SAPO-34 Samples Research Articles

Shape-selective catalysts of Mg2+ ion exchange modified SAPO-11 molecular sieves for alkylation of 2-methylnaphthalene

The conversion of 2-methylnaphthalene (2-MN) and methanol by molecular zeolites to 2,6-dimethylnaphthalene (2,6-DMN) is significant for the preparation of polyethylene naphthalate. However, there is still a challenge to develop catalysts with efficient selectivity and activity. In this work, the hydrothermally synthesized SAPO-11 samples were modified by ion-exchange of Mg2+ for the catalytic alkylation of 2-MN, and thus the selectivity of 2,6-DMN was greatly improved. The results show that the Mg2+ ion-exchanged SAPO-11 molecular sieves could maintain the original main structure and morphology. However, the introduction of Mg2+ regulated the pore structure, acid content, acid strength and the distribution ratio of Brönsted acid and Lewis acid sites in the molecular sieves, and thus the Mg/SAPO-11 catalyst presented better catalytic performance than the pure SAPO-11. After 6 h of reaction, the selectivity of 2,6-DMN could still maintain 41.3% and the ratio of 2,6-/2,7-DMN was 1.87 over 0.06M-Mg/SAPO-11 sample. The deep isomerization of methylnaphthalene was reduced due to the Mg2+ ion exchange resulting in a shape-selective effect from passivation of the outer surface of the catalyst and adjustment of the open pore size. Therefore, this work presents a shape-selective catalysis in zeolites using Mg2+ ion exchange strategy for the alkylation of 2-MN.

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.

Optimization of the pore structure and acidity of SAPO-11 for highly efficient hydroisomerization on the long-chain alkane

To obtain both high conversion and selectivity on the long-chain alkane hydroisomerization is still challenging. Herein, we report an excellent hydroisomerization catalyst with flower-like morphology, using the dual-additive synthetic method to simultaneously modulate the pore structure and acidity of SAPO-11 molecular sieve, with the activated carbon and n -butanol as additives. Various characterization results show that the dual additives have a synergistic promotion effect on the as-synthesized samples: (i) the dual additives promote the formation of higher external surface area and more mesoporous structure with suitable mesopore distribution; (ii) the total Brønsted acid sites of prepared SAPO-11 samples are enhanced by the dual additives and Brønsted acid strength are optimized as well. The resulting SAPO-11-B/C 0.6 loaded with 0.5 wt% Pt exhibited excellent performance on a series of alkanes hydroisomerization ( n -C 6 , n -C 8 , n -C 10 , n -C 12 , and n -C 16 ). In addition, the Pt-SAPO-11-B/C 0.6 showed the highest i -C 16 yield of 90.7% on the n -hexadecane hydroisomerization, outperforming the reported conventional Pt/SAPO-11 catalysts; and it also presents high catalytic activity over 1700 h, which is promising in the real industrial field. • SAPO-11 was synthesized using a dual-additive synthetic approach with simultaneously modulated pore structure and acidity. • The synthesis method is efficient and simple, avoiding costly and complicated processes. • The resulting catalyst exhibits ultra-high n -C 16 hydroisomerization performance and catalytic stability.

Revealing inherent factors of SAPO-34 zeolites etching towards the fabrication of hierarchical structure

Fabrication of hierarchical SAPO-34 zeolites by chemical etching is a facile, economic and efficient route to address their intrinsic diffusion limitation. Various leaching strategies have been developed to prepare hierarchical SAPO-34 zeolites. However, the effect of inherent factors of SAPO-34 crystals on the etching, such as crystal size and Si content, have not been systematically investigated. In the present work, a series of SAPO-34 zeolites with different Si contents and crystal sizes are prepared and leached in the mother liquor. The crystal morphology, textural properties, framework environments, and acidity of the synthesized SAPO-34 samples are comprehensively characterized through transmission electron microscope (TEM), nitrogen adsorption-desorption, solid-state MAS NMR, and NH3-TPD measurements. The formation of hierarchical porosity by etching is dependent on the Si contents and particle sizes of SAPO-34 samples. After etching in the mother liquor, the nanosized SAPO-34 zeolites with low Si content exhibit remarkably prolonged lifetime and higher selectivity to ethylene and propylene than other counterparts in methanol-to-olefin reactions, owing to the more accessible sites and improved mass transport. This work will inspire the more suitable and efficient preparation of hierarchical SAPO-34 catalysts via etching route.

MTO performance over seed-assisted SAPO-34 zeolites synthesized by reducing template consumption

SAPO-34 samples were prepared via a seeding-induced method with a considerable reduction of template concentration. The resultant SAPO-34 zeolites were investigated by XRD, FESEM, EDS, N2 adsorption, and NH3-TPD analyses. The samples represent different catalytic activity in the MTO process due to their differences in the physic-chemical properties, including crystallite/particle sizes, surface area, acid strength and concentration. Pure SAPO-34 was obtained with a 60% reduction of organic template for the first time. However, due to the increase of particle sizes, it did not show the desired catalytic performance. An excellent catalytic performance was achieved for the seeding-induced catalyst prepared by a 40% reduction of template content according to its appropriate high acidity and relatively large surface area. This sample exhibited 91.8% selectivity toward light olefins and about 330 min of lifetime, which were 14.4% higher in term of selectivity and more than twice lifetime than the unseeded sample. This substantial achievement was obtained under the industrial feed conditions (72%wt methanol in water) and provided a cost-effective and environmentally friendly route for preparing promising MTO catalyst with notably decreased template dosage.

Synthesis of Fine-Crystalline SAPO-11 Zeolites and Analysis of Their Physicochemical and Catalytic Properties

Results of crystallization of two 1.0Al2O3 ⋅ 1.0P2O5 ⋅ 0.4SiO2 ⋅ 1.0DPA ⋅ 50H2O silicoaluminophosphate gels are compared; the gels are synthesized using pseudoboehmite in one case and aluminum isopropoxide in the other. It is shown that the choice of aluminum source significantly affects the phase composition of the resulting silicoaluminophosphate gels and the physicochemical properties of SAPO-11 samples crystallized from the gels and their catalytic properties in the vapor-phase isomerization of cyclohexanone oxime to caprolactam.

Time-resolved operando DRIFTS-MS study of the moisture tolerance of small-pore SAPO-34 molecular sieves during CH4/CO2 separation

This study pretends to evaluate and understand the effect of moisture presence during CO2/CH4 separation on small-pore SAPO-34 molecular sieves. Two SAPO-34 samples with different physicochemical properties (composition, crystal size and texture) were prepared by hydrothermal synthesis using either one or a mixture of two templates. Transient operando DRIFTS-MS measurements revealed that the sample's hydrophobic character is associated to the presence of Si islands, which enhanced sample's moisture tolerance during repetitive adsorption/desorption cycles. This knowledge is fundamental to achieve the rational design of efficient SAPO-34 membranes under realistic conditions.

Polyoxometalate modified SAPO-34: A highly stable and selective catalyst for methanol conversion to light olefins

Abstract Highly stable and selective SAPO-34 catalysts were synthesized with direct synthesis incorporation of tungstophosphoric acid (HPW) and silver salt of HPW (AgPW) in SAPO-34 framework. The physicochemical properties of synthesized SAPO-34 samples were investigated using various analyses, including XRD, FTIR, UV–vis/DRS, NH3-TPD, ICP-AES, FESEM, BET and TGA. Furthermore, the catalytic performances of SAPO-34 samples in the reaction of methanol to olefins (MTO) were studied at 450 °C and 1atm. Incorporation of a moderate amount of HPW (HPW/Al2O3 = 0.010) as a Bronsted acid promoter in the SAPO-34 framework significantly reduced the SAPO-34 crystals size, enhanced the BET surface area and boosted the acidic properties. MTO catalytic tests revealed that the existence of a higher amount of Bronsted acid site as an active site could promote the light olefins selectivity and lifetime of HPW-modified SAPO-34 samples. The best HPW-SAPO-34 sample had a 375 min lifetime and 95.34% selectivity to light olefins, while the unmodified SAPO-34 represented 185 min and 83.28% of catalytic lifetime and selectivity to light olefins, respectively. AgPW-SAPO-34 with AgPW/Al2O3 = 0.010 illustrated superior catalytic performance and a lower deactivation rate due to the small well-defined crystals, the highest BET surface area and sufficient created Bronsted acid sites with a lower strength than the other synthesized samples. The AgPW-SAPO-34 sample showed a 403 min lifetime and 96.61% light olefins selectivity in the MTO process.

Synthesis of hierarchical SAPO-34 catalysts modified with manganese nanoparticles for conversion of methanol to light olefins: a deactivation and regeneration study

The hierarchical type 34 silicoaluminophosphate (SAPO-34) catalysts containing manganese were synthesized in the presence of carbon nanotube as mesopore template and tested in the transformation of methanol to light olefin. Also, the regenerability of spent catalysts after methanol to olefins (MTO) reaction was studied. In order to investigate the effect of manganese on the framework and extra framework of SAPO-34 structure, manganese species were added to SAPO-34 by isomorphous substitution and impregnation methods. The physicochemical properties of modified hierarchical samples such as crystallinity, acidity, porosity and reducibility were strongly dependent on the metal addition method. The modified hierarchical samples showed superior performance in the terms of activity and longevity compared to unmodified hierarchical SAPO-34. Among the samples, hierarchical MnAPSO-34 catalyst prepared by isomorphous substitution exhibited the best performance in the MTO reaction. The characterization of the used hierarchical catalysts by TGA analysis revealed that the deposited coke on modified samples was lower compared to unmodified hierarchical SAPO-34. The regenerated modified hierarchical SAPO-34 samples showed more enhanced ethylene selectivity in the MTO reaction and longer lifetime due to the existence of more methylated naphthalenes and methylated benzenes in the residual coke after regeneration.

Seed-assisted grinding synthesis of SAPO-34 catalyst and its prolonged catalytic lifetime in the conversion of methanol to olefins

A cost-effective route has been developed for the synthesis of nano-sized triclinic SAPO-34 zeolite via seed-assisted grinding method using lower dosage of morpholine as the sole template. The synthesis conditions including silica source, silica concentration, crystallization temperature and time were refined to obtain SAPO-34 zeolite with high phase purity and crystallinity. Particularly, seed crystals preactivated by different methods were utilized to induce the synthesis of nano-sized SAPO-34 zeolites in the subsequent study. The resultant SAPO-34 samples were characterized by XRD, SEM, N2 physisorption and NH3-TPD techniques. It was found that the introduction of seed crystals activated by mechanical milling for 20 min and chemical etching with 0.0001 M and 0.01 M H3PO4 can not only effectively reduce the crystal size of SAPO-34 zeolites from 3–4 μm to 500–800 nm level, but also can modify their texture and acid properties. This nano-sized SAPO-34 catalyst exhibits a remarkably prolonged catalytic lifetime in methanol to olefins (MTO) reaction in comparison to the conventional micron-sized counterpart. Analogous to solvent-free synthesis of zeolites, this seed-assisted grinding synthesis method is simpler, more efficient than conventional hydrothermal synthesis. More importantly, this method provides a new avenue for preparing superior MTO catalyst.

Seed-assisted synthesis of hierarchical SAPO-18/34 intergrowth and SAPO-34 zeolites and their catalytic performance for the methanol-to-olefin reaction

Abstract Hierarchical silicoaluminophosphate SAPO-18/34 intergrowth and SAPO-34 zeolites were synthesized by adding SAPO-34 seed crystals to a SAPO-18 zeolite precursor in an aminothermal system, in which triethylamine was used as both the solvent and the template. The prepared samples were characterized by XRD, SEM, TEM, ICP-OES, N2 adsorption–desorption, NMR, TPD, TGA and GC–MS and a possible formation mechanism was proposed. The XRD and NMR results indicated that as the amount of SAPO-34 seed crystals increased, the phase of the products changed from SAPO-18 to SAPO-18/34 intergrowth and then to pure-phase SAPO-34. SEM and TEM results showed that the SAPO samples are the aggregates of many nanosized plate-like nanoparticles containing mesopores and/or macropores. These samples had higher external surface areas and mesopore volumes than the single-phase SAPO-18. The NH3-TPD results showed that the amount and strength of the strong acid sites in the SAPO-18/34 intergrowth and SAPO-34 samples were influenced by the amount of added SAPO-34 seed crystals, but all values were higher than those of pure SAPO-18. The SAPO-18/34 intergrowth and SAPO-34 zeolites with the hierarchical structure and appropriate acidic properties exhibited excellent catalytic properties for the methanol to olefin reaction. Moreover, the selectivities of light olefins varied with the cage type, the acidic properties and hierarchical structure of SAPO-18/34 intergrowth and SAPO-34 zeolites.

The hydroisomerization of n-decane over Pd/SAPO-11 bifunctional catalysts: The effects of templates on characteristics and catalytic performances

Two series of pure SAPO-11 silicoaluminophosphates (S11-B(x) and S11-P(x)) with different SiO2/Al2O3 molar ratios are synthesized by employing Di-n-butylamine (DBA) and Di-n-propylamine (DPA) templates, respectively. The effects of templates on the physicochemical properties of SAPO-11 samples are investigated by XRD, N2-adsorption, SEM, XRF, 29Si MAS NMR and Py-IR measurements. The results demonstrate that S11-B(x) samples reveal different morphology and lower strong Brønsted acid density compared with S11-P(x) samples. In addition, the linear correlation between detected and calculated total Brønsted acid densities of all samples is established. The Pd/S11-B(x) and Pd/S11-P(x) bifunctional catalysts are prepared by depositing 0.5 wt% Pd on SAPO-11 samples via the incipient wetness impregnation and hydrogen reduction methods and the n-decane hydroisomerization over all catalysts are tested. The catalytic results suggest that, due to the larger CPd/CH+ ratios and fewer strong Brønsted acid sites, Pd/S11-B(x) catalysts show higher yield of i-decanes compared with Pd/S11-P(x) catalysts, while the Pd/S11-B(0.4) shows the highest i-decanes yield of 76.75% among all catalysts. The results of long-term tests of 120 h suggest that Pd/S11-B(0.4) catalyst also has better stability because of slighter aggregation of Pd metal particles and fewer blockages of micropore openings.

Selective catalytic reduction of NO with NH3 over the Cu/SAPO-34 catalysts derived from different Cu precursors

Abstract Hydrothermal stability of the Cu(A, N, Cl or S)/SAPO-34 samples derived from different Cu precursors (A: Cu-acetate; N: Cu-nitrate; Cl: Cu-chloride; and S: Cu-sulfate) was investigated. The physical and chemical properties of the samples were investigated by various analytical techniques, and their catalytic activities for NO conversion and NH3 oxidation were evaluated. The results of NH3-SCR activity show that the Cu(A)/SAPO-34 sample was better than that of the Cu(N, Cl or S)/SAPO-34 sample, which was due to the existence of a less amount of CuO species and a more amount of the isolated Cu2+ species. Moreover, catalytic activities of all aged catalysts decreased in the whole temperature range, which was attributed to the drop in the amount of isolated Cu2+ species in the hydrothermally treated Cu/SAPO-34 samples. After hydrothermal aging treatment, part of the isolated Cu2+ was transformed to CuO, leading to structural instability and deactivation of the catalysts.

Fabrication of nanometer-sized high-silica SAPO-5 and its enhanced photocatalytic performance for methyl orange degradation

Higher efficient degradation of methyl orange (MO) was demonstrated with nanometer-sized high-silica SAPO-5. By a hydrothermal process, synthesized high-silica SAPO-5 and low-silica SAPO-5 showed Si-to-Al ratios of 4.20 and 0.11, respectively. High-silica SAPO-5 showed much better MO degradation efficiency with a dosage of 70 mg in MO solution with a concentration of 10 mg/L under ultraviolet illumination. High-silica SAPO-5 also exhibited good producibility for preparation and stable photocatalytic activity even after the fifth recycling test. Optical characterizations of DRS, XPS, photocurrent density and time-resolved fluorescence were carried out for SAPO-5 samples. Finally, free radical and hole scavenging experiments were investigated for high-silica SAPO-5, and a MO photodegradation mechanism based on the charge transfer excited state of [Al2+–O−]* was proposed. This work highlights great prospects of high-silica SAPO-5 for organic pollutant removal with virtues of ideal efficiency and environmental friendliness.

Sucrose facilitated synthesis of mesoporous silicoaluminophosphate SAPO-11 with different crystalline phases of MoO3 for highly-efficient oxidative desulfurization

The mesoporous silicoaluminophosphate SAPO-11 materials were synthesized by using the green and low-cost sucrose as template. The SAPO-11 were characterized by SEM, TEM, N2 physisorption and FT-IR. Sucrose was incorporated into the crystal structure of SAPO-11 crystals to form secondary mesoporosity. Meanwhile, the mesoporous MoVI/SAPO-11 samples with different MoO3 crystalline phases were synthesized. In addition, the pre-prepared optimal catalyst (with 3.6% molybdenum mass content) showed significantly high yield and durability for oxidative desulfurization (ODS). Interestingly, the yield of α-MoO3 composites was more than twice that of pure mesoporous SAPO-11 samples, due to the synergistic effect of secondary mesoporosity and molybdenum oxide. Then, the ODS reaction products were determined by GC–MS and 1H NMR. The leaching of active species in the liquid under the reaction conditions were evaluated. Besides, the kinetic properties were studied to calculate the activation energy of the reaction, and then a plausible mechanism of oxidative desulphurization reaction was also proposed.

Selective Desilication, Mesopores Formation, and MTO Reaction Enhancement via Citric Acid Treatment of Zeolite SAPO-34

Adjusting the silica composition/structure and thus tuning the acidity besides introducing hierarchical pore structure is the key factor in zeolite SAPO-34 research. In this work, hierarchical zeolite SAPO-34 with well-organized mesopores was prepared via citric acid treatment. The mesopores presented a novel slit shape, which starts from the crystal surfaces then ends at the center of the crystal. It was found that, after citric acid treatment, silicon species of Si(OSi)1(OAl)3 in the SAPO-34 framework were extracted selectively, at the same time that both the total Lewis acid amount (by NH3–IR) and the Bronsted acid amount on the external surface (by Pyridine-IR) of SAPO-34 zeolite obviously increased. Consequently, the hierarchical SAPO-34 sample exhibited superior catalytic performance in the MTO reaction with about 2.5 times prolonged catalytic lifetime and a nearly 8% improvement of selectivity for ethylene and propylene; this is very important for industrial processes.

Synthesis and stability evaluation of hierarchical silicoaluminophosphates with different structural frameworks in the methanol to olefins process

Silicoaluminophosphates (SAPOs) with different pore structures were synthesized through the implementation of polyethylene glycol (PEG) as a mesopores impregnation agent. Using PEGs with different molecular weights (MWs) and concentrations in the synthesis precursor, several samples were synthesized and characterized. Applying a PEG capping agent to the precursors led to the formation of tuned mesopores within the microporous matrix of the SAPO. The effects of the PEG molecular weight and PEG/Al molar ratio were investigated to maximize the efficiency of the catalyst in the methanol-to-olefin (MTO) process. Using PEG with a MW of 6000 resulted in the formation of both Zeolite Rho and chabazite structural frameworks (i.e., DNL-6 and SAPO-34). Pure SAPO-34 samples were successfully prepared using PEG with a MW of 4000. Our results showed that the PEG concentrations affect the porosity and acidity of the synthesized materials. Furthermore, the SAPO-34 sample synthesized with PEG (MW of 4000) and a PEG/Al molar ratio of 0.0125 showed a superior catalytic stability in the MTO reaction owing to the tuned bi-modal porosity and tailored acidity pattern. Finally, through reactivation experiments, it was found that the catalyst is stable even after several regeneration cycles.

Ionothermal preparation of triclinic SAPO-34 and its catalytic performance in the MTO process

This work reports the ionothermal synthesis of SAPO-34 material, which is the per-excellence catalyst in the methanol-to-olefins (MTO) process. The direct addition of Si sources to the aluminophosphate and ionic liquid (1-ethyl-3-methyl imidazolium) mixture gave rise to the undesired AEL-structured materials. Therefore, some other strategies were necessary to apply. In particular, two unexplored strategies have been developed: (i) the addition of further heteroatom ions able to direct CHA materials, V ions being particularly efficient; and (ii) to carry out the synthesis in open systems rather than in autoclaves under autogenous pressure. Interestingly, the combination of both strategies led to V4+-free SAPO-34 samples, so any Brönsted acidity of the samples should be assigned to the incorporated Si atoms. These materials, far from being conventional SAPO-34, have triclinic CHA structure, which provides some structural singularities and have not been tested as catalysts in the MTO reaction yet. Despite their conversion level achieved was lower than that given by conventional SAPO-34, probably because of the scarce optimization of the physicochemical properties of the material, the selectivity towards the different olefins is interestingly different, favoring C4 olefins at the expense of ethylene and propylene.

Solvent-free synthesis of SAPO-34 nanocrystals with reduced template consumption for methanol-to-olefins process

SAPO-34 nanocrystals were synthesized by solvent-free method with significantly reduced template consumption. The obtained SAPO-34 samples were characterized by XRD, SEM, nitrogen adsorption, NMR, NH3-TPD, XPS and XRF. The combination of various Si and Al sources had big impact on the physical-chemical properties of the obtained SAPO-34 crystals, including crystal size, surface area and pore volume, acid strength and distribution and Si environment in the zeolite framework. The nano-sized SAPO-34 crystals exhibited excellent performance in MTO reaction with comparable selectivities to light olefins(combined ∼80% ethylene and propylene selectivity with 50:50 split) and substantially extended catalytic lifetime (from 200min to 840min), compared with micron-sized SAPO-34 catalyst synthesized by conventional hydrothermal method. The extended lifetime could be attributed to the presence of abundant mesopores generated by the stacking of nanocrystals, which alleviated the diffusion constrain and allowed more coke deposition. The unique acid strength and distribution as well as Si environment of the SAPO-34 samples may also contribute to long catalytic lifetime. The solvent-free synthesis method provides a cheap and sustainable way of preparing excellent MTO catalyst with significantly reduced template consumption&waste water emission and improved autoclave efficiency.