Isothermal and temperature-programmed oxidation of CH over Pt{110}-(1 x 22)

The isothermal oxidation of adsorbed CH4 on Pt{110} has been studied using a supersonic molecular beam system. CH4 oxidation was found to be much more facile than C-4 oxidation and takes place at surface temperatures as low as 330 K. Over the surface temperature range 350-450 K the gas phase products are CO2 and H2O. We conclusively show that the first step of the reaction is CH4 + O-4 --> CO4 + H-4 and that H abstraction to produce OH4 and C-4 does not occur. CO2 is produced by the subsequent surface reaction of CO4 with O-4 while H2O is produced by H-4 oxidation. An Arrhenius analysis yields values for the pre-exponential factor and activation energy for the CH4 + O-4 reaction of (2.1 +/- 1.5) x 10(-6) molecule(-1) cm(2) s(-1) and 71 +/- 3 kJ mol(-1), respectively. We also studied the temperature programmed reaction CH4 + O-4 reaction and found that the product selectivity is very sensitive to the atomic O-4 pre-coverage. (C) 2001 Elsevier Science B.V. All rights reserved.