On the remarkable resistance to coke formation of nanometer-sized and hierarchical MFI zeolites during ethanol to hydrocarbons transformation

Lakiss, Louwanda; Ngoye, Francis; Canaff, Christine; Laforge, S.; Pouilloux, Yannick; Qin, Zhengxing; Tarighi, Mehrad; Thomas, Karine; Valtchev, Valentin; Vicente, Aurélie; Pinard, Ludovic; Gilson, Jean‐Pierre; Fernandéz, Christian

doi:10.1016/j.jcat.2014.12.030

Cited by 84 publications

(93 citation statements)

References 43 publications

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“…It has been reported that ethanol transformation to hydrocarbons is more sensitive to changes in the textural properties of zeolites than other model reactions such as methylcyclohexane cracking. 33,48 However, the results are similar to those reported for methanol conversion. During ethanol to hydrocarbon conversion at 623 K and 3 MPa, a carbonaceous material is formed due to unwanted side reactions.…”

Section: View Article Onlinesupporting

confidence: 87%

“…In general, coking occurs mainly due to poisoning and to a much lesser extent due to pore blocking. 33 As visualized in Fig. 7, data obtained so far indicate that the shortening of the diffusion path length by reducing the crystal dimensions (preparation of either nanocrystals or zeolite nanosheets) results in enhanced catalyst lifetime.…”

Section: View Article Onlinementioning

confidence: 89%

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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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Section: View Article Onlinesupporting

confidence: 87%

Section: View Article Onlinementioning

confidence: 89%

Catalytic test reactions for the evaluation of hierarchical zeolites

2016

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“…The most plausible explanation for this phenomenon was the shorter diffusion path in the nanosized sample, which allows a substantial part of the coke to migrate and deposit on the external surface of the crystallites. This statement is based on a previous study that showed that the coke species are deposited on the external surface of nanosized ZSM‐5 crystals, in contrast to the abundant coke formation in the pores of the micron‐sized counterpart . The different nature of the coke formed in the nano‐ and micron‐sized crystals could also contribute to the observed differences in the accessibility at similar coke content.…”

Section: Resultsmentioning

confidence: 99%

Tuning Zeolite Properties for a Highly Efficient Synthesis of Propylene from Methanol

Palčić

Ordomsky

Qin

et al. 2018

Chemistry A European J

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A series of nanosized ZSM-5 samples was synthesized at 170, 150, 120, and 100 °C. Experimental data show that the decrease of crystallization temperature leads to significant changes in zeolite properties. Crystals synthesized at 100 °C exhibit many framework defects with lower acid-site density, strength, and a larger external surface area. The selectivity to light olefins and the propylene-to-ethylene ratio increases as the crystallization temperature decreases. A propylene-to-ethylene ratio of above 6 with the highest selectivity to propylene of 53 % was obtained over ZSM-5 catalyst prepared at 100 °C. The stability of the nanosized zeolite in methanol to olefins (MTO) was also improved compared to the industrial sample with a similar Si/Al ratio. This catalytic performance is a result of the decrease in the acid-site density, strength, and the crystals' size, providing a shorter diffusion path and larger external surface area. The presence of structural defects and a different external surface in the crystals has been shown to play an important role in the MTO catalyst performance.

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“…They also studied the effect of crystal size of ZSM-5 zeolite on the rate-limiting step of the n-hexane cracking using the Thiele modulus, and they concluded that the cracking reaction could be proceed when the crystal size was in nano-scale [102]. Besides, ZSM-5 zeolite with short diffusion length facilitated the transport of BTEX (carbon precursors), thus preventing the formation of carbon deposition, which improved the catalytic stability [99,100,103,104]. The nano-sized ZSM-5 zeolite can be synthesized by hydrothermal method or bead milling method.…”

Section: Nano-sized Zsm-5 Zeolitementioning

confidence: 99%

Strategies to Enhance the Catalytic Performance of ZSM-5 Zeolite in Hydrocarbon Cracking: A Review

Yang

Yan

2017

Catalysts

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ZSM-5 zeolite is widely used in catalytic cracking of hydrocarbon, but the conventional ZSM-5 zeolite deactivates quickly due to its simple microporous and long diffusion pathway. Many studies have been done to overcome these disadvantages recently. In this review, four main approaches for enhancing the catalytic performance, namely synthesis of ZSM-5 zeolite with special morphology, hierarchical ZSM-5 zeolite, nano-sized ZSM-5 zeolite and optimization of acid properties, are discussed. ZSM-5 with special morphology such as hollow, composite and nanosheet structure can effectively increase the diffusion efficiency and accessibility of acid sites, giving high catalytic activity. The accessibility of acid sites and diffusion efficiency can also be enhanced by introducing additional mesopores or macropores. By decreasing the crystal size to nanoscale, the diffusion length can be shortened. The catalytic activity increases and the amount of carbon deposition decreases with the decrease of crystal size. By regulating the acid properties of ZSM-5 with element or compound modification, the overreaction of reactants and formation of carbon deposition could be suppressed, thus enhancing the catalytic activity and light alkene selectivity. Besides, some future needs and perspectives of ZSM-5 with excellent cracking activity are addressed for researchers' consideration.

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On the remarkable resistance to coke formation of nanometer-sized and hierarchical MFI zeolites during ethanol to hydrocarbons transformation

Cited by 84 publications

References 43 publications

Catalytic test reactions for the evaluation of hierarchical zeolites

Catalytic test reactions for the evaluation of hierarchical zeolites

Tuning Zeolite Properties for a Highly Efficient Synthesis of Propylene from Methanol

Strategies to Enhance the Catalytic Performance of ZSM-5 Zeolite in Hydrocarbon Cracking: A Review

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