The interaction of molecular hydrogen with Cu (110) (2×1) -O, Cu (110) c (6×2) -O, Cu (110) amorphous-O, and Cu (110) c (2×2) -O structures has been studied by low energy electron diffraction for determining the reaction mechanism of hydrogen-oxygen reaction on copper surfaces. After these surface structures were exposed in molecular hydrogen atmosphere at a pressure of 1 ×10^-6Torr, LEED patterns were observed in ultra high vacuum, raising the temperature successively at definite steps and rate. A great difference was found in reactivity of the different surface structures. The Cu (110) (2 × 1) -O structure reacted with molecular hydrogen at 300°C, but the Cu (110) c (6×2) -O structure did not react up to 700°C. In ultra high vacuum (10^-10Torr), all the structures investigated became clean by heating for 20 minutes at 750°C. The Cu (110) amorphous-O structure changed to Cu (11) c (6× 2) -O structure at 350°C and did not react with molecular hydrogen up to 700°C in molecular hydrogen atmosphere. The Cu (100) c (2×2) -O structure reacted with molecular hydrogen at 300°C. From these results obtained, the following mechanism is proposed. The reaction of oxygen chemisorbed on copper surfaces with molecular hydrogen is supposed to require dissociative adsorption of hydrogen on the surface mesh. According to the reconstruction theory, copper atoms are put in a row of [001] direction on the reactive surface structure and oyygen atoms do not exist between copper atoms, while on the inreactive surface structures copper and oxygen atoms are put in a row of [001] direction alternatively. Dissociative adsorption is suppose to be possible on the former surface structures, but impossible on the latter ones. Surface reaction of adsorbed hydrogen and oxygen atoms may be facilitated only on the reactive surface structures.

View full abstract