Stable co-production of olefins and aromatics from ethane over Co<sup>2+</sup>-exchanged HZSM-5 zeolite

Hu, Wenjin; Xu, Yuebing; Xin, Jian; Liu, Bing; Jiang, Feng; Liu, Xiaohao

doi:10.1039/d2cy00664b

Cited by 5 publications

(10 citation statements)

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“…At the ethane contents of 20 and 5%, the ethane conversions close to the equilibrium ones (31.2 and 61.0%) were only realized at 3000 mL/g/h and lower, respectively. This fact may suggest that the catalyst was suffering a diffusion restriction in the MFI zeolite channels (∼0.55 nm) for ethane molecules …”

Section: Resultsmentioning

confidence: 99%

“…In addition to the reaction time, reaction temperature is more majorly responsible for the separation. Previously, we observed that the exchanged Co 2+ species in the Co-exchanged Co/ZSM-5 (Si/Al = 12.5, 1.4 wt % of Co) were de-anchored from their exchange sites in MDA (>700 °C) but were still stable in ethane dehydroaromatization (600 °C) . Due to coverage by coke deposition, identification of the Co 0 clusters in the spent samples was not sensitive for using the XPS technique (Figure e).…”

Section: Resultsmentioning

confidence: 99%

“…For EDH or PDH over the Co-based catalysts, when Co species are easily reduced and sintered into metallic Co 0 clusters on the external surface of the MFI zeolite, both C−C and C−H bond cleavages will be dominated, leading to the formations of coke and CH 4 . 69 Hence, the Co-impregnated Co/MFI catalysts, especially with high Co contents (3−6 wt %), could promote alkane decomposition with a much lower selectivity to olefins (Figure 4) due to the inevitable formation of the reducible cobalt oxide clusters (Figures 1 and 2). However, Chen et al observed that when tiny CoO x clusters entered zeolite channels using the impregnation method at a low Co content, the Co/ZSM-5 catalyst could suppress alkane decomposition and only promote dehydrogenation.…”

Section: Conversion−selectivity Trade-off Relationship Of Co Species ...mentioning

confidence: 99%

“…This fact may suggest that the catalyst was suffering a diffusion restriction in the MFI zeolite channels (∼0.55 nm) for ethane molecules. 69 Surprisingly, the deviation in ethane conversion from the equilibrium one was enlarged at lowering reaction temperature. As shown in Figure 6, at 550 °C and ethane content of 20%, the ethane conversion over the 6 wt % Co@MFI catalyst was only 4.5%, showing a high degree of deviation from the equilibrium conversion that should be 18.7%.…”

Section: Characterizations Of the Ligand-free-synthesizedmentioning

confidence: 99%

“…However, they always showed a low one-pass conversion far from the thermodynamic equilibrium values, which is certainly due to a low metal loading in the catalyst. Because of the limitation of the number of exchangeable sites (−Al–(O–Si) n =1,2 –O–Al–, Al pairs) in a zeolite, the metal loading has to be limited under the exchange rule. , In our previous work, therefore, we proposed the remaining challenge of how to upgrade the potential Co-based catalysts that could reach the equilibrium conversion easily in a one-pass reaction . Obviously, a totally different synthesis strategy has to be adopted to gain a higher Co loading in the catalyst.…”

Section: Introductionmentioning

confidence: 99%

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Manipulating the Cobalt Species States to Break the Conversion–Selectivity Trade-Off Relationship for Stable Ethane Dehydrogenation over Ligand-Free-Synthesized Co@MFI Catalysts

et al. 2023

ACS Catal.

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Nonoxidative dehydrogenation of low-cost alkanes provides a promising route to produce valuable olefins. Herein, we hydrothermally synthesized various non-noble-metal-based, environment-friendly, and Al-free Co@MFI catalysts without the assistance of any additional coordination agents. The Co 2+ species were successfully incorporated into well-crystallized MFI to form a stable and atomically dispersed −Co δ+ −O δ− − structure. The Co@MFI catalyst could show a stably high activity for ethane dehydrogenation with equilibrium-approached conversions at 600 °C and at the same time gave an extremely high selectivity to ethylene (∼99%), which is owed to the relatively unreducible −Co−O− species and its appropriate chemical state at the right reaction-temperature window. However, the Co@MFI catalyst showed equilibrium-deviated conversions at lower temperatures (such as 550 °C) and a suppressed activity in the H 2 O or CO 2 co-feeding tests. Then, with characterizations, density functional theory calculations, and abundant experiments over different catalysts, including impregnated Co/MFI and amorphous Co@MFI, this study has impressively demonstrated that the chemical state of Co δ+ species manipulates the conversion−selectivity trade-off relationship in the conversion of alkanes. It is suggested that Co with a lower valence like Co 0 promotes both C−C and C−H bond scissions of alkanes into coke and CH 4 , while Co with a higher one shows a decreased activity or even inactivity for alkane dehydrogenation. In this study, the possible causes for the success in the synthesis of the ligand-unassisted Co@MFI catalyst, the catalyst deactivation modes and the strategies for improving catalyst stability were also demonstrated in detail. This work not only contributes a performance-advanced Co-based catalyst for alkane dehydrogenation but also provides new insights into incorporation of a metal into zeolites.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Conversion−selectivity Trade-off Relationship Of Co Species ...mentioning

confidence: 99%

Section: Characterizations Of the Ligand-free-synthesizedmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Manipulating the Cobalt Species States to Break the Conversion–Selectivity Trade-Off Relationship for Stable Ethane Dehydrogenation over Ligand-Free-Synthesized Co@MFI Catalysts

et al. 2023

ACS Catal.

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Obtaining highly stable T_d‐Co(II) site by coupling hydrothermal method and CO₂ introduction for propane dehydrogenation

Deng,

Sun,

Zheng

et al. 2024

AIChE Journal

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The preparation of Co‐based catalysts with a single, highly dispersed active site is challenging and crucial for the high‐performance propane dehydrogenation (PDH) owing to harsh reaction conditions. Herein, the synergetic strategies including catalyst hydrothermal treatment and CO2 introduction are adopted to realize the highly dispersed and stable Td‐Co(II) site and applied for PDH. According to systematic characterizations and catalytic performance evaluation, the facial hydrothermal treatment improves the C3H6 formation rate from 456 to 771 mmol C3H6 gCo−1 h−1 and catalyst stability via the transformation of Co3O4 species to the Td‐Co(II) species. Meanwhile, the further introduction of CO2 into the PDH system as a protective reagent for Co state would facilitate PDH with superior catalytic performance with TOF of 700 h−1 and C3H6 formation rate of 970 mmol C3H6 gCo−1 h−1. It is revealed that the introduction of CO2 maintains Co state with the Td‐Co(II) species via inhabiting the generation of metallic Co spices.

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Tuning Pt Location and Intimacy between Pt–Acid Active Sites in Pt/ZSM-5 Bifunctional Catalysts for Effective Alkylation of Benzene with Ethane

Zhou,

Zhang,

Shang

et al. 2024

Ind. Eng. Chem. Res.

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The rational design of bifunctional catalysts is an effective strategy for improving the reaction performance. In this work, three Pt/ZSM-5 catalysts (all of the loading of platinum is relatively low, about 0.2 wt %) were prepared through three different preparation methods, and then their application in the alkylation of benzene with ethane to ethylbenzene was studied. Among the three catalysts, the one prepared by the in situ encapsulation method contains nanoparticles of Pt mainly located in the interior of ZSM-5, and there is a low intimacy between the Pt−acid sites on the support. This catalyst shows the lowest benzene conversion. On the other hand, for the catalyst prepared by the impregnation method, the platinum particles are mainly located on the external surfaces of ZSM-5, and there is high intimacy between the Pt−acid active sites. This catalyst delivers high benzene conversion but low ethylbenzene selectivity due to easy access to the Pt−acid active sites for the side reactions. The best catalytic activity with a 90.6% ethylbenzene selectivity and a benzene conversion of 9.8% is achieved by the catalyst produced by ion exchange. This catalyst contains Pt located on both the external and interior of ZSM-5, with the highest intimacy between the Pt− acid active sites. It achieves not only high benzene conversion but also high ethylbenzene selectivity. This study reveals the relationship between the location and intimacy between two active sites of Pt/ZSM-5 catalysts in alkylation reactions and demonstrates a great significance for the rational design of other bifunctional or multifunctional metal−zeolite catalysts.

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Stable co-production of olefins and aromatics from ethane over Co²⁺-exchanged HZSM-5 zeolite

Abstract: Catalytic conversion of ethane into olefins and aromatics is an effective approach for the monetization of the low-cost light paraffins. In this study, with ion-exchange method, Co-exchanged HZSM-5 catalysts were...

Cited by 5 publications

References 70 publications

Manipulating the Cobalt Species States to Break the Conversion–Selectivity Trade-Off Relationship for Stable Ethane Dehydrogenation over Ligand-Free-Synthesized Co@MFI Catalysts

Manipulating the Cobalt Species States to Break the Conversion–Selectivity Trade-Off Relationship for Stable Ethane Dehydrogenation over Ligand-Free-Synthesized Co@MFI Catalysts

Obtaining highly stable T_d‐Co(II) site by coupling hydrothermal method and CO₂ introduction for propane dehydrogenation

Tuning Pt Location and Intimacy between Pt–Acid Active Sites in Pt/ZSM-5 Bifunctional Catalysts for Effective Alkylation of Benzene with Ethane

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Stable co-production of olefins and aromatics from ethane over Co2+-exchanged HZSM-5 zeolite

Abstract: Catalytic conversion of ethane into olefins and aromatics is an effective approach for the monetization of the low-cost light paraffins. In this study, with ion-exchange method, Co-exchanged HZSM-5 catalysts were...

Cited by 5 publications

References 70 publications

Manipulating the Cobalt Species States to Break the Conversion–Selectivity Trade-Off Relationship for Stable Ethane Dehydrogenation over Ligand-Free-Synthesized Co@MFI Catalysts

Manipulating the Cobalt Species States to Break the Conversion–Selectivity Trade-Off Relationship for Stable Ethane Dehydrogenation over Ligand-Free-Synthesized Co@MFI Catalysts

Obtaining highly stable Td‐Co(II) site by coupling hydrothermal method and CO2 introduction for propane dehydrogenation

Tuning Pt Location and Intimacy between Pt–Acid Active Sites in Pt/ZSM-5 Bifunctional Catalysts for Effective Alkylation of Benzene with Ethane

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Stable co-production of olefins and aromatics from ethane over Co²⁺-exchanged HZSM-5 zeolite

Obtaining highly stable T_d‐Co(II) site by coupling hydrothermal method and CO₂ introduction for propane dehydrogenation