Hierarchical SAPO-34 Catalysts Research Articles

High-Yield Synthesis of Hierarchical SAPO-34 by Recrystallization Method for Efficient Methanol-to-Olefin Reactions.

Prolonging the lifetime of SAPO-34 catalysts and enhancing their olefin selectivity in methanol-to-olefin (MTO) reactions are critical yet challenging objectives. Here, a series of hierarchical SAPO-34 catalysts were synthesized using a straightforward recrystallization method. The incorporation of triethylamine into the recrystallization mother liquor facilitated the formation of mesopores, achieving a high solid yield of up to 90%. Notably, the addition of phosphoric acid and ammonium polyvinyl phosphate alcohol during the recrystallization process significantly enhanced the crystallinity and regularity of the hierarchical SAPO-34 crystals, consequently increasing the mesopore size. Due to the substantially improved mass transfer efficiency and moderated acidity, the SP34-0.14P-0.06R catalysts exhibited a prolonged operational life of 344 min and80.3%selectivity ofethylene and propylene at aWHSV of 2h-1. This performance markedly surpasses that of the parent SP34 catalyst, which demonstrated a lifetime of 136 min and a selectivity of 78.0%. Remarkably, the SP34-0.14P-0.06R maintained a lifetime of 166 minutes even at a high WHSV of 10h-1, which is more than 5-fold greater than that of the original microporous SP34. This research offers valuable insights into the design and development of hierarchically porous zeolites with high yields, enhancing the efficiency of MTO reactions and other applications.

Hierarchical SAPO-34 Catalysts as Host for Cu Active Sites.

Cu-containing hierarchical SAPO-34 catalysts were synthesized by the bottom-up method using different mesoporogen templates: CTAB encapsulated within ordered mesoporous silica nanoparticles (MSNs) and sucrose. A high fraction of the Cu centers exchanged in the hierarchical SAPO-34 architecture with high mesopore surface area and volume was achieved when CTAB was embedded within ordered mesoporous silica nanoparticles. Physicochemical characterization was performed by using structural and spectroscopic techniques to elucidate the properties of hierarchical SAPO-34 before and after Cu introduction. The speciation of the Cu sites, investigated by DR UV-Vis, and the results of the catalytic tests indicated that the synergy between the textural properties of the hierarchical SAPO-34 framework, the high Cu loading, and the coordination and localization of the Cu sites in the hierarchical architecture is the key point to obtaining good preliminary results in the NO selective catalytic reduction with hydrocarbons (HC-SCR).

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.

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.

Polyacrylamide-assisted synthesis of hierarchical porous SAPO-34 zeolites with excellent MTO catalytic performance

Silicoaluminophosphate zeolite SAPO-34 with a CHA topological structure has been highlighted for its high methanol conversion and excellent selectivity for light olefins in the methanol-to-olefin (MTO) reaction. In this work, hierarchical porous SAPO-34 zeolite with excellent catalytic properties was first prepared by introducing water-soluble polyacrylamide (PAM) hydrogel into the synthesis system of conventional SAPO-34 by using a one-step hydrothermal synthesis method. The effects of PAM concentration and PAM type on the morphology and pore structure of hierarchical SAPO-34 catalysts and the formation mechanism of hierarchically structured zeolites were studied. Compared to conventional microporous SAPO-34, the hierarchically structured SAPO-34 exhibits excellent performance in the MTO reaction with an approximately three times longer catalytic lifetime (740 min) and remarkably improved selectivity for light olefins of up to 87.5%. A butterfly-shaped hierarchical porous SAPO-34 with a micro-meso-macroporous structure was directly synthesized in the presence of polyacrylamide hydrogel. The tri-level hierarchically structured SAPO-34 exhibits long catalytic lifetime and good thermal stability in the MTO reaction. • A hierarchical porous SAPO-34 with a micro-meso-macroporous structure was directly synthesized in the presence of PAM hydrogel. • The morphology and pore structure of SAPO-34 crystals could be controlled by adjusting the PAM amount and PAM type. • The hierarchically structured SAPO-34 exhibits long catalytic lifetime and good thermal stability in the MTO reaction.

Busting the efficiency of SAPO-34 catalysts for the methanol-to-olefin conversion by post-synthesis methods

Abstract As an effective non-petroleum based process for producing light olefins, the methanol-to-olefin (MTO) route has become an indispensable alternative to the industrial production of light olefins. The silicoaluminophosphate SAPO-34 zeolite (CHA-type structure) has proven to be an efficient industrial catalyst for the production of ethylene and propylene by the MTO reaction. However, the inherent structure and related diffusion limitations of SAPO-34 limit the mass transport and thus cause rapid deactivation of the catalyst. Fabrication of hierarchical SAPO-34 zeolite is one of the most effective strategies to address the intrinsic diffusion limitation. As simple, inexpensive, and efficient approach, the post-synthetic route has attracted considerable attention and widely used to introduce secondary meso-/macropores into the microporous SAPO-34 material. Significant effort has been dedicated to the development of post-synthesis strategies to prepare hierarchical SAPO-34 zeolite, thereby enhancing its catalytic performance in the MTO process. This mini-review addresses the post-synthesis preparation of hierarchical SAPO-34 catalysts and their MTO performance. Furthermore, some current problems and prospects of the post-synthesis route to hierarchical SAPO-34 catalysts are also revised. We expect this mini-review to inspire the more efficient preparation of hierarchical SAPO-34 catalysts for the MTO process.

Synthesis of Zirconium Modified Hierarchical Sapo-34 Catalysts using Carbon Nanotube Template for Conversion of Methanol to Light Olefins

Two types of zirconium-containing hierarchical SAPO-34 catalysts were successfully synthesized by isomorphous substitution and impregnation methods and applied for the conversion of methanol to light olefins. Carbon nanotube was employed as a mesopore template to create mesopores in the crystals of SAPO-34. Physical and chemical characterizations of the catalysts demonstrated that the modification of SAPO-34 with Zr by isomorphous substitution and impregnation methods gives rise to differences in acidity, porosity and crystal size. MTO results showed that the lifetime of the catalysts was in the order of ZrAPSO-34 > SAPO-34 > Zr/SAPO-34 while the selectivity to ethylene was in the order of Zr/SAPO-34 > ZrAPSO-34 > SAPO-34.

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.

Synthesis of hierarchical SAPO-34 and its enhanced catalytic performance in methanol to propylene conversion process

ABSTRACTHierarchical SAPO-34 molecular sieve was synthesized hydrothermally in the presence of different concentrations of n-propylamine (NPA) as the mesoporous generating agent. It has been found that the mesoporous structure and morphology of the hierarchical SAPO-34 was depended to the amount of NPA used. The catalytic activity of the synthesized materials for methanol to propylene conversion were evaluated. A high selectivity for propylene (44.5%) compared to a conventional microporous SAPO-34 (28.7%) was observed with propylene to ethylene (P/E) ratio (3.6) which was attributed to the less total acidic sites measured by NH3-TPD and the optimal combination of mesoporous and microporous reaction paths. The synthesized hierarchical SAPO-34 catalysts were characterized by XRD, FE-SEM, BET, NH3-TPD and TGA techniques.

Efficient post-synthesis of hierarchical SAPO-34 zeolites via organic amine etching under hydrothermal conditions and their enhanced MTO performance

A cost-effective post-treatment strategy has been developed to prepare hierarchical SAPO-34 catalysts by triethylamine etching with a hydrothermal recrystallization process.

Cost-effective synthesis of hierarchical SAPO-34 zeolites with abundant intracrystalline mesopores and excellent MTO performance.

Hierarchical SAPO-34 catalysts with abundant intracrystalline mesopores have been prepared using morpholine as the template combined with a cheap nonsurfactant cationic surfactant. Significantly, the hierarchical SAPO-34 catalysts exhibit more than 5-fold improved lifetime and 12% enhanced selectivity for ethylene and propylene compared to conventional microporous counterparts in methanol-to-olefin (MTO) reactions.

The state-of-the-art synthetic strategies for SAPO-34 zeolite catalysts in methanol-to-olefin conversion

Methanol-to-olefin (MTO) conversion has proven to be one of the most successful non-petrochemical routes for producing light olefins. Silicoaluminophosphate (SAPO) zeolite SAPO-34 is one of the best industrial catalysts for MTO conversion, but suffers from rapid deactivation due to the inherent diffusion bottleneck limited by the narrow eight-ring pore openings. To improve the MTO performance, considerable synthetic efforts have been devoted to decrease the crystal size of zeolites or introduce secondary larger pores in zeolite crystals to form hierarchical structures. This review mainly focuses on presenting the state-of-the-art synthetic strategies for nanosized and hierarchical SAPO-34 catalysts with excellent MTO performance. Furthermore, the industrialization of SAPO-34 catalysts for the MTO reaction, and some current problems and future prospects for the synthesis of SAPO-34 catalysts, are also pointed out. We expect that this review can not only shed some light on the preparation of SAPO-34 catalysts, but also stimulate the future development of high-performance SAPO-34 catalysts to meet the increasing demands of the chemical industry.

Synthesis, characterization, and catalytic application of hierarchical SAPO-34 zeolite with three-dimensionally ordered mesoporous-imprinted structure

Hierarchical SAPO-34 zeolites with three-dimensionally ordered mesoporous-imprinted structure (3DOm-i SAPO-34) were first confined synthesized within three-dimensionally ordered mesoporous carbons by multiple hydrothermal (MHT) treatments. With perfect structure replication, the obtained 3DOm-i SAPO-34 zeolite particles exhibited unique ordered structures consisting of primary spherical elements of sizes determined by mesopore cages of the corresponding carbon templates, and the sizes of mesopores constituted by the adjacent spherical elements can be precisely tuned from 5.5 to 13.0 nm by varying the 3DOm carbon. The as-synthesized hierarchical 3DOm-i SAPO-34 catalysts showed superior catalytic performance in the MTO reaction with prolonged catalytic lifetime and significant improvement of selectivity for light olefins (ethylene and propylene) compared to the conventional microporous SAPO-34.

Carbon nanotube templated synthesis of metal containing hierarchical SAPO-34 catalysts: Impact of the preparation method and metal avidities in the MTO reaction

Hierarchical SAPO-34 was synthesized hydrothermally using carbon nanotube as hard template and modified with Co and Ni by isomorphous substitution and impregnation methods. The prepared catalysts were characterized by XRD, SEM, TEM, XRF, UV–vis, NH3-TPD, H2-TPR, FTIR and N2 physisorption measurements and their catalytic performance was evaluated for transformation of methanol to light olefins (MTO). There were meaningful differences in terms of crystallinity, acidity, porosity and reducibility among the synthesized catalysts modified by impregnation and isomorphous substitution methods. In addition, the ethylene and propylene yields and the catalytic longevity were strongly dependent on Ni and Co avidities as well as on the modification procedure. The results indicated that compared to the unmodified hierarchical SAPO-34, the catalyst modified with Ni by means of isomorphous substitution improved the yield of ethylene while methane production was promoted over SAPO-34 impregnated with Ni. On the other hand, the Co-containing SAPO-34 samples enhanced the production of both ethylene and propylene relative to the unmodified mesostructured SAPO-34 and these modifications prolonged the catalyst lifetime. These changes in the catalytic behaviors could be ascribed to the changes in the acid sites and porous structure.

A top-down approach to hierarchical SAPO-34 zeolites with improved selectivity of olefin

A facile and effective fluoride post-treated route has been systematically applied for the preparation of hierarchical zeolite catalysts in three different SAPO-34 systems using morpholine, triethylamine and tetraethylammonium hydroxide as template, respectively. Secondary pores in SAPO-34 zeolite crystals are formed by etching with HF-NH4F containing solutions under ultrasonic condition. The samples were characterized by XRD, SEM, N2 adsorption-desorption, XRF, TG, 29Si MAS NMR and NH3-TPD techniques. The set of experimental data demonstrate that the organic templates impact the etching process by fluoride route, most probably the distribution of active sites, thus influence the catalytic properties. It is worth underline that the selectivity to C2H4 and C3H6 over the obtained hierarchical SAPO-34 catalysts in the methanol-to-olefin (MTO) reaction is improved as compared to the parent SAPO-34 catalysts, while an undesired diminished catalyst lifetime is observed for hierarchical SAPO-34 templated by morpholine and tetraethylammonium hydroxide.

Carbon nanotube templated synthesis of hierarchical SAPO-34 catalysts with different structure directing agents for catalytic conversion of methanol to light olefins

Crystalline silicoaluminophosphate of the CHA framework type (SAPO-34) with a hierarchical pore structure was hydrothermally synthesized using carbon nanotube as the mesopore template and TEAOH and/or morpholine as structure directing agents. The synthesized samples were characterized by XRD, SEM, TEM, FTIR, NH3-TPD, XRF and N2-physisorption techniques and their catalytic performance was tested in MTO reaction. N2-adsorption results showed that the population of mesopores created inside the SAPO-34 crystals could be controlled by tuning the amount of carbon nanotube applied. It was also found that the structure directing agents could lead to significant effects in the crystallinity and mesoporosity of hierarchical SAPO-34 samples. Increasing molar ratio of TEAOH in the initial gel increased the mesoporosity of SAPO-34, but decreased its crystallinity and particle size. The hierarchical SAPO-34 samples showed superior catalytic performance in the MTO reaction with longer lifetime compared to the conventional SAPO-34. The hierarchical SAPO-34 prepared by the mixture of TEAOH and morpholine exhibited longer catalyst lifetime compared to those of other hierarchical SAPO-34 obtained by only TEAOH or morpholine. The characterization of the spent catalysts indicated that both rate of coke formation and coke-susceptibility of hierarchical SAPO-34 was lower than conventional SAPO-34.

Dual template-directed synthesis of SAPO-34 nanosheet assemblies with improved stability in the methanol to olefins reaction

Hierarchical SAPO-34 catalysts with different morphologies were synthesized by using dual template [3-(trimethoxysilyl)propyl]octadecyldimethylammonium chloride and diethylamine. Because of its optimal porosity and acidity, hierarchical SAPO-34 exhibited excellent catalytic performance in the MTO reaction.

The Synthesis of Hierarchical SAPO-34 and its Enhanced Catalytic Performance in Chloromethane Conversion to Light Olefins

Hierarchical SAPO-34 molecular sieve was successfully synthesized by hydrothermal crystallization method with cetyltrimethyl ammonium bromide as mesoporous generating agent. The influence of different addition amounts of CTAB on the crystalline structures, morphology features, textural properties and acidity of hierarchical SAPO-34 catalysts were characterized by XRD, SEM, BET and NH3-TPD techniques. The results exhibit that the crystal size, mesoporous structure and the total acid amounts of hierarchical SAPO-34 are affected greatly by the molar ratio of CTAB/Al2O3. The selectivity of light olefins (ethane and propylene) can achieve 80 % for all SAPO-34 samples tested in the conversion of chloromethane to light olefins. Compared with the conventional SAPO-34, the hierarchical SAPO-34 samples show better catalytic stability and less carbon deposit in this conversion due to the reduction in total acid sites and the increasing mesopore volume.

Organosilane surfactant-directed synthesis of hierarchical porous SAPO-34 catalysts with excellent MTO performance.

Using an organosilane surfactant as the mesopore director, hierarchical porous silicoaluminophosphate SAPO-34 is obtained as an assembly of nanocrystallites intergrown into cubic micrometer-sized crystals, which show excellent performance in MTO reactions with a remarkably prolonged catalyst lifetime and enhanced selectivity of ethylene and propylene compared to the conventional microporous SAPO-34.

Pore-structure-mediated hierarchical SAPO-34: Facile synthesis, tunable nanostructure, and catalysis applications for the conversion of dimethyl ether into olefins

Hierarchical cross-like SAPO-34 catalysts with different pore size distributions were obtained via hydrothermal synthesis with polyethylene glycol (PEG) as the mesopore-generating agent. The hierarchical SAPO-34 molecular sieves were characterized using X-ray diffraction, scanning electron microscopy, N2 adsorption–desorption, thermogravimetric analysis, and temperature-programmed NH3 desorption. The cross-like SAPO-34 catalysts exhibited enriched multi-porosity, and the sizes of their mesopores ranged from 10 to 50nm. Both the mesoporous structures and morphologies of the hierarchical SAPO-34 could be further tuned through adjustments of the amount of PEG used. The as-obtained SAPO-34 showed dramatic catalytic performance in the conversion of dimethyl ether into olefins. A maximum selectivity of olefins of 96% was achieved, which was attributed to the rapid transport of the reactants and products in zeolitic micropores through mesopores.