Silicoaluminophosphate Molecular Sieves Research Articles

Silicoaluminophosphate Molecular Sieves with Different Silica Contents and Their Catalytic Properties in the Oligomerization of α-Methylstyrene

Silicoaluminophosphate Molecular Sieves with Different Silica Contents and Their Catalytic Properties in the Oligomerization of α-Methylstyrene

Bifunctional catalysts based on hierarchical SAPO-41 nanosheet for Highly-efficient hydroisomerization of n-Hexadecane

Conversion of long-carbon chain n-alkanes into iso-alkanes is a key technology to improve the low-temperature fluidity of petroleum-based diesel and lubricating oil, as well as produce second-generation biodiesel from vegetable oils. Developing a highly efficient bifunctional catalysts is the key to realize this process. In this work, a series of hierarchical silicoaluminophosphate molecular sieves SAPO-41 nanosheet (S41-xBCl) were synthesized by using various amounts of 1-butyl-3-methylimidazolium chloride ionic liquid (BMIMCl) as a crystal growth inhibitor. The bifunctional catalysts Pd/S41-xBCl with merely 0.1 wt% Pd loading on the S41-xBCl samples were prepared by wetness impregnation, and the catalytic performance for hydroisomerization of n-hexadecane was tested. The catalytic performance of Pd/S41-xBCl markedly improved because of the enhanced diffusion properties of reactants and iso-alkene intermediates, as well as the realizing synergistic catalysis of metal and acid sites. The yield of iso-hexadecane over the catalyst Pd/S41-2BCl were as high as 83.4% at n-hexadecane conversion of 94.6%. This efficient catalyst with lower noble metal loadings has wide application potential in the production of petroleum-based diesel and green biodiesel with excellent low-temperature fluidity.

Hierarchical, amine functionalized silicoaluminophosphate molecular sieves for the synthesis of cyclic carbonate via CO2 utilization

Hierarchical, amine functionalized silicoaluminophosphate molecular sieves for the synthesis of cyclic carbonate via CO2 utilization

Influence of Additives and Growth Inhibitors in Improving the Physicochemical Properties of Silicoaluminophosphate Molecular Sieve, SAPO-11.

Silicoalumiophosphates (SAPOs) are microporous crystalline materials extensively utilized as adsorbents and catalysts. The present work utilized two strategies to synthesize nanocrystalline SAPO-11. The first strategy involves a surfactant as a mesoporogen to reduce the crystallite size and increase the surface area for the materials synthesized at 200 °C in 2 days. In the second strategy, the synthesis temperature and time were significantly reduced to 160 °C and 3 h using propylene oxide as a pH accelerator. The reduction in the particle size and the improvement in the surface area were achieved using propyltriethoxysilane, which inhibited the growth of SAPO-11 particles. The materials were thoroughly characterized using XRD, N2-sorption, FTIR, pyridine-adsorbed FTIR, electron microscopy, XPS, and NMR. The surfactant-assisted synthesis formed a nanorod morphology with a large external and BET surface area. The low-temperature synthesis involving silane as a growth inhibitor demonstrated a rectangular nanoplatelet morphology with a large surface area. The synthesis was scaled up to 10 g with no change in the experimental parameters. A synthesis strategy facilitating nuclei formation and retarding the growth of particle size will attract academia and industrial researchers to utilize these strategies for the manufacturing of zeolites of different frameworks on a large scale.

Synthesis and Characterization of Silicoaluminophosphate CIT-16P and Its Transformation to SAPO-17

A silicoaluminophosphate molecular sieve, CIT-16P, is synthesized using butane-1,4-bis(quinuclidinium) [(C7H13N)-(CH2)4-(NC7H13)]2+ dihydroxide (DiQ-C4-(OH)2) as an organic structure-directing agent (OSDA). Upon the removal of the OSDA, either by thermal treatment in air at temperatures exceeding 490 °C or by extended ozone treatment at 150 °C, CIT-16P transforms to SAPO-17 (ERI topology). The structure solution of CIT-16P in its as-synthesized form is obtained using a Rietveld refinement of the powder X-ray diffraction pattern. The primary composite building units (CBUs) of CIT-16P are highly distorted cancrinite (can) CBUs that transform into stable can units of the ERI-type framework as a result of the OSDA removal. The distortion of can CBU is maintained without transformation by the presence of tightly bound DiQ-C4 dications in the as-synthesized form of CIT-16P. The transformed material is characterized and evaluated as a catalyst in the methanol-to-olefins (MTO) reaction. The catalytic behavior of the formed SAPO-17 (Si/T-atom = 0.022) (T = Si + Al + P) at 400 °C and WHSV of 1.3 h-1 produces elevated C3+ olefin products (i.e., propylene, butenes, and pentenes) in early stages of the reaction. However, as the reaction proceeds, the C3+ fraction decreases in favor of more ethylene.

Effective synergies in indium oxide loaded with zirconia mixed with silicoaluminophosphate molecular sieve number 34 catalysts for carbon dioxide hydrogenation to lower olefins

Tandem catalysts consisting of metal oxides and zeolites have been widely studied for catalytic carbon dioxide (CO2) hydrogenation to lower olefins, while the synergies of two components and their influence on the catalytic performance are still unclear. In this study, the composite catalysts composed of indium oxide loaded with zirconia (In2O3/ZrO2) and silicoaluminophosphate molecular sieve number 34 (SAPO-34) are developed. Performance results indicate that the synergies between these two components can promote CO2 hydrogenation. Further characterizations reveal that the chabazite (CHA) structure and acid sites in the SAPO-34 are destroyed when preparing In-Zr/SAPO by powder milling (In-Zr/SAPO-M) because of the excessive proximity of two components, which inhibits the activation of CO2 and hydrogen (H2), thus resulting in much higher methane selectivity than the catalysts prepared by granule stacking (In-Zr/SAPO-G). Proper granule integration manner promotes tandem reaction, thus enhancing CO2 hydrogenation to lower olefins, which can provide a practicable strategy to improve catalytic performance and the selectivity of the target products.

Rapid synthesis of hierarchical silicoaluminophosphate molecular sieves using carbon-silicon composites from rice husk ash for deoxygenation of stearic acids

To improve the low temperature fluidity of bio-diesel, a Ni/SAPO catalyst is prepared using hierarchical silicoaluminophosphate (i.e., SAPO-11/SAPO-31) molecular sieves as supports. A rapid, cost-effective, and eco-friendly approach is proposed using carbon-silicon composites from rice husk ash (RHA). The carbon-silicon composite is obtained via an anaerobic calcination of RHA, which acts as the silicon source and mesopore filler, simultaneously. As-synthesized SAPO-11/SAPO-31 intergrowth molecular sieve has a high mesopore volume due to the mesopore filler function of carbon in RHA. A lower crystallization temperature and shorter duration are achieved with the assistance of microwave irradiation. Ni/SAPO catalysts exhibit a high conversion of stearic acids (concentration, 0.5–5 wt%) to form n-/isoparaffins. These results are important to develop a potential efficient catalyst for the upgrade of bio-oil and the novel synthesis method provides reference to the synthesis of other types of SAPO molecular sieves.

Synthesis of Hierarchical Silicoaluminophosphate (SAPO) Molecular Sieves by Post‐Synthetic Modification and Their Catalytic Application

AbstractSilicoaluminophosphates SAPO‐34 (CHA topology) and SAPO‐5 (AFI topology) molecular sieves are selectively prepared by hydrothermal method using templates tetraethylammonium hydroxide and triethylamine, respectively and suitably modified. Hierarchical SAPO‐34 & SAPO‐5 catalysts were post‐synthetically prepared by facile acid (HNO3 and HCl) and base (NaOH) etching. X‐ray diffraction (XRD), Thermogravimetric analysis (TG), FT‐IR and Scanning Electron Microscope (SEM) were employed to investigate structural changes of the molecular sieves. Hierarchical SAPO‐34 & SAPO‐5 were used for the ring opening reaction of propylene oxide with morpholine producing the corresponding β‐amino alcohols, and catalytic activity of the acid‐treated SAPO‐34 & SAPO‐5 was compared with that of alkali treated counterparts. The catalytic performance of the acid treated materials was found better than the base treated one. 91 % conversion was achieved using acid treated SAPO‐34, whereas 74 % conversion was achieved using alkali treated SAPO‐34.

Hydrothermal Synthesis of Silicoaluminophosphate with AEL Structure Using a Residue of Fluorescent Lamps as Starting Material.

Silicoaluminophosphate molecular sieves of SAPO-11 type (AEL structure) were synthesized by the hydrothermal method, from the residue of a fluorescent lamp as a source or Si, Al, and P in the presence of water and di-propyamine (DPA) as an organic template. To adjust the P2O5/SiO2 and Si/Al and ratios, specific amounts of silica, alumina, or alumina hydroxide and orthophosphoric acid were added to obtain a gel with molar chemical composition 1.0 Al2O3:1.0 P2O5:1.2 DPA:0.3 SiO2:120 H2O. The syntheses were carried out at a temperature of 473 K at crystallization times of 24, 48, and 72 h. The fluorescent lamp residue and the obtained samples were characterized by X-ray fluorescence, X-ray diffraction, scanning electron microscopy, and BET surface area analysis using nitrogen adsorption isotherms. The presence of fluorapatite was detected as the main crystalline phase in the residue, jointly with considered amounts of silica, alumina, and phosphorus in oxide forms. The SAPO-11 prepared using aluminum hydroxide as Al source, P2O5/SiO2 molar ratio of 3.6 and Si/Al ratio of 0.14, at crystallization time of 72 h, achieves a yield of 75% with a surface area of 113 m2/g, showing that the residue from a fluorescent lamp is an alternative source for development of new materials based on Si, Al, and P.

Silicoaluminophosphate Molecular Sieves SAPO-11 and SAPO-41: Synthesis, Properties, and Applications for Hydroisomerization of C16+ n-Paraffins. Part 2: Current State of Research on Methods to Control the Crystal Morphology, Dispersion, Acidic Properties, Secondary Porous Structure, and Catalytic Properties of SAPO-11 and SAPO-41 in Hydroisomerization of C16+ n-Paraffins (A Review)

Silicoaluminophosphate Molecular Sieves SAPO-11 and SAPO-41: Synthesis, Properties, and Applications for Hydroisomerization of C16+ n-Paraffins. Part 2: Current State of Research on Methods to Control the Crystal Morphology, Dispersion, Acidic Properties, Secondary Porous Structure, and Catalytic Properties of SAPO-11 and SAPO-41 in Hydroisomerization of C16+ n-Paraffins (A Review)

Selective Crystallization of Silicoalumophosphate Sapo-11 With A Micromesoporous Structure

ABSTRACT:The authors have proposed a method for the selective crystallization of a SAPO-11 silicoaluminophosphate molecular sieve with a micro-mesoporous structure. It has been shown that crystallization of a silicoaluminophosphate gel, in the preparation of which its isopropoxide is used as a source of aluminum, makes it possible to obtain a SAPO-11 molecular sieve with a specific surface area of ​​~ 207 m2 / g, a volume of micro- and mesopores of ~ 0.08 and 0.09 cm3 / g. , respectively. Using scanning electron microscopy, it was demonstrated that the crystals of the material are pseudospherical particles ~ 8-10 microns in size, consisting of aggregates of nanocrystals ~ 100-200 nm in size.

Chromium Environment within Cr-Doped Silico-Aluminophosphate Molecular Sieves from Spin Density Studies.

X-/Q-band electron paramagnetic resonance (EPR) and hyperfine sublevel correlation (HYSCORE) spectroscopies have been employed, in conjunction with density functional theory (DFT) modeling, to determine the location of Cr5+ions in SAPO-5 zeotype materials. The interaction of the unpaired electron of the paramagnetic Cr5+ species with 27Al could be resolved, allowing for the first detailed structural analysis of Cr5+ paramagnetic ions in SAPO materials. The interpretation of the experimental results is corroborated by DFT modeling, which affords a microscopic description of the system investigated. The EPR-active species is found to be consistent with isolated Cr5+ species isomorphously substituted in the framework at P5+ sites.

SAPO-34 synthesis by combinations of structure-directing agents: Experimental and Monte Carlo simulations studies

In the present work, the effect of different mixtures of structure-directing agents (SDAs) on the structure and morphology of silicoaluminophosphate (SAPO-34) molecular sieves has been investigated. For this reason, triethylamine (TEA), diethylamine (DEA), n-butylamine (BA), and various combinations of them were used as organic templates for the synthesis of SAPO-34. The prepared samples were well characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and N2 adsorption-desorption techniques. To explain the effect of the template on the SAPO-34 structure, Monte Carlo simulations were performed. In the simulation section, to survey the effect of the template nature on the formation of SAPO-34, the relation between the host framework and guest template was considered. The experimental studies revealed that the TEA template has an effective role in the mesoporosity and surface area of the prepared samples. The theoretical calculations showed that the prepared samples with the participation in the TEA template present more non-bonding interactions with the SAPO-34 molecular sieves.

Transformation of atomically dispersed platinum in SAPO-37 into platinum clusters: catalyst for ethylene hydrogenation

Atomically dispersed supported platinum catalysts were synthesized by the reaction of Pt(acac)2 (acac = acetylacetonato) with the silicoaluminophosphate molecular sieve SAPO-37, with infrared spectra showing that the reaction involved SAPO OH groups.

Unusually Low Heat of Adsorption of CO2 on AlPO and SAPO Molecular Sieves.

The capture of CO2 from post-combustion streams or from other mixtures, such as natural gas, is an effective way of reducing CO2 emissions, which contribute to the greenhouse effect in the atmosphere. One of the developing technologies for this purpose is physisorption on selective solid adsorbents. The ideal adsorbents are selective toward CO2, have a large adsorption capacity at atmospheric pressure and are easily regenerated, resulting in high working capacity. Therefore, adsorbents combining molecular sieving properties and low heats of adsorption of CO2 are of clear interest as they will provide high selectivities and regenerabilities in CO2 separation process. Here we report that some aluminophosphate (AlPO) and silicoaluminophosphate (SAPO) materials with LTA, CHA and AFI structures present lower heats of adsorption of CO2 (13–25 kJ/mol) than their structurally analogous zeolites at comparable framework charges. In some cases, their heats of adsorption are even lower than those of pure silica composition (20–25 kJ/mol). This could mean a great improvement in the regeneration process compared to the most frequently used zeolitic adsorbents for this application while maintaining most of their adsorption capacity, if materials with the right stability and pore size and topology are found.

Effect of the Aging Temperature of Gel on the Synthesis and Properties of the Silicoaluminophosphate Molecular Sieve SAPO-11

The effect of the aging temperature of the starting silicoaluminophosphate gel on the crystallization of the SAPO-11 molecular sieve was studied. When pseudoboehmite was used as an aluminum source, a gel containing di-n-propylamine phosphate, undissolved pseudoboehmite, and amorphous silicoaluminophosphate were formed. An increase in the aging temperature of the gel from 25 to 90°C led to an increase in the fraction of the amorphous phase in the latter. Crystallization of the silicoaluminophosphate gel aged at 90°C allows crystallization of SAPO-11 of high phase purity and nearly 98% crystallinity. High activity and selectivity for linear dimers (86%) of SAPO-11 in the dimerization of α-methylstyrene was shown.

The Influence of Temperature of Gel Ageing on Synthesis and Properties of the Silicoaluminophosphate Molecular Sieve SAPO-11

The influence of temperature of ageing of the initial silicoaluminophosphate gel on crystallization of the molecular sieve SAPO-11 was studied. It was established that with pseudoboehmite used as the source of aluminum, a gel containing di-n-propylamine phosphate, non-dissolved pseudoboehmite and amorphous silicoaluminophosphate was formed. Elevation of the gel ageing temperature from 25 to 90 °C was shown to result in an increase in the proportion of the amorphous phase in the gel. Crystallization of the silicoalumophosphate gel at 90 °C allowed SAPO-11 to be crystallized at high phase purity and close to 98 % crystallinity. A high activity and selectivity (86 %) of SAPO-11 to linear dimmers was observed during dimerization of α-methylstirene.

Conversion of methanol to dimethyl ether over silicoaluminophosphates: Isolated acid sites and the influence of silicon islands. A DFT-ONIOM study

Abstract ONIOM(DFT:PM3) calculations were analyzed here in order to examine if, and how the isolated Bronsted acid sites, the silicon islands and the pore diameter affect the activation energies in the dimethyl ether formation from methanol for a series of silicoaluminophosphate (SAPO) molecular sieves, SAPO-5, SAPO-11, SAPO-34 and SAPO-41. Three density functionals were employed: B3LYP, ωB97X and ωB97X-D. The results revealed that the CH3OH adsorption energy increases with the type of functional used, according to the trend B3LYP

A chemical approach for ultrafast synthesis of SAPO-n molecular sieves

Silicoaluminophosphate (SAPO-n) molecular sieves are important microporous materials for chemical processes like MTO. Classical synthesis route for SAPO-n, i.e. hydrothermal method, generally requires dozens of hours (>24 h). In this work, we reported a chemical approach to significantly reduce required crystallization time to 40–120 min by adding citric acid (CA) in synthesis gel. The time consumed with the proposed process is comparable with that by special heating intensification method while it is simpler, cheaper, and greener than latter. The ultrafast crystallization was attributed to the non-classical nucleation theory inspired by kinetic analysis, in which chelation interaction between CA and Al3+ favored metastable phase generation evidenced by XRD and 27Al NMR. Other chelate agents (tartaric acid, ethylenediaminetetraacetic acid) with multi carbonic group also showed promising interaction. Moreover, the superior crystallization promotion effect could be applicable in the synthesis of other SAPO-n molecular sieves like SAPO-11, which indicates its great potentials in the future. With further optimization by structure promoter, the obtained SAPO-34 demonstrated sub-micron particle size, high ratio isolated Q0 state Si specie, and hierarchical structure, characterized by the SEM, XPS, 29Si NMR, TEM, and N2-isotherms. The promoted physiochemical properties favored superior performance during MTO test. This work opens up a new perspective to synthesize SAPO-n molecular sieves by a simple chemical approach in a highly efficient and environment friendly manner.

Key Stages in the Formation of AlPO4-11 via the Crystallization of a Boehmite-Based Aluminophosphate Gel

The staged crystallization of aluminophosphate AlPO4-11 from a commercially available aluminum source based on boehmite is studied for the first time by means of X-ray diffraction, 27Al and 31P magic-angle spinning nuclear magnetic resonance, low-temperature nitrogen adsorption–desorption, and scanning election microscopy. It is shown that the synthesis of AlPO4-11 proceeds via the formation of an intermediate phase based on crystalline aluminophosphate with a layered structure. It is found that AlPO4-11 with a high degree of crystallinity and phase purity forms in 6–24 h at 200°C. Lengthening the time of crystallization at 200°C to more than 48 h results in the transformation of AlPO4-11 into nonporous cristobalite. The results can be used to develop means for directional control of the phase purity and degree of crystallinity of commercially important silicoaluminophosphate molecular sieves SAPO-11 with desired properties. These can be used as a base for the synthesis of promising domestic catalysts for the commercial hydroisomerization of higher n-paraffins.