A COMBINED INFRARED, TEMPERATURE PROGRAMMED DESORPTION AND TEMPERATURE PROGRAMMED REACTION SPECTROSCOPY STUDY OF CO2 AND H2 INTERACTIONS ON REDUCED AND OXIDIZED SILICA-SUPPORTED COPPER-CATALYSTS

The nature and strength of bonding of carbon dioxide to a high area (136 m2 g-1) polycrystalline copper supported on silica has been determined by the combined techniques of Fourier transform infrared spectroscopy (FTIR) and temperature programmed desorption (TPD). These show the room temperature interaction to be initially dissociative producing carbon monoxide (bonded both on a Cu(I) site and on a stepped, high index surface) and surface oxygen. Further carbon dioxide adsorption interacts with the surface oxygen to produce a symmetric carbonate species. The adsorption and surface reaction of co-adsorbed hydrogen and carbon dioxide has also been studied by the combined techniques. At room temperature the adsorption of both is simply dissociative producing adsorbed hydrogen atoms and the symmetric carbonate species. Heating these adsorbates to 388 K causes them to react producing a surface formate species -the dominant intermediate when methanol is synthesized from these reactants. This paper therefore elucidates the detailed mechanism of the hydrogen-carbon dioxide reaction on copper and shows the surface reaction of the hydrogen atoms and the carbonate species to be activated.