Robust CON-type zeolite nanocatalyst in methanol-to-olefins reaction: downsizing, recrystallisation and defect-healing treatments toward prolonged lifetime

Takemoto, Masanori; Iyoki, Kenta; Otsuka, Yuki; Onozuka, Hiroaki; Anand, Chokkalingam; Yokoi, Toshiyuki; Tsutsuminai, Susumu; Takewaki, Takahiko; Wakihara, Toru; Okubo, Tatsuya

doi:10.1039/d2ma00343k

Cited by 6 publications

(5 citation statements)

References 37 publications

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“…Our group recently demonstrated a novel liquid-mediated treatment method. − The treatment of beta, MFI, and MOR zeolites in a solution containing ammonium fluoride and tetraethylammonium hydroxide significantly decreased the number of internal defects by causing the migration of silicate species into Si atom vacancies. The treated MFI zeolite exhibited superior hydrothermal stability compared to MFI zeolites synthesized with fluoride media, maintaining over 90% of the relative crystallinity even after steaming at 1150 °C.…”

Section: Introductionmentioning

confidence: 99%

Simultaneous Control of Aluminum Atoms and Defects in the MOR Zeolite Framework by Postsynthetic Treatments

Fujikawa,

Yoshioka,

Iyoki

et al. 2024

J. Phys. Chem. C

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The framework Al sites and defects in zeolite structures realize their functionalities as catalysts, adsorbents, and ion exchangers. Therefore, controlling the number and state of Al atoms and silanol species in zeolites is crucial for achieving better performance. Among the numerous synthetic approaches for this purpose, postsynthetic approaches show promise for achieving the modification of Al atoms and defects for various zeolites. In this study, the effects of steam, acid, and fluoride treatment on MOR zeolites were analyzed. Steam treatment eliminated framework Al atoms to form extra-framework Al species, and framework vacancies formed by dealumination were healed by silicate migration. A 27Al triple-quantum magic-angle spinning nuclear magnetic resonance (3QMAS NMR) spectroscopy study combined with gauge-including projector augmented wave (GIPAW) calculations for comprehensive defect models revealed the increased distortion of tetrahedral coordination around Al atoms and the change in Al siting during steam treatment. Acid treatment removed extra-framework Al species. Fluoride treatment caused realumination without changing the bulk composition. Additionally, fluoride treatment decreased the number of defects, whereas fluoride treatment of steamed zeolite increased the number of defective silanol sites in the case of MOR zeolites. The different roles of the postsynthesis treatments in this study are expected to aid in facilitating the postsynthetic modification of the atomic distribution in various zeolites.

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Section: Introductionmentioning

confidence: 99%

Simultaneous Control of Aluminum Atoms and Defects in the MOR Zeolite Framework by Postsynthetic Treatments

Fujikawa,

Yoshioka,

Iyoki

et al. 2024

J. Phys. Chem. C

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“…16,17 An aluminoborosilicate CON-type zeolite, which can be prepared by both postsynthetic modification 18 and direct synthesis 19 to introduce acid sites generated by framework aluminum, has exhibited excellent catalytic performances. Unlike typical zeolites such as ZSM-5, SAPO-34, mordenite, and beta, 20−24 CON-type zeolites have demonstrated a long catalytic lifetime 25 and high selectivity for key plastic feedstocks such as propylene and butane. 26 However, two significant problems hinder the utilization of CON-type zeolite: (i) a long synthesis duration (ii) a highly expensive OSDA with a complex structure (N,N,N-trimethyl-(−)-cis-myrtanylammonium (TMMAOH)).…”

Section: Introductionmentioning

confidence: 99%

“…Owing to their high accessibility and diffusibility by large pores, as well as superior selectivity due to medium pores, a CON-type zeolite is expected to be a promising catalyst, especially for the methanol-to-olefins (MTO) reaction, which is considered a clean alternative path to produce light olefins. , An aluminoborosilicate CON-type zeolite, which can be prepared by both postsynthetic modification and direct synthesis to introduce acid sites generated by framework aluminum, has exhibited excellent catalytic performances. Unlike typical zeolites such as ZSM-5, SAPO-34, mordenite, and beta, − CON-type zeolites have demonstrated a long catalytic lifetime and high selectivity for key plastic feedstocks such as propylene and butane . However, two significant problems hinder the utilization of CON-type zeolite: (i) a long synthesis duration (7 days) and (ii) a highly expensive OSDA with a complex structure ( N , N , N -trimethyl-(−)- cis -myrtanylammonium (TMMAOH)).…”

Section: Introductionmentioning

confidence: 99%

Control of Competitive Structure-Directing Effect in CON-Type Zeolite Synthesis via Intermediate Addition Method

Shibuya

Iyoki

Onozuka

et al. 2023

Crystal Growth & Design

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The development of efficient and economical synthesis methods for CON-type aluminoborosilicate zeolite, a promising catalyst for methanol-to-olefins reactions, is in high demand. Herein, we propose the dual use of organic structure-directing agents that have different roles in the formation of CON-type zeolite. Although N,N,N-trimethyl-(−)-cis-myrtanylammonium hydroxide (TMMAOH) has a strong structure-directing effect on the formation of CON-type zeolite, it is considerably expensive. Conversely, the relatively inexpensive tetraethylammonium hydroxide (TEAOH) has a weak structure-directing effect on the formation of CON-type zeolite and/or even directs the formation of other impurity phases. The intermediate addition method of TEAOH, developed herein, could control these competitive structure-directing effects and enhance the crystallization of CON-type zeolite from economically viable raw materials. The timing of intermediate TEAOH addition was found to be a critical factor to obtain a pure CON phase, and TEA+ was occluded in the final product, suggesting the pore filler role of TEAOH, while TMMAOH is required in the early stage of crystallization.

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“…With the aid of pore-filling hydroxide (e.g., tetraethylammonium hydroxide), fluoride species induce framework reconstruction and defect healing in the aforementioned zeolites through silicate migration. Through this method, several zeolites with fewer defects and improved hydrothermal stability were prepared. , Compared with conventional zeolites, defect healing-treated zeolites maintained their stability up to 1150 °C under steaming conditions. It is important to highlight that hydrophobic TS-1, featuring adjustable Si–OH groups, has been synthesized using a direct hydrothermal method in the presence of hydrofluoric acid (HF) .…”

Section: Introductionmentioning

confidence: 99%

“…Through this method, several zeolites with fewer defects and improved hydrothermal stability were prepared. 17,18 Compared with conventional zeolites, defect healing-treated zeolites maintained their stability up to 1150 °C under steaming conditions. It is important to highlight that hydrophobic TS-1, featuring adjustable Si−OH groups, has been synthesized using a direct hydrothermal method in the presence of hydrofluoric acid (HF).…”

Section: ■ Introductionmentioning

confidence: 99%

Hydrophobicity Manipulation of Titanium Silicalite-1 with Enhanced Catalytic Performance via Liquid-Mediated Defect Healing Treatment

Li,

Iyoki,

Techasarintr

et al. 2023

ACS Catal.

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As a high-performance catalyst in the industry, titanium silicalite-1 (TS-1) has received extensive attention from researchers for decades. Using aqueous hydrogen peroxide as an oxidant, TS-1 exhibits high activity and selectivity for various oxidation reactions. However, the existence of silanol defects compromises its catalytic activity and leads to byproduct formation. In this research, we report a successful elimination of silanol defects and significant improvements in the catalytic activity of TS-1 via defect healing treatment. As confirmed by Fourier transform infrared spectroscopy (FT-IR), solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR), and water vapor adsorption isotherms, defect healing-treated samples are free of silanol defects with significantly improved hydrophobicity. To evaluate the catalytic performance, epoxidation of 1-hexene with H 2 O 2 was carried out. All defect healing-treated samples exhibit highly enhanced catalytic performance. The conversions of 1-hexene are increased by up to 70% compared to the corresponding pristine samples. After defect healing treatment, the turnover frequency is as high as 159 h −1 .

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Robust CON-type zeolite nanocatalyst in methanol-to-olefins reaction: downsizing, recrystallisation and defect-healing treatments toward prolonged lifetime

Abstract: CON-type zeolites have great potential as highly propene-selective catalysts in methanol-to-olefins reactions; however, their insufficient lifetime is a major limitation. This study demonstrates the remarkably prolonged lifetime of CON-type zeolite...

Cited by 6 publications

References 37 publications

Simultaneous Control of Aluminum Atoms and Defects in the MOR Zeolite Framework by Postsynthetic Treatments

Simultaneous Control of Aluminum Atoms and Defects in the MOR Zeolite Framework by Postsynthetic Treatments

Control of Competitive Structure-Directing Effect in CON-Type Zeolite Synthesis via Intermediate Addition Method

Hydrophobicity Manipulation of Titanium Silicalite-1 with Enhanced Catalytic Performance via Liquid-Mediated Defect Healing Treatment

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