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Molecular modelling and experimental studies on steam gasification of low-rank coals catalysed by iron species

Paper ID Volume ID Publish Year Pages File Format Full-Text
43064 45953 2008 14 PDF Available
Title
Molecular modelling and experimental studies on steam gasification of low-rank coals catalysed by iron species
Abstract

Pyrolysis and catalytic steam gasification of brown coal containing iron hydroxyl complexes have been investigated experimentally and with semi-empirical and density functional theory molecular modelling. Pyrolysis yielded mainly CO2, CO, and reduced iron species. Catalytic steam gasification at 900 °C after 15 min, consumed 20 wt.% additional char and a higher than expected yield of H2 due to post-gasification reactions; inorganic and organic oxygen in char increased compared to pyrolysis. Apparent turnover numbers for catalytic gasification were 12–22 mole of carbon per mole of iron. The distribution of iron species in brown coal indicated small iron clusters are likely to form on heating; pyrolysis was thus modelled using molecules of char with [Fe3], [Fe5] and [Fe3O], and the active site for gasification was shown to be [Fe–C]. The mechanism of catalytic gasification involved H2O chemi-adsorbed on [Fe–C], formation of the [Fe ← OH2] coordination bond, with H2 produced via iron hydride complexes. Formation of CO was via oxygen insertion into [Fe–C] to form [Fe–O–C] that decomposed into CO and another [Fe–C] site. Lower activation barriers were obtained for concerted chemistry involving iron-hydrides. Active sites in char were accessible to H2O as pores had developed around iron species; large sized iron species were not catalytically active but caused large pores to form in char.

Graphical abstractCatalytic steam gasification of brown coal containing iron species at 900 °C gave an apparent turn-over of 12–22 mole C/mole Fe, and high H2 yield. The molecular mechanism was H2O sticking on [Fe–C] to form the coordination bond [Fe ← OH2], hydrogen abstraction and iron hydride to yield H2, and oxygen insertion into [Fe–C], followed by decomposition of [Fe–O–C] into [Fe–C] and CO. Figure optionsDownload full-size imageDownload as PowerPoint slide

Keywords
Steam gasification; Brown coal; Iron catalyst; Molecular models
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Molecular modelling and experimental studies on steam gasification of low-rank coals catalysed by iron species
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 340, Issue 1, 15 May 2008, Pages 105–118
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us