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Oxidative dehydrogenation of light alkanes on metal oxide catalysts

Record Type:	Electronic resources : Monograph/item
Title/Author:	Oxidative dehydrogenation of light alkanes on metal oxide catalysts
Author:	Argyle, Morris Dee.
Description:	146 p.
Notes:	Chairs: Alexis T. Bell; Enrique Iglesia.
Notes:	Source: Dissertation Abstracts International, Volume: 65-02, Section: B, page: 0877.
Contained By:	Dissertation Abstracts International65-02B.
Subject:	Engineering, Chemical.
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3121387
ISBN:	0496687387

Oxidative dehydrogenation of light alkanes on metal oxide catalysts
Argyle, Morris Dee.

Oxidative dehydrogenation of light alkanes on metal oxide catalysts [electronic resource] - 146 p.

Chairs: Alexis T. Bell; Enrique Iglesia.

Thesis (Ph.D.)--University of California, Berkeley, 2003.

Alkane oxidative dehydrogenation (ODH) on supported vanadia catalysts is a thermodynamically-favored alternative to thermal and non-oxidative catalytic alkene production processes. Vanadia surface structures and ODH turnover rates vary with vanadia surface density and with concomitant changes in size and dimensionality of VOx domains on gamma-Al2O3 . Monovanadates, prevalent below &sim;2.3 V/nm2, lead to low turnover rates compared to polyvanadate domains, which become prevalent >7.5 V/nm2. Three-dimensional V2O5 crystallites, present at higher V surface densities, have similar ODH rates (per surface V) as polyvanadates, but subsurface V-atoms become inaccessible for reaction. Primary alkene selectivities are &sim;80% for ethane and propane ODH; they vary only slightly with vanadia surface density, reactant concentrations, and reaction temperature. The ratio of alkene combustion and alkene formation rate constants is large (>10) and leads to low alkene yields except at low vanadia surface densities (<1.4 V/nm2) and high temperature (>743 K); these ratios increase with increasing vanadia surface density and decrease with increasing reaction temperature.

ISBN: 0496687387Subjects--Topical Terms:

226989
Engineering, Chemical.

Oxidative dehydrogenation of light alkanes on metal oxide catalysts
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245 1 0 $a Oxidative dehydrogenation of light alkanes on metal oxide catalysts $h [electronic resource]
300 $a 146 p.
500 $a Chairs: Alexis T. Bell; Enrique Iglesia.
500 $a Source: Dissertation Abstracts International, Volume: 65-02, Section: B, page: 0877.
502 $a Thesis (Ph.D.)--University of California, Berkeley, 2003.
520 # $a Alkane oxidative dehydrogenation (ODH) on supported vanadia catalysts is a thermodynamically-favored alternative to thermal and non-oxidative catalytic alkene production processes. Vanadia surface structures and ODH turnover rates vary with vanadia surface density and with concomitant changes in size and dimensionality of VOx domains on gamma-Al2O3 . Monovanadates, prevalent below &sim;2.3 V/nm2, lead to low turnover rates compared to polyvanadate domains, which become prevalent >7.5 V/nm2. Three-dimensional V2O5 crystallites, present at higher V surface densities, have similar ODH rates (per surface V) as polyvanadates, but subsurface V-atoms become inaccessible for reaction. Primary alkene selectivities are &sim;80% for ethane and propane ODH; they vary only slightly with vanadia surface density, reactant concentrations, and reaction temperature. The ratio of alkene combustion and alkene formation rate constants is large (>10) and leads to low alkene yields except at low vanadia surface densities (<1.4 V/nm2) and high temperature (>743 K); these ratios increase with increasing vanadia surface density and decrease with increasing reaction temperature.
520 # $a Reduced centers during propane ODH were measured using in situ UV-visible spectroscopy by comparing pre-edge feature intensities during H2 reduction and O2 uptakes during subsequent reoxidation. Average extents of V reduction are low (&sim;0.1 e- /Vactive), confirming that lattice oxygen is the most abundant reactive intermediate; the extent of reduction increases with vanadia surface density. Only 30--40% of reduced centers actively participate in turnovers and undergo redox cycles on turnover timescales.
520 # $a Reduction and reoxidation rate constants and average active site fractions were measured during transient propane ODH using in situ UV-visible spectroscopy. Rate constants, determined as fitting parameters in non-linear models derived from the mechanism modified to account for combustion, show the reoxidation rate constant is 103--105 times larger than that of reduction. The fraction of active sites per surface V-atom is 0.6--0.7 and decreases with increasing vanadia surface density.
520 # $a The ethane ODH rate law derived from a mechanism consisting of a sequence of elementary steps accurately describes experimental rate data. Isotopic labeling experiments showed that C--H bond activation is the kinetically relevant step in which surface oxygen abstract H-atoms from ethane. ODH and combustion reactions occur on similar active sites that are reduced and reoxidized during each turnover.
590 $a School code: 0028.
650 # 0 $a Engineering, Chemical. $3 226989
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710 0 # $a University of California, Berkeley. $3 212474
773 0 # $g 65-02B. $t Dissertation Abstracts International
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790 1 0 $a Bell, Alexis T., $e advisor
790 1 0 $a Iglesia, Enrique, $e advisor
791 $a Ph.D.
792 $a 2003
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