(419c) Role Of Lattice Oxygen In The Partial Oxidation Of Methane Over Ceria-Based Catalysts
Ceria-based catalysts were utilized to study the mechanistic aspects of the conversion of methane to syn-gas. Four types of experiments were conducted: partial oxidation of methane (POM) over 18O labeled catalysts, isotopic exchange experiments, POM reaction in the absence of gaseous oxygen and Nuclear reaction analysis. Results showed strong evidence that CO is generated through methane oxidation with surface lattice oxygen from the catalyst. The amount of C18O was significantly higher for the first 15 minutes of time on stream and its production lasted for approximately two hours. Prior and post POM tests conducted by Nuclear Reaction Analysis confirmed that lattice oxygen was consumed during the POM reaction. Temperature-programmed isotopic exchange (TPIE) experiments over 18O labeled catalysts indicated that bulk oxygen played an important role in the oxygen exchange reaction. In addition, it was observed that Rh had a higher effect than Pt on enhancing the amount of exchanged atoms and in decreasing the temperature of the maximal rates of exchange, in comparison with the oxide supports. This could be correlated by the difference in reducibility between Pt and Rh/ceria-based catalysts. Comparison of results between Rh/ZDC50 and Rh/ÿ-Alumina catalysts during isothermal isotopic exchange reactions showed that the non-oxygen conducting catalyst exhibited a significant lower amount of oxygen exchange than catalysts with higher oxygen mobility. Product formation trends during the POM reaction in the absence of gaseous oxygen showed the same number of active sites in the supports and metal-deposited catalysts.