The synthesis of new coke‐resistant support and its application in propane dehydrogenation to propene

Zhou, Shijian; Zhou, Yuming; Zhang, Yiwei; Sheng, Xiaoli; Zhang, Zewu

doi:10.1002/jctb.4686

Cited by 17 publications

(14 citation statements)

References 55 publications

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“…The pore structure of the support is another factor which has a significant role in coke formation. 96 The acidity of the support was decreased after the modification of the pore structure of ZSM-5 by introducing hierarchicalpores, 96 which inhibits the formation of coke on the metal and improves the capacity of the support for coke. Moreover, the pore size has a direct effect on performance of PDH.…”

Section: Suppression and Elimination Of Coke Depositionmentioning

confidence: 99%

Coke Deposition on Pt-Based Catalysts in Propane Direct Dehydrogenation: Kinetics, Suppression, and Elimination

et al. 2021

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Pt-based catalysts are widely used in propane dehydrogenation to meet the dramatically increased demand of propylene from an on-purpose catalytic process. Although the process has been commercialized with high selectivity for decades, the prevention of coke deposition is still a daunting challenge. Herein, in order to provide a full coverage of the impact of coke deposition, we critically analyze the process of coke formation on Pt-based catalyst. First, the intrinsic nature of coke, including composition, distribution, and effects, is presented. The developments of kinetics model of coke growth are discussed and compared to offer insight into mechanism of coke formation. Moreover, the focus is put on the ways to prevent coke, which included cofeeding reductant gas, promoter, and support engineering. The advantage and limitation of each method is well elaborated, and the unique working principle behind each prevention method is uncovered. The new developments of single atom/site and confined metal cluster strategies are indicated. The regeneration of the deactivated catalyst is also discussed, which has a direct influence on the coke elimination and metal dispersion. In the end, the possible optimization strategies are suggested for the future Pt catalyst rational design. The current work provides a comprehensive summary of the coke formation, which lays out a solid and essential base for the further developments of Pt catalysts in propane direct dehydrogenation.

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Section: Suppression and Elimination Of Coke Depositionmentioning

confidence: 99%

Coke Deposition on Pt-Based Catalysts in Propane Direct Dehydrogenation: Kinetics, Suppression, and Elimination

et al. 2021

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“…However, the subnanometer (<1 nm) micropores of zeolites often limit accessibility of reactant molecules to the internal catalytic sites. This creates a number of limitations such as the inability to convert larger molecules, as well as issues of deactivation due to formation of side products that are too large to be removed though the micropores. , One way of overcoming this problem is by means of hierarchical zeolites, which contain both the subnanometer micropores as well as mesopores (>2 nm) in the same particle. , The introduction of mesopores improves accessibility of reactants to catalytic sites, leading to higher activity and capability for processing molecules that are larger than the micropores, as well as an increased catalyst lifetime by providing faster transport paths for removal of products and byproducts. , …”

Section: Introductionmentioning

confidence: 99%

Hierarchical Ga-MFI Catalysts for Propane Dehydrogenation

Kim

Choi

et al. 2017

Chem. Mater.

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We report the synthesis, characterization, and enhanced propane dehydrogenation properties of hierarchical Ga-MFI zeolite catalysts synthesized by two different methods: (i) repetitive branching and (ii) utilization of a long chain alkyl SDA. Structural, compositional, and morphological characterizations confirm that the Ga-MFI catalyst materials have hierarchical structures including micropores and mesopores in a single particle and show that Si/Ga ratios comparable to bulk Ga-MFI catalysts can be obtained. Acid site analysis using NH 3 -TPD and pyridine adsorption followed by in situ IR spectroscopy allowed quantification of the number and types of acid sites present and show that the hierarchical catalysts have considerably higher Lewis acid site concentrations than the bulk catalysts. The hierarchical Ga-MFI catalysts show superior PDH performance (at 600 °C) compared to bulk Ga-MFI catalysts. Propane conversion rates are increased 2−6-fold and propylene selectivities are 10−100% higher. We also examine the effects of synthesis variationssuch as addition of 3-mercaptopropyltrimethoxysilane during synthesis and H + ion-exchangeand find that both these steps have a beneficial effect on PDH properties. Calculations suggest that PDH in both the bulk and the hierarchical Ga-MFI is not diffusion-limited. Therefore, the superior performance of hierarchical Ga-MFI is due to intrinsically higher activity and selectivity. Potential reasons for this behavior are outlined. The present findings showing enhancement of PDH in hierarchical Ga-MFI catalysts suggests that the utility of the hierarchical zeolites is not limited to diffusion-limited reactions involving large, bulky molecules and that they may be useful in more diverse applications involving gas-phase reactions with small molecules.

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“…These results can be explained with the following considerations. First, the super diffusibility of the shortened channel in one dimension of the Zn-SH-HZSM-5 crystal significantly reduced the retention time of light aromatics in micropores and effectively restrained their further evolution to form large-size coke molecules. ,,− ,, Second, the shortened micropores were also beneficial to a migration behavior that some coke molecules formed inside the channel diffuse out with the help of the stretching vibration of both ZSM-5 framework and coke molecules. ,,, Moreover, the higher external surface area and the increased mesopores caused by the stacking of nanosheet grains also allow external surface to accommodate more coke species (especially including the coke molecules diffusing out from micropores). ,,− These phenomena effectively prevent the blockage of pore mouths and channels caused by coke deposition, allowing Zn-SH-HZSM-5 to maintain a good catalytic stability even in a 100 h on-stream MTA reaction. Of course, it is clear that the fast deactivation of Zn-C-HZSM-5 is mainly due to the acidic invalidation entailed by the rapid blockage of pore mouths and channels, caused by both the higher coke deposition rate inside the channel and its weak capability in accommodating coke.…”

Section: Resultsmentioning

confidence: 99%

High-Efficiency Conversion of Methanol to BTX Aromatics Over a Zn-Modified Nanosheet-HZSM-5 Zeolite

Gong

Fang

Xie

et al. 2021

Ind. Eng. Chem. Res.

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A Zn-modified nanosheet-HZSM-5 zeolite (Zn-SH-HZSM-5) was prepared and tested as a catalyst in the methanol-to-aromatics (MTA) reaction. First, both an effective suppression of C9+ aromatics formation and a significantly enhanced yield of benzene, toluene, and xylene (BTX) aromatics were achieved by reasonably controlling the reactive pathways in this catalytic reaction system. Further alkylation of BTX aromatics to form C9+ byproducts was effectively limited by the significantly reduced retention time of BTX molecules in the micropore system, with a significantly shortened diffusion-reaction path. Furthermore, the conversion of methanol to BTX was significantly improved by introducing new surface Zn-Lewis acid sites, achieving a synergistic catalysis with Brönsted acid sites. Second, this catalyst also exhibited strong capabilities both to limit the formation and deposition of large-size coke molecules, thanks to its shortened diffusion-reaction path, and to accommodate carbon, due to the high external surface area and considerable stacking mesopores. As a result, our Zn-SH-HZSM-5 catalyst demonstrated good stability in a 100 h on-stream reaction, providing a BTX yield higher than 54.5%, with a C9+ aromatic byproduct formation lower than 5.1%. The present work may provide a promising way for developing an elegant catalyst for a more sustainable MTA process.

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The synthesis of new coke‐resistant support and its application in propane dehydrogenation to propene

Cited by 17 publications

References 55 publications

Coke Deposition on Pt-Based Catalysts in Propane Direct Dehydrogenation: Kinetics, Suppression, and Elimination

Coke Deposition on Pt-Based Catalysts in Propane Direct Dehydrogenation: Kinetics, Suppression, and Elimination

Hierarchical Ga-MFI Catalysts for Propane Dehydrogenation

High-Efficiency Conversion of Methanol to BTX Aromatics Over a Zn-Modified Nanosheet-HZSM-5 Zeolite

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