SAPO-34 Molecular Sieves Research Articles

Two-Step Hydrothermal Synthesis of Submicrometric and Hierarchical Hollow SAPO-34 with Superior Catalytic Performance in Methanol to Olefin (MTO) Reaction.

A submicrometric and hierarchical hollow SAPO-34 molecular sieve was synthesized by an easy and low-cost two-step hydrothermal method. First, the crystallized mixture was obtained by direct drying after a first-step hydrothermal reaction. Then, the SAPO-34 product was obtained by adding the crystallized mixture to silicon-free gel and using cheap and common template agents. Compared to conventional SAPO-34, the submicrometric and hierarchical hollow SAPO-34 exhibits superior catalytic activity in the MTO reaction.

Dehydration of Alcohols to Olefins Catalyzed by ZrAPSO-34 Molecular Sieve

The lower olefins (Ethylene, propylene, and butylene) are considered the key to the polymeric and petrochemical industries. Dehydration of alcohols to produce light olefins (Methanol-to-olefins reaction) over SAPO-34 molecular sieve has attractedintoigh attention. Modified SAPO-34 zeolite catalyst with Zr metal was successfully prepared under microwave irradiation using morpholine as a structure direct agent. The microwave energy power used was 800 w and the crystallization time was 200 min. The catalyst sample was characterized by XRD, SEM, EDX, BET, FTIR, and TGA analysis. XRD analysis exhibited a typical chabazite structure with high crystallinity. The analysis showed macrocrystalline particles with moderate distribution of silica in the framework structure and a low surface area of 77 m2/g. The vibration peaks of the prepared catalyst showed agreement with the SAPO-34 CHA structure. Catalyst performance towards methanol-to-olefins conversion was performed in a trickle bed reactor with temperatures of 350, 400, 450, and 500 oC at a weight hourly space velocity of 7.7 h-1. The results also reveal at a temperature of 400 oC , that the best olefins selectivity was obtained, reaching 70%, with a longer lifetime of 500 min. methanol conversion was almost 100% at all reaction temperatures. In addition, the effect of methanol concentration was investigated and the results showed that increasing of water content plays a role in increasing catalyst lifetime and preventing coke depositions in pores.

Synthesis, Modification, and Performance Regulation of SAPO-11 Molecular Sieve and Development of n-Alkane Hydroisomerization Catalyst: A Mini-Review

Synthesis, Modification, and Performance Regulation of SAPO-11 Molecular Sieve and Development of <i>n</i>-Alkane Hydroisomerization Catalyst: A Mini-Review

Enhanced CO2 Capture through SAPO-34 Impregnated with Ionic Liquid.

The concurrent utilization of an adsorbent and absorbent for carbon dioxide (CO2) adsorption with synergistic effects presents a promising technique for CO2 capture. Here, 1-butyl-3-methylimidazole acetate ([Bmim][Ac]), with a high affinity for CO2, and the molecular sieve SAPO-34 were selected. The impregnation method was used to composite the hybrid samples of [Bmim][Ac]/SAPO-34, and the pore structure and surface property of prepared samples were characterized. The quantity and kinetics of the sorbed CO2 for loaded samples were measured using thermogravimetric analysis. The study revealed that SAPO-34 could retain its pristine structure after [Bmim][Ac] loading. The CO2 uptake of the loaded sample was 1.879 mmol g-1 at 303 K and 1 bar, exhibiting a 20.6% rise compared to that of the pristine SAPO-34 recording 1.558 mmol g-1. The CO2 uptake kinetics of the loaded samples were also accelerated, and the apparent mass transfer resistance for CO2 sorption was significantly reduced by 11.2% compared with that of the pure [Bmim][Ac]. The differential scanning calorimetry method revealed that the loaded sample had a lower CO2 desorption heat than that of the pure [Bmim][Ac], and the CO2 desorption heat of the loaded samples was between 30.6 and 40.8 kJ mol-1. The samples exhibited good cyclic stability. This material displays great potential for CO2 capture applications, facilitating the reduction of greenhouse gas emissions.

Improving the stability and reactivity of SAPO-11 catalyst for gas-phase beckmann rearrangement by a simple and effective alkali-treated approach

ε-Caprolactam (CPL) is an important organic chemical raw material for preparing nylon-6 fiber and polyamide engineering plastics. Traditional production technology based on concentrated sulfuric acid leads to serious environmental pollution. Herein, we develop an economical and environmentally friendly strategy based on SAPO-11 molecular sieve as catalyst to produce CPL. Importantly, alkali engineering strategy to treat SAPO-11 molecular sieve was profited to remove the framework P and increase much Si island edge structures, consequently formatting the larger mesopores and enhancing the acidic properties, thus the catalytic performance and stability of the catalyst were significantly improved. Compared with the original SAPO-11, SAPO-11-TH had outstanding catalytic performance, the conversion of CHO and the selectivity for CPL were still more than 92% and 87% respectively when the reaction continuous reacted for 5 h at 6 h−1 weight hourly space velocity (WHSV). Interestingly, we found that the reactants can complete the conversion within an extremely short residence time (0.86 s), thereby obtaining higher spatiotemporal yields. What else, the catalyst obtained from simple calcination still exhibited excellent catalytic performance. We provide a facile, intriguing and scalable approach to treat catalyst SAPO-11 molecular sieve to form larger mesopores and high acidic strength that can be applied in the many catalytic fields.

Changing Template/Al2O3 Ratio in Reaction Gel-An Effective Way to Regulate Nature of Intermediate Phases and Properties of SAPO-11 Molecular Sieves during Crystallization.

A study has been conducted to investigate the formation of intermediate phases during the crystallization of SAPO-11 molecular sieves from reaction mixtures with a varying template (di-n-propylamine) DPA/Al2O3 ratio. It was found that changing the DPA/Al2O3 ratio from 1.0 to 1.8 in the initial reaction gels leads to the formation of different intermediate phases during crystallization into a SAPO-11 molecular sieve. It is shown that at the ratio template/Al2O3 = 1.0, an intermediate amorphous silicoaluminophosphate is formed; at 1.4, a mixture consisting of amorphous and layered phases forms; and at 1.8, a layered phase is present. A simple and innovative approach for controlling the morphology, size, and characteristics of primary crystals and the secondary porous structure in hierarchical SAPO-11 is proposed. The method is based on regulating the DPA/Al2O3 ratio in the reaction gel. The synthesized SAPO-11 molecular sieves with a hierarchical porous structure exhibited high selectivity in the hydroisomerization of n-hexadecane.

Enhancing catalytic isomerization ability of SAPO-11 by typical acid modification in preparation of green diesel by one-step hydrotreatment of FAME

SAPO-11 molecular sieve is a promising candidate for preparation of hydrocarbon-based biofuels. Herein, two typical acids including citric acid (CA) and nitric acid (NA) are used to modify SAPO-11. The results show that the acid concentration was within the range of 0.05–1.0 mol L−1, SAPO-11 maintained a complete crystal framework structure, and more (002) crystal planes were exposed. The specific surface area, pore diameter and acid content of molecular sieve by acid modification are significantly higher than those of the fresh SAPO-11. The pore size increased from 7 nm to 17 and 18 nm, an increase of the total acid from 104 μmol g−1 to 174 and 162 μmol g−1, respectively, when SAPO-11 was treated by CA with 0.5 mol L−1 and NA with 0.3 mol L−1. Pt–Sn/SAPO-11-CA-0.5 showed the best catalytic activity with selectivity of C15–C18 alkanes of 95.8% and iso-alkanes of 33.1%. Additionally, the deoxygenation ability of Pt–Sn/SAPO-11-CA-0.5 decreased 30% after running 1200 h. Using propionic acid (PA) as the model probe molecule, the DFT reveals steps of the hydrodecarbonylation pathway of PA absorbed on the Pt (111) plane as below: CH3CH2COOH*→CH3CH2CO*→CH3CHCO*→CH3CCO*→CH3C*+CO*, and the rate-limiting step is CH3CH2COOH*→CH3CH2CO*+OH*.

Effect of kaolin calcined temperature on the preparation and crystallization mechanism of SAPO-34 molecular sieve for methanol-to-olefins performance

SAPO-34 molecular sieves synthesized using calcined kaolin as partial raw material under three-stage of high-low-high temperature hydrothermal condition are explored systematically. Especially, the effect of kaolin calcination temperature on the crystallization mechanism of SAPO-34 and the methanol to olefin performance are investigated thoroughly. It is found that the sample (SP-500) synthesized by using kaolin calcined at 500 °C (MK-500) demonstrates clean cubic structure, large specific surface area and mild acidity, providing the initially activated Si and Al source for the synthesis of SAPO-34 molecular sieve due to the well scattered structure of MK-500. From the crystallization mechanism consideration, it can be proposed that the SAPO-34 molecular sieves will be controlled by the low degree of Si aggregation in metakaolin and quantity of Si (3Al,1Si) species. As a result, SP-500 displays excellent catalytic lifetime during methanol to olefin reaction for its special Si coordination environment, showing the highest stable light olefin yield of 80.6 % and a methanol conversion above 90 % for more than 720 min. In contrast, SP-800 sample with the most strong acid sites is only 390 min, even if showcasing the highest selectivity of light olefins (84.5%).

Hierarchical SAPO-11 Molecular Sieves Prepared with the Presence of Designedly Phosphorylated Poly(Vinyl Alcohol)s

Hierarchical SAPO-11 Molecular Sieves Prepared with the Presence of Designedly Phosphorylated Poly(Vinyl Alcohol)s

Ultra-fast synthesis of hierarchical SAPO-11 molecular sieves with the assistance of hydroxyl radicals.

Considering the traditional time-consuming synthesis route and diffusion-limited micropore system of SAPO-11 (i.e., SAPO-11W), a hydroxyl radical assisted method has been developed to prepare hierarchical SAPO-11 within 5 min (i.e., SAPO-11M). Compared to previous reports, the unique contribution is to induce hydroxyl radicals by exposing carbon materials to microwave irradiation in an oxygen-containing atmosphere. Carbon materials play a dual role as mesopore filler and hydroxyl radical initiator. When employed to prepare deoxygenation catalysts for stearic acids, a higher selectivity for C15-C18 and isomers is observed due to the mild acidity of SAPO-11M. The Lewis-rich acidity of SAPO-11M exhibits an electron deficiency to interact with the hydroxyl oxygen atoms and promotes the hydrodeoxygenation of stearic acids with excellent atom economy. These results are important for opening up a new prospect of synthesizing SAPO molecular sieves (e.g., SAPO-11 and SAPO-5) by an efficient and facile route.

Synthesis of hierarchically radiated SAPO-11/Silica composites to boost n-alkane hydroisomerization

Hierarchically radiated SAPO-11 molecular sieves (RS-11-x, x was the initial SiO2/Al2O3 molar ratio) were prepared by employing different amounts of un-calcined radiated mesoporous SiO2 nanoparticles (RMSNs) as silicon source and template, and the corresponding Pt-based catalysts were applied for n-decane hydroisomerization. During the synthesis of RS-11-x, RMSNs were hydrolyzed into active Si species slowly due to the supporting of CTAB in their channels, and these active Si species interacted with Al and P species on the RMSNs to generate SAPO-11 crystal nuclei. Ultimately, hierarchical SAPO-11 molecular sieves with radiated morphologies were dispersed on the RMSNs. Among RS-11-x, RS-11-0.4 possessed the greatest medium and strong Brønsted acid sites (MSBAS) content (14.9 μmol/g) as well as superior external surface area (247 m2 g−1) and mesopore volume (0.433 cm3 g−1). Furthermore, compared with the SAPO-11 synthesized by tetraethyl orthosilicate (TEOS) and the mixture of CTAB and TEOS as silicon precursors, respectively, RS-11-0.4 possessed a larger external surface area, a higher mesopore volume and the optimal MSBAS content. Consequently, the Pt/RS-11-0.4 catalyst showed a higher selectivity of branched C10 isomers (93.5%), a better selectivity of multi-branched C10 isomers (33.8%), and a lower cracking selectivity (6.3%) than the counterpart catalysts. This work offers a new strategy for preparing hierarchical molecular sieves with superior catalytic performances.

Tailored synthesis of plate-like SAPO-11 molecular sieve and its application in non-noble metal-supported catalyst for efficient hydroisomerization of long-chain n-alkanes

The tailored synthesis of plate-like SAPO-11 molecular sieve was achieved by introducing seed-surfactant directing agent into the synthesis system for the first time. The effects of morphological change of SAPO-11 molecular sieve on the physicochemical properties of SAPO-11 and the active phase properties of the catalyst were analyzed via a series of characterization techniques. The hydroisomerization of n-hexadecane was used as the model reaction to evaluate the catalytic performance of NiWS supported catalysts based on SAPO-11 molecular sieve with different morphologies. The plate-like SAPO-11 possessed better textural properties and acidity than pseudo-spherical SAPO-11. Meanwhile, the stacking number, dispersion and metal sulfidation degree of the active phase of sulfided NiW/SAPO-11-P were improved, and its high proportion of type II active phase optimized the metal–acid synergistic catalytic mechanism. Through tracking and analyzing the crystallization process of plate-like SAPO-11, the formation mechanism of plate-like SAPO-11 was investigated and revealed. The adsorption kinetics, diffusion behavior and catalytic kinetics of n-hexadecane on the catalysts were emphatically investigated. The optimized support structure and active phase properties improved the intrinsic catalytic activity and hydroisomerization reaction path priority of NiW/SAPO-11-P. It was found that the hydroisomerization reaction on NiW/SAPO-11-P was carried out under the reaction-limiting conditions, while the hydroisomerization reaction on NiW/SAPO-11-C was carried out under the reaction-controlling conditions. The effects of plate-like SAPO-11 on the activity stability of the catalyst was investigated, and the essential reasons for the differences in activity stability of the catalysts were revealed through comprehensively analyzing the coke formation difference and diffusion behavior difference. It is expected to provide reference for the tailored design of SAPO-11 molecular sieve with special morphology and the preparation of efficient hydroisomerization catalyst.

Рt/SAPO-11 Catalytic Systems Differing in Acidity and Secondary Pore Structure in n-Hexadecane Hydroisomerization

SAPO-11 molecular sieve samples differing in the acid properties, crystal morphology and size, and secondary pore structure characteristics were obtained by crystallization of reaction gels with the SiO2/Al2O3 molar ratios of 0.1 and 0.3, prepared using aluminum isopropoxide or boehmite as an aluminum source. Platinum (0.5 wt %) was deposited onto the molecular sieves prepared, and the catalytic properties of the resulting samples in n-hexadecane hydroisomerization were studied. The hydrocarbon conversion on these samples varies from 76.8 to 87.7 wt %, and the isoparaffin formation selectivity, from 76.7 to 91.2 wt %.

Synthesis and Characterization of Proton-Conducting Composites Prepared by Introducing Imidazole or 1,2,4-Triazole into AlPO-5 and SAPO-5 Molecular Sieves.

The present work concerns proton-conducting composites obtained by replacing the water molecules present in aluminophosphate and silicoaluminophosphate AFI-type molecular sieves (AlPO-5 and SAPO-5) with azole molecules (imidazole or 1,2,4-triazole). Both the introduction of azoles and the generation of Brønsted acid centers by isomorphous substitution in aluminophosphate materials were aimed at improving the proton conductivity of the materials and its stability. In the presented study, AlPO-5 and several SAPO-5 materials differing in silicon content were synthesized. The obtained porous matrices were studied using PXRD, low-temperature nitrogen sorption, TPD-NH3, FTIR, and SEM. The proton conductivity of composites was measured using impedance spectroscopy. The results show that the increase in silicon content of the porous matrices is accompanied by an increase in their acidity. However, this does not translate into an increase in the conductivity of the azole composites. Triazole composites show lower conductivity and significantly higher activation energies than imidazole composites; however, most triazole composites show much higher stability. The different conductivity values for imidazole and triazole composites may be due to differences in chemical properties of the azoles.

In situ synthesis of Co modified SAPO-5 molecular sieves and the application in quinoline hydrodenitrogenation of their NiWS supported catalysts

To improve the hydrodenitrogenation (HDN) ability of conventional Al2O3-based catalysts, SAPO-5 molecular sieves with different cobalt (Co) contents were synthesized by one-pot hydrothermal method and doped as catalyst supports. The characterization results show that the Co atoms can be effectively introduced into the skeleton of SAPO-5 molecular sieve, which improved the amount of Brønsted acid site and modulated interaction between the active metals and the support (MSI). Moreover, the introduction of Co atoms also promoted the dispersion and sulfidation of the NiW active metals, resulting in more NiWS edge active sites, which contributed to the accessibility of nitrogen-containing compounds to the active center and the hydrogenation conversion performance. Together with the synergistic effect of C-N bond breaking by matching Brønsted acid between Co-modified SAPO-5 molecular sieve and the NiWS active phase, the hydrodenitrogenation activity of the catalyst was substantially improved. Hence, the catalysts containing Co modified SAPO-5 molecular sieves exhibited higher HDN activity compared with that of containing unmodified SAPO-5 molecular sieve. Among all the catalysts investigated, the NiW/CSA-3 was found to show the highest HDN performance due to the highest number of Brønsted acid sites in the Co modified SAPO-5 molecular sieve and the maximum sulfidation degree of the active phase.

Novel construction and synthesis mechanism of b-axis oriented flower-like SAPO-11 molecular sieve in OSC-containing system for efficient hydroisomerization of long-chain n-alkanes

In view of the fact that different kinds of flower-like zeolites and materials have been synthesized for catalysis, but there are few reports on the construction of flower-like SAPO-11 molecular sieve. In this work, we successfully synthesized b-axis oriented flower-like SAPO-11 molecular sieve with multi-layered structure in the organosilicon compounds (OSC)-containing system for the first time. The morphology and b-axis thickness of SAPO-11 flakes were controlled and the tailored synthesis of b-axis oriented flower-like SAPO-11 with multi-layered structure was realized by adding [3-(trimethoxysilyl) propyl] octadecyl dimethyl ammonium chloride (DMC) into the synthesis system. The NiWS supported catalyst for hydroisomerization of n-hexadecane was prepared by using the synthesized flower-like SAPO-11 as support. Through a series of characterization techniques, the effects of morphological changes of SAPO-11 molecular sieve on the textural properties, acidity, element composition and silicon distribution of SAPO-11 molecular sieve were investigated, and the influence mechanism of morphological changes of the support on the active phase properties of the catalyst was studied. The formation mechanism of multi-layered flower-like SAPO-11 was proposed, the influence mechanism of the morphological change of the support on the catalytic performance of the catalyst and the catalytic reaction kinetics was investigated, and the structure–activity relationship between flower-like SAPO-11 and NiWS supported catalyst was systematically expounded. It provides a reference for enriching the morphological types of SAPO-11 molecular sieve and preparing catalyst for high-efficiency hydroisomerization of long-chain n-alkanes.

Bifunctional catalyst consisting of In-modified GaZrOx ternary solid solution oxide and SAPO-34 for efficiently converting CO2 into light olefins

Converting CO2 into light olefins (C2=–C4=) using oxide–zeolite bifunctional catalyst is a new strategy for producing light olefins. Herein, a series of bifunctional catalysts comprising In-doped GaZrOx oxides and SAPO-34 molecular sieves for CO2 hydrogenation to light olefins are reported, and their catalytic mechanisms are investigated using in situ spectroscopy. After optimizing the In doping amount, oxide calcination temperature, oxide coupling mode with SAPO-34, and reaction conditions, the bifunctional catalysts achieved 82.8% C2=–C4= selectivity, 24% CO2 conversion, and up to 10.1% C2=–C4= yield. Furthermore, no considerable deactivation was observed after 100 h of the reaction. Various characterization and experimental results indicate that adding In to GaZrOx promotes oxygen-vacancy generation and enhances the adsorption activation of CO2 and H2, thereby promoting the formation of formate (HCOO*) and methoxy (CH3O*) intermediates and improving the catalytic performance of the C2=–C4= synthesis from CO2.

Efficient cycloaddition of carbon dioxide with epoxide to produce five-membered cyclic carbonates by amine-functionalized silicoaluminophosphates molecular sieves

The synthesis of functionalized microporous materials as very effective catalysts is a significant and rapidly increasing research topic with the goal for providing more efficient energy alternatives and contributing to the reduction of atmospheric CO2 levels. Carbon dioxide is a greenhouse gas that traps heat in the atmosphere, contributing to global warming and climate change. SAPO-5 and SAPO-34 molecular sieves were post-synthetically –NH2 functionalized, and the existence of –NH2 functionalities in the SAPO structure wall was demonstrated by FT-IR, CHN analysis. Powder XRD confirmed the crystalline structures of the modified SAPO-34 materials with amine functionalities. FE-SEM examined the morphology of the materials. The functionalized silicoaluminophosphate materials were investigated in the cyclo-addition of CO2 to epoxide (cyclohexene oxide and styrene oxide), where the catalytic performance of post-synthetically functionalized materials as catalyst were found to be superior. The amine group of the silicoaluminophosphates materials were essential for the activation of CO2. For treated SAPO-34, reactant conversion in cyclohexene oxide and styrene oxide was reported to be 94% and 93%, respectively. Because of the high recyclability of these materials, the catalysts are found to be both cost-effective and environmentally benign.

Rapid synthesis of SAPO-34 molecular sieve with cheap template for improving MTO performance

Low-silicon SAPO-34 was rapidly synthesized with the assistance of citric acid using inexpensive triethylamine as a template. The effects of citric acid on the crystal structure, morphology, and acidity were investigated using XRD, SEM, FT-IR as well as ICP characterization methods. The results show that citric acid promotes the growth of SAPO-34, shortens the crystallization time and improves the yield of solids. Furthermore, citric acid facilitates the synthesis of low-silicon SAPO-34, which exhibits improved MTO catalytic performance. Compared with conventional SAPO-34, low-silicon SAPO-34 generated higher selectivity of ethylene and propylene.

Activated metal Bi and La modified SAPO-34 molecular sieve and its photocatalytic degradation of formaldehyde in aqueous solution

Activated metal Bi and La modified SAPO-34 molecular sieve and its photocatalytic degradation of formaldehyde in aqueous solution