The Haag–Dessau mechanism of protolytic cracking of alkanes

Kotrel, S.; Knözinger, Helmut; Gates, Bruce C.

doi:10.1016/s1387-1811(99)00204-8

Cited by 279 publications

(191 citation statements)

References 39 publications

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“…Upon pyridine adsorption at room temperature and outgassing at 150°C, absorption bands associated with the chemisorbed pyridine were observed at 1547, 1491, and 1454 cm )1 . According to previous reports on the IR studies in the pyridine chemisorption [20,21], the pyridine band at 1547 cm )1 is assignable to pyridinum ions and the band at 1454 cm )1 to Lewis acid-coordinated pyridine, respectively. The band at 1491 cm )1 consists of bands due to the Bro¨nsted and Lewis sites.…”

Section: Reaction Performance Of Vk/zsm-5 Catalysts In Butene Catalytmentioning

confidence: 73%

Butene Catalytic Cracking to Propene and Ethene over Potassium Modified ZSM-5 Catalysts

et al. 2005

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Catalytic cracking of butene over potassium modified ZSM-5 catalysts was carried out in a fixed-bed microreactor. By increasing the K loading on the ZSM-5, butene conversion and ethene selectivity decreased almost linearly, while propene selectivity increased first, then passed through a maximum (about 50% selectivity) with the addition of ca. 0.7-1.0% K, and then decreased slowly with further increasing of the K loading. The reaction conditions were 620°C, WHSV 3.5 h )1 , 0.1 MPa 1-butene partial pressure and 1 h of time on stream. Both by potassium modification of the ZSM-5 zeolite and by N 2 addition in the butene feed could enhance the selectivity towards propene effectively, but the catalyst stability did not show any improvement. On the other hand, addition of water to the butene feed could not only increase the butene conversion, but also improve the stability of the 0.7%K/ZSM-5 catalyst due to the effective removal of the coke formed, as demonstrated by the TPO spectra. XRD results indicated that the ZSM-5 structure of the 0.07% K/ZSM-5 catalyst was not destroyed even under this serious condition of adding water at 620°C.

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Section: Reaction Performance Of Vk/zsm-5 Catalysts In Butene Catalytmentioning

confidence: 73%

Butene Catalytic Cracking to Propene and Ethene over Potassium Modified ZSM-5 Catalysts

et al. 2005

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“…As a result, the monomolecular and bimolecular cracking reactions [82][83][84][85][86][87] (Figure 12) occurred under the experimental conditions and the consecutive reaction of light olefins proceeded to form aromatics. Accordingly, the suppression of aromatic formation is indispensable to an increase in olefin yields, as for the ATO reaction discussed below.…”

Section: N-hexane Cracking Over Nano-sized Zeolitementioning

confidence: 99%

Size-Controlled Synthesis of Nano-Zeolites and Their Application to Light Olefin Synthesis

et al. 2012

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For the application of zeolites as heterogeneous catalysts, low diffusion resistance for hydrocarbons within the micropore is essential for improving product selectivity and catalyst lifetime. This problem has been overcome by reducing the crystal size. This review introduces size-controlled preparation of nano-sized zeolites via hydrothermal synthesis in water/surfactant/organic solvent (emulsion method) and their application to heterogeneous catalysts. The ionicity of the hydrophilic group in surfactant molecules and the concentration of the Si source affected the crystallinity and morphology of zeolites prepared using the emulsion method. When using a non-ionic surfactant, mono-dispersed silicalite-1 nanocrystals approximately 60 nm in diameter were successfully prepared. Nano-and macro-ZSM-5 zeolites with crystal sizes of approximately 150-200 nm and 1.5 µm, respectively, were prepared and applied to n-hexane cracking and acetone-to-olefin reactions to investigate the effect of zeolite crystal size on catalytic stability and light olefin yield. Application of nano-zeolite to light olefin production was effective in achieving faster mass transfer of hydrocarbon molecules within the micropore, which led to improvements in olefin yields and catalyst lifetime.

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“…1). At low conversions the formation of cracked products on solid acids such as zeolites can be explained (in simplified terms) by the formation of carbonium ion intermediates (35,36) resulting from protonation of the alkane by Brønsted acid centers. The decomposition of the carbonium ion leads either to a carbenium ion and H 2 or to a carbenium ion and an alkene and ultimately to cracked products.…”

Section: Discussionmentioning

confidence: 99%

“…In contrast to the conversion in the presence of SZ, in our work no hexane or other longer-chain alkanes were detected in the product, which argues against the bimolecular mechanism. To explain the fact that butanes and hexanes were not formed in equimolar amounts on SZ as predicted by the simple bimolecular mechanism, secondary cracking of hexanes was postulated (36). The higher reaction temperature employed with WZ could lead to smaller cracking products, which are thermodynamically favored over the longer-chain products, and the absence of hexane might be explained by quantitative cracking to give products with carbon numbers less than six.…”

Section: Discussionmentioning

confidence: 99%

Reaction pathways in n-pentane conversion catalyzed by tungstated zirconia: effects of platinum in the catalyst and hydrogen in the feed

Kuba

Lukinskas

Ahmad

et al. 2003

Journal of Catalysis

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The catalytic isomerization of n-pentane catalyzed by tungsted zirconia (WZ) was investigated to elucidate the effects of H2 in the feed and platinum in the catalyst. In the reaction catalyzed by WZ with or without platinum, when no H2 was present, a complex reaction network was observed, associated with organic deposits on the catalyst, giving mainly cracked products. The alkane is inferred to be activated in a redox step forming W 5+ on the catalyst and unsaturated intermediates that react to form polyalkenylic surface species, which were detected by in-situ UVvisible spectroscopy. Promotion of WZ with platinum dramatically improved the catalytic activity and the isomerization selectivity in n-pentane conversion. The improvement was only marginal in the absence of H2, but it became substantial in the presence of H2, with the conversion increasing from 3 to 55% for the platinum-promoted catalyst, which underwent only little deactivation. The selectivity for isopentane was about 95% at 523 K. The results indicate that the complex reaction network operative with the WZ catalyst is suppressed on the platinum-containing catalysts in the presence of H2. A fast and selective monomolecular isomerization reaction takes over in this case. The adsorbed unsaturated C5 intermediates are rapidly desorbed via hydrogenation on the reduced tungstate surface. This rapid desorption minimizes the formation of highermolecular-weight organic species such as polyalkenyls that are necessary for the complex reaction path observed with the unpromoted catalyst. The observed side products are interpreted not as cracking products accompanying the acid-catalyzed isomerization reaction but instead as hydrogenolysis products formed directly on the platinum particles.

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The Haag–Dessau mechanism of protolytic cracking of alkanes

Cited by 279 publications

References 39 publications

Butene Catalytic Cracking to Propene and Ethene over Potassium Modified ZSM-5 Catalysts

Butene Catalytic Cracking to Propene and Ethene over Potassium Modified ZSM-5 Catalysts

Size-Controlled Synthesis of Nano-Zeolites and Their Application to Light Olefin Synthesis

Reaction pathways in n-pentane conversion catalyzed by tungstated zirconia: effects of platinum in the catalyst and hydrogen in the feed

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