ARRESTED FORMATION OF CARBON OXIDES IN PROGRAMMED OXIDATION OF METHANE ON NONSTOICHIOMETRIC SAMARIA

COx species evolved during transient exposure of Sm2O3 catalysts to ve ry low pressure CH4/O-2 mixtures are monitored in real time by molecul ar beam mass spectrometry at 1100 K. The rise of m/z = 28 and 44 signa ls is significantly delayed relative to the onset of CH4 decay only on substoichiometric Sm2O3-y samples. This observation rules out CO and CO2 as primary products of methane heterogeneous oxidation and implies that their immediate precursor, most probably CH3(g), is slowly oxidi zed during the initial stages of Sm2O3-y surface reconstruction. Prese nt results suggest the possibility of suppressing carbon oxides in the oxidative dimerization of methane by dynamic control of selective sit e populations.