J.Z. Wang

Synthesis and characterization of boron-containing MCM-48 cubic mesoporous molecular sieves

Boron-containing MCM-48 cubic mesoporous molecular sieves with different boron contents were synthesized and characterized by XRD, N-2 adsorption, TEM, and NMR spectroscopy. All BMCM-48 samples possess high porosities with a relatively narrow pore size distribution, and the pore structure of BMCM-48 is relatively uniform. In the as-synthesized form boron is tetrahedrally coordinated. Most of the boron is not removable by calcination and/or rehydration treatments

Vanadium- and chromium-containing mesoporous MCM-41 molecular sieves with hierarchical structure

The structures and properties of materials are profoundly altered under high pressure due to a large change of atom spacing, chemical bonding and Gibbs free energies. Therefore, materials with novel structures and properties call be created via a process known as pressure-induced phase transition. Here we report the investigations of pressure effects on the elastic properties and the glass transition of Zr-, Pd-based bulk metallic glasses (BMGs), The elastic constants and the Debye temperatures, of a Zr41Ti14Cu12.5Ni10Be22.5C1 and a Pd39Ni10Cu30P21 BMGs are measured by using an ultrasonic technique, and their pressure dependence is exhibited. The equations of state (EOS) of the two BMGs are established. The acoustic attenuation behaviors are also monitored with various pressure in the two BMGs, and a marked difference between the two BMGs is revealed, The effects of pressure-induced structural relaxation on the glass transition of the Pd39Ni10Cu30P21 BMG are investigated by a temperature-modulated differential scanning calorimetry technique. The pressure dependence of the reversible and irreversible glass transition is explained.

06-P-09 - Controlled synthesis of microporous and mesoporous silica-based molecular sieves in the presence of dodecyldimethylbenzylammonium chloride

Publisher Summary This chapter discusses a controlled synthesis of microporous and mesoporous silica-based molecular sieves in the presence of dodecyldimethylbenzylammonium chloride (DDBAC). Microporous silicas with the pore size of 12.2 A are prepared by either S + X - I + or S + I - pathways at room temperature using DDBAC surfactant. The pore size of the synthesized materials could be tuned from microporous to mesoporous range by the crystalline temperature or using the mixed surfactants of DDBAC and cetylpyridinium chloride. The pore structure can transfer from disordered tubular array to ordered hexagonal phase by the increase of the molar ratio of cetylpyridium chloride (CPCl) to DDBAC.

Characterization of sodium cations in zeolite omega by solid-state23Na NMR spectroscopy

Sodium cations localized at crystallographically distinct cation sites in the hydrated zeolite omega were characterized by various solid-state23Na NMR techniques, such as23Na MAS,1H-23Na CP/MAS,23Na quadrupolar nutation and variable temperature NMR spectroscopy. In the23Na NMR spectrum of zeolite omega two signals were identified, a low-field Gaussian line at ca. −3 ppm (its quadrupole coupling constant was estimated approximately on the order of magnitude of 0.2 MHz) and a high-field quadrupole pattern with an isotropic chemical shift of −8 ppm and a quadrupole coupling constant of 2.3 MHz. The former signal is attributed to sodium cations in the 12-ring channels and the latter one to sodium cations in gmelinite cages of zeolite omega. The variable temperature NMR experiments reveal the interactions between the sodium cation and the adsorbed water molecules in zeolite omega. The sodium cations in the 12-ring channels are highly hydrated and so mobile as to average the1H-23Na dipole interaction. Hence, these sodium cations give no contribution to the1H-23Na cross polarization process. By contrast, the sodium cations in the gmelinite cages are less hydrated and more rigid. They are closely bonded not only to the adsorbed water molecules but also to the lattice oxygen of the gmelinite cages, which leads to an effective1H-23Na polarization transfer.

Sodium cation locations in zeolite omega studied by 23Na VASS NMR

Abstract Overlapping 23 Na NMR signals of zeolite Na-omega are observed by a 2D MAS quadrupolar nutation NMR spectrum and VASS NMR spectra. The low-field Lorentzian shape component centered at − 3 ppm is assigned to the signal of mobile Na + cations located in twelve-membered ring channels. The high-field component, varying considerably with the spinning angles of VASS NMR spectra, is assigned to the signal of less mobile Na + cations located in gmelinite cages. The partition between two categories of Na + cations is determined by the simulation of VASS NMR spectra with the theoretical consideration extended to more general case that both the quadrupolar and chemical shift anisotropic interactions coexist.

Synthesis of B-Beta zeolite and its modification with orthophosphoric acid

Abstract Hydrothermal synthesis of borosilicate zeolites with BEA structure and the modification of HB-Beta zeolites with orthophosphoric acid were performed. The samples were characterized by the X-ray diffraction, FT-IR, nitrogen adsorption, chemical analysis, 11 B and 31 P MAS NMR technique. The effects of the phosphorus-modification on the structure, crystallinity, acidity, framework vibrations and textural properties of the HB-Beta were investigated systematically. The coordination environments of boron and phosphorus in the framework of P-HB-Beta zeolites were revealed. The formation of P(BO) 4-n (SiO) n -like species is observed.

Synthesis and characterization of nano-sized copper-silicate with mel structure

Abstract Nano-sized copper silicalite with MEL structure has been hydrothermally synthesized for the first time under static conditions. The physicochemical property of this novel material was characterized by means of XRD, TEM, FT-IR, ESR, TG-DTA and NH 3 -TPD techniques. The results revealed that the as-synthesized copper silicalite was highly thermally stable owing to its siliceous nature. This monophased crystalline material was quite uniform in size around 1×10 −8 m. Cupric ions were highly dispersed and mainly resided in distorted tetrahedral and square pyramidal environments before and after calcination. However, most of the incorporated copper ions left from the framework upon calcination and NH 4 Ac extraction, which resulted in a high density of lattice defect in the framework. Incorporation of cupric ions into the silicalite framework during crystallization also resulted in a weak acidity on this material.

Novel synthesis and characterization of vanadium aluminosilicates with bea structure

Abstract A synthesis strategy has been developed for the hydrothermal crystallization of microporous vanadium aluminosilicate with BEA structure. Influence of temperature, time, vanadium source and addition of alkaline metal ions on the synthesis was evaluated. XRD SEM, ICP-AES, framework IR, UV-Vis DRS, ESR and oxidation-reduction were applied to characterize these materials. It revealed that, by using vanadyl acetylacetonate as vanadium source, vanadium could be effectively incorporated into zeolite beta framework. Vanadium ions were thermally stable and atomically dispersed in zeolite beta lattice. V(IV) was the predominant oxidation state for vanadium in the as-synthesized vanadium aluminosilicate beta, while V(V) was the sole oxidation state after calcination in air. Tetrahedral or square-pyramidal coordinated V(IV) and V(V) were found over the as-synthesized vanadium aluminosilicate beta, which were incorporated into the zeolitic lattice and were stable enough against extraction with NH4Ac solution. The framework vanadium ions showed a good reversibility in the V(IV)↔V(V) redox process.

04-P-08-A novel method for the synthesis of chromium aluminosilicate with BEA structure

Publisher Summary This chapter presents a novel method for the synthesis of chromium aluminosilicate with BEA structure. A novel method has been developed for the hydrothermal synthesis of zeolite beta with high chromium content and low aluminum content under static conditions. The crystalline phase and spectroscopic property of this material are characterized by means of X-ray diffraction (XRD), infrared (IR), electron spin resonance (ESR), and scanning electron microscopy (SEM). The results reveal that part of the chromium ions are incorporated into the zeolite framework during crystallization. Using tris(acetylacetonato) chromium(III), [Cr(C 5 H 7 O 2 ) 3 ], as a chromium source, chromium/silicon (Cr/Si) molar ratio can be up to 1/48 in the calcined and ion-exchanged sample. The chromium aluminosilicate exhibit a high oxidative activity in the presence of dilute hydrogen peroxide (H 2 O 2 ).