Controlling the distribution of aluminum in a Cu–zeolite catalyst by seed-assisted synthesis to improve its NH<sub>3</sub>-SCR activity

Lee, Hwangho; Kim, Jong-Hyun; Song, In Kyu; Jeon, Se Won; Cho, Sung June; Kim, Do Heui

doi:10.1039/d2cy00745b

Cited by 6 publications

(2 citation statements)

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“…The influence of proximate Al pairs has been shown for methanol to aromatics conversion, , benzene alkylation, , alkane/alkene cracking, , olefin aromatization, and alcohol dehydration . For applications involving the inclusion of metal cations at proximate sites, reduced Ga species over Al pairs have been shown as active centers for alkane dehydrocyclization and dehydrogenation. , The relevance of Cu balanced by paired sites in zeolites has been investigated for low-temperature ammonia selective catalytic reduction, − as well as the impact of water vapor for the ion-mediated chemistries over proximate Al pairs . Al pairs have also been reported to influence alkane separation, water adsorption, and CO 2 adsorption .…”

Section: Introductionmentioning

confidence: 99%

Paired Site Characterization in Aluminosilicate Zeolites through Limited Alkylammonium Stability

Lawal,

Abdelrahman

2023

J. Phys. Chem. C

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The spatial distribution of tetrahedrally coordinated aluminum incorporated into a mordenite framework zeolite was investigated through the proton-site-selective probe chemistry of alkylamine Hofmann elimination. Protons associated with paired Al sites were exclusively exchanged with divalent cobalt, while isolated protons remained intact and readily quantified through the Hofmann elimination of adsorbed alkylammonium species. Through a combination of temperature-programmed methods and spectroscopic characterization, the stability of the adsorbed alkylammonium was found to be crucial to the accurate estimation of isolated protons. Only alkylammonium species undergoing Hofmann elimination through a primary carbocation were found to exclusively probe isolated protons on the surface of cobalt-exchanged ZSM-5. More stable secondary and tertiary carbocations typically used in the characterization of acid sites resulted in significant overestimates of protonic site densities. The result is contrary to that of purely protonic zeolites, where alkylammonium stability is inconsequential to the quantification of the acid sites they are coordinated with. Consequently, n-propylamine was found to be a suitable reactive probe molecule for the quantification of isolated protonic sites on divalent metal-cation zeolite surfaces, forming n-propylammonium upon adsorption. Ensuring accurate probing of isolated protons on the surface of metal cation exchanged zeolites was also demonstrated to require control of ion-exchange conditions and a sufficient extent of zeolite exposure to the adsorbing n-propylamine. The fraction of paired Al sites in ZSM-5 was measured to systematically increase with Al content, ranging between 6 and 63% across Si/Al values of 140 and 11.5, respectively. Experimentally measured Al pairing was in excellent quantitative agreement with a binomial distribution, suggesting random incorporation of Al into the tetrahedral sites of ZSM-5 at next-nearest-neighboring positions.

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Section: Introductionmentioning

confidence: 99%

Paired Site Characterization in Aluminosilicate Zeolites through Limited Alkylammonium Stability

Lawal,

Abdelrahman

2023

J. Phys. Chem. C

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“…56 For applications involving the inclusion of metal cations at proximate sites, reduced Ga species over Alpairs have been shown as active centers for alkane dehydrocyclization and dehydrogenation. [57][58] The relevance of Cu balanced by paired sites in zeolites has been investigated for low-temperature ammonia selective catalytic reduction, [59][60][61] as well as the impact of water vapor for the ion-mediated chemistries over proximate Al-pairs. 62 Al-pairs has also been reported to influence alkane separation, 63 water adsorption, 64 and CO2 adsorption.…”

mentioning

confidence: 99%

Paired Site Characterization in Aluminosilicate Zeolites through Limited Alkylammonium Stability

Abdelrahman

Lawal

2023

Preprint

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The spatial distribution of tetrahedrally coordinated aluminum incorporated into a mordenite framework inverse framework zeolite was investigated through the proton site-selective probe chemistry of alkylamine Hofmann elimination. Protons associated with paired Al sites were exclusively exchanged with divalent cobalt, while isolated protons remained intact and readily quantified through Hofmann elimination of adsorbed alkylammonium species. Through a combination of temperature-programmed methods and spectroscopic characterization, the stability of the adsorbed alkylammonium was found to be crucial to the accurate estimation of isolated protons. Only alkylammonium species undergoing Hofmann elimination through a primary carbocation were found to exclusively probe isolated protons on the surface of cobalt-exchanged ZSM-5. More stable secondary and tertiary carbocations typically used in the characterization of acid sites, resulted in significant overestimates of protonic site densities. The result is contrary to purely protonic zeolites, where alkylammonium stability is inconsequential to the quantification of the acid sites they are coordinated with. Consequently, n-propylamine was found to be a suitable reactive probe molecule for the quantification of isolated protonic sites on divalent metal-cation zeolite surfaces, forming n-propylammonium upon adsorption. Ensuring accurate probing of isolated protons on the surface of metal cation exchanged zeolites was also demonstrated to require control of ion-exchange conditions and sufficient extent of zeolite exposure to the adsorbing n-propylamine. The fraction of paired Al sites in ZSM-5 was measured to systematically increase with Al content, ranging between 6 and 63 % across a Si/Al of 140 and 11.5, respectively. Experimentally measured Al pairing was in excellent quantitative agreement with a binomial distribution, suggesting a random incorporation of Al into the tetrahedral sites of ZSM-5 at next-nearest-neighboring positions.

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Synthesis‐Structure‐Catalysis Relations in CHA Zeolites Applied for Selective Catalytic Reduction of NO_x with Ammonia

Tsunoji,

Onishi,

Sonoda

et al. 2024

ChemCatChem

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Microporous aluminosilicate zeolites are useful industrial catalysts. However, their hydrothermal synthesis is a multistep process with complicated and unclear reactions, limiting their rational functional design. Herein, we compare the formation pathway and the structural and catalytic properties of several CHA zeolites to obtain fundamental knowledge for intentionally controlling the catalytic function of zeolites. Three CHA zeolites were synthesized using different starting silica/alumina sources in the presence of tetraethylammonium hydroxide as an inexpensive organic structure‐directing agent. FAU zeolite and an amorphous synthesis gel prepared using two different methods were used as starting materials. The obtained CHA zeolites were applied for exhaust gas purification (selective catalytic reduction of NOx with ammonia, NH3‐SCR), and their structural characteristics and formation pathways were investigated using a combination of analytical methods. Stepwise gel preparation (SGP), which divides the compositional control of the amorphous synthesis gel, promotes the decomposition of the initial additive (zeolite seed), resulting in the formation of CHA zeolites with abundant micropores and paired Al sites. This structural feature obtained using the SGP method improves the catalytic durability of the NH3‐SCR reaction. The present relationship, including different crystallization phenomena, structures, and catalytic abilities, provides useful insights into rational zeolite synthesis and its application.

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Controlling the distribution of aluminum in a Cu–zeolite catalyst by seed-assisted synthesis to improve its NH₃-SCR activity

Abstract: Modulating the Al sites in zeolites has been regarded as a promising but difficult strategy for designing high-performance catalysts for various reactions. To this end, a simple seed-assisted strategy was...

Cited by 6 publications

References 72 publications

Paired Site Characterization in Aluminosilicate Zeolites through Limited Alkylammonium Stability

Paired Site Characterization in Aluminosilicate Zeolites through Limited Alkylammonium Stability

Paired Site Characterization in Aluminosilicate Zeolites through Limited Alkylammonium Stability

Synthesis‐Structure‐Catalysis Relations in CHA Zeolites Applied for Selective Catalytic Reduction of NO_x with Ammonia

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Controlling the distribution of aluminum in a Cu–zeolite catalyst by seed-assisted synthesis to improve its NH3-SCR activity

Abstract: Modulating the Al sites in zeolites has been regarded as a promising but difficult strategy for designing high-performance catalysts for various reactions. To this end, a simple seed-assisted strategy was...

Cited by 6 publications

References 72 publications

Paired Site Characterization in Aluminosilicate Zeolites through Limited Alkylammonium Stability

Paired Site Characterization in Aluminosilicate Zeolites through Limited Alkylammonium Stability

Paired Site Characterization in Aluminosilicate Zeolites through Limited Alkylammonium Stability

Synthesis‐Structure‐Catalysis Relations in CHA Zeolites Applied for Selective Catalytic Reduction of NOx with Ammonia

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Controlling the distribution of aluminum in a Cu–zeolite catalyst by seed-assisted synthesis to improve its NH₃-SCR activity

Synthesis‐Structure‐Catalysis Relations in CHA Zeolites Applied for Selective Catalytic Reduction of NO_x with Ammonia