Dry Gel Conversion Method Research Articles

Fluoride-free synthesis of a Sn-BEA catalyst by dry gel conversion

A Sn-BEA catalyst was synthesized in a fluoride-free medium for the first time via a dry gel conversion method. The use of alkali ions, zeolite BEA seed crystals and ion-exchange before the removal of the organic template has been shown to be indispensable to obtain the desired material.

Rapid synthesis of SAPO-34 nanocatalyst by dry gel conversion method templated with morphline: Investigating the effects of experimental parameters

SAPO-34 nanoparticles were successfully synthesized by a dry gel conversion method using morpholine as a structure-directing agent. In this study, the effects of synthesis parameters, such as crystallization time, gel drying temperature and water content added in the crystallization stage, on crystallinity, shape and particle size of SAPO-34 are investigated and the advantages of the dry-gel conversion (DGC) method are described for the synthesis of SAPO-34 molecular sieves. The products were characterized by XRD, SEM, TEM, EDX, BET and NH3-TPD. The results show that the favorable phase of crystallinity has been improved by increasing the crystallization time, gel drying temperature and water content. Most of the particles have particle sizes lower than 500nm and it is an excellence of employing the DGC method despite using morpholine as a structure-directing agent. The high nucleation density and slow crystal growth after nucleation for SAPO-34 crystals in the dry gel conversion method result in the formation of nanoparticles. Contrary to the hydrothermal method in which at least 24h of the synthesis time is required to obtain crystalline SAPO-34, dry-gel conversion synthesis of samples leads to formation of fully crystalline SAPO-34 crystals taking only 6h. This has been observed as an important influence of dry-gel conversion synthesis on the activity and selectivity of the samples in the MTO reaction.

Synthesis and catalytic ammoxidation performance of hierarchical TS-1 prepared by steam-assisted dry gel conversion method: the effect of TPAOH amount

The hierarchical titanium silicalite-1 (TS-1) was synthesized by the steam-assisted dry gel conversion method in one step and characterized by XRD, SEM, N2 adsorption/desorption, UV–Vis, FT-IR, and Raman spectroscopies. And its catalytic activity was tested for ammoxidation of methyl ethyl ketone with hydrogen peroxide as oxidant. The results show that the amount of tetrapropylammonium hydroxide (TPAOH) as template has a major influence on the physicochemical and catalytic properties of the hierarchical TS-1 prepared. When lower amount of TPAOH (TPAOH/SiO2 = 0.08 mol) was used, hierarchical TS-1 can be successfully synthesized. With an increase in TPAOH amount in synthesis solution, the crystal size of TS-1 is decreased and mesoporous surface area is increased; if the excess template was used in the synthesis of TS-1, more extra-framework Ti would be formed in the TS-1 samples prepared. The hierarchical TS-1 exhibits higher catalytic activity than TS-1 prepared hydrothermally for ammoxidation of methyl ethyl ketone. Using hierarchical TS-1 synthesized under TPAOH/SiO2 = 0.18 as the catalyst, which has more tetrahedrally coordinated Ti species in the TS-1 framework, 94.2 % conversion of reactant and 100 % selectivity to methyl ethyl ketone oxime can be obtained after 2 h of reaction at 70 °C.

ChemInform Abstract: Synthesis of Metal‐Organic Frameworks: A Mini Review

AbstractReview: 124 refs.

A Career in Catalysis: Takashi Tatsumi

On the occasion of Professor Takashi Tatsumi’s retirement and winning of the Alwin Mittasch Prize, some of his main achievements in zeolite catalysis are summarized, with a focus on the design, synthesis, and catalytic application of new titanosilicate catalysts. He and his co-workers succeeded in the direct synthesis of the MWW-type titanosilicate, Ti-MWW, by employing boric acid in the synthesis and thereafter developed a dry gel conversion method for boron-reduced Ti-MWW as well as a secondary isomorphous substitution route for boron-free Ti-MWW molecular sieves. In particular, the postsynthetic conversion involved a reversible structure interchange between three-dimensional silicalite and a two-dimensional layered precursor. Taking advantage of the structural diversity of the layered MWW zeolite precursor, phase-delaminated Ti-MMW and interlayer expanded Ti-MWW were also prepared. Using hydrogen peroxide as an oxidant, the Ti-MWW/H2O2 system was highly efficient for liquid-phase oxidation of a variety of substrates, particularly the epoxidation of alkenes and ammoximation of ketones. Some of the Ti-MWW-catalyzed reactions have already led to or are becoming practical catalytic technologies in industrial practice. Several other recent achievements in the synthesis and catalytic applications of other titanosilicates, zeolitic hydrid materials, and solid acid zeolite catalysts are also briefly summarized.

Dry-gel synthesis of hierarchical TS-1 zeolite by using P123 and polyurethane foam as template

Hierarchical TS-1 zeolites have been prepared via a rapid dry-gel conversion (DGC) technique from carbon–titanosilicate composite. The carbon–titanosilicate composite was fabricated by dipping the silicon source, titanium source and P123 tri-block copolymer into polyurethane (PU) foam, and then carbonized in situ. The carbon–titanosilicate composite was transformed into TS-1 zeolites by DGC method with the aid of zeolite seeding gel. The dual carbon templates with different size obtained from carbonation of P123 and PU were used to direct mesostructure and macroporous architectures respectively. The resulting samples were characterized by X-ray diffraction, IR spectroscopy, SEM and N2 adsorption to evaluate the textural properties. The hierarchical zeolites exhibits large pore volumes (0.3–0.8cm3g−1), hierarchical pore sizes (2–50nm), and high external surface areas (158–211m2g−1). Epoxidation of 1-hexene and cyclohexene were used as probe reaction to survey the catalytic capacity of the resulted zeolites and this hierarchical zeolite showed well catalytic capacities to epoxidation of cyclohexene.

Crystallization kinetics of Sn-MFI molecular sieve formation by dry gel conversion method

The conversion of amorphous stannosilicate dry gel into crystalline molecular sieve with MFI structure (Sn-MFI) was achieved by dry gel conversion (DGC) method at 413, 443 and 473K. For comparison purpose, Sn-MFI molecular sieve with similar SiO2/SnO2 mole ratio was also obtained by hydrothermal crystallization route. Crystallization curves were established by conducting time dependant studies on progressive crystallization processes for both the systems. The values of activation energy of nucleation (En), activation energy of crystallization (Ec), and their pre-exponential factors (lnAn, lnAc respectively) were calculated from Arrhenius plots. Compared to the hydrothermal method, shorter induction period was observed when DGC method was employed. Both the En (49.70kJ/mol) and Ec (52.82kJ/mol) for DGC method were found to be lower than that of the En (55.70kJ/mol) and Ec (60.23kJ/mol) for hydrothermal method. The kinetics parameters viz. K and q were derived from kinetic expressions and DGC method showed higher value of K and lower value of q compared to hydrothermal crystallization method at identical temperature. Various DGC method parameters such as water content at the bottom of autoclave and SiO2/SnO2 mole ratio have shown the influence on the kinetics of crystallization of Sn-MFI.

Formation of and silicon incorporation in SAPO-5 synthesized via dry-gel conversion

Molecular sieves have been scientifically and industrially important materials since their discovery. These porous, crystalline networks of tetrahedrally coordinated atoms bridged by oxygen are known as excellent catalysts. The framework of the aluminophosphate family of molecular sieves is itself non-catalytic, but through heteroatomic substitution these materials can diversify into, for example, the silicoaluminophosphate (SAPO) family of heterogeneous acid catalysts. Research into the methods by which these substitutions occur, as discoveries can lead to refined control over material property and function. SAPO-5 was chosen as model system of study. 27Al, 29Si and 31P solid state NMR and PXRD were used as the primary methods of investigation. The SAPO-5 study determined that the dry gel conversion (DGC) methods of steam assisted conversion (SAC) and vapor phase transport (VPT) follow similar reaction pathways. After an initial difference caused by the lack of organic structure directing agent in the gel for the VPT method, crystallization is similar between methods, and silicon incorporation results in two populations of silicon sites. One represents isolated Si(OAl)4 species well incorporated into the framework, while the other represents silica islands within the framework. The initial core of the nuclei is AlPO4 in nature and the Si is gradually incorporated into the lattice as the crystals grow. The vapor phase silicon uptake (VPSU) method provides a contrast to this data, inducing nucleation that occurs concurrently with Si incorporation and producing only isolated Si(OAl)4 species.

Synthesis of metal-organic frameworks: A mini review

Metal organic frameworks (MOFs) are porous crystalline materials of one-, two-, or three-dimensional networks constructed from metal ions/clusters and multidentate organic linkers via coordination bonding, which are emerging as an important group of materials for energy storage, CO2 adsorption, alkane/alkene separation, and catalysis. To introduce newcomers in chemical engineering discipline to the rapidly expanding MOF research works, this review presents a brief introduction to the currently available MOFs synthesis methods. Starting from the conventional solvothermal/hydrothermal synthesis, microwave-assisted, sonochemical, electrochemical, mechanochemical, ionothermal, drygel conversion, and microfluidic synthesis methods will be presented. Examples will be limited to those representative MOF structures that can be synthesized using common organic ligands of 1,4-benzenedicarboxylic acid (and its functionalized forms) and 1,3,5-benzenetricarboxylic acid, in conjunction with metal nodes of Zn2+, Cu2+, Cr3+, Al3+, Fe3+ and Zr4+. Synthesis of widely-investigated zeolitic imidazolate framework (ZIF) structure, ZIF-8 is also included.

Synthesis of framework-substituted Co-mordenite by dry gel conversion

Framework-substituted Co-mordenite zeolite was synthesized by a dry gel conversion (DGC) method, using inorganic raw materials of silica sol, aluminum sulfate, cobalt nitrate and sodium hydroxide. Typical synthesis conditions were Co/SiO2 = 0.01–0.05, SiO2/Al2O3 = 20–50, H2O/SiO2 = 40, Na2O/SiO2 = 0.4 molar ratios, 170 °C, and 3 days. The obtained samples were characterized by X-ray diffraction, UV–vis, scanning electron microscope, and nitrogen sorption technique. The results showed that Co ions were incorporated into the tetrahedral framework structure of mordenite without forming extra-framework Co species. Products obtained by the present all-inorganic systems possessed open micropores and required no traditional high-temperature calcination. The DGC approach also avoided the separation of the final product from solvent phase.

A neural network prediction of conversion of benzothiophene oxidation catalyzed by nano-Ti-beta catalyst

The oxidation of benzothiophene (BT) in isooctane with hydrogen peroxide was performed in a batch reactor in a non-severe condition using nano-crystalline Ti-beta catalyst synthesized by dry gel conversion method. The Ti-beta catalyst was characterized by XRD and HRTEM analysis. A three layered feedforward neural network was employed to predict the BT conversion with respect to reaction time, catalyst concentration, hydrogen peroxide to BT mole ratio, temperature and initial BT concentration. The sensitivity analysis of process parameters showed that the BT conversion is highly sensitive to the reaction time, initial BT concentration and temperature.

Influence of synthesis parameters on NaA zeolite crystals

Abstract The influences of the crystallization temperature, time, and alkalinity of the reaction system and aluminum sources (aluminum chloride and aluminum sulfate) on the synthesis of NaA zeolite have been systematically investigated using the dry-gel conversion method (DGC). The phase and morphology of the synthesis products were characterized using X-ray diffraction and SEM, respectively. This study showed that the alkalinity and temperature affected the NaA zeolite crystallization process and the size distribution of the crystalline end products. Furthermore, as the reaction time increased, the metastable phase transformed into a more stable phase. It was worth mentioning that the final NaA zeolite product contained a small quantity of NaX zeolite when aluminum chloride was used as the aluminum source while using aluminum sulfate as the aluminum source, the final product was mostly sodalite, indicating that the anions in the different aluminum sources have a significant effect on the crystallization process, most likely due to their electrostatic and steric interactions with the zeolite framework. To obtain NaA zeolite crystals with uniform sizes and high crystallinity, the optimal synthesis parameters for the two aluminum sources were determined.

Differential pathogen loads affecting quality of life during Lapita colonisation of the Pacific: Skeletal pathology in the SAC Watom and Teouma samples

Molecular sieves have been scientifically and industrially important materials since their discovery. These porous, crystalline networks of tetrahedrally coordinated atoms bridged by oxygen are known as excellent catalysts. The framework of the aluminophosphate family of molecular sieves is itself non-catalytic, but through heteroatomic substitution these materials can diversify into, for example, the silicoaluminophosphate (SAPO) family of heterogeneous acid catalysts. Research into the methods by which these substitutions occur, as discoveries can lead to refined control over material property and function. SAPO-5 was chosen as model system of study. 27Al, 29Si and 31P solid state NMR and PXRD were used as the primary methods of investigation. The SAPO-5 study determined that the dry gel conversion (DGC) methods of steam assisted conversion (SAC) and vapor phase transport (VPT) follow similar reaction pathways. After an initial difference caused by the lack of organic structure directing agent in the gel for the VPT method, crystallization is similar between methods, and silicon incorporation results in two populations of silicon sites. One represents isolated Si(OAl)4 species well incorporated into the framework, while the other represents silica islands within the framework. The initial core of the nuclei is AlPO4 in nature and the Si is gradually incorporated into the lattice as the crystals grow. The vapor phase silicon uptake (VPSU) method provides a contrast to this data, inducing nucleation that occurs concurrently with Si incorporation and producing only isolated Si(OAl)4 species.

Preparation and characterization of nanosized silicalite-2 zeolites by steam-assisted dry gel conversion method

Nanosized silicalite-2 zeolite was successfully synthesized by steam-assisted dry-gel conversion technique with TBAOH (tetrabutylammonium hydroxide) as structure directing agent and TEOS (tetraethoxysilane) as silica source. The products were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, N2 adsorption and desorption (BET) and Field emission scanning electron microscopy (FESEM). XRD pattern confirmed the crystallization of silicalite-2 obtained at 170°C for 48h, the diffraction lines of samples were broadened as a result of the decreased in particle size with the content of TBAOH increased. FESEM images showed that the silicalite-2 nanocrystals with a particle size of about 70–90nm. N2 adsorption and desorption provides manifest evidence that the porosity is fully accessible from the external surface of the zeolite crystal. The vibration bands at around 551.5 and 1229.2cm−1 indicated the presence of double 5-ring in the pentasil zeolite structure of MEL, values of the 550cm−1/460cm−1 band intensity ratios demonstrated that the crystallinity of zeolite closed to 100%.

Titanium Silicalite Synthesized by Dry Gel Conversion Method and Its Catalytic Performance

Titanium Silicalite Synthesized by Dry Gel Conversion Method and Its Catalytic Performance

Binderless nano-HZSM-5 zeolite coatings prepared through combining washcoating and dry-gel conversion (DGC) methods

Binderless nano-HZSM-5 zeolite coatings were successfully prepared through a two-step process: washcoating zeolites on the surface of the substrates with controllable thickness, and then converting SiO2 binders into the crystal structure by dry-gel conversion (DGC) method to remarkably improve the adhesion strength. Ethylene diamine, tetrapropylammonium hydroxide and triethylamine were used as organic amines in DGC. The conversion of SiO2 binders into MFI structure around the nano-HZSM-5 zeolite crystals was confirmed by characterizations of X-ray diffraction, 29Si and 27Al nuclear magnetic resonance and transmission electron microscopy. As a result, the adhesion strength of the prepared coatings was significantly improved by ca. one order, which is ascribed to the higher interlocking between the crystals and the aggregates after DGC treatment. NH3-Temperature programmed desorption characterization showed that the total amount of acid sites of the coatings were improved by ca. 30% due to the incorporation of extra-framework Al species of nano-HZSM-5 crystals into the framework of ZSM-5 through DGC treatment. Slight differences in DGC mechanism and thus the acidities as well as adherences of the obtained coatings were also observed depending on the amines used in DGC.

Dry Gel Conversion Method for the Synthesis of Organic–Inorganic Hybrid MOR Zeolites with Modifiable Catalytic Activities

Dry gel conversion (DGC) technique is first applied in the synthesis of organic-inorganic hybrid aluminosilicate zeolites. By using the DGC method, methylene-bridged organic-inorganic hybrid zeolites with an MOR topology are synthesized without organic additive, which are structurally characterized by powder XRD, FTIR, solid-state Si-29, C-13, Al-27 MAS NMR, SEM, elemental analysis, XRF, XPS, and N-2 adsorption techniques. This work first reports that thus-synthesized methylene-bridged hybrid zeolites can be successfully bestowed with excellent catalytic activities through different modification treatments. Co2+-exchanged hybrid zeolites are applied in the epoxidation of alkenes with air to achieve good conversions and selectivities. Especially, methylene-bridged hybrid zeolites can be sulfonated with fuming sulfuric acid to form acidic MOR-SO3H catalyst, which exhibits highly catalytic activity for the acid-catalyzed condensation reaction of cyclohexanone and glycol. This method will be one potential route for the fabrication of organic-inorganic hybrid zeolite or related molecular sieve catalysts.

Synthesis of SUZ-4 zeolite by a dry gel conversion method

SUZ-4 zeolite was synthesized by the dry gel conversion (DGC) process with water vapor as gas phase, and characterized by XRD, SEM and N2 adsorption. The dry gel was prepared with the assistance of a small amount of crystalline seed and organic template tetraethylammonium hydroxide (TEAOH). Molar ratios of SiO2/Al2O3, KOH/SiO2, TEAOH/SiO2 and H2O/SiO2, amounts of seed and dry gel, types of silica sources, and crystallization temperature and time, were changed to optimize synthesis conditions. The results show that the DGC method leads to formation of SUZ-4 zeolite in a broad range of crystallization temperature 120–180 °C. Under the optimal conditions, i.e., SiO2/Al2O3 = 22.5, KOH/SiO2 = 0.44, TEAOH/SiO2 = 0.044, H2O/SiO2 = 22.2, seed amount = 0.1 wt%, fumed silica as the silica source, 160 °C and 5 days, SUZ-4 zeolite is obtained with a high crystallinity. Compared to hydrothermal synthesis, the present DGC approach employs far less amount of organic template and allows using inert fumed silica as silica source, producing smaller rod-like SUZ-4 zeolite crystals.

Isomerization and Cracking of Hexane over Beta Zeolites Synthesized by Dry Gel Conversion Method

Isomerization and Cracking of Hexane over Beta Zeolites Synthesized by Dry Gel Conversion Method

Characterization and hydroisomerization performance of SAPO-11 molecular sieves synthesized by dry gel conversion

SAPO-11 molecular sieves were synthesized by two types of dry gel conversion (DGC) methods, namely, steam-assisted conversion (SAC) and vapor phase transport (VPT), and by conventional hydrothermal (CHT) method. The properties of these samples were characterized by XRD, XRF, SEM, N 2-adsorption, Pyridine-IR and 29Si MAS NMR methods. The results show that di- n-propylamine (DPA) is a suitable structure-directing agent (SDA) for the preparation of impurity-free SAPO-11. SAPO-11 molecular sieves synthesized by SAC and VPT exhibit higher crystallinity, higher Si content and more strongly acidic sites than that synthesized by CHT. 29Si MAS NMR results demonstrated that the two samples obtained by the DGC methods contain more Si(nAl)(0 < n < 4) species than that obtained by CHT. These facts suggest that the SAC and VPT methods contribute either to better Si incorporation into the AlPO 4 framework or to better Si dispersal, thus decreasing the size of Si islands and increasing the number and strength of acidic sites. The results from the hydroisomerization of n-dodecane indicate that the Pt/SAPO-11 synthesized by SAC possesses the highest hydroconversion activity and isomer yield among those three catalysts, due to the high acidity of the molecular sieve supporter.