Junlin Zheng

Hydrothermally stable mesoporous aluminosilicates with tubular morphology

Abstract Hydrothermally stable mesoporous aluminosilicates with hollow tubular morphology were fabricated via the controlled coassembly of protozeolitic nanoclusters and soluble silica species. The introduction of protozeolitic nanoclusters not only enhanced the hydrothermal stability but also facilitated the tailoring of the hierarchical structure of the ‘tubules-within-a-tubule’ mesoporous aluminosilicates.

Hydrothermally Stable Mesoporous Aluminosilicates with Strongly Acidic Sites

Mesoporous aluminosilicates were synthesized through S+X-I+ route using preformed beta zeolitic nanoclusters as building units in acidic media and subsequent ammonia hydrothermal treatment. The ordered mesoporous aluminosilicates were characterized by XRD, N-2 adsorption and desorption, HRTEM, SEM, NMR and NH3-TPD methods. The results indicated that the sample had the same hexagonal mesostructures as normal MCM-41 synthesized in acidic media. The presence of strongly acidic sites was substantiated by NH3-TPD study, and the hexagonal mesoporous structure was maintained even after 120 h treatment in boiling water. The synthesized materials were superior to conventional MCM-41 with respect to their stronger acidity and higher hydrothermal stability. The short period of assembly in acidic media and the ambient temperature reduced the dealumination effect considerably. The retention of zeolite-like connectivity of tetrahedral AlO4 and SiO4 units upon assembling the nanoclusters into mesostructured materials and the thicker framework pore walls contributed to the especially good hydrothermal stability greatly, which also gave rise to the presence of strong acidity.

Novel non-surfactant pathway to controllable micro/mesoporous bimodal xerogels

We describe the synthesis and characterization of amorphous micro/mesoporous xerogels using mixed polymethylhydrosiloxane (PMHS) and tetraethyl orthosilicate (TEOS) as the inorganic source in the presence of ethyldiamine (EDA) as catalyst via a controllable sol-gel route, without additional introduction of any structure-directing agent. The resultant materials were thoroughly characterized by X-ray diffraction (XRD), nitrogen adsorption, Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and (29)Si MAS NMR. It was interestingly shown from these characterization results that the present amorphous samples exhibited disordered pore structure, high specific surface areas and pore volumes, though neither solvent extraction nor calcination was utilized. More interestingly, the relative content of micropore and mesopore could be finely tuned by facilely adjusting the mass ratio of PMHS to TEOS.

Preparation of hydrothermally stable mercapto-functionalized mesoporous silicas via assembly of nanoclustered zeolite Y seeds and 3-mercaptopropyltrimethoxysilane

The preparation of a series of 3-mercaptopropyl-functionalized mesoporous silicas of MSU was achieved by a one-pot synthesis process involving the assembly of nanoclustered zeolite Y seeds and 3-mercaptopropyltrimethoxysilane (MPTMS) in the presence of Brij 76 (C18EO20). The effect of synthetic parameters, such as reaction temperature, MPTMS content and pH value of reaction mixture on the properties of materials was investigated systemically. It was found that the sample with 10% organo-functionalization of the framework silicon sites prepared at 348 K and pH 6.0 retained both its structural integrity and functionalities after the treatment in water at 373 K for 150 h. Enhanced hydrothermal stability of the materials in this study was greatly attributed to the successful introduction of zeolite Y seeds into the mesostructured framework walls.

Synthesis and characterization of mesoporous aluminosilicates from zeolitic precursors and TEOS

Mesoporous aluminosilicates with improved hydrothermal stability were prepared via the controlled coassembly of zeolitic precursors and TEOS in alkaline media. XRD, N 2 sorption, and TEM methods showed that the coassembled sample had hexagonal mesostructures, and the hydrothermal stability was largely improved compared to normal MCM-41. 29 Si MAS NMR spectra indicated that the product had higher cross-linking degree compared to normal MCM-41 through the extra introduction of protozeolitic nanoclusters. 27 Al MAS NMR spectra implied that most Al species had been tetrahedrally incorporated into the framework. The catalytic cracking conversion rate of 1,3,5-triisopropylbenzene over this sample was as high as 97.66%. At the same time, the hydrolysis behavior of TEOS and synergic polymerization process of protozeolitic nanoclusters and silicate oligomers were outlined.