SAPO-34 Molecular Sieves Research Articles

Crystallization of SAPO-11 Molecular Sieves from Silicoaluminophosphate Gels with Various SiO2/Al2O3 Ratios

Crystallization of SAPO-11 Molecular Sieves from Silicoaluminophosphate Gels with Various SiO2/Al2O3 Ratios

SAPO-11 Molecular Sieves Synthesized from Aluminum Isopropoxide and SiO2 with Various Dispersions

SAPO-11 Molecular Sieves Synthesized from Aluminum Isopropoxide and SiO2 with Various Dispersions

Synthesis of nano-sized small-crystal and hierarchical SAPO-11 molecular sieves and superior catalytic performance of their NiWS-supported catalysts in hydroisomerization of n-hexadecane

The nano-sized small-crystal and hierarchical SAPO-11 molecular sieves were successfully synthesized with l-Lysine as the crystal growth inhibitor, and their particle size reached 80 nm at the minimum, and the crystal size was 22.1 nm. With the synthesized SAPO-11 molecular sieve as support, the corresponding NiW supported catalyst was prepared for the hydroisomerization of n-hexadecane. The properties of small-crystal and hierarchical SAPO-11 molecular sieve and catalyst were analyzed by a series of physicochemical characterizations, and the formation mechanism of small-crystal and hierarchical SAPO-11 molecular sieve was proposed. The results showed that the reduction of crystal size greatly improved the BET specific surface area, mesopore volume of SAPO-11 molecular sieve. The decrease of crystal size increased the surface Si content of SAPO-11 molecular sieve, thus improving the surface acidity of SAPO-11 molecular sieve, and weakening the interaction between active metals and supports of the catalysts. In addition, the decrease of crystal size increased the dispersion and stacking number of the active phases, thus greatly improving the catalytic performance of the catalysts. Compared with the catalyst corresponding to the conventional SAPO-11 molecular sieve, the yield of i-hexadecane of the catalyst corresponding to small-crystal and hierarchical SAPO-11 molecular sieve increased by 45.34%.

Enhanced methanol-to-olefins (MTO) performance over SAPO-34 molecular sieves synthesized using novel sources of silicon and aluminium

Abstract As the core technology of methanol-to-olefins (MTO), the development of a high-efficiency and low-cost molecular sieve catalyst has always been the most important challenge. Herein, SAPO-34 molecular sieves were synthesized by using three different compositions of amorphous aluminium silicate as both Si and Al source under the same conditions. The structure and composition of synthesized SAPO-34s were investigated using X-ray diffraction and X-ray fluorescence, while the morphology and physical properties were characterized using scanning electron microscopy, N2 adsorption–desorption and ammonia temperature-programmed desorption measurements. Compared to the silica sol as the Si source, the SAPO-34s prepared with amorphous aluminium silicate show the higher solid yields and crystallinity, larger surface area and lower numbers of acid sites. Besides the effect of Si, the effect of the Al source on the textural structure and catalytic performance of SAPO-34s in MTO reactions was investigated in detail. The results confirmed that the SAPO-34s prepared using amorphous aluminium silicate have low Si content and hierarchical structure, which results in a longer catalytic lifetime and higher selectivity for light olefins. The sample S2 exhibited the longest lifetime of 214 min and the highest selectivity for light olefins of 85.37%. This also provides a potential for the approach to obtain a high-efficiency catalyst with enhanced catalytic performance and low cost.

Nanosheets of Ni-SAPO-34 Molecular Sieve for Selective Oxidation of Cyclohexanone to Adipic Acid.

Nanosheets of nickel doped SAPO-34 molecular sieves in thickness of ∼10 nm (denoted as NS-Ni-SAPO-34) has been successfully prepared through a morphology-reserved method of synthesis. A special aluminum phosphate in two-dimensional layered structure is used as precursor and converts to crystallized SAPO-34 molecular sieve, in nanosheet morphology reserved from the aluminum phosphate precursor, under hydrothermal conditions with tetraethyl orthosilicate and templates of mixed amines added. It is found that adequate amount of nickel, ∼5 wt %, added to the synthetic system is a key factor for the morphology-reserved synthesis. By characterization, the nickel is proved to be doped in the framework of the molecular sieve, which more likely helps to balance the high surface energy of nanosheet products. The NS-Ni-SAPO-34 shows excellent catalytic performance for oxidation of cyclohexanone to adipic acid by gaseous oxygen.

Small-crystal and hierarchical SAPO-11 molecular sieve synthesized via three-stage crystallization method and hydroisomerization performance of corresponding NiWS supported catalyst

In order to prepare non-noble metal supported hydroisomerization catalyst with high catalytic performance, this work first proposed a novel three-stage crystallization method to synthesize small-crystal and hierarchical SAPO-11 molecular sieve, and prepared the corresponding NiWS supported catalyst for the hydroisomerization of n-hexadecane. The physicochemical properties of the small-crystal and hierarchical SAPO-11 molecular sieve and the NiWS supported catalyst were analyzed via a series of characterization methods. It was found that the crystal size of SAPO-11-S was reduced to 21.8 nm and the particle size was reduced to 70–140 nm. SAPO-11-S was superior to SAPO-11-C in pore properties and acidity. The reason for the increase of the number of medium-strong B acid sites in SAPO-11-S was investigated by 29Si MAS NMR characterization, and the formation mechanism of SAPO-11-S was proposed by tracking and analyzing the crystallization process of SAPO-11-S. The decrease of crystal size of SAPO-11 molecular sieve effectively improved the sulfidation degree of active metals and the dispersion degree of the active phase of the catalyst, and promoted more active phases to form “type II active phase”. Compared with NiW/SAPO-11-C, NiW/SAPO-11-S showed higher catalytic activity and isomerization selectivity, and the maximum i-hexadecane yield of NiW/SAPO-11-S was 44.77% higher than that of NiW/SAPO-11-C.

Acid properties and morphology of SAPO-11 molecular sieve controled by silica source

This paper reports on the control of strong acid sites in SAPO-11 molecular sieve crystals using different silica sources. The crystallization process of the SAPO-11 molecular sieves was performed using silicon sources with different particle sizes, i.e., fumed silica (200 nm), colloidal silica (22 nm), and SiO2 sol prepared by the sol-gel method (4 nm). The SiO2 sol proved to have a significant effect on the acidic properties, morphology and crystal size of SAPO-11 molecular sieve. Moreover, more efficient incorporation of silicon is achieved, providing an increased concentration of acid sites. The SAPO-11 intergrown crystals with a size of 100–300 nm exhibited hierarchical pore structure (SBET – 250 m2/g and Vmeso – 0.27 cm3/g) were synthesized using the SiO2 sol precursor. The SAPO-11 molecular sieves were tested in the reaction of a-methylstyrene dimers synthesis. The SAPO-11 samples, synthesized by SiO2 sol showed the highest monomer conversion and linear dimer selectivity.

Hydroisomerization of n-Hexadecane Over Nickel-Modified SAPO-11 Molecular Sieve-Supported NiWS Catalysts: Effects of Modification Methods.

The complexation-excessive impregnation modification method, which was original in this study, and the ion-exchange method and the in situ modification method were used to synthesize Ni-modified SAPO-11 molecular sieves. With the Ni-modified SAPO-11 samples as support, the corresponding NiWS-supported catalysts for the hydroisomerization of n-hexadecane were prepared. The effects of Ni-modification on SAPO-11 characteristics and the active phase were studied. The structure, morphology, and acidity of SAPO-11, as well as the interaction between active metals and support, the morphology, dispersibility, and stacking number of the active phase, were all changed by Ni-modification methods. The complexation-excessive impregnation modification method deleted a portion of Al from SAPO-11 molecular sieves while simultaneously integrating Ni into the skeletal structure of the surface layer of SAPO-11 molecular sieves, considerably enhancing the acidity of SAPO-11 molecular sieves. Furthermore, during dealumination, ethylenediaminetetraacetic acid generated more mesoporous structures and increased the mesoporous volume of SAPO-11 molecular sieves. Because the complexation-excessive impregnation modification method increased the amount of Ni in the surface framework of the SAPO-11 molecular sieve, it has weakened the interaction between the active phase and the support, improved the properties of the active phase, and greatly improved the hydroisomerization performance of NiW/NiSAPO-11. The yield of i-hexadecane of NiW/NiSAPO-11 increased by 39.3% when compared to NiW/NiSAPO-11. It presented a realistic approach for increasing the acidity of SAPO-11, reducing the interaction between active metals and support, and improving the active phase stacking problem.

Synthesis of Low Silicon Submicron-Sized SAPO-34 Molecular Sieve by Micron Seed Activation Method to Improve the Performance of MTO

Synthesis of Low Silicon Submicron-Sized SAPO-34 Molecular Sieve by Micron Seed Activation Method to Improve the Performance of MTO

N-Octyltrichlorosilane Modified SAPO-34/PDMS Mixed Matrix Membranes for Propane/Nitrogen Mixture Separation

In this study, zeolite molecular sieve SAPO-34/polydimethylsiloxane (PDMS) mixed matrix membranes (MMMs) were prepared to recover propane. n-Octyltrichlorosilane (OTCS) was introduced to improve compatibility between SAPO-34 and PDMS, and enhance the separation performance of the MMMs. Physicochemical properties of the MMMs were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and water contact angle (WCA). Results showed that, after modification, alkyl chains were successfully grafted onto SAPO-34 without changing its crystal structure, particles in the MMMs were evenly distributed in the base film, and the hydrophobicity of the MMMs was enhanced. Moreover, the effects of SAPO-34 filling content, operating pressure, and feed gas concentration on the separation performance was explored. This indicated that the modification with OTCS effectively enhanced the separation performance of SAPO-34/PDMS MMMs. When the filling content of modified SAPO-34 was 15%, the maximal separation factor of 22.1 was achieved, and the corresponding propane permeation rate was 101 GPU.

Relation between Morphology and Porous Structure of SAPO-11 Molecular Sieves and Chemical and Phase Composition of Silicoaluminophosphate Gels.

The formation of silicoaluminophosphate gels using boehmite, Al isopropoxide, and di-n-propylamine as a template of silicoaluminophosphate gels as well as their subsequent crystallization into SAPO-11 molecular sieves was studied in detail using X-ray fluorescence spectroscopy (XRF), powder X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption–desorption methods. The effect of the chemical and phase composition of silicoaluminophosphate gels on the physicochemical properties of SAPO-11 molecular sieves was shown. The secondary structural units that the AEL lattice is composed of were found to be formed at the initial stage of preparation involving aluminum isopropoxide. Several approaches to control their morphology and secondary porous structure are also proposed.

Synthesis and hydrogen isomerization performance of ordered mesoporous nanosheet SAPO-11 molecular sieves

In this study, ordered mesoporous nanosheet SAPO-11 molecular sieves were synthesized using uncalcined SBA-15 molecular sieves as a Si source. The effects of different Si sources on the structure and properties of SAPO-11 molecular sieves were examined, and their growth mechanism was elucidated. An electrostatically polarized region was formed between a P123 template (triblock copolymer) contained in uncalcined SBA-15 and two-dimensional channels of SBA-15 molecular sieves. When AlO2− and PO2+ species diffused into this region, its electrostatic polarization promoted the preferential growth of SAPO-11 molecular sieves along the c-axis, which contained a large number of exposed catalytically active sites with acidic properties. During the isomerization of long-chain alkanes, the synthesized sieves exhibited high isomerization activity and selectivity. When the conversion rate of n-dodecane reached 87.96%, the yield of i-dodecane was 68.08%, and the yield of multi-branched i-dodecane was 31.65%.

SAPO-11 molecular sieves synthesized in alcohol-water concentrated gel system with improved acidity, mesoporous volume and hydroisomerization performance

A series of SAPO-11 molecular sieves were synthesized in the concentrated gel system by reducing the water content in the synthesis system. With SAPO-11 molecular sieves as supports, NiW-supported catalysts were prepared for the hydroisomerization of n-hexadecane. SAPO-11 molecular sieves and catalysts were characterized by XRD, SEM, N2 adsorption–desorption, NH3-TPD, Py-IR, HRTEM and XPS. The results showed that reducing the water content in the synthesis system could increase the mesoporous volume of SAPO-11 molecular sieve and improve the acidity of SAPO-11. For the corresponding catalysts, using SAPO-11 synthesized in concentrated gel system as the support weakened the interaction between the active phase and the support, and increased the dispersion and stacking number of the active phase, which effectively improved the catalytic performance of the catalyst. The yield of i-hexadecane of the catalyst NiW/45W-SA corresponding to SAPO-11 synthesized in conventional water content system was 28.14%, while that of the catalyst NiW/5W-SA corresponding to SAPO-11 synthesized in concentrated gel system was 52.24%. According to the distribution of isomers, it is inferred that hydroisomerization of n-hexadecane over NiW/SAPO-11 follows the pore-mouth mechanism.

Morphology control of SAPO-34 and its catalytic performance for methanol to olefin reaction

SAPO-34 molecular sieves with various special morphologies were synthesized using mixed templates and by varying the silicon content in the gel.

Designed synthesis of single-crystalline silicoaluminophosphate zeolite via interzeolite transformation for n-dodecane hydroisomerization

Single-crystalline zeolites are highly desirable in this field owing to their high hydrothermal stability and high mass transfer efficiency. However, the preparation of single-crystalline silicoaluminophosphate SAPO-11 zeolite remains a significant challenge due to its complex synthesis process. Herein, we firstly report a facile and direct approach to synthesize single-crystalline SAPO-11 by interzeolite transformation via a kinetic-modulated process. The crystallization process of single-crystalline SAPO-11 was monitored by the time-dependent characterizations. A panel of characterizations by XRD, SEM, N 2 -adsorption and solid-state NMR provided evidence that the formation mechanism of single-crystalline SAPO-11 involved fast interzeolite transition process between two different topologies from AlPO 4 -8 (AET) to SAPO-11(AEL), thus it avoids the aggregation of small nanocrystals during the conventional polycrystalline SAPO-11 synthesis. In addition, the Brønsted acid sites of the prepared samples could be precisely regulated. The resulting single-crystalline catalyst exhibits superior isomer selectivity (92.3% vs. 70.6%) and yield (77.9% vs. 62.3%) in the n -dodecane hydroisomerization compared with the conventional polycrystalline sample due to the unique morphology and suitable acidity. This synthetic strategy provides a new orientation to design other single-crystalline zeolite catalysts. Single-crystalline SAPO-11 molecular sieve is synthesized through interzeolite transformation mechanism and has outstanding catalytic performance for the hydroisomerization of n -dodecane. • A new strategy to prepare a single-crystalline SAPO-11 by interzeolite transformation under kinetic-modulated process. • A clear recognition for the formation mechanism involved interzeolite transition process from AlPO 4 -8 to SAPO-11. • The acidity of single-crystalline SAPO-11 could be precisely regulated. • The Pt/S-SAPO-11 catalysts exhibit excellent catalytic performance for the hydroisomerization of n -dodecane.

Evaluating pore characteristics and acid site locations in hierarchical SAPO-11 by catalytic model reactions

Hierarchical SAPO-11 molecular sieves were synthesized with three different mesopore structure directing agents (meso-SDAs): cetyltrimethylammonium bromide (CTAB), polyvinyl alcohol (PVA) and [3-(trimethoxysilyl) propyl] dimethyloctadecylammonium chloride (TPOAC). Two model reactions, methanol-to-hydrocarbons (MTH) and the Beckmann rearrangement (BMR) of cyclohexanone oxime, were employed to evaluate the pore topology and acid site locations of the hydrothermally synthesized hierarchical SAPO-11s. Initially, the modified porosity of the hierarchical SAPO-11s was thoroughly probed by employing a set of general characterization methods and by comparing the results to the conventional microporous C-SAPO-11. The nitrogen physisorption results revealed that CTAB-11 had a uniform distribution of mesopores centered at 2.8 nm, whereas the presence of mesopores in PVA-11 could not be convincingly resolved through conventional methods. Instead, the pore topology of PVA-11 was determined by utilizing model reactions, where the shape selective MTH model reaction revealed that the sample had mesopores present through an increased production of large products compared to the conventional C-SAPO-11. Additionally, the MTH model reaction showed that while PVA shifted the location of the Brønsted acid sites (BAS) towards the mesopores, CTAB did not affect the BAS location of SAPO-11. Finally, the BMR model reaction elucidated the excellent intrapore connectivity of the hierarchical SAPO-11s through an increased lifetime compared to the conventional C-SAPO-11. • Hierarchical SAPO-11 (H-S11) with interconnected micro- and mesopores was synthesized with CTAB and PVA as meso-SDAs. • Model reactions are crucial for understanding the topological differences between microporous SAPO-11 (µ-S11) and H-S11. • CTAB significantly alters the textural properties of the resulting H-S11, while PVA shows similar properties to µ-S11. • PVA directs formation of Brønsted acid sites to mesopores, whereas CTAB forms silanols in mesopores. • Superior lifetime for the isomerization of cyclohexanone oxime revealed the intraconnected pore topology for H-S11.

A comprehensive review on sustainability-motivated applications of SAPO-34 molecular sieve

A comprehensive review on sustainability-motivated applications of SAPO-34 molecular sieve

Synthesis and Applications of SAPO‐34 Molecular Sieves

Silicoaluminophosphate zeolite (SAPO-34) has been attracting increasing attention due to its excellent form selection and controllability in the chemical industry, as well as being one of the best industrial catalysts for methanol-to-olefin (MTO) reaction conversion. However, as a microporous molecular sieve, SAPO-34 easily generates carbon deposition and rapidly becomes inactivated. Therefore, it is necessary to reduce the crystal size of the zeolite or to introduce secondary macropores into the zeolite crystal to form a hierarchical structure in order to improve the catalytic effect. In this review, the synthesis methods of conventional SAPO-34 molecular sieves, hierarchical SAPO-34 molecular sieves and nanosized SAPO-34 molecular sieves are introduced, and the properties of the synthesized SAPO-34 molecular sieves are described, including the phase, morphology, pore structure, acid source, and catalytic performance, in particular with respect to the synthesis of hierarchical SAPO-34 molecular sieves. We hope that the review can provide guidance to the preparation of the SAPO-34 catalysts, and stimulate the future development of high-performance hierarchical SAPO-34 catalysts to meet the growing demands of the material and chemical industries.

A novel adsorption-based method for revealing the Si distribution in SAPO molecular sieves: The case of SAPO-11

A novel adsorption-based method for quantitative estimation of the phosphorus atom replacement for a (Si, H+) pair in the SAPO-11 framework is suggested. The most probable configurations and regularities in the location of silicon atoms and protons in the SAPO-11 structure containing 1, 2, 3 and 5 Si atoms per unit cell were determined by computations. A new force field for adsorption simulation in the H2 – SAPO system was developed. The dependence of averaged Henry's constants for H2 adsorption at 77 K on the amount of substituted Si was calculated. The effect of model used for computation of the Si distribution probability in the SAPO-11 on the adsorption properties in the H2 – SAPO system was studied. Practical applications of the method for several SAPO-11 frameworks with different Si concentrations are demonstrated.

Synthesis of SAPO-34 Nanoplates with High Si/Al Ratio and Improved Acid Site Density.

Two-dimensional SAPO-34 molecular sieves were synthesized by microwave hydrothermal process. The concentrations of structure directing agent (SDA), phosphoric acid, and silicon in the gel solution were varied and their effect on phase, shape, and composition of synthesized particles was studied. The synthesized particles were characterized by various techniques using SEM, XRD, BET, EDX, and NH3-TPD. Various morphologies of particles including isotropic, hyper rectangle, and nanoplates were obtained. It was found that the Si/Al ratio of the SAPO-34 particles was in a direct relationship with the density of acid sites. Moreover, the gel composition and preparation affected the chemistry of the synthesized particles. The slow addition of phosphoric acid improved the homogeneity of synthesis gel and resulted in SAPO-34 nanoplates with high density of acid sites, 3.482 mmol/g. The SAPO-34 nanoplates are expected to serve as a high performance catalyst due to the low mass transfer resistance and the high density of active sites.