Yingcai Long

Synthesis and characterization of colloidal TBA-silicalite-2

Abstract Colloidal TBA-silicalite-2 (MEL type) was hydrothermally synthesized in the reactant system TBAOH–TEOS–H2O. The influences of reactant composition, reaction temperature, and crystallization period on particle size of the zeolite were investigated. The colloidal silicalite-2 was characterized by XRD, SEM, TEM, FT-IR, 29Si MAS NMR, 13C CP MAS NMR, thermogravimetric analysis and N2 adsorption. The as-synthesized colloidal zeolite with a particle size of 100 nm is an agglomerate composed of nano-sized crystals of about 20 nm, displaying unique structural characteristics such as high content of silanol defects in the framework, splitting of the double-ring vibration in FT-IR spectrum and an unusual signal for methyl groups of TBA in 13C CP MAS NMR spectrum.

Synthesis and structural characterization of B-Al-ZSM-5 zeolite from boron–silicon porous glass in the vapor phase

Abstract B-Al-ZSM-5 zeolite was synthesized on granules of boron–silicon porous glass in a vapor mixture of ethylamine and water at 180°C. The as-synthesized zeolite obtained by vapor–solid reaction and the calcined B-Al-ZSM-5 zeolites were characterized with 11 B, 29 Si, 27 Al, 13 C MAS NMR, XRD, IR, and TG/DTG/DTA. The various states of the species of BO, AlO, and SiO in both the amorphous porous glass and the as-synthesized zeolite were inspected in detail with 11 B, 29 Si and 27 Al MAS NMR. The complete incorporation of BO, AlO, and SiO into the framework of the zeolite was confirmed. The possible position of the template in the zeolite was investigated with 13 C MAS NMR. The unit cell of the zeolite contracts with the incorporation of boron atoms into the framework. The crystallinity of the as-synthesized zeolite is about 93% with orthorhombic symmetry both before and after calcination. After calcination, the crystallinity of the zeolite decreases due to B removal. The number of ethylamine molecules located at different positions of the zeolite channels is discussed in relation to TG/DTG/DTA data.

Separation of p-xylene from C8 aromatics on binder-free hydrophobic adsorbent of MFI zeolite. I. Studies on static equilibrium

Abstract The static equilibrium of C8 aromatics in liquid phase was studied on a binder-free MFI zeolite adsorbent, which possesses perfect framework and high hydrophobicity. The selectivity factor for para-xylene/ethylbenzene and para-xylene/ortho-xylene is determined as 7.95 and 104, respectively. A series of desorbents matched with adsorbents such as benzene, toluene, butylbenzene, monochlorobenzene, para-diethylbenzene and para-dichlorobenzene were investigated as well. The adsorbent can be regenerated and used without controlling the content of water. The isotherms for each isomer of C8 aromatics and the desorbents possess the adsorption characteristics of Langmuir type. The saturation adsorption capacities of the adsorbates were determined. Unusually, no adsorption of meta-xylene on the adsorbent was found, which is much different from those observed on the zeolite of ZSM-5. The competitive adsorption curves of the multi-component feed were also investigated. The high shape selectivity of separation is related to the perfect structure of the adsorbent.

Fast synthesis of nanosized zeolite beta from a low-seeded, low-templated dry gel with a seeding-steam-assisted conversion method

Nanosized zeolite beta with a tuneable crystal morphology and size, rich intercrystalline mesoporosity and high catalytic activity for low-density polyethylene cracking, was fast transformed from a low-seeded, low-templated dry gel by a seeding-steam-assisted conversion method with a small quantity of water; the crystallization of zeolite beta is well induced within 28 h at a TEAOH/SiO2 of 0.1 with the aid of 1% seeds.

Templating of high-silica zeolites by tetrahydrofuran in the Na2O–SiO2–Al2O3–H2O system

The spontaneous crystallization of high-silica MOR, FER, MFI, MTN zeolites was investigated in the reactant system tetrahydrofuran (THF)–Na2O–SiO2–Al2O3–H2O in the temperature range 180–230°C. 13C CP MAS NMR spectra, TG/DTG/DTA and energy dispersive X-ray (EDX) analysis were used to characterize the molecules of THF trapped in the channels or the cages of the as-synthesized zeolites. The regular patterns and the distinct shift of the resonance peaks for THF in 13C MAS NMR spectra, and the higher temperatures for THF escaping from the as-synthesized zeolites confirm that THF interacts strongly with the framework of the zeolites, playing the role of a template. The mechanism of the interaction between the framework and THF is also discussed.

A guest/host material of LiCl/H-STI (stilbite) zeolite assembly: preparation, characterization and humidity-sensitive properties

The novel zeolite guest/host material, LiCl/H-STI (stilbite) assembly was synthesized by a thermal dispersion method, and characterized in detail by powder XRD, 7Li MAS NMR, SEM/EDX, DTA and FT-IR. The loading threshold of LiCl was confirmed by XRD to be 0.14 g/g. The 7Li MAS NMR spectra were measured for a solution of LiCl, LiCl crystallites, LiCl/H-STI assembly, Li+ ion-exchanged STI (Li-STI) as well as LiCl dispersed on supports of zeolite ZSM-39, zeolite ZSM-5, silica gel and quartz. According to the chemical shifts, the states of Li+ can be identified as Li+ ions in solution, LiCl isolated in zeolite channels, Li+ cations balancing the framework charges and LiCl as a crystalline phase or cluster. Characterization results proved the LiCl guest was highly dispersed into the channels of the host at the threshold assembly loading. The interactions of LiCl with the zeolite framework and H2O are also discussed. The threshold loading LiCl/H-STI material was found to possess optimum humidity-sensitive performance with a linear change of 4 orders of magnitude in electrical conductivity over the whole range of relative humidity. In addition, it also shows satisfactory reversibility and fast responses to environmental moisture changes.

Preparation of an MFI-type zeolite membrane on a porous glass disc by substrate self-transformation

An MFI-type zeolite membrane containing boron has been prepared on the surface of a boron–silicon porous glass disc by substrate self-transformation in the vapor of ethylamine (EA) and H2O; both XRD and SEM show that the zeolite crystals on the surface of the porous glass disc were in random orientation; the thickness of the membrane layer was ca. 10–20 μm; permeation of O2 and N2, and the chemical composition of the membrane were measured.

Crystallization of zeolite ZSM-39 studied by 13C and 29Si magic-angle spinning nuclear magnetic resonance spectroscopy

13 C CP MAS NMR, 29Si MAS NMR and XRD have been used to study the crystallization of zeolite ZSM-39 in the tetramethylethylenediamine (TMEDA)–SiO2–H2O system. With the formation of the precursor from SiO2 species surrounding TMEDA followed by nucleation, the 13C chemical shift of the —C2H4— group moves progressively to higher field. This indicates that one molecule of TMEDA is shared by two neighbours of the [51264] cage and that the —C2H4— group of TMEDA interacts strongly with oxygen atoms located at the 6-ring window between the two cages.

Synthesis, characterization of an AlPO-CJ2 analogue containing heteroatomic Eu

An analogue of AlPO-CJ2 microporous aluminophosphate containing heteroatomic Eu was hydrothermally synthesized in situ in the reactant system of carbamide-NH4-F-Al2O3-P2O5-H2O, and characterization by ICP, powder XRD, Mössbauer spectra, 31P MAS NMR and luminescent spectroscopy prove that Eu is incorporated into the framework.

The generation mechanism of silicon oxide–aluminum oxide compound clusters by laser ablation of siliceous materials

Abstract The generation of silicon dioxide–aluminum oxide compound clusters under 308 nm XeCl excimer laser ablation of ZSM-5 zeolites with different SiO 2 /Al 2 O 3 ratios was studied by time-of-flight mass spectrometry. Two Al-containing cluster sequences [(SiO 2 ) n −1 (AlO 2 )] − and [(SiO 2 ) n OAl] − are observed in the negative ion channel. Through the relationship between the abundance distribution of cluster sequences and the silicon aluminum ratio, the growth mechanism of [(SiO 2 ) n −1 (AlO 2 )] − is discussed. Owing to the high electron affinity of AlO 2 compared to small (SiO 2 ) n clusters, AlO 2 is considered to be the core of growth of the compound cluster [(SiO 2 ) n −1 (AlO 2 )] − .