Catalytic partial oxidation of methane and isotopic oxygen exchange reactions over 18O labeled Rh/Gadolinium doped ceria
✍ Scribed by Maria D. Salazar-Villalpando; Adam C. Miller
- Publisher
- Elsevier Science
- Year
- 2011
- Tongue
- English
- Weight
- 637 KB
- Volume
- 36
- Category
- Article
- ISSN
- 0360-3199
No coin nor oath required. For personal study only.
✦ Synopsis
Oxygen isotopic exchange
Doped ceria
Isotopic exchange
Pulse experiments a b s t r a c t 18 O labeled catalysts, Rh/(Ce 0.91 Gd 0.09 )O 2Àx (Rh/GDC10) and Rh/g-Al 2 O 3 (Rh/ALU) were used to study the catalytic partial oxidation of methane (CPOM) and oxygen isotopic exchange reactions. During the CPOM tests, higher C 18 O than C 16 O concentrations were observed over 18 O labeled Rh/GDC10 than Rh/ALU, which is explained by the higher oxygen storage capacity and oxygen mobility of the former catalyst. Similarly, Rh/GDC10 showed higher oxygen exchange rates than Rh/ALU during the isotopic exchange experiments. The oxygen exchange between the gas phase and the solid is limited by the oxygen mobility in/ on the catalyst. This catalytic behavior is due to the fact that ceria has two stable oxidation states, Ce 3þ and Ce 4þ and the addition of Gd 3þ to ceria lattice enhanced the oxygen mobility by the creation of oxygen vacancies. These higher oxygen exchange rates also correlate to higher concentrations of C 18 O than C 16 O during the CPOM experiments. Pulse experiments suggest that the reaction mechanism for the CPOM on Rh/GDC10 occurred through a mixed (direct and indirect) mechanism. The direct mechanism assumes that H 2 and CO are primary reaction products formed in the oxidation zone at the catalyst entrance. Thus, CO formed from the reaction between lattice oxygen in Rh/GDC10 and adsorbed atomic carbon. CO 2 is formed through an indirect mechanism, where CH 4 reacts with O 2 to form CO 2 and H 2 O. CO forms through the reactions between 1) CO 2 and CH 4 and 2) CH 4 and H 2 O.