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Your search keyword '"Takeshi Ohnishi"' showing total 3 results
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3 results on '"Takeshi Ohnishi"'

1. Synthesis and Structural Analysis of High‐Silica ERI Zeolite with Spatially‐Biased Al Distribution as a Promising NH3‐SCR Catalyst

Author

Jie Zhu, Koki Muraoka, Takeshi Ohnishi, Yutaka Yanaba, Masaru Ogura, Akira Nakayama, Toru Wakihara, Zhendong Liu, and Tatsuya Okubo

Subjects
density functional calculations, high‐silica ERI zeolite, NH3‐SCR catalyst, NMR spectroscopy, spatially‐biased Al distribution, Science
Abstract

Abstract Erionite (ERI) zeolite has recently attracted considerable attention for its application prospect in the selective catalytic reduction of NOx with NH3 (NH3‐SCR), provided that the high‐silica (Si/Al > 5.5) analog with improved hydrothermal stability can be facilely synthesized. In this work, ERI zeolites with different Si/Al ratios (4.6, 6.4, and 9.1) are synthesized through an ultrafast route, and in particular, a high‐silica ERI zeolite with a Si/Al ratio of 9.1 is obtained by using faujasite (FAU) as a starting material. The solid‐state 29Si MAS NMR spectroscopic study in combination with a computational simulation allows for figuring out the atomic configurations of the Al species in the three ERI zeolites. It is revealed that the ERI zeolite with the highest Si/Al ratio (ERI‐9.1, where the number indicates the Si/Al ratio) exhibits a biased Al occupancy at T1 site, which is possibly due to the presence of a higher fraction of the residual potassium cations in the can cages. In contrast, the Al siting in ERI‐4.6 and ERI‐6.4 proves to be relatively random.

Published
2024
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2. Multiple templating strategy for the control of aluminum and phosphorus distributions in AFX zeolite

Author

Nao, Tsunoji, Kazuyoshi, Tsuchiya, Naoto, Nakazawa, Satoshi, Inagaki, Yoshihiro, Kubota, Toshiki, Nishitoba, Toshiyuki, Yokoi, Takeshi, Ohnishi, Masaru, Ogura, Masahiro, Sadakane, Tsuneji, Sano, Nao, Tsunoji, Kazuyoshi, Tsuchiya, Naoto, Nakazawa, Satoshi, Inagaki, Yoshihiro, Kubota, Toshiki, Nishitoba, Toshiyuki, Yokoi, Takeshi, Ohnishi, Masaru, Ogura, Masahiro, Sadakane, and Tsuneji, Sano

Abstract

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.

Published
2023

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