Kinetics and mechanism of the heterogeneous oxidation of ethane and ethylene on samarium(III) oxide

The rates and products of the purely heterogeneous oxidations of C2H6(g) and C2H4(g) on Sm2O3 in the presence of O2(g) were investigated in a very low-pressure flow reactor by on-line molecular beam mass spectrometry, about 1000 ± 100 K. Ethane is oxidized to ethyl radicals, which undergo unimolecul...

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Detalles Bibliográficos
Publicado: 1996
Materias:
ethane
ethylene
article
catalysis
drug synthesis
oxidation
reaction analysis
thermodynamics
Acceso en línea:https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00027863_v118_n42_p10236_Amorebieta
http://hdl.handle.net/20.500.12110/paper_00027863_v118_n42_p10236_Amorebieta
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Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires
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spelling paper:paper_00027863_v118_n42_p10236_Amorebieta2023-06-08T14:22:35Z Kinetics and mechanism of the heterogeneous oxidation of ethane and ethylene on samarium(III) oxide ethane ethylene article catalysis drug synthesis oxidation reaction analysis thermodynamics The rates and products of the purely heterogeneous oxidations of C2H6(g) and C2H4(g) on Sm2O3 in the presence of O2(g) were investigated in a very low-pressure flow reactor by on-line molecular beam mass spectrometry, about 1000 ± 100 K. Ethane is oxidized to ethyl radicals, which undergo unimolecular decomposition into (C2H4 + H) or further oxidation to CO. C2H4 oxidation leads to CO as initial product, that is subsequently converted into CO2. Steady state rates are proportional to k(i)'([O2]) x [C2H(n)], with k(i)'([O2]) = k(i) x (K(i)[O2])( 1/4 )/{1+(K(i)[O2])( 1/4 )}] (i = 3, 4 for n = 6, 4, respectively), which is consistent with the direct oxidation of hydrocarbons on surface oxygen species in dissociative equilibrium with O2(g). Alternate or simultaneous measurement of the oxidation rates for C2H6, C2H4, and CH4, the latter proportional to k1'[CH4], on the same Sm2O3 sample as function of [O2] and temperature, led to the following expressions: log (k3/k1) = -(0.14 ± 0.30) + (663 ± 300)/T (I), log(k4/k1) = (1.08 ± 0.35) - (646 ± 365)/T (II), log (K1/nM-1) = (2.76 ± 0.46) - (4363 ± 468)/T (III) log (K3/nM-1) = (1.85 ± 0.22) - (4123 ± 260)/T (IV), log(K4/nM-1) = (5.31 ± 0.65) - (6480 ± 647)/T (V) (nM = 10-9 M), that are independent of catalyst mass, active area, or morphology. Equations I-V imply that ethane and ethylene are oxidized faster than methane at all relevant temperatures. Although the activation energies, E4 > E1 > E3, correlate with the corresponding BDE(C-H) energies suggesting a common H-atom abstraction mechanism, the A-factor for the oxidation of ethylene is about tenfold larger. Oxidations occur on distinguishable O(s) species generated by endothermic, exentropic O2 chemisorption involving cooperative participation of the solid. 1996 https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00027863_v118_n42_p10236_Amorebieta http://hdl.handle.net/20.500.12110/paper_00027863_v118_n42_p10236_Amorebieta
institution Universidad de Buenos Aires
institution_str I-28
repository_str R-134
collection Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic ethane
ethylene
article
catalysis
drug synthesis
oxidation
reaction analysis
thermodynamics
spellingShingle ethane
ethylene
article
catalysis
drug synthesis
oxidation
reaction analysis
thermodynamics
Kinetics and mechanism of the heterogeneous oxidation of ethane and ethylene on samarium(III) oxide
topic_facet ethane
ethylene
article
catalysis
drug synthesis
oxidation
reaction analysis
thermodynamics
description The rates and products of the purely heterogeneous oxidations of C2H6(g) and C2H4(g) on Sm2O3 in the presence of O2(g) were investigated in a very low-pressure flow reactor by on-line molecular beam mass spectrometry, about 1000 ± 100 K. Ethane is oxidized to ethyl radicals, which undergo unimolecular decomposition into (C2H4 + H) or further oxidation to CO. C2H4 oxidation leads to CO as initial product, that is subsequently converted into CO2. Steady state rates are proportional to k(i)'([O2]) x [C2H(n)], with k(i)'([O2]) = k(i) x (K(i)[O2])( 1/4 )/{1+(K(i)[O2])( 1/4 )}] (i = 3, 4 for n = 6, 4, respectively), which is consistent with the direct oxidation of hydrocarbons on surface oxygen species in dissociative equilibrium with O2(g). Alternate or simultaneous measurement of the oxidation rates for C2H6, C2H4, and CH4, the latter proportional to k1'[CH4], on the same Sm2O3 sample as function of [O2] and temperature, led to the following expressions: log (k3/k1) = -(0.14 ± 0.30) + (663 ± 300)/T (I), log(k4/k1) = (1.08 ± 0.35) - (646 ± 365)/T (II), log (K1/nM-1) = (2.76 ± 0.46) - (4363 ± 468)/T (III) log (K3/nM-1) = (1.85 ± 0.22) - (4123 ± 260)/T (IV), log(K4/nM-1) = (5.31 ± 0.65) - (6480 ± 647)/T (V) (nM = 10-9 M), that are independent of catalyst mass, active area, or morphology. Equations I-V imply that ethane and ethylene are oxidized faster than methane at all relevant temperatures. Although the activation energies, E4 > E1 > E3, correlate with the corresponding BDE(C-H) energies suggesting a common H-atom abstraction mechanism, the A-factor for the oxidation of ethylene is about tenfold larger. Oxidations occur on distinguishable O(s) species generated by endothermic, exentropic O2 chemisorption involving cooperative participation of the solid.
title Kinetics and mechanism of the heterogeneous oxidation of ethane and ethylene on samarium(III) oxide
title_short Kinetics and mechanism of the heterogeneous oxidation of ethane and ethylene on samarium(III) oxide
title_full Kinetics and mechanism of the heterogeneous oxidation of ethane and ethylene on samarium(III) oxide
title_fullStr Kinetics and mechanism of the heterogeneous oxidation of ethane and ethylene on samarium(III) oxide
title_full_unstemmed Kinetics and mechanism of the heterogeneous oxidation of ethane and ethylene on samarium(III) oxide
title_sort kinetics and mechanism of the heterogeneous oxidation of ethane and ethylene on samarium(iii) oxide
publishDate 1996
url https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00027863_v118_n42_p10236_Amorebieta
http://hdl.handle.net/20.500.12110/paper_00027863_v118_n42_p10236_Amorebieta
_version_ 1768542863456468992

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