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Interzeolite conversion, which refers to the synthesis of zeolites using a pre-made zeolite as the starting material, has enabled promising outcomes that could not be easily achieved by the conventional synthesis from a mixture of amorphous aluminum and silicon sources. Understanding the mechanism of interzeolite conversion is of particular interest to exploit this synthesis route for the preparation of tailor-made zeolites as well as the discovery of new structures. It has been assumed that the structural similarity between the starting zeolite and the target one is crucial to a successful interzeolite conversion. Nevertheless, an image as to how one type of zeolite evolves into another one remains unclear. In this work, a series of dealuminated FAU zeolites were created through acid leaching and employed as the starting zeolites in the synthesis of AEI zeolite under various conditions. This experimental design allowed us to create a comprehensive diagram of the interzeolite conversion from FAU to AEI as well as to figure out the key factors that enable this kinetically favourable crystallization pathway. Our results revealed different scenarios of the interzeolite conversion from FAU to AEI and pinpointed the importance of the structure of the starting FAU in determining the synthesis outcomes. A prior dealumination was proven effective to modify the structure of the initial FAU zeolite and consequently facilitate its conversion to the AEI zeolite. In addition, this strategy allowed us to directly transfer the knowledge obtained from the interzeolite conversion to a successful synthesis of the AEI zeolite from dealuminated amorphous aluminosilicate precursors. These results offer new insights to the design and fabrication of zeolites via the interzeolite conversion as well as to the understandings of the crystallization mechanisms.

The modification of Cu-exchanged zeolites with phosphorus represents a promising method to enhance their hydrothermal stability, which is of pivotal importance for catalysts that promote the selective catalytic reduction of NO with ammonia (NH3–SCR). In this study, we investigated the reaction mechanism of NH3–SCR catalyzed by a phosphorus-modified CHA zeolite that contains active Cu species (Cu-P-CHA), and assessed the effect of the phosphorus modification on the hydrothermal stability of the catalyst by employing in situ/operando spectroscopic methods. In their entirety, the combined results from in situ/operando IR, UV–vis, and XANES experiments revealed that the NH3–SCR process over Cu-P-CHA proceeds via the reduction of Cu(II) to Cu(I) followed by a reoxidation of Cu(I) to Cu(II). In addition, we found that the phosphorus modification improved the hydrothermal durability of the catalyst by retaining a higher amount of the redox-active Cu species and the zeolite framework.

Small-pore zeolites are gaining increasing attention owing to their superior catalytic performance. Despite being critical for the catalytic activity and lifetime, postsynthetic tuning of bulk Si/Al ratios of small-pore zeolites has not been achieved with well-preserved crystallinity because of the limited mass transfer of aluminum species through narrow micropores. Here, we demonstrate a postsynthetic approach to tune the composition of small-pore zeolites using a previously unexplored strategy named pore-opening migration process (POMP). Acid treatment assisted by stabilization of the zeolite framework by organic cations in pores is proven to be successful for the removal of Al species from zeolite via POMP. Furthermore, the dealuminated AFX zeolite is treated via defect healing, which yields superior hydrothermal stability against severe steam conditions. Our findings could facilitate industrial applications of small-pore zeolites via aluminum content control and defect healing and could elucidate the structural reconstruction and arrangement processes for inorganic microporous materials.

Phosphorus-modified AFX zeolite was synthesized by the hydrothermal conversion of FAU zeolite, which was impregnated with tetraethylphosphonium hydroxide (TEPOH). For the optimization of the introd...

AFX zeolite is a small-pore zeolite that has attracted significant attention because of its potential as a high-performance catalyst for the selective catalytic reduction of NOx by ammonia (NH3-SCR). Long time and high cost for the synthesis of AFX zeolite, however, limit the practical applications of this small-pore zeolite. Herein, we report an ultrafast synthesis route that can yield highly crystalline AFX zeolite in as short as 12 min. The ultrafast synthesis was realized on the basis of interzeolite conversion, where FAU zeolite was employed as a source of silicon and aluminum. Moreover, the addition of acid-leached seeds was found to be crucial for promoting the crystallization of AFX zeolite while effectively eliminating the formation of byproducts. Detailed studies of the original and acid-leached seeds revealed that acid leaching could cause structural alterations to the original seeds, thereby significantly enhancing the seeding effect. Secondary nucleation occurred when the acid-leached seeds were added, which is assumed to be one of the primary reasons for the accelerated crystallization rate. Based on the ultrafast synthesis, continuous-flow synthesis of AFX zeolite in 10 min was also demonstrated. The ultrafast and continuous-flow synthesis of AFX zeolite is expected to facilitate the large-scale production and broad applications of AFX zeolite.

Thermal migration of sodium cation in the cavity of Preyssler-type phosphotungstate is reported here. Heating of a Preyssler-type compound, [P5W30O110Na(side)(H2O)]14¹, in which a sodium cation occupies one of the two side cavities, at 300 °C forms a new compound, [P5W30O110Na(center)]14¹, in which the sodium cation is encapsulated in the central cavity. Characterization by single crystal X-ray structure analysis, NMR spectroscopy, elemental analysis, IR, and ESI-MS confirmed the structure of the compound. The thermal displacement ellipsoid of the central sodium, estimated by the crystallographic study, is elongated along the direction perpendicular to the equatorial plane of the Preyssler molecule. These results confirmed prediction using DFT calculation by López and Poblet (ref. 21, J. Am. Chem. Soc. 2007, 129, 12244.) that the most stable site for sodium is the central cavity with a slight shift from the center of the molecule., This research was supported by the Furukawa Foundation for the Promotion of Technology, JSPS KAKENHI Grant Numbers JP18H02058 (Grant-in-aid for scientific research (B)) and JP19K05510 (Grant-in-aid for scientific research (C)), the Center for Functional Nano Oxide at Hiroshima University, and JSPS Core-to-Core program. MNKW thankfully acknowledges the financial support from the Indonesia Endowment Fund for Education (LPDP), Ministry of Finance, Republik Indonesia for PhD scholarship (PRJ-36/LPDP.3/2017).

Zeolites have been successfully employed in many catalytic reactions of industrial relevance. The severe conditions required in some processes, where high temperatures are frequently combined with the presence of steam, highlight the need of considering the evolution of the catalyst structure during the reaction. This review attempts to summarize the recently developed strategies to improve the hydrothermal framework stability of zeolites., This review attempts to summarize the recently developed strategies to improve the hydrothermal framework stability of zeolites.

Hydrothermal stability and productivity of zeolite are important concerns when considering its industrial applications. In this study, we used 1-butanol as an organic additive for the synthesis of ...

Zeolites are commercially used crystalline microporous materials. Understanding their crystallization mechanism and corresponding synthesis development is still of scientific and technological sign...

Porous materials with different pore structure were synthesized and modified with Preyssler-type heteropolyacid material by post-synthetic wet-impregnation method. The functionalized materials were thoroughly characterized by different physic-chemical techniques. As reveled by characterization, the structures were well preserved after the modification. All the materials were catalytically active as proved by the catalytic results in dehydration of alcohol to ethylene. On comparison with Preyssler (without any support), which did not show activity at all, mesoporous matrices provided active support for hosting heteropolyacids which was found to be an excellent catalyst for this reaction.

Owing to the economic and environmental benefits, photocatalytic organic transformation via C–H activation is a crucially important, while still challenging area. We report a photocatalytic process for partial cyclohexane oxidation with enhanced catalytic activity that exploits chlorine and titanium atoms spatially arranged on a silica substrate. Silica-based catalysts bearing grafted titanium that effectively interacts with photochemically adsorbed chlorine were prepared. The catalysts were synthesized by reacting a layered silicate with titanium(IV) acetylacetonate and subsequent chlorination treatment. Characterization by a variety of techniques revealed that the organic ligand of the titanium species that is grafted onto the silicate layer surface is converted into chlorine while maintaining its coordination state. However, upon subsequent hydration, the chlorine existed as HCl. We investigated the performance of the catalyst for the production of cyclohexanol and cyclohexanone from cyclohexane with m...

Development of microporous materials, like zeolites and metal-organic frameworks (MOFs), with unique and better properties, is crucially important, while yet challenging, for many energy applications. Herein, we report on a new family of microporous hybrids having well-defined permanent porosity, which is formed by pillaring a layered silicate with packed coordination polymers. This inorganic-organic hybrid material, having well-defined/two-faced micropores surrounded by the polymers and silicate walls, exhibits superior adsorption toward methanol due to co-operative interactions compared with conventional microporous materials. The material could be used as an adsorbent to selectively and effectively recover methanol from a methanol/water vapour mixture.

Small-pore zeolites, composed of 8-membered ring windows, exhibit high catalytic performances in the selective catalytic reduction of NOx with ammonia (NH3-SCR) and the light olefin production from methanol or ethanol (MTO or ETO). As these processes are performed at high reaction temperatures in the presence of steam, the enhancement of the thermal and hydrothermal resistances of zeolites is essential for the development of high-performance catalysts that retain their high catalytic activity and selectivity. This paper reports on the syntheses of phosphorus-modified small-pore zeolites with high thermal/hydrothermal stabilities, prepared by the hydrothermal conversion of FAU zeolite in the presence tetraalkylphosphonium cations as both organic structure directing agents and phosphorus modifying agents. Several phosphorus-modified small-pore zeolites with different framework structures and a controlled phosphorus modification degree were synthesized. Moreover, it was found that the phosphorus-modified small-pore zeolites exhibit a good catalytic activity and durability in the NH3-SCR and ETO processes even after severe thermal or hydrothermal treatment.

Zeolite synthesis using faujasite-type (FAU) zeolites as the starting silica/alumina source in the presence of various organic structure-directing agents (OSDAs) with cyclic alkylammonium structures was investigated. The obtained zeolite phases strongly depended on the structure of the OSDA and the Si/Al ratio of the starting FAU. Zeolites with different framework structures, such as BEA, MFI, CHA, and LEV, were obtained. Among the used OSDAs, methylpropylpyrrolidinium, butylmethylpyrrolidinium, and methylpropylpiperidinium effectively produced nanosized BEA and MFI zeolites, whereas dimethylpiperidinium and cyclohexyltrimethylammonium produced CHA and LEV zeolites, respectively. The nanosized MFI and BEA zeolites obtained through zeolite hydrothermal conversion exhibited remarkably smaller particle sizes and higher external surface area as compared to those of the conventional MFI and BEA zeolite samples synthesized using tetrapropylammonium and tetraethylammonium, respectively. We also found that the highly crystalline nanosized BEA and MFI zeolites exhibited better catalytic performance in the dehydration of benzyl alcohol to benzyl ether as compared to the conventional zeolites with large particle sizes. In addition, nanosized MFI zeolites, synthesized using FAU as a starting material and cyclic ammonium compounds, showed catalytic activities superior to those of the nanosized MFI zeolites synthesized from amorphous starting materials and cyclic ammonium compounds.

Zeolites Y from organic-free system with adjustable Si/Al ratios (2.15–2.87) were synthesized and compared to the commercial zeolite Y (HSZ-320NAA, Tosoh Co., Japan). We found that the as-synthesized and commercial zeolites with similar X-ray crystallinity and Si/Al ratios tend to show different susceptibility to removal of framework aluminium. Furthermore, our study indicates that increased extraction of framework aluminium atoms not always result in lower crystallinity. We attribute this behaviour to different distribution of Si(nAl) building units and structural defects as revealed by 29Si MAS-NMR, 27Al MAS-NMR and powder XRD analyses. We also found that the progressively increasing amount of extra-framework aluminium is inversely related with the Si/Al ratios of the dealuminated samples and contributes to higher catalytic activity. Finally, we evaluated the influence of X-ray crystallinity and Si/Al ratios on the catalytic performance of the as-synthesized and commercial samples.

Highly crystalline gmelinite (GME) zeolites with Si/Al ratio of ~ 3 were successfully synthesized from FAU zeolites as the starting silica/alumina source using the dual-template method with a mixture of tetraethylphosphonium and N,N-dimethyl-3,5-dimethylpiepridinium cations as an organic structure-directing agent (OSDA). It was also found that the prepared GME zeolite exhibited high porosity when the as-made GME zeolite was K+ ion-exchanged and then calcined at 580 °C at 6 h to remove OSDAs in the zeolitic pores.

Hydrothermal conversion of cubic (FAU) zeolite into hexagonal (EMT) zeolite using 1,1’-(1,4-butanediyl)bis (1-azonia-4-azabicyclo [2,2,2]octane) dihydroxide ([Dab-4]2+(OH)2) instead of 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6), a well-known organic structure-directing agent (OSDA) for the synthesis of EMT zeolite, was investigated. A systematic study concerning hydrothermal synthesis parameters such as H2O/SiO2, NaOH/SiO2, and [Dab-4]2+(OH)2/SiO2 ratios in the starting synthesis mixture, and temperature and time of synthesis revealed that pure, highly crystalline EMT zeolite can be easily obtained within a short crystallization period of 6 h.

In contrast to usual iron oxides, molecularly small iron oxides synthesized and stabilized on a porous silica scaffold exhibited an unprecedentedly high photocatalytic performance unrealized by previous photocatalysts like TiO2., Although iron oxides have been extensively studied as photocatalysts because of their abundance and environmental compatibility, their performance is notoriously low due to factors such as low photoinduced charge-separation efficiency. Iron oxides, thus, must be modified with expensive and/or toxic materials to attain higher performances, which devalues their appeal as sustainable materials. Here, we design an iron oxide exhibiting an unprecedentedly high photocatalytic performance unrealized by previous photocatalysts such as TiO2 for reactions including the selective oxidation of cyclohexane to industrial nylon precursors. The iron oxide photocatalyst consists of ferric dimers, otherwise extremely unstable, formed via etching of Fe and O sites from ferric oxide nanoparticles immobilized within porous silica. We demonstrate a remarkably high photoinduced charge-separation efficiency (long lifetime of active species) of the ferric dimers due to their electronic structure and the potential of this supported photocatalyst for many more reactions.

During AEI zeolite synthesis using acid treated FAU (AcT-FAU), we found the recrystallization of high-silica FAU with high crystallinity and Si/Al ratio of 6.1 using N,N-dimethyl-3,5-dimethylpiperidinium hydroxide (DMDMPOH) after 2 h, followed by the crystallization of AEI via FAU-to-AEI interzeolite conversion at a longer synthesis time. In order to understand the formation mechanism of high-silica FAU and generalize its direct synthesis, we have investigated this synthesis process. An analysis of the short-range structure of AcT-FAU revealed that it has an ordered aluminosilicate structure having a large fraction of 4-rings despite its low crystallinity. The changes in the composition of the products obtained at different synthesis times suggested that DMDMP+ plays a certain role in the stabilization of the FAU zeolite framework. Moreover, the results of thermogravimetric analysis showed that the thermal stability of DMDMP+ changed with the zeolite conversion. To the best of our knowledge, this is the first study to clarify the structure-directing effect of DMDMP+ on FAU zeolite formation.

A chabazite (CHA zeolite) was synthesized using high-silica faujasite (FAU) zeolites with a Si/Al ratio of 93, an additional alumina source (aluminum hydroxide) combined with seed crystals, and N,N,N-trimethyl-1-adamantammonium hydroxide. We compared the crystallization behavior of the starting material (HSY + Al) with that of other combinations of silica/alumina sources (high-silica and low-silica FAU, fumed silica, and aluminum hydroxide). HSY + Al rapidly yielded nanosized CHA zeolites with a crystal size of approximately 70 nm, exhibited high product crystallinity and high yield and offered a wide synthesis window. A combination of analytic experiments using electrospray-ionization mass spectrometry and nuclear magnetic resonance (NMR) suggested that in the early stage, the pre-introduced CHA seeds provide a crystal nucleus and the FAU zeolites decompose to form oligomer species in the liquid phase. Meanwhile, aluminum hydroxide retains its solid phase. Subsequent crystallization of the zeolites is accelerated by the liquid silicate oligomer and solid aluminate sources, resulting in a high yield and rapid synthesis of nanosized CHA zeolites. We observed that phosphorus-modified CHA zeolites synthesized using HSY + Al perform well as a catalyst for ethanol conversion reactions. Controlled Si/Al ratios and additional phosphorus modifications improve catalytic durability, thereby exhibiting a higher propylene yield from the reaction within the zeolite pore system.

Hydrothermal conversion of FAU zeolite was carried out in the presence of both 1,1'-(1,4-butanediyl)bis(1-azonia-4-azabicyclo[2,2,2]octane) (Dab-4) cation as a structure-directing agent and tetraethylphosphonium (TEP) cation as a phosphorus modification agent. By optimizing the synthesis parameters such as the TEPOH/SiO2, [Dab-4](OH)2/SiO2, NaOH/SiO2, and H2O/SiO2 ratios in the starting reaction mixtures, we successfully synthesized highly crystalline phosphorus-modified (P-modified) AFX zeolite with truncated hexagonal bipyramidal morphology. The P-modification of the AFX zeolite needed a TEP/(Dab-4+TEP) ratio higher than 0.9 because TEP cations have no structure-directing ability for the AFX phase. The obtained P-modified AFX zeolite with a Si/Al ratio of 5–6 and a P/Al ratio of 0.07–0.2 exhibited high thermal stability compared to the P-free one.

Aluminosilicate molecular-sieve zeolites are widely used in industrial processes, mostly as catalysts or adsorbents, and advances in the synthesis are still required in order to progress further applications. To further expand the zeolite synthesis system, herein we report the stepwise preparations of synthesis gels through divided compositional control; this strategy is applied to the effective synthesis of a CHA zeolite in the presence of an inexpensive organic structure directing agent (OSDA), benzyltrimethylammonium. Highly crystalline nanosized CHA zeolites were prepared at higher crystallization rates compared to those prepared using the conventional one-step gel-preparation method. The stepwise method also provided CHA zeolite in a wide range of starting gel compositions, and aluminum content within the formed CHA could be tuned. The aluminosilicate-formation process, investigated by the combination of analytical methods including X-ray diffractometry, NMR and Raman spectroscopy, and electrospray-i...

Covalently linked sulfonic acid (–SO3H)-modified ordered mesoporous silicas MCM-48, MCM-41, and SBA-15 were synthesized, characterized and their catalytic activities were evaluated in the transesterification reaction of triacetin with methanol. Acid modified materials were prepared by oxidative transformation of immobilized functionalized unit, 3-mercaptopropyltriethoxysilane (MPTES) as a precursor. The mesophase and porosity of the catalysts were determined by means of X-ray diffraction and N2 adsorption techniques. No degradation of structure was observed in the preparation process. The acid concentrations were calculated using TG–DTA and NH3–TPD analysis. The acid modified materials were found to be active catalysts for the transesterification of triacetin with methanol. Especially, three-dimensional-MCM-48-SO3H showed better catalytic activity compared to its two-dimensional counterparts MCM-41 and SBA-15.

Novel AFX/CHA aluminosilicate intergrowth zeolites ZTS-1 and ZTS-2 were synthesized using the dual structure-directing agent (dual-SDA) approach. ZTS-1 was obtained using the 1,1′-(1,4-butanediyl)bis(1-azonia-4-azabicyclo[2,2,2]octane) dication (Dab-4 2+ ) and the N,N,N -trimethyl-1-adamantylammonium cation (TMAda + ) as organic structure-directing agents (OSDAs) for AFX and CHA phases, respectively. The obtained materials were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES), electron diffraction, high-resolution transmission electron microscopy (HRTEM), solid-state 13 C dipolar decoupled magic-angle-spinning nuclear magnetic resonance ( 13 C DD/MAS NMR), thermogravimetric and differential thermal analysis (TG/DTA), CHN analysis, and N 2 adsorption. The combined results of these characterizations and those of the DIFFaX simulation showed that the AFX/CHA ratio of ZTS-1 was 80–85% AFX and 15–20% CHA (based on the number of unit cells). Control of the AFX/CHA ratio by simple variation of the hydrothermal synthetic parameters proved to be challenging. The catalytic performance of Cu-loaded ZTS-1 was tested in the selective catalytic reduction of NO x with NH 3 (NH 3 -SCR), and its higher hydrothermal stability compared to the Cu-loaded AFX catalyst was confirmed. ZTS-2 was synthesized using K + instead of TMAda + , under synthetic conditions completely different from those used for ZTS-1. The AFX/CHA ratio of ZTS-2 was estimated as 15–20% AFX and 80–85% CHA, strongly indicating the possibility of controlling the above ratio.

A multiple templating strategy using both bulky and small organic structure-directing agents (SDAs) was adapted for AFX zeolite synthesis in order to control the distribution of aluminum and phosphorus. An AFX zeolite with an Si/Al ratio of 4.8 was obtained in the presence of a bulky and rigid SDA, N,N,N',N'-tetraethylbicyclo[2.2.2]oct-7-ene-2,3:5,6-dipyrrolidinium cation (TEBOP2+), and co-existing Na+ cations. The use of a tetramethylammonium cation (Me4N+) as the SDA instead of Na+ provided AFX zeolite with a middle Si/Al ratio of 7.9. Elemental analysis and 13C and 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy suggested that TEBOP2+ existed in the wide aft cage in both AFX zeolites, while the higher Si/Al ratio was derived from the lower charge density of Me4N+ occupying the narrow gme cage. We also attempted to control the distribution of phosphorus in phosphorus-modified AFX zeolite. The large tetraethylphosphonium cation (Et4P+) and small tetramethylphosphonium cation (Me4P+) were selectively incorporated into aft and gme cages during the hydrothermal synthesis, respectively. As a result, phosphorus oxide with different polymerization degrees were formed by calcination treatment according to the size of the cage occupied by the phosphorus-modifying agents (P-MAs). This direct phosphorus modification using alkylphosphonium was characterized by elemental analysis and 13C, 27Al, and 31P MAS NMR and two-dimensional (2D) 31P–27Al heteronuclear correlation NMR spectroscopies.

Heterometal atom incorporation in CHA aluminosilicate zeolites ([Al, M]-CHA, M = Fe, Ga, Sn) was successfully achieved by hydrothermal conversion of heterometal-incorporated FAU aluminosilicates ([Al, M]-FAU). X-ray powder diffraction (XRD), scanning electron microscopy, diffuse reflectance UV–vis spectroscopy, magic angle spinning NMR, and nitrogen adsorption measurements confirmed the formation of [Al, M]-CHA zeolites with heterometal atoms occupying homogeneously distributed tetrahedral coordination sites. The choice of hydrothermal conversion using [Al, M]-FAU was prompted by the inability to produce [Al, M]-CHA zeolites from amorphous hydrogels. The hydrothermal conversion of [Al, Fe]-FAU to [Al, Fe]-CHA was characterized by XRD, electrospray ionization mass spectrometry, and UV–vis spectroscopy. Analyses of liquid and solid phases during synthesis indicated that metal species present in the solid phase play an important role in the transformation process. We also investigated the effectiveness of Cu-loaded CHA zeolites for the selective catalytic reduction (SCR) of NOx by ammonia (NH3-SCR). Catalytic performance depended strongly on the kind and/or amount of heterometal atom in the [Al, M]-CHA zeolite. Although all fresh catalysts exhibited similar NO conversion efficiencies, there was a difference in NH3 conversion effectiveness at low reaction temperatures. Cu-loaded [Al, Ga]-CHA provided almost 100% NH3 conversion at 150 °C. The [Al, Sn]-CHA catalyst exhibited high stability even after hydrothermal treatment at 900 °C for 4 h. These results confirm hydrothermal conversion as an effective method for synthesizing heterometal-incorporated zeolite catalysts with high NH3-SCR performance.

The ordered mesoporous silicas MCM-48, MCM-41, and SBA-15 were synthesized and functionalized with 3-aminopropyltriethoxysilane (APTES). The X-ray diffraction patterns before and after functionalization revealed no structural degradation during the process. FT-IR spectra of the materials clearly indicated the anchoring of the aminopropyl moiety with silanol groups. The amine concentrations were calculated using TG-DTA and CHN analysis. The amine-loaded materials were assessed as catalysts for the transesterification of triacetin with methanol. MCM-48-NH2, in which the pores are interconnected in a three-dimensional manner, exhibited superior catalytic activity to one- dimensional MCM41-NH2 and SBA-15-NH2, even with lower concentrations of the amine group.

Crystalline layered silicates are promising materials for the rational design of innovative catalysts owing to their wide variety and easily tunable surfaces. However, diffusional limitation in their interlayer spaces limits their catalytic efficiency. Herein, we have developed a novel synthesis route to a highly active layered silicate catalyst utilizing Hiroshima University Silicates (HUSs). We attempted to tune the stacking structure of the silicate layers of HUS-2 and HUS-7 ion-exchanged with hexadecyltrimethylammonium (C16TMA) using organic-solvent treatment, and found that cyclohexane treatment of HUS-7 gave an aggregate of randomly restacked silicate nanosheets without degradation of the original silicate framework. We prepared amine-modified base catalysts by grafting with aminopropyltriethoxysilane, and investigated their catalytic performances in the transesterification of triacetin with methanol. The catalyst based on HUS-7 exhibited a much higher catalytic activity than that based on HUS-2 despite their similar framework topology. Moreover, the activity of the HUS-7-based catalyst was far superior to those of other base catalysts, such as amine-modified mesoporous silica, catalyst resin, and alkylamine. Detailed characterization of the catalysts revealed that the improved accessibility of reactant molecules to the immobilized functional units, which is derived from both the randomly stacked silicate layers and the bulky interlayer molecules incorporated, is the primary reason for the high catalytic efficiency of the layered silicate catalyst.

One-pot synthesis of nanosized zeolites with high crystallinity and stability is an attractive way to meet the demand for innovative catalyst and adsorbent designs. We successfully synthesized highly crystalline nanosized LEV zeolites approximately 30 nm in size that exhibited higher thermal stability than conventional LEV zeolites. The nanosized LEV zeolites were prepared by hydrothermal conversion of faujasite (FAU) zeolites in the presence of N,N-dimethylpiperidinium hydroxide as a starting silica/alumina source and an organic structure-directing agent (OSDA), respectively. It was found that the combined effect of the starting material (FAU) and a suitable OSDA yielded a suitable crystallization system of nanosized LEV zeolites with a high crystallization rate, wide synthesis window, and various aluminum contents (Si/Al = 10–30). Although the structural framework of the conventional LEV sample, with the crystal size exceeding 200 nm, nearly collapsed after thermal treatment at 950 °C for 1 h, the nanosized LEV zeolites maintained their crystallinity. The catalytic performance of protonated nanosized LEV zeolites was evaluated by studying the conversion of ethylene to propylene and butene. The nanosized LEV zeolites showed a longer lifetime owing to the suppression of catalytic deactivation arising from carbonaceous deposition on the outer surface of the crystal.

Phosphorus-modified zeolite with an intergrowth structure of AFX and CHA (P-AFX/CHA) was synthesized by a triple-template system. The synthesis system involved two nitrogen-containing organic structure directing agents (N-OSDAs, N,N,N-trimethyl-1-adamantammonium hydroxide and 1,1'-(1,4-butanediyl)bis(1-azonia-4-azabicyclo[2,2,2]octane) dibromide) for developing the intergrowth zeolite phase. Tetraethylphosphonium cation (TEP) was also added as a phosphorus-modifying agent. The calcination treatment causes the decomposition and oxidation of TEP to form a phosphorus oxide species that interacts with the zeolite framework, thereby realizing direct-phosphorus modification in the zeolite cavity. We optimized the synthesis condition of P-AFX/CHA, tuning the synthesis gel composition and selecting the counter anion in TEP, and found that tetraethylphosphonium bromide (TEPBr) is useful for effectively incorporating phosphorus into the intergrowth zeolite. 31P magic angle spinning (MAS) NMR confirmed the phosphorus modification via the decomposition of P-OSDA, whereas X-ray diffraction and transmission electron microscopy revealed the intergrowth structure. In addition, 13C dipolar decoupling (DD) MAS NMR, elemental analysis, and other synthesis results suggested the selective modification of phosphorus into the CHA phase in the intergrowth zeolite. Phosphorus modification was effective in improving the thermal stability of P-AFX/CHA. The thermal stability increased with increasing the phosphorus modification degree.

Filiació URV: SIInclòs a la memòria: SI Dipotassium cation (K+)-encapsulated Preyssler-type phosphotungstate, [P5W30O110K2]13-, was prepared by heating monobismuth (Bi3+)-encapsulated Preyssler-type phosphotungstate, [P5W30O110Bi(H2O)]12-, in acetate buffer in the presence of an excess amount of potassium cations. Characterization of the isolated potassium salt, K13[P5W30O110K2] (1a), and its acid form, H13[P5W30O110K2] (1b), by single crystal X-ray structure analysis, 31P and 183W nuclear magnetic resonance (NMR), Fourier transform infrared (FT-IR) spectroscopy, cyclic voltammetry (CV), high-resolution electrospray ionization mass spectroscopy (HR-ESI-MS), and elemental analysis revealed that two potassium cations are encapsulated in the Preyssler-type phosphotungstate molecule with formal D5h symmetry, which is the first example of a Preyssler-type compound with two encapsulated cations. Incorporation of two potassium cations enhances the thermal stability of the potassium salt, and the acid form shows catalytic activity for hydration of ethyl acetate. Packing of the Preyssler-type molecules was observed by high-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM).

Nanosized CHA zeolites approximately 100 nm in size with high thermal and hydrothermal stability were synthesized by hydrothermal conversion of FAU zeolites in the presence of N , N , N -trimethyl-1-adamantammonium hydroxide (TMAdaOH) as a structure-directing agent. The crystal size of CHA zeolites depended strongly on the silica/alumina source (FAU zeolite or amorphous aluminosilicate hydrogel) and the Si/Al ratio of starting material. An increase in the hydrothermal synthesis temperature enhanced the thermal stability of nanosized CHA zeolites without increasing the crystal size, and the structural framework of the nanosized CHA zeolites was maintained even after thermal treatment at 1000 °C for 1 h. The potential of nanosized CHA zeolites as solid acid catalysts and as catalyst supports was evaluated by the ethanol conversion reaction and the selective catalytic reduction (SCR) of NO x with NH 3 , respectively. A protonated nanosized CHA zeolite catalyst effectively produced propylene from ethanol by suppressing catalytic deactivation arising from carbonaceous deposition. A Cu-loaded nanosized CHA zeolite catalyst exhibited good performance for the NH 3 -SCR of NO x even after hydrothermal treatment at 900 °C for 4 h. The results indicate that hydrothermal zeolite conversion is very effective in producing nanosized CHA zeolites with high thermal and hydrothermal stabilities.