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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todo:paper_00027863_v118_n42_p10236_Amorebieta2023-10-03T13:53:27Z Kinetics and mechanism of the heterogeneous oxidation of ethane and ethylene on samarium(III) oxide Amorebieta, V.T. Colussi, A.J. 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. JOUR info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar 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 Amorebieta, V.T. Colussi, A.J. 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. |
| format |
JOUR |
| author |
Amorebieta, V.T. Colussi, A.J. |
| author_facet |
Amorebieta, V.T. Colussi, A.J. |
| author_sort |
Amorebieta, V.T. |
| 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 |
| url |
http://hdl.handle.net/20.500.12110/paper_00027863_v118_n42_p10236_Amorebieta |
| work_keys_str_mv |
AT amorebietavt kineticsandmechanismoftheheterogeneousoxidationofethaneandethyleneonsamariumiiioxide AT colussiaj kineticsandmechanismoftheheterogeneousoxidationofethaneandethyleneonsamariumiiioxide |
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1807317681276190720 |