Quantitative Studies of Methyl Radicals Reacting with Metal Oxides

Article abstract of DOI:10.1021/j100039a042

The reactive sticking coefficients of CH3^. radicals, produced by the thermal decomposition of azomethane, were determined over ZnO, CeO2, La2O3, Sr/La2O3, and Li/MgO at 650 deg C.The intrinsic sticking coefficients ranged from 6*10^-8 for La2O3 activated at 900 deg C to 3*10^-5 over ZnO.In the presence of even o.1 mTorr of O2 the sticking coefficient for the La2O3 sample increased to 3*10⁰⁶.Although the other nonreducible oxides exhibited similar behaviours, the magnitude of the effect was not as great.Methyl radicals are believed to react via electron transfer at the surface.The electron transfer may be either to metal ions, in the case of reducible oxides, or to O2, in the case of nonreducible oxides.Reactions of CH3^. radicals with several high surface area, porous silicas and zeolites were also studied.The sticking coefficient on a high-purity silica was found to be 1*10^-8 at 200 deg C.An analysis of the stable products indicated that the reaction of CH3^. radicals with these surfaces exceeded the coupling reactions that might have occured at the surfaces.That is, the surfaces did not function as an effective "third body" in the coupling reaction.