supported MoO3/SBA-15 showed a significant reduction in surface area due to the deposition of MoO3 nanoparticles into the SBA-15 channels. XPS studies revealed that a high concentration of Mo5+ species appeared in doped Mo-SBA-15 whereas supported MoO3/SBA-15 and MoO3/SiO2 only contained Mo6+ species. The metathesis reaction of 1-butene and ethene to propene was used to evaluate the catalytic performance of Mo-containing materials. The doped Mo-SBA-15 illustrated a superior catalytic performance over the supported MoO3/SBA-15 and MoO3/SiO2 catalysts. The enhancement of catalytic performance for doped Mo-SBA-15 was assigned to the incorporation of Mo species into the SBA-15 framework. Due to the doping method, Mo-SBA-15 exhibited a well-ordered mesoporous structure, a high surface area, and a high concentration of Mo5+ species, which is beneficial to the catalytic performance for metathesis reactions.

Oxygen-assisted reduction of Au species on Au/SiO2 catalyst in room temperature CO oxidation

An unexpected oxygen-assisted reduction of cationic Au species by CO was found on a Au/SiO(2) catalyst at room temperature and the produced metallic Au species plays an essential role in CO oxidation on Au/SiO(2).

Controlled synthesis of Pd–NiO@SiO2 mesoporous core–shell nanoparticles and their enhanced catalytic performance for p-chloronitrobenzene hydrogenation with H2

In this work, Pd–NiO@SiO2 core–shell mesoporous nanocatalysts with ~4 nm Pd–NiO heteroaggregate nanoparticle cores and ~17 nm mesoporous silica shells were successfully synthesized by a sol–gel method. The surfactant-capped PdNi alloy nanoparticles were coated with SiO2 through hydrolysis of tetraethylorthosilicate to obtain PdNi@SiO2 nanoparticles, and the mesoporous Pd–NiO@SiO2 core–shell nanocatalysts were formed after removal of surfactants by calcination at 500 °C and subsequent H2 reduction at 200 °C. The characterization results by XRD, TEM and BET revealed that Pd–NiO@SiO2 nanocatalysts were highly stable with the maintenance of intact core–shell structures under high-temperature thermal treatments. The Pd–NiO@SiO2 nanocatalysts illustrated a superior catalytic performance for p-chloronitrobenzene hydrogenation with H2 to the control Pd@SiO2 nanocatalysts. The catalytic performance enhancement of Pd–NiO@SiO2 nanocatalysts is ascribed to the strong interaction between Pd and NiO in the cores, where the interfaces may be beneficial for hydrogenation reactions.

Sol-gel Auto-combustion Synthesis of Ni-CexZr1-xO2 Catalysts for Carbon Dioxide Reforming of Methane

Carbon dioxide reforming of methane (methane dry reforming) over Ni–Ce0.8Zr0.2O2 catalysts prepared by a sol–gel auto-combustion method and a conventional co-precipitation method were comparatively studied. We show that sol–gel auto-combustion is very promising for preparing thermal stable homogeneous mixed metal oxide catalysts. The auto-combustion synthesized catalyst exhibited higher initial activity and stability due to its smaller Ni crystalline size and intimate interaction between Ni and Ce0.8Zr0.2O2. In contrast, the co-precipitated catalyst showed poor activity and deactivated rapidly. The rapid deactivation was caused by a higher graphitization degree of the deposited carbon over co-precipitated catalyst with larger Ni crystalline size. We also found that the physico-chemical properties and catalytic activity of sol–gel auto-combustion synthesized catalysts were closely related to the metal nitrate (MN)/citric acid (CA) ratio. High MN/CA ratio led to more violent combustion behaviour and an accordingly higher degree of crystallization of the synthesized catalyst. In contrast, a low MN/CA ratio resulted in more carbon species residues and poor catalytic performance. The Ce/Zr ratio also had a profound influence on the phase structure, reducibility, oxygen vacancies and catalytic performance of Ni–Ce0.8Zr0.2O2 catalysts. Ni–Ce0.8Zr0.2O2 catalyst with cubic phase exhibited the best catalytic performance because of high reducibility, high Ni dispersion and strong Ni-CexZr1−xO2 interaction, and considerable amounts of oxygen vacancies.

Self-assembly of metal oxide nanoparticles into hierarchically patterned porous architectures using ionic liquid/oil emulsions.

Hierarchically patterned macroporous TiO2 structures can be fabricated via the spontaneous self-assembly of TiO2 nanoparticles prepared using a mixture of 1-octadecene (ODE) and an ODE-immiscible 1-alkyl-3-methylimidazolium-based ionic liquid as the reaction medium. A study of the influence of side chain lengths of ionic liquids (n=4, 8, or 16) reveals that this parameter can be further used to fine-tune the morphologies of the products. This synthetic methodology can also be extended to the formation of patterned macroporous ZrO2 and Fe3O4 structures. Finally, the potential reasons for the formation of hierarchical structures are discussed and the implications to further research are proposed.

Architecture controlled PtNi@mSiO2 and Pt–NiO@mSiO2 mesoporous core–shell nanocatalysts for enhanced p-chloronitrobenzene hydrogenation selectivity

Architecture controlled PtNi@mSiO2 and Pt–NiO@mSiO2 mesoporous core–shell nanocatalysts were synthesized for selective p-chloronitrobenzene hydrogenation to p-chloroaniline. Tetradecyl trimethyl ammonium bromide (TTAB) capped PtNi nanoparticles (NPs) were coated by SiO2 through the hydrolysis of tetraethylorthosilicate. The resultant PtNi@SiO2 core–shell NPs were calcined to remove TTAB to obtain mesoporous Pt–NiO@SiO2 core–shell nanocatalysts (Pt–NiO@mSiO2), which were subsequently reduced by hydrogen to form mesoporous PtNi@SiO2 core–shell nanocatalysts (PtNi@mSiO2). The relevant characterizations such as XRD, TEM, H2-TPR, and BET confirm that the PtNi@mSiO2 NPs consist of PtNi alloy nanoparticle cores and mesoporous SiO2 shells while the Pt–NiO@mSiO2 NPs contain Pt–NiO heteroaggregate nanoparticle cores and mesoporous SiO2 shells. The catalytic results for selective hydrogenation of p-chloronitrobenzene show that the selectivity of p-chloroaniline formation over the PtNi@mSiO2 and Pt–NiO@mSiO2 nanocatalysts is significantly improved relative to that of control Pt@mSiO2 nanocatalysts. Moreover, the PtNi@mSiO2 and Pt–NiO@mSiO2 nanocatalysts demonstrate high stability during multiple cycles of catalytic hydrogenation reactions. The enhanced catalytic performance is ascribed to the metal–metal interaction for the PtNi@mSiO2 catalysts and metal–oxide interaction for the Pt–NiO@mSiO2 catalysts.

Gold Nanoparticles on Mesoporous SiO2-Coated Magnetic Fe3O4 Spheres: A Magnetically Separatable Catalyst with Good Thermal Stability

Fe3O4 spheres with an average size of 273 nm were prepared in the presence of CTAB by a solvothermal method. The spheres were modified by a thin layer of SiO2, and then coated by mesoporous SiO2 (m-SiO2) films, by using TEOS as a precursor and CTAB as a soft template. The resulting m-SiO2/Fe3O4 spheres, with an average particle size of 320 nm, a high surface area (656 m2/g), and ordered nanopores (average pore size 2.5 nm), were loaded with gold nanoparticles (average size 3.3 nm). The presence of m-SiO2 coating could stabilize gold nanoparticles against sintering at 500 °C. The material showed better performance than a conventional Au/SiO2 catalyst in catalytic reduction of p-nitrophenol with NaBH4. It can be separated from the reaction mixture by a magnet and be recycled without obvious loss of catalytic activity. Relevant characterization by XRD, TEM, N2 adsorption-desorption, and magnetic measurements were conducted.