•Thin and highly H2 permeable SAPO-34 membranes were synthesized.•High-quality seed layers were prepared by steam-assisted conversion (SAC) seeding.•Nano-seeds were effectively coated on low-cost macroporous supports.•The SAC method was sample, effective and highly reproduceable.An effective steam-assisted conversion (SAC) seeding method was proposed for the growth of a thin and high-quality SAPO-34 membrane on a low-cost and coarse macroporous α-Al2O3 tubular support. This seeding technique was composed of depositing the seeds-containing paste on a support and transforming the paste into continuous and compact seed layer by the SAC process. The paste could serve as the binder to prevent small seeds penetrating into the support. With the aid of the perfect seed layer, a high-quality SAPO-34 membrane with the thickness about 4 μm was synthesized by secondary growth. The as-synthesized membrane exhibited a high H2 permeance of 6.96 × 10−6 mol m−2 s−1 Pa−1 at room temperature, with H2/CO2, H2/N2, H2/CH4, H2/C2H6, H2/C3H8, H2/n-C4H10 and H2/i-C4H10 ideal selectivities of 1.83, 7.58, 14.80, 18.24, 26.51, 40.15 and 53.02, respectively.

Highly ordered mesoporous MCM-48 molecular sieve has been successfully synthesized using mixed surfactant of cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl sulfate (SDS) as templates at low surfactant-to-silica ratio (molar) of 0.177. Our work provides a commercially important approach to synthesize ordered mesoporous material by introducing cheap anionic surfactant SDS as co-template. The molar composition of surfactant mixture was CTAB: SDS = 6.08. The characterization of the material shows that the pore diameter and BET surface area of as-prepared MCM-48 is 2.72 nm and 861.8 m2 g− 1, respectively. The possible formation mechanism of MCM-48 using mixed surfactant template has been discussed according to Gibbs free energy theory and surfactant packing parameter theory.Highlights► Cheap anionic surfactant SDS was introduced to synthesis MCM-48 as co-template. ► MCM-48 have been synthesized at low surfactant-to-silica cost of 0.177. ► Gibbs free energy theory was included to discuss formation mechanism.

Using pyridine as template, polycrystalline Na-ferrierite membrane with thickness of about 30 μm was prepared successfully on macroporous α-Al2O3 support in a short crystallization time by conventional and vacuum-assisted secondary growth. The effects of synthesis parameters such as template, alkalinity and dilution were investigated. The characterization and properties of Na-ferrierite membrane prepared using parent gel with molar composition of 1Al2O3:60SiO2:6Na2O:1835H2O:64C5H5N were detected. The three-stage synthesized Na-ferrierite membrane had the best properties with the single-gas permeances of H2 > CH4 > O2 > N2 > CO2 > C3H8 > SF6. The separation properties of Na-ferrierite membrane were evaluated by benzene/p-xylene pervaporation test. With increasing the benzene feed concentration, the fluxes of benzene and p-xylene increased and decreased, respectively, and the separation factor decreased firstly and increased afterward. Furthermore, the formation mechanism of the compact Na-ferrierite membrane was proposed.Graphical abstractHighlights► The vacuum-assisted secondary growth method was first introduced in this paper. ► The cost of synthesis was reduced. ► The gas permeances and fluxes of membranes were larger than that in the literatures. ► The formation mechanism of the Na-ferrierite membrane was proposed first time.

Continuous and polycrystalline NaY zeolite membranes were synthesized successfully on porous α-Al2O3 tubes by zeolite structure-directing agent (ZSDA) method. This ZSDA method consists of two steps: preparation of NaY ZSDA and growth of NaY zeolite membranes with ZSDA by the secondary hydrothermal treatment. The synthesis parameters, such as aging time, aging temperature and the amount of ZSDA added, etc. were investigated. Scanning electron microscopy and X-ray diffraction technology were used to characterize the morphology and the crystal structure of the as-synthesized zeolite membranes, respectively. The results indicated that the growth of NaY zeolite membranes on the supports depended strongly on ZSDA, which could not only accelerate the formation of NaY zeolite membranes but also inhibit the transformation of NaY zeolite phase. It was also found that the prolonged aging time, the lower aging temperature and the increasing amount of ZSDA resulted in a crystal size diminution of the product, thus linking the aging process directly to the increasing number of formed nuclei. Compared with the larger crystal NaY zeolite membrane, the small crystal NaY zeolite membrane exhibited much higher separation selectivity. At 308 K, the highest separation selectivities achieved towards 1,3-propanediol/glycerol and 1,3-propanediol/glucose were 80 and 2,400, respectively.

With one step of vacuum coating and pyrolysis, the thin zeolite L/carbon nanocomposite membranes (about 3–4 μm) were obtained on the porous alumina tubes by incorporating nano-sized zeolite L (about 100 nm) into polymeric precursor (polyfurfuryl alcohol (PFA)). The permeation properties of pure H2, CO2, N2 and CH4, together with CO2/CH4 and CO2/N2 mixtures through the composite membrane were measured and analyzed. A notable increase was observed in the permeances of gas species in comparison with the pure carbon membrane owing to the enhancement of the pore structure properties, including pore volume, surface area, pore size and its distribution. Due to the restricted diffusion of non-adsorbable gas by adsorbable component in the micropores, the CO2/CH4 and CO2/N2 permselectivities in the mixed gas system were higher than the results from pure gas permeation. The effects of permeation temperature, pressure difference and CO2 content in feed gases on separation performances of the composite membranes were also investigated. It was found that the CO2/CH4 and CO2/N2 separation factors decreased with increasing the permeation temperature and pressure difference, and increased with increasing CO2 content in the mixtures.

A specific synthesis mode, based on precursor diffusion through the support channels, the restricting growth method (RGM) with ultra-dilute precursor has been designed to prepare silicalite-1 zeolite membranes on seeded macroporous α-Al2O3 tubular supports. Several parameters were systematically investigated to evaluate their influence on performance of the membranes, including the H2O/SiO2 ratio, template type and crystallization temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM) and single-gas permeation tests were used to characterize the as-prepared membranes. Results showed the membrane prepared under optimum parameters (H2O/SiO2 ratio of 800, TPAOH as template and crystallization at 443 K) was continuous, dense and with a controllable section thickness almost the same as that of the seed layer. It displayed preferable hydrogen permeance (1.2 × 10−6 mol m−2 s−1 Pa−1) and permselectivity (αH2/SF6 = 134) at 298 K under 0.1 MPa pressure drop. Moreover, due to the utilization of ultra-dilute precursor, this technique has the advantage of reduced chemical consumption. On the contrary, the uncompacted membranes with poor permeation behavior were obtained by the conventional secondary growth method under the same synthesis parameters.

Silicalite-1 membranes supported on macroporous alumina tubes for hydrogen separation were successfully prepared by a specific synthesis protocol called counter-diffusion hydrothermal crystallization (CDHC). This method introduced silica source (tetraethyl orthosilicate, TEOS) and template agent (tetra-propyl ammonium bromide, TPABr) from opposite directions of the support wall, overwhelming the conventional in situ hydrothermal crystallization (ISHC). After an optimization process, the optimum molar composition of silicon precursor was 1SiO2:0.135Na2O:100H2O:2EtOH and that of template precursor was 1.5TPABr:100H2O. XRD and SEM analysis showed the as-prepared membranes were typical silicalite-1 membranes with high internal crystalline order as well as dense and continuous surface morphology. Single-gas permeation tests indicated the membrane prepared with optimized recipe combined high H2 permeance (1.24 × 10−6 mol m−2 s−1 Pa−1) and good H2 selectivity (αH2/SF6=155αH2/SF6=155) at room temperature, 0.1 MPa pressure drop. Moreover, the consumption of template in this novel method was about one third of that used in conventional hydrothermal synthesis. This concept can also be extended to other many types of zeolite membranes.

In this paper, a novel hierarchical ZSM-5 microsphere (simplified as ZSM-5-MS hereafter) of about 3 μm, which is assembled by many French fries-like crystals (in shape of French fries) of about 100 nm in width, was synthesized by using SBA-15 as the silica source. ZSM-5-MS exhibited a unique geometrical shape which was entirely distinct from the conventional MFI shape. The N2 adsorption isotherm suggested that the ZSM-5-MS had a uniform mesopores of 15 nm with a tail up to 45 nm. The ZSM-5-MS was modified to form a Mo/HZSM-5-MS catalyst which exhibited good catalytic performance in methane dehydroaromatization (MDA) due to the presence of both micropores and mesopores. A time trial study was carried out by SEM, XRD and TEM analysis for the insight into the growth of the obtained ZSM-5-MS. A growth model via self-assembly combined with crystallization process was proposed based on the time trial observations. The demonstrated route may be extended to synthesize other types of zeolites with unusual structure and properties.

In this work, zeolite NaA was successfully synthesized by a hydrothermal method using kaolin as a combined source for silica and alumina. Zeolite NaA with high static water adsorption was synthesized from the low-cost raw material, kaolin, and the reaction parameters were optimized. Metakaolin was obtained by calcining kaolin at temperatures ranged from 953 K to 1173 K. The synthesis mixture was pre-crystallized at 343 K and crystallized at 373 K successively. Zeolite NaA was obtained, which was confirmed by SEM, XRD and the water adsorption analysis. The optimized metakaolinization temperature was found at 973 K. The influence of Na2O/SiO2 molar ratio, pre-crystallization time and seed on the crystallization of NaA zeolite was investigated. A thorough mixing of metakaolin and NaOH solution was favourable for the nucleation/crystallization rate. The obtained NaA zeolite under the optimized conditions shows excellent crystallinity and static water adsorption of 28.0 wt-%, which was higher than 25.9 wt-% of the commercial NaA zeolite. Kaolin was suggested to be a feasible and economical raw material for the practical industrial applications for NaA zeolite.

A feasible route, preparing hierarchical structure zeolite (MCM-22 and ZSM-5) aggregates catalysts directly without using any secondary template, was presented to improve catalytic performance dramatically in methane dehydroaromatization reaction. The zeolites hierarchical aggregates possessed both mesopores and the inherent micropores, which was beneficial to the effective combination Mo species with zeolite acidic sites and giving rise to high quality bifunctional catalysts. Besides, mesopores provided easier access to the active sites for both reactant and larger product molecules. All these led to very high methane conversion and very strong coking-resistance and thus exceptional catalyst stability.