Kinetics of the catalytic cracking of naphtha over ZSM-5 zeolite: effect of reduced crystal size on the reaction of naphthenes

Konno, Hiroki; Ohnaka, Ryota; Nishimura, Jun-ichi; Tago, Teruoki; Nakasaka, Yuta; Masuda, Toshio

doi:10.1039/c4cy00733f

Cited by 66 publications

(33 citation statements)

References 44 publications

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“…The enhanced activity, selectivity, and stability of hierarchical zeolites have often been attributed to reduced transport limitations and increased accessibility to active sites as a result of added meso‐ and macropores. However, despite the significant effort devoted to the design of new hierarchical zeolites, limited progress has been achieved for quantitatively establishing the link between the observed performance and the hierarchical structure . Such quantitative connection between the structural characteristics and the catalytic behavior could lead to the rational design of improved catalysts.…”

Section: Introductionmentioning

confidence: 99%

A quantitative study of the structure–activity relationship in hierarchical zeolites using liquid‐phase reactions

Abdelrahman

Ahn

et al. 2019

AIChE Journal

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Instructions for contributors Inside back coverCover illustration. Hierarchical zeolites made of intergrown nanosheets offer short diffusion lengths allowing for catalytic reactions to proceed in the zeolite micropores in the absence of diffusion limitations. At the same time, catalysis of desirable or undesirable reactions can take place in the mesopores. Using a model reaction and by systematic variation of nanosheet thickness with nanometer (single-unit-cell) precision, it is demonstrated that reaction-diffusion in micro-/meso-porous zeolites can be quantitatively analyzed by mathematical modelling, and finetuned towards a desirable product distribution. Images courtesy of Dandan

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Section: Introductionmentioning

confidence: 99%

A quantitative study of the structure–activity relationship in hierarchical zeolites using liquid‐phase reactions

Abdelrahman

Ahn

et al. 2019

AIChE Journal

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“…In recent years, catalytic cracking of naphtha into light alkenes has been attracting extensive attention owing to its advantages in product control and energy conservation . According to the reported catalyst candidates, ZSM‐5, containing abundant protonic sites, has been considered as one of the most promising ones for this process . However, the catalytic applications of ZSM‐5 zeolites are limited by mass transport in the microporous network if bulky molecules are involved in the reaction .…”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3][4][5][6] According to the reported catalyst candidates, ZSM-5, containing abundant protonic sites, has been considered as one of the most promising ones for this process. [7,8] However,t he catalytic applications of ZSM-5 zeolitesa re limited by mass transport in the microporous network if bulky molecules are involved in the reaction. [9][10][11][12][13] In this regard,t he introduction of mesopores into microporous zeolites to obtain hierarchical ones,p ossessing the catalytic features of microporosity andt he improved mass transport consequence of mesoporosity, [14][15][16][17][18][19][20] would be an optimal choice for better performance.…”

Section: Introductionmentioning

confidence: 99%

The Role of External Acidity of Hierarchical ZSM‐5 Zeolites in n‐Heptane Catalytic Cracking

et al. 2018

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The hierarchical ZSM‐5 zeolite, which contains mesopores in addition to intrinsic micropores, is expected to enhance the bulky molecular diffusion and accessibility of acid sites. These sites, distributed in the internal surface (micropore) or external environment (including external surface and mesopore walls), play different roles in chemical reactions. To explore the effect of internal/external acidity on the reaction, in this study, a series of hierarchical ZSM‐5 zeolites with similar pore structures but different external acid properties were synthesized. Tartaric acid was employed to poison the acidic sites in the external environment selectively and extract Al from the framework. The catalytic cracking of n‐heptane (the main compound of naphtha) was chosen as a model reaction. The results show that elimination of external active sites tends to reduce the coke formation. The more external acid sites are selectively eliminated, the better catalytic performance can be achieved because of suppressing the bimolecular reactions of ethylene and propylene.

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“…The kinetics of the catalytic cracking of the (model) naphtha compounds cyclohexane, methylcyclohexane and n-heptane over ZSM-5 has been studied by Konno et al 52 The catalytic cracking was found to follow first-order kinetics with respect to the alkane concentrations and the activation energies for cyclohexane, methylcyclohexane and n-hexane cracking over nano-ZSM-5 (crystal size = 100 nm) were determined to be 119, 116 and 126 kJ mol À1 , respectively, which are significantly higher compared to the conventional catalyst (macro-ZSM-5; crystal size = 2 mm). In order to elucidate the rate-limiting step in the cracking process, the Thiele modulus and the effectiveness factor were determined.…”

Section: Catalytic Crackingmentioning

confidence: 99%

Catalytic test reactions for the evaluation of hierarchical zeolites

2016

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Catalytic test reactions for the evaluation of hierarchical zeolitesStudies on the synthesis, characterization and catalytic performance of hierarchical zeolites and related porous materials are currently revitalizing the mature field of zeolite research. This review discusses the challenges in evaluating the catalytic performance of a hierarchical zeolite catalyst compared to its parent zeolite. zeolites and the facilitated access and transport in the additional meso-or macropore system. In this tutorial review, we discuss several test reactions that have been explored to show the benefit of the hierarchical pore system with respect to their suitability to prove the positive effects of hierarchical porous zeolites. It is important to note that positive effects on activity, stability and less frequently selectivity observed for hierarchically structured catalysts not necessarily are only a consequence of the additional meso-or macropores but also the number, strength and location of active sites as well as defects and impurities. With regard to these aspects, the test reaction has to be chosen carefully and potential changes in the chemistry of the catalyst have to be considered as well. In addition to the determination of conversion, yield and selectivity, we will show that the calculation of the activation energy and the determination of the Thiele modulus and the effectiveness factor are good indicators of the presence or absence of diffusion limitations in hierarchical zeolites compared to their parent materials. Key learning pointsHierarchical zeolites are an emerging technology in the mature field of industrial catalysts. Several test reactions are suggested to prove the advantage of their hierarchical structure. In addition to an increase in activity and selectivity suppression of coke formation is often observed. Concept of the Thiele modulus and the effectiveness factor is required to judge the presence of diffusion limitations in hierarchical catalysts.

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Kinetics of the catalytic cracking of naphtha over ZSM-5 zeolite: effect of reduced crystal size on the reaction of naphthenes

Cited by 66 publications

References 44 publications

A quantitative study of the structure–activity relationship in hierarchical zeolites using liquid‐phase reactions

A quantitative study of the structure–activity relationship in hierarchical zeolites using liquid‐phase reactions

The Role of External Acidity of Hierarchical ZSM‐5 Zeolites in n‐Heptane Catalytic Cracking

Catalytic test reactions for the evaluation of hierarchical zeolites

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