N{sub 2}O decomposition over manganese oxides
- Pennsylvania State Univ., University Park, PA (United States)
The catalytic decomposition of N{sub 2}O was studied over four different oxides of manganese-MnO, Mn{sub 3}O{sub 4}, Mn{sub 2}O{sub 3}, and MnO{sub 2}. The respective specific activities were 6.3 x 10{sup {minus}4}, 2.5 x 10{sup {minus}3}, 4.8 x 10{sup {minus}3}, and 8.1 x 10{sup {minus}4} {mu}mol/s{center_dot}m{sup 2} at 623 K and 0.066 atm of N{sub 2}O. Apparent activation energies fell between 19 and 27 kcal/mol, and the reaction orders with respect to N{sub 2}O were between 0.74 and 0.89. XRD patterns showed that pretreatment at 773 K under He converted MnO{sub 2} into Mn{sub 2}O{sub 3}, which gave a specific activity similar to that of the original Mn{sub 2}O{sub 3} sample; therefore, MnO{sub 2} was pretreated under pure oxygen at 645 K which gave a specific activity similar to that of the original Mn{sub 2}O{sub 3}, which gave a specific activity similar to that of the original Mn{sub 2}O{sub 3} sample; therefore, MnO{sub 2} was pretreated under pure oxygen at 645 K prior to reaction to retain the bulk MnO{sub 2} phase. On the other hand, MnO was oxidized to Mn{sub 3}O{sub 4} during the course of N{sub 2}O decomposition. Thus Mn{sub 2}O{sub 3} is the phase associated with the highest catalytic activity. A detailed kinetic study with the most active Mn{sub 2}O{sub 3} sample found that the reaction order at 648 K with respect to N{sub 2}O was near 0.8 over a wide pressure range, and the reaction rate was retarded by oxygen. The experimental data fit a simple Langmuir-Hinshelwood model well and both kinetic and thermodynamic parameters could be determined. The activation energy for the rate determining step-dissociation of adsorbed N{sub 2}O into N{sub 2}(g) and adsorbed oxygen-was 31 kcal/mol. 46 refs., 8 figs., 4 tabs.
- OSTI ID:
- 471622
- Journal Information:
- Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 1 Vol. 161; ISSN 0021-9517; ISSN JCTLA5
- Country of Publication:
- United States
- Language:
- English
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