Eley-Rideal type surface reaction--Direct reaction of gaseous CO_2 with surface atomic hydrogen on Cu (111)

摘要

The reaction of CO_2 with hydrogen to form formate species on Cu (111) was found to take place via an Eley-Rideal type mechanism by molecular beam experiments, in which CO_2 molecule directly reacts with surface atomic hydrogen. First, atomic hydrogen was prepared on Cu (111) using a heated tungsten wire. The H/Cu(111) surface cooled at 170 K was then exposed to CO_2 molecular beam in an ultra-high vacuum apparatus. At a CO_2 temperature of 720 K, formate was found to form on Cu(111) by TPD experiments in which desorption of CO_2 was observed at 400 K. This is the characteristic temperature for the decomposition of formate into CO_2 and H_2. At lower CO_2 temperatures, no formation of formate was observed, indicating that the formate synthesis takes place by using kinetic energy of CO_2 without equilibrating to the surface temperature. This is evidence for the Eley-Rideal type surface reaction.