Yueming Liu

Methodology for synthesizing crystalline metallosilicates with expanded pore windows through molecular alkoxysilylation of zeolitic lamellar precursors

Postalkoxysilylation with diethoxydimethylsilane has been carried out on the zeolitic lamellar precursors of various topologies such as MWW, FER, CDO and MCM-47 aiming to construct new crystalline structures with expanded pore apertures between the layers. The silylation process and the crystalline and pore structures of the resulting materials have been investigated with the techniques of XRD, IR, (13)C and (29)Si MAS NMR, ICP, SEM, HRTEM, elemental analyses, and N 2 adsorption. In contrast to forming known three-dimensional zeolite structures after direct calcination of the lamellar precursors, the silylation led to new crystalline structures with opener pores, as evidenced by the shift of layer-related diffractions to the lower-angle region in XRD patterns and the enlarged interlayer pores found by HRTEM images. After optimizing the treatment conditions, particularly the amount of silane agent, a maximum and homogeneous silylation was realized, which guaranteed the phase purity in interlayer expanded zeolites. The expanded structures were well preserved after calcination at 823 K or reflux in water for 1 to 2 weeks, indicating a high thermal stability and also a hydrothermal stability. The interlayer expanded zeolites prepared from the metallosilicate precursors of MWW topology exhibited higher catalytic activities in the redox and solid acid-catalyzed reactions of bulky molecules than that of their counterparts with conventional MWW topology.

Core/shell-structured TS-1@mesoporous silica-supported Au nanoparticles for selective epoxidation of propylene with H2 and O2

Hierarchically ordered materials with core/shell structures were synthesized through a layer-by-layer approach. The novel microporous/mesoporous hybrid materials were composed of a TS-1 zeolite particle for the core and mesoporous silica for the shell. The as-synthesized TS-1 crystals were modified with polydiallyldimethylammonium chloride to make their external surface positively charged, which induced an oriented self-assembly of tetraethoxysilane (TEOS) with cetyltrimethyl ammonium bromide on the TS-1 particle surface to form a shell of mesophase silica. The thickness of the mesoporous silica shell was controlled to be in the range 30–55 nm by changing the amount of TEOS added in the synthesis. The mesoporous channels in the shell were perpendicular to the zeolite core, which made the micropores inside the core accessible from the outside through the mesopores. Taking advantage of the confining effect of the mesopores, Au nanoparticles were incorporated into the shell, resulting in bifunctional catalysts which were more selective than conventional Au/TS-1 catalysts in the direct epoxidation of propylene to propylene oxide with H2 and O2.

Alkoxysilylation of Ti-MWW lamellar precursors into interlayer pore-expanded titanosilicates

Silylation of Ti-MWW lamellar precursor and subsequent calcination constructed an interlayer expanded structure, leading to novel titanosilicates with large pores. The silylating agents suitable for pore expansion were diethoxydimethylsilane, trimethylethoxysilane and triethoxymethylsilane containing methyl groups, which inhibited the intermolecular condensation of silanes effectively. In contrast to well-known 3D Ti-MWW with only medium pores of 10-membered rings, the silylation led to new crystalline structures with more open pores by ca. 2.5 A, as evidenced by the shift of layer-related diffractions to the lower-angle region in XRD patterns and the enlarged interlayer pores in HRTEM images. The interlayer expanded Ti-MWW was prepared readily from the corresponding hydrothermally synthesized precursors with a wide range of Ti contents (Si/Ti = 20–100). In addition, the pore expansion by silylation was realized under mild acid conditions with 0.1 M HNO3. The interlayer expanded Ti-MWW exhibited 3–7 times higher turnover number than 3D Ti-MWW in the oxidation of cyclohexene with H2O2.

Mesopolymer solid base catalysts with variable basicity: preparation and catalytic properties

A series of amine- or diamine-functionalized mesopolymers with cubic or hexagonal mesostructures have been prepared by two-step chemical modification procedures involving chloromethylation of the FDU-type mesoporous resol materials first with chloromethyl methyl ether, and a subsequent amination reaction with methylamine, dimethylamine or ethylenediamine. Various techniques such as XRD, SEM, TEM, N2 adsorption, FTIR, 13C NMR and elemental analysis have been adopted to track the functionalization processes, and to characterize the structures, porosity, chemical compositions and basicity of the materials. The amino group-containing mesopolymer materials prove to be efficient heterogeneous base catalysts in Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate. The possible mechanisms of Knoevenagel reaction on different mesopolymer base catalysts have also been discussed.

Synthesis of ZSM-5 zeolite hollow spheres with a core/shell structure

Hollow and core/shell ZSM-5 spheres were simply synthesized through in situ transformation of mesoporous silica spheres (MSS) into MFI-type zeolite with the assistant of isopropylamine (IPA) as a structure-directing agent (SDA). IPA, with a mild structure-directing ability for the construction of MFI structure, triggered a stepwise crystallization of MSS after Al addition. First, the sphere surface was crystallized to a shell of ZSM-5 crystals. The silica and alumina species in the core condensed and crystallized to ZSM-5 thereafter, forming zeolite crystal aggregates inside the spheres. The obtained ZSM-5 spheres were highly crystalline materials and maintained the shape of pristine MSS, but exhibited a hollow and core/shell structure. The techniques of XRD, FT-IR, SEM, N2 adsorption-desorption, 29Si and 27Al MAS NMR were employed to trace the crystallization process, which allowed us to propose a “templating and surface to core” crystallization mechanism. This strategy may serve as an alternative way for synthesizing hollow zeolite spheres.

Catalytic Oxidation of Benzothiophene and Dibenzothiophene in Model Light Oil Ti-MWW

Abstract An oxidative desulfurization process for model light oil over Ti-MWW was investigated. Benzothiophene and dibenzothiophene are oxidized to their corresponding sulfoxides and sulfones, which can be removed by extraction using acetontrile. The conversion of benzothiophene and dibenzothiophene is 100% and 95%, respectively, at 343 K. The effect of solvent was also studied. Under the same conditions, the conversion of benzothiophene in three solvents decreases in the order acetonitrile > methanol > water.

Oxidative Desulfurization of Aromatic Sulfur Compounds over Titanosilicates

The application of several titanosilicates to the oxidation of aromatic sulfur compounds such as thiophene, benzothiophene, dibenzothiophene, and 4,6‐dimethyldibenzothiophene with H2O2 under mild conditions is reported. Superior to other titanosilicates, Ti‐MWW demonstrates a higher activity for the oxidation of 4,6‐dimethyldibenzothiophene owing to the unique pore structure of the MWW topology. The effects of solvent, temperature, catalyst amount, and H2O2/S ratio on the oxidation of 4,6‐dimethyldibenzothiophene over this catalyst are studied in detail. The catalyst is also applied to the oxidative desulfurization of commercial diesel. The sulfur compounds in the commercial diesel were oxidized to the corresponding sulfones, which could be readily extracted by acetonitrile, resulting in a maximum sulfur removal of 88 % .

Synthesis of core–shell structured TS-1@mesocarbon materials and their applications as a tandem catalyst

Core–shell structured TS-1@mesocarbon (TS-1@MC) materials with mesoporous carbon as the shell and microporous TS-1 titanosilicate as the core were synthesized through a nanocasting and selective silica etching strategy. The faithful replica structure was constructed from the composite of TS-1@mesosilica and carbon when tetrapropylammonium hydroxide (TPAOH) was employed to selectively remove the amorphous mesosilica shell while the core zeolite crystal structure was not destroyed. In contrast, the protective effect was not seen when sodium hydroxide or hydrogen fluoride was employed as a silica-leaching agent. The obtained TS-1@MC had a bimodal pore structure consisting of 2.9 nm mesopores in the carbon shell and 0.51 nm micropores in the TS-1 core. Its specific surface area and total pore volume reached 883 m2 g−1 and 0.63 cm3 g−1, respectively. TS-1@MC was used as the support to load palladium nanoparticles (Pd NPs) in the carbon shell. Having an average particle size of approximately 2 nm, the Pd NPs were highly dispersed and confined in the mesopores of the carbon shell. Pd/TS-1@MC thus obtained served as an efficient tandem catalyst in the direct epoxidation of propylene with hydrogen and oxygen.

Fluorine-planted titanosilicate with enhanced catalytic activity in alkene epoxidation with hydrogen peroxide

Fluorine species were successfully implanted into a MWW-type titanosilicate via post-treatment, which generates the SiO3/2F units in the zeolite framework. The incorporated fluorine species significantly improved the catalytic performance in the epoxidation of alkenes as a result of enhancing the Lewis acid strength and the hydrophobicity of the zeolite.

An Efficient and Recyclable Mesostructured Polymer-Supported N-Heterocyclic Carbene-Palladium Catalyst for Sonogashira Reactions

Abstract Palladium catalyst systems are the most widely used for the formation of C-C and C-N bonds. Environmentally friendly heterogeneous palladium catalysts have strongly stimulated growth in this research area. Herein, a FDU (Fudan University)-15 mesopolymer with p6mm mesostructures that combine the advantages of organic polymers and mesoporous materials was investigated as a new solid support for Pd complexes. The FDU-15 mesopolymer-supported N -heterocyclic carbene (NHC) precursor was developed by a simple chemical functionalization approach. It has been used as a phosphine-free ligand to prepare the novel heterogeneous palladium catalyst FDU-NHC/Pd(II), which efficiently catalyzes Sonogashira reactions between aryl halides and terminal alkynes to afford the corresponding products in good yields. Various techniques such as X-ray diffraction, N 2 adsorption-desorption isotherms, high resolution transmission electron microscopy, and X-ray photoelectron spectroscopy have been used to characterize the catalyst. The results indicate that the mesoporous structure of FDU-15 was not affected by immobilization, however, the pore diameter, pore volume, and BET surface area decrease. The stability of the heterogeneous catalyst was also studied. The FDU-NHC/Pd(II) complex catalyst was easily separated from the reaction system by a simple filtration of the reaction mixture and it has been shown to be robust without a significant loss of catalytic activity after recycling and reuse in 10 times.