Characterization of Coke on Zeolites

Bauer, Frank; Karge, Hellmut G.

doi:10.1007/3829_005

Cited by 74 publications

(70 citation statements)

References 278 publications

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“…By relating these peaks to the coke characterisitics, the peaks located at lower temperature (around 430-480 ) were assigned to slightly developed coke, whereas the peaks located around 480-560 corresponded to more condensed coke, with a lower H/C ratio 28) . These cokes match types I and II in Bauer and Karge's classification 29) , according to their degree of development towards polyaromatic structures. To compare the results obtained in Fig.…”

Section: Effect Of Catalyst Regenerationsupporting

confidence: 51%

Evaluation of PtPd-modified Zeolite Catalysts (ZSM-5, Beta, USY) for Pyrolysis of Jatropha Waste

和久

Khongwong

Larpkattaworn

et al. 2014

J. Jpn. Petrol. Inst.

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Fast pyrolysis with three typical modified zeolite catalysts was evaluated to produce bio-oil from Jatropha waste. Jatropha waste was pyrolyzed in a stainless-steel reactor at 600 under N2 gas flow. The aromatic hydrocarbon selectivity in the bio-oil was in the order: PtPd/ZSM(30) (73.7 %) PtPd/Beta(22.5) (68.6 %) PtPd/USY(20) (48.7 %), where the weight ratio of Jatropha/catalyst was 1. In addition, catalyst regeneration was carried out to study the catalyst efficiency. The analysis of fresh and regenerated catalysts by XRD, NH3-TPD, and TG/DTG, as well as product selectivity and surface properties showed that coke deposition and removal were associated with the zeolite structure and surface acid property. Due to pore size regulation, H-ZSM-5 with 10-membered ring (10 MR) could promote the pyrolysis reaction on the outside surface rather than in the inside channels. In USY zeolite with 12 MR, the reaction could occur inside the channels, but the moderate acid nature resulted in only slightly developed coke formation, which could be removed, at least partly, after regeneration. In beta zeolite with 12 MR, the total amount of surface acidity was more than twice that of USY, which undergoes more condensed coke formation, and was more difficult to remove by regeneration than the coke over USY. Thus, under these pyrolysis conditions, PtPd/ZSM(30) seems to be a better candidate for pyrolysis of Jatropha waste compared to PtPd/Beta(22.5) and PtPd/USY(20).

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Section: Effect Of Catalyst Regenerationsupporting

confidence: 51%

Evaluation of PtPd-modified Zeolite Catalysts (ZSM-5, Beta, USY) for Pyrolysis of Jatropha Waste

和久

Khongwong

Larpkattaworn

et al. 2014

J. Jpn. Petrol. Inst.

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“…Considering the reaction pathways of aromatization and coke formation [3,12,13], the slow coke deposition confirmed by the low absorption intensity indicates slow dehydration or cracking of paraffin to smaller olefin within H-ZSM-5 crystals. Although one can assume that the transformation of paraffin to olefin is fast and olefinic or polyolefinic coke precursor (coke type I) may be formed in the pore, it is not plausible because these polyenylic cations are easily transformed to coke type II (typically small aromatic carbocations and bulky polyaromatics) at high temperature [3].…”

Section: In-situ Optical Microspectroscopymentioning

confidence: 98%

“…Although one can assume that the transformation of paraffin to olefin is fast and olefinic or polyolefinic coke precursor (coke type I) may be formed in the pore, it is not plausible because these polyenylic cations are easily transformed to coke type II (typically small aromatic carbocations and bulky polyaromatics) at high temperature [3]. In addition, it is difficult to confirm the existence of the light cokes due to a limitation in the detection range of optical microscopy (400~700 nm).…”

Section: In-situ Optical Microspectroscopymentioning

confidence: 99%

“…The absorption band around 410 nm is assigned to the π -π* transition of lowcondensed aromatics, e.g., diphenyl and polyalkylaromatics, while the band around 550 nm is responsible for the optical absorption of extended conjugated aromatic species such as polyphenyl and polyaromatic cations [3,11]. The broad background absorption across the optical region suggests the relevant growth of condensed aromatic species to larger delocalized polyaromatics with graphitic nature [14].…”

Section: In-situ Optical Microspectroscopymentioning

confidence: 99%

“…However, the nature of the carbonaceous species is still a matter of debate and the subject of many investigations. Although various characterization techniques, e.g., infrared (IR), ultraviolet and visible spectroscopy (UV-Vis), electron spin resonance (ESR), nuclear magnetic resonance (NMR), and X-ray excited photoelectron spectroscopy (XPS) have been applied to elucidate the nature of coke [3], the investigation of coke formation under reaction conditions is still limited. In this regard, it is natural that in-situ characterization technique has drawn attention with hope that the versatile method adopting a broad range of analytical techniques offers new insight into the investigation of active site and the related reaction mechanism in a working catalyst [4,5].…”

Section: Introductionmentioning

confidence: 99%

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Investigation of Coke Formation on H-ZSM-5 Catalyst During Aromatization of C5 Paraffin and Olefin Using Optical and Fluorescence Microscopy

Chung¹

2013

Clean Technology

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: Space-and time-resolved in-situ optical and fluorescence microspectroscopy techniques have been applied to investigate the coke formation during aromatization of C5 paraffin and olefin over H-ZSM-5 crystal. In-situ UV/vis absorption measurement offers space-and time-resolved information for the coke formation. Different coking trends have been observed with respect to the location of a crystal as well as the reactant types. From in-situ confocal fluorescence microspectroscopy study, it is revealed that the concentration of certain species photo-excited at 488 nm becomes high at the central region, whereas the compounds emitting fluorescence by 561 nm laser move towards the boundary region of the crystal. The different fluorescence patterns obtained varying excitation lasers suggest the existence of distinct fluorescence emitting species having different degree of coke growth.

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Unambiguous Observation of Electron Transfer from a Zeolite Framework to Organic Molecules

Li¹,

Zhou²,

Li³

et al. 2009

Angewandte Chemie

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Zeolites are crystalline aluminosilicates with microporous structures. These materials have been widely used in the field of heterogeneous catalysis. [1] In most catalytic reactions involving a zeolite catalyst, the acidic sites of the zeolite play a pivotal role; hence, much attention has been paid to the nature of the acidic sites and the interactions of these sites with organic molecules.[2] The oxidation states of the framework atoms (Si, Al, and O) are thought to remain unchanged during acid-catalyzed reaction processes. However, electron loss from the zeolite framework may occur when a zeolite is subjected to a high temperature [3] or high-energy g-ray (or Xray) irradiation.[4] Electron transfer between zeolites and occluded molecules has also been proposed previously.[5] The electron-donating ability of the zeolite framework [6] and the ability of zeolites to generate organic radical cations [7] have been established by several research groups. Although it is recognized that electrons may be transferred between zeolites and occluded guest species, the nature of the electron donor/ acceptor in zeolites has not yet been elucidated clearly, and the whereabouts of the electrons/holes formed in the electron-transfer process has been under intense debate. [5,7] In particular, when zeolites act as electron donors, only occluded molecules that accept electrons from zeolites can be observed to change, whereas a difference in the zeolite framework can hardly be detected after the electron-transfer process.Herein, we demonstrate that aluminosilicate zeolites in the protonated form lose their framework electrons when alkyl bromides are introduced into the pores of the zeolites. The loss of the framework electrons results in paramagnetic centers, which function as single-electron redox sites and can be detected by electron paramagnetic resonance (EPR) spectroscopy. More importantly, this process of electron transfer accompanies the acid-catalyzed reaction between zeolites and alkyl bromides; thus, framework electron transfer of acidic zeolites should be considered to be partially responsible for the formation of some of the organic products during acid-catalyzed reactions involving zeolites.A mixture of the dehydrated zeolite HY (protonated zeolite Y with a framework Si/Al ratio of 2.46; see Figure S2 in the Supporting Information) and ethyl bromide was stirred and heated at reflux in an airtight vessel at 50 8C under argon for 24 h. We refer to this process as the "liquid-solid" (L-S) reaction. After the L-S reaction, the HY material (designated Y-R) was orange in liquid ethyl bromide and turned light pink upon the removal of the liquid alkyl bromide with a liquid-nitrogen trap (see Figure S3 in the Supporting Information). The liquid ethyl bromide remained colorless throughout the whole reaction process, both before and after trapping; in the gas phase of the product of the catalytic reaction, a small quantity of ethane was detected, besides ethene and hydrogen bromide. Figure 1 a shows the EPR spectrum of the HY zeo...

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Characterization of Coke on Zeolites

Cited by 74 publications

References 278 publications

Evaluation of PtPd-modified Zeolite Catalysts (ZSM-5, Beta, USY) for Pyrolysis of Jatropha Waste

Evaluation of PtPd-modified Zeolite Catalysts (ZSM-5, Beta, USY) for Pyrolysis of Jatropha Waste

Investigation of Coke Formation on H-ZSM-5 Catalyst During Aromatization of C5 Paraffin and Olefin Using Optical and Fluorescence Microscopy

Unambiguous Observation of Electron Transfer from a Zeolite Framework to Organic Molecules

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