THE INTERACTION OF CH4 AT HIGH-TEMPERATURES WITH CLEAN AND OXYGEN PRECOVERED CU(100)

The decomposition of CH4 on Cu(100) has been studied by XPS in the temperature range 800-1000 K. In addition the interaction of CH4 with oxygen adsorbed on Cu(100) has been studied in the temperature range 700-800 K. In both cases the pressure of CH4 was 10 Torr. Measurable deposition on the clean surface was observed at temperatures above about 800 K. The dissociative chemisorption probability is exceedingly low, about 8.6 x 10(-9) at 1000 K. The activation energy of the chemisorption probability on the clean surface (the initial "sticking coefficient") is about 201 kJ/mol. The amount of carbon in the saturation layer and the C ls XPS binding energy show that a graphite layer is formed on the surface. The shape of the carbon growth curves indicate that the layer is formed through the growth of graphite islands. The CH4 gas molecules react with oxygen atoms chemisorbed on Cu(100) already at temperatures below 700 K. The activation energy of the initial reaction rate at an oxygen coverage theta(o) almost-equal-to 0.5 ML is about 125 kJ/mol.