Preparation of zeolite-metal composite membrane

A NaA zeolite membrane was synthesized on the surface of the stainless steel stab. The membrane was characterized by XRD and SEM. The membrane was continuous and highly intergrown. The size of NaA zeolite crystals was about 5 similar to 6 mum.

Titanium-based perovskite-type mixed conducting ceramic membranes for oxygen permeation

A titanium-based perovskite-type oxide was synthesized by an improved method of combining EDTA acid and citric acid complexes. High structural stability, good sintering ability, and relatively high oxygen permeation flux were obtained simultaneously for disks synthesized from this ceramic oxide. (C) 2002 Elsevier Science B.V All rights reserved.

Synthesis of NaA zeolite membranes from clear solution

NaA zeolite membranes were successfully synthesized on a porous alpha -Al2O3 support from clear solution. The synthesis parameters, such as surface seeding, synthesis time, synthesis stages, etc. were investigated. Surface seeding can not only accelerate the formation of NaA zeolite on the support surface, but can also inhibit the transformation of NaA zeolite into other types of zeolites. A continuous NaA zeolite membrane formed on the seeded support after 2 h of synthesis. Gas permeation results showed that a synthesis time of 3 h produced the best NaA zeolite membrane. When the synthesis time was longer than 4 h, the NaA zeolite on the support surface began to transform into other types of zeolites, and the quality of the NaA zeolite membrane decreased. The quality of the NaA zeolite membrane can be improved by employing the multi-stage synthesis method. The NaA zeolite membrane with a synthesis time of 2 h after a two-stage synthesis showed the best gas permeation performance. The permeances of H-2, O-2, N-2, and n-C4H10 decreased as the molecular kinetic diameter of the gases increased. which showed the molecular sieving effect of the NaA zeolite membrane. The permselectivities of H-2/n-C4H10 and O-2/N-2 were 19.1 and 1.8, respectively. These values are higher than the Knudsen diffusion ratios of 5.39 and 0.94. However, the permeation of n-C4H10 also indicated that the NaA zeolite membrane had certain defects with diameters larger than the pore size of NaA zeolite. A synthesis model was proposed to clarify the effect of surface seeding. (C) 2001 Elsevier Science B.V. All rights reserved.

Synthesis of NaA zeolite membrane by microwave heating

The synthesis of NaA zeolite membrane on a porous alpha -Al2O3 support by microwave heating (MH) was investigated. The formation of a NaA zeolite membrane was drastically promoted by MH. The synthesis time was reduced from 3 h for conventional heating (CH) to 15 min for MH. Surface seeding cannot only promote the formation of NaA zeolite on the support, but also inhibit the transformation of NaA zeolite into other types of zeolites. The thickness of the NaA zeolite membrane synthesized by MH was about 4 mum, thinner than that of NaA zeolite membrane synthesized by CH. The permeance of NaA zeolite membrane synthesized by MH was four times higher than that of the NaA zeolite membrane synthesized by CH, while their permselectivities were comparable. Multi-stage synthesis resulted in the transformation of NaA zeolite into other types of zeolites, and the perfection of the as-synthesized membrane decreased.

Synthesis and perfection evaluation of NaA zeolite membrane

The synthesis of NaA zeolite membrane on a porous alpha -Al2O3 support from clear solution and the evaluation of the perfection of the as-synthesized membrane by gas permeation were investigated. When an unseeded support was used, the NaA zeolite began to transform into other types of zeolites before a continuous NaA zeolite membrane formed. When the support was coated with nucleation seeds, not only the formation of NaA zeolite on the support surface was accelerated, but also the transformation of NaA zeolite into other types of zeolites was inhibited. A continuous NaA zeolite membrane can be formed. Perfection evaluation indicated that the NaA zeolite membrane with the synthesis time of 3 h showed the best perfection after a one-stage synthesis. The perfection of NaA zeolite membrane can be improved by employing the multi-stage synthesis method. The NaA zeolite membrane with a synthesis time of 2 h after a two-stage synthesis showed the best gas permeation performance, The permselectivity of H-2/n-C4H10 and O-2/N-2 were 19.1 and 1.8, respectively, higher than those of the corresponding Knudsen diffusion selectivity of 5.39 and 0.94, which showed the molecular sieving effect of NaA zeolite. However, the permeation of n-C4H10 also indicated that the NaA zeolite membrane had certain defects, the diameter of which were larger than the NaA zeolite channels. (C) 2001 Elsevier Science B.V. All rights reserved.

Synthesis and characterization of gallium-based perovskite-type dense membrane with oxygen semipermeability

La0.15Sr0.85Ga0.3Fe0.7O3-delta (LSGFO) and La0.15Sr0.85Co0.3Fe0.7O3-delta (LSCFO) mixed oxygen-ion and electron conducting oxides were synthesized by using a combined EDTA and citrate complexing method, and the corresponding dense membranes were fabricated. The properties of the oxide powders and membranes were characterized with combined SEM, XRD, H-2-TPR, O-2-TPD techniques, mechanical strength and oxygen permeation measurement. The results showed that LSGFO had much higher thermochemical stability than LSCFO due to the higher valence stability of Ga3+. After the temperature-programmed reduction by 5% H-2 in Ar from 20 degreesC to 1020 degreesC, the basic perovskite structure of LSGFO was successfully preserved. LSGFO also favors the oxygen vacancy formation better than LSCFO. Oxygen permeation measurement demonstrated that LSGFO had higher oxygen permeation flux than LSCFO, but they had similar activation energy for oxygen transportation, with a value of 110 and 117 kJ . mol(-1), respectively The difference in oxygen permeation fluxes was correlated with the difference in oxygen vacancy concentrations for the two materials.

Synthesis of titanium silicalites in different template systems and their catalytic performance

Titanium silicalites have been synthesized in the TPABr+ammonia, TPABr+hexanediamine, TPABr+ethylenediamine, TPABr+diethylamine, TPABr+TEAOH, TPABr+n-butylamine, TPABr+TBAOH and TBAOH+n-butylamine systems. As-synthesized titanium silicalites were characterized by XRD, IR and C-13 CP MAS NMR. Catalytic performance in epoxidation of propylene and template effect was investigated. It has been shown that both TPABr and TBAOH serve as templating agent in TPABr+TBAOH system. But in other systems, when there is enough TPABr, organic amines or ammoniums only act as the bases. TEAOH or n-butylamine can take the role of template when less TPABr is added. It indicates that the ability of organic amines or ammoniums to direct the Pentasil structure decreases as follows: TPA(+)>TBA(+)>TEA(+)>n-butylamine. Catalysts exhibiting good performance in epoxidation of propylene can be attained using TPABr as the template and ammonia, n-butylamine, diethylamine, hexanediamine or TBAOH as bases. (C) 1999 Elsevier Science B.V. All rights reserved.

Surface structure and reaction performances of highly dispersed and supported bimetallic catalysts

Surface structures of Pt-Sn and Pt-Fe bimetallic catalysts have been investigated by means of Mossbauer spectroscopy, Pt-L-III -edge EXAFS and H-2-adsorption. The results showed that the second component, such as Sn or Fe, remained in the oxidative state and dispersed on the gamma-Al2O3 surface after reduction, while Pt was completely reduced to the metallic state and dispersed on either the metal oxide surface or the gamma-Al2O3 surface. By correlating the distribution of Pt species on different surfaces with the reaction and adsorption performances, it is proposed that two kinds of active Pt species existed on the surfaces of both catalysts, named M-1 sites and M-2 sites. M-1 sites are the sites in which Pr directly anchored on the gamma-Al2O3 surface, while M-2 sites are those in which Pt anchored on the metal oxide surface. M-1 sites are favorable for low temperature H-2 adsorption, and responsible for the hydrogenolysis reaction and carbon deposition, while M-2 sites which adsorb more H-2 at higher temperature, are more resistant to the deactivation due to less carbon deposition, and provide major contribution to the dehydrogenation reaction.

Titanium species in titanium silicalite TS-1 prepared by hydrothermal method

The titanium species existing in titanium silicalite TS-1, which is prepared by hydrothermal method, were investigated using chemical analysis, XRD, FT-IR, Si-29 MAS NMR, UV-VIS, ESR. It has been observed that several kinds of titanium species may exist in titanium silicalite. The form that titanium atoms incorporate into the framework of titanium silicalite synthesized using tetrapropylammonium bromide (TPABr) as template differs from that using the classical method. But, the symmetry of titanium silicalite, changes from monoclinic to orthorhombic with the increase of titanium content in both methods. The Ti-O-2(-) originated from framework titanium and H2O2 has the moderate stability and may be active site in oxidation reaction. TS-1 synthesized using TPABr as template does not contain anatase, but contains a kind of partly condensed titanium species with six-fold coordination. The titanium species may correspond to 270-280 mn band in UV-VIS spectra and also can form Ti-O-2(-). But, this kind of Ti-O-2(-) is very stable and cannot be catalytic active site. So, the six-fold coordination titanium species may be inactive in both the oxidation reaction and the decomposition of H2O2. The hypothesis has been further proved by the phenomena that the titanium species is easily washed off using acid, and acid treating will not influence the catalytic performance of TS-1. (C) 2001 Elsevier Science B.V. All rights reserved.

Partial oxidation of methane over the perovskite oxides

Ba0.5Sr0.5Co0.8Fe0.2O3-delta and Ba0.5Sr0.5Co0.8Ti0.2O3-delta oxides were synthesized by a combined EDTA-citrate complexing method. The catalytic behavior of these two oxides with the perovskite structure was studied during the reaction of methane oxidation. The pre-treatment with methane has different effect on the catalytic activities of both the oxides. The methane pre-treatment has not resulted in the change of the catalytic activity of BSCFO owing to its excellent reversibility of the perovskite structure resulting from the excellent synergistic interaction between Co and Fe in the oxide. However, the substitution with Ti on Fe-site in the lattice makes the methane pre-treatment have an obvious influence on the activity of the formed BSCTO oxide.

Modeling of a compact plate-fin reformer for methanol steam reforming in fuel cell systems

The characteristics of a compact plate-fin reformer (PFR) which integrates endothermic and exothermic reactions into one unit have been investigated by experiment as well as by numerical simulation. One reforming chamber was integrated with two vaporization chambers and two combustion chambers to constitute a single unit of PFR. In the PFR, which is based on a plate-fin beat exchanger, catalytic combustion of the reforming gas is used to simulate the fuel cell anode off gas (AOG) which supplies the necessary heat for the methanol steam reforming. Temperature distributions in all chambers and composition distribution in reforming chamber have been studied, and the effect of the ratio of H2O/CH3OH on the performance of the PFR has also been investigated. A model of the PFR was derived using a three-dimensional numerical model for a cross-current flow arrangement. Theoretical predictions of the temperature distributions in the PFR were in good agreement with experimental values. In addition, the numerical model was able to accurately predict the methanol conversion and the reformate composition in reforming chamber. © 2005 Elsevier B.V. All rights reserved.

Synthesis of zeolite NaA membranes with high permeance under microwave radiation on mesoporous-layer-modified macroporous substrates for gas separation

This article reported the NaA zeolite membranes with high permeance synthesized with microwave heating method under different conditions: (1) on a macroporous substrate in gel, (11) on a mesoporous/macroporous (top-mesoporous-layer-modified macroporous) substrate in gel, and (111) on a mesoporous/macroporous substrate in sol. In general, the H-2 permeance of the NaA membranes by microwave heating in gel was usually at the level of 10(-6) mol s(-1) m(-2) Pa-1, much higher than that by the conventional hydrothermal synthesis. At similar H-2/C3H8 permselectivity. On the substrate modified mesoporous top layer, the H-2 permeance of the NaA membranes by microwave heating in gel or sol was further enhanced, while maintaining comparable H-2/C3H8 permselectivity, due to the prevention of penetration of the reagent into the pores of the macroporous substrate. Meanwhile, the synthesis took less time in sol than in gel on the mesoporous/macroporous substrate. The NaA membranes synthesized in sol had larger permeance than those in gel and underwent transformation in shorter time. The permeation of C3H8 suggested that there existed unwanted intercrystalline pores or defects in the membranes. © 2005 Elsevier B.V. All rights reserved.