Toward Intrinsic Catalytic Rates and Selectivities of Zeolites in the Presence of Limiting Diffusion and Deactivation

Hullfish, Cole W.; Tan, Jun Zhi; Adawi, Hayat I.; Sarazen, Michele L.

doi:10.1021/acscatal.3c03559

Cited by 7 publications

(2 citation statements)

References 86 publications

(146 reference statements)

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“…5,6 However, the sole presence of micropores (<2 nm) imposes a significant limitation on the intracrystalline diffusion of bulk reactant molecules, causing side reactions as well as subsequent coke formation and eventual catalyst deactivation. 7–9…”

Section: Introductionmentioning

confidence: 99%

Anisotropic ZSM-5 nanorod assemblies: facile synthesis, epitaxial growth, and strikingly enhanced stability in benzene alkylation

Zhu,

Yu,

Gao

et al. 2024

Inorg. Chem. Front.

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Section: Introductionmentioning

confidence: 99%

Anisotropic ZSM-5 nanorod assemblies: facile synthesis, epitaxial growth, and strikingly enhanced stability in benzene alkylation

Zhu,

Yu,

Gao

et al. 2024

Inorg. Chem. Front.

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“…A variety of hydrocarbon conversions rely on zeolites, since their microporous channels and voids impose confinement effects on guest species via van der Waals interactions, thereby altering reactivity and selectivity. − These interactions can stabilize the carbenium/carbonium ion transition states that govern hydrocarbon reactions, including beta scission, , which proceeds via a carbenium ion pathway and is typically the main Bro̷nsted acid-catalyzed reaction responsible for the deconstruction of long-chain polymers or shorter-chain alkenes into smaller fragments at milder temperatures (<673 K). However, the microporosity of zeolites also restricts the diffusion of bulky molecules into internal active Bro̷nsted acid sites (BAS), − leading to lower overall catalyst efficiency. One common approach to alleviate diffusion limitations for microporous materials is to introduce a new level of porosity (e.g., mesoporosity or macroporosity) to yield hierarchical zeolites. − …”

Section: Introductionmentioning

confidence: 99%

Catalytic Consequences of Hierarchical Pore Architectures within MFI and FAU Zeolites for Polyethylene Conversion

Tan,

Ortega,

Miller

et al. 2024

ACS Catal.

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The benefits of hierarchical zeolites for the conversion of bulky molecules like polymeric waste have been reported in the literature; however, the impact of mesopore sizes and connectivities on rates, product selectivities, and catalyst deactivation in the context of plastic upcycling has not been systematically probed. Here, we synthesized a suite of hierarchical MFI and FAU zeolites via desilication under varying conditions for metal-free polyethylene conversion reactions under batch and flow conditions (473−523 K). Polyethylene (solid) conversion rates (normalized by Bro̷ nsted acid site density) were higher on hierarchical than parent microporous MFI regardless of mesopore connectivities, i.e., open or constricted, suggesting that the incorporation of mesopores facilitates diffusion of intermediate products to access medium-pore protons for successive scission events. Furthermore, higher branched:linear gaseous product ratios were produced on hierarchical than parent MFI, since mesopores allow for egress of bulkier molecules without undergoing further secondary events, e.g., isomerization back to linear alkanes/alkenes or beta scission. Solid conversion rates on hierarchical FAU synthesized via desilication with cetyltrimethylammonium bromide (CTABr), however, were not higher than parent FAU, likely because the presence of CTABr facilitates recrystallization of leached species to form composites (hierarchical FAU and ordered mesoporous materials) with more isolated mesopores. The stagnation in rates, despite increased mesopore volumes (>0.22 cm 3 g −1 ), highlights the importance of confinement effects provided by micropores for cleaving C−C bonds at modest reaction conditions. In situ 1 H MAS NMR performed on polyethylene with MFI zeolite show that PE isomerizes (and potentially deconstructs) at temperatures near 450 K, highlighting the role of Bro̷ nsted acid sites in activating C−C bonds under mild reaction conditions. Catalyst recyclability studies showed that all catalysts undergo deactivation during plastic upcycling reactions, but to varying extents. Overall, hierarchical materials have better catalyst stability than parent materials, although the differences in stability between hierarchical and parent FAU are smaller than those for MFI. Taken together, these findings demonstrate how rates, selectivities, and catalyst deactivation from plastic upcycling reactions can be controlled via fine-tuning the identity and connectivity of mesopores.

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Enhanced catalytic performance of ferrierite zeolites via finned morphology for carbonylation of dimethyl ether

Liu,

Huang,

Liu

et al. 2024

Chemical Engineering Science

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Toward Intrinsic Catalytic Rates and Selectivities of Zeolites in the Presence of Limiting Diffusion and Deactivation

Cited by 7 publications

References 86 publications

Anisotropic ZSM-5 nanorod assemblies: facile synthesis, epitaxial growth, and strikingly enhanced stability in benzene alkylation

Anisotropic ZSM-5 nanorod assemblies: facile synthesis, epitaxial growth, and strikingly enhanced stability in benzene alkylation

Catalytic Consequences of Hierarchical Pore Architectures within MFI and FAU Zeolites for Polyethylene Conversion

Enhanced catalytic performance of ferrierite zeolites via finned morphology for carbonylation of dimethyl ether

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