Shiyang Bai

A Yolk–Shell Nanoreactor with a Basic Core and an Acidic Shell for Cascade Reactions

Smart yolk-shell nanoparticles (hollow nanoparticles with a movable core) with an acidic shell and a basic core were fabricated through an organosilane-assisted selective etching method and acted as efficient nanoreactors for catalyzing a deacetalization-Henry cascade reaction with high activity and high selectivity. This strategy is very promising for the design of multifunctional nanoreactors for cascade reactions.

The nanocomposites of SO3H-hollow-nanosphere and chiral amine for asymmetric aldol reaction

The nanocomposites formed by SO3H-hollow-nanospheres and chiral amines are highly efficient catalysts for the direct asymmetric aldol reaction of cyclohexanone and 4-nitrobenzaldehyde. The catalyst showed 91% yield with 96% ee under optimized reaction conditions. SO3H-hollow-nanospheres were synthesized by oxidation of thiol-hollow-nanospheres, which were fabricated through a one-pot co-condensation of 1,2-bis(trimethoxysilyl)ethane and 3-mercaptopropyltrimethoxysilane around F127 micelles in the presence of NaOAc. Chiral amines could be combined with SO3H-hollow-nanospheres through facile electrostatic interactions. The obtained nanocomposites showed a much higher reaction rate than the catalyst formed from the combination of chiral amine and SO3H-mesoporous-organosilica (ribbon shaped particles with particle size of tens of micrometres) in the direct asymmetric aldol reaction. This is mainly attributed to the hollow spherical morphology and nano-scale particle size (16–20 nm) of the SO3H-hollow-nanospheres.

Oxygen evolution from water oxidation on molecular catalysts confined in the nanocages of mesoporous silicas

Here, we report that the water oxidation activity can be significantly increased by confining ruthenium molecular catalysts, such as RuII(bda)(pic)2, in the nanocage of SBA-16. The TOF of RuII(bda)(pic)2 confined in the nanocage increased from 1.2 to 8.7 s−1 by simply increasing the number of RuII(bda)(pic)2 molecules from one to seven in each nanocage, which is direct evidence for the “cooperative activation” mechanism involved in a binuclear reaction pathway for water oxidation reactions. The TOF of RuII(bda)(pic)2 confined in the nanocage can be as high as two times that of the homogeneous RuII(bda)(pic)2 due to the enhanced “cooperative activation” in the limited space of nanocages. Moreover, preliminary kinetic studies suggest that the stability of the molecular catalysts can be greatly improved after confinement in the nanocage. This strategy not only provides a new strategy for the preparation of highly efficient solid-hosted catalysts for water oxidation, but also gives direct evidence for the oxygen evolution mechanism.

Bifunctionalized Hollow Nanospheres for the One-Pot Synthesis of Methyl Isobutyl Ketone from Acetone

Pd-doped propyl sulfonic acid-functionalized hollow nanospheres proved to be efficient bifunctionalized catalysts for the one-pot synthesis of methyl isobutyl ketone (MIBK) from acetone and hydrogen in liquid phase. These hollow nanospheres exhibited a higher activity than their bulk mesoporous counterparts (SBA-15 or FDU-12), mainly due to the short diffusion resistance of hollow nanospheres. Hollow nanospheres with silica frameworks showed higher activity and selectivity for MIBK than those with ethane-bridged frameworks, suggesting that hollow nanospheres with hydrophilic surface properties favor the formation of MIBK. This is probably due to the increased affinity of the hydrophilic surface towards acetone and its decreased affinity towards MIBK, which precludes deep condensation of MIBK with acetone. Under optimal conditions, up to 90 % selectivity for MIBK can be obtained with conversions of acetone as high as 43 %. This result is among the best reported so far for mesoporous silica-based catalysts. The control/fine-tuning of morphology and surface properties provides an efficient strategy for improving the catalytic performance of solid catalysts.

Enantioselective carbonyl-ene reaction on BINOLate/titanium catalyst encapsulated in magnetic nanoreactors.

An asymmetric multicomponent catalyst, BINOLate/titanium, successfully encapsulated in the nanocages of mesoporous silicas exhibits much higher activity than the homogeneous counterpart in quasi solvent-free enantioselective carbonyl-ene reaction, owing to the confinement effect of the nanoreactor.

Enhanced thermostability of enzymes accommodated in thermo-responsive nanopores

The crowded and hydrophobic microenvironment was created for immobilized enzymes via the thermally-initiated shrinkage of PNIPAM polymers anchored in the nanopores of mesoporous silica. This extraordinary microenvironment can greatly enhance both the catalytic efficiency and thermostability of lipases, which provides a new approach for fabricating robust heterogeneous biocatalysts.

Promoted activity of Cr(Salen) in a nanoreactor for kinetic resolution of terminal epoxides

Cr(Salen) catalyzed kinetic resolution of terminal epoxides via asymmetric ring opening (ARO) with TMSN3 is an important approach for the synthesis of enantiopure 1,2-amino alcohols, however, the high catalyst usage amount (1–2 mol%) impedes its practical applications. An efficient solid nanoreactor was constructed by encapsulation of Cr(Salen) and pyridine in the nanocages of mesoporous silica. This solid nanoreactor exhibits high activity (TOF: 1325 h−1) and high enantioselectivity (91% ee) for the kinetic resolution of 1,2-epoxyhexane via ARO with TMSN3 at a catalyst concentration as low as 0.002 mol%, whereas the homogeneous counterpart affords almost no conversion of epoxide under similar reaction conditions. The high activity of the solid nanoreactor is mainly attributed to the greatly intensified cooperative activation in the nanocages as evidenced by the sharply increased TOF in parallel with Cr(Salen) concentration in each nanocage. The increased nucleophilicity of Cr(Salen) after coordination to pyridine could also promote the catalytic activity. The solid nanoreactor can be easily separated and recycled. We demonstrated the possibility for designing an efficient solid nanoreactor for asymmetric catalysis by taking the advantages of the cooperative activation.

Hollow Carbon Spheres with Abundant Micropores for Enhanced CO2 Adsorption

The interest in the design and controllable fabrication of hollow carbon spheres (HCSs) emanates from their tremendous potential applications in adsorption, energy conversion and storage, and catalysis. However, the effective synthesis of uniform HCSs with high surface area and abundant micropores remains a challenge. In this work, HCSs with tunable microporous shells were rationally synthesized via the hard-template method using resorcinol (R) and formaldehyde (F) as a carbon precursor. HCSs with a very high surface area (1369 m2/g) and abundant micropores (0.53 cm3/g) can be obtained with the assistance of additional inorganic silanes (TEOS) simultaneously with the carbon source (RF). Interestingly, the extra-abundant micropores showed favorable adsorption for CO2, resulting in a 1.5 times increase in the CO2 adsorption capacity compared to that of normal HCSs under the same conditions. Meanwhile, these HCSs hold potential for use in the separation of gases such as CO2 and N2.

Asymmetric hydrogenation by RuCl2(R-Binap)(dmf)(n) encapsulated in silica-based nanoreactors

The Noyori catalyst RuCl2(R-Binap)(dmf)n has been successfully encapsulated in C-FDU-12 by using the active chlorosilane Ph2Cl2Si as the silylating agent. 31P-NMR results show that there is no strong interaction between the molecular catalyst and the solid support, thus the encapsulated molecular catalyst could move freely in the nanoreactor during the catalytic process. The solid catalyst exhibits high activity and enantioselectivity for the asymmetric hydrogenation of a series of β-keto esters due to the preserved intrinsic properties of RuCl2(R-Binap)(dmf)n encapsulated in the nanoreactor. The solid catalyst could be recycled by simple filtration and be reused at least four times.

Engineering the Mesopores of Fe3O4@Mesosilica Core–Shell Nanospheres through a Solvothermal Post-Treatment Method

A solvothermal post-treatment method was developed to synthesize Fe(3)O(4)@mesosilica core-shell nanospheres (CSNs) with a well-preserved morphology, mesoporous structure, and tunable large pore diameters (2.5-17.6 nm) for the first time. N,N-Dimethylhexadecylamine (DMHA), which was generated in situ during the heat-treatment process, was mainly responsible for this pore-size enlargement, as characterized by NMR spectroscopy. This pore-size expansion can be strengthened with the aid of hexamethyldisilazane (HMDS), whilst the nature of the surface of the Fe(3)O(4)@mesosilica CSNs can be easily modified with trimethylsilyl groups during the pore-size-expansion process. The hydrophobicity of the Fe(3)O(4)@mesosilica CSNs increased for the enlarged mesopores and the adsorption capacity of these CSNs for benzene (up to 1.5 g g(-1)) is the highest ever reported for Fe(3)O(4)@mesosilica CSNs. The resultant Fe(3)O(4)@mesosilica CSNs (pore size: 10 nm) showed a 3.6-times higher adsorption capacity of lysozyme than those without the pore expansion (pore size: 2.5 nm), thus making them a good candidate for loading large molecules.