Site- and surface species-dependent propylene oxidation with molecular oxygen on gold surface

Fundamental understandings of Au-catalyzed oxidation reactions with molecular oxygen are of great importance. Herein we report a successful preparation of molecularly-adsorbed O₂ species on a stepped Au(997) single crystal model surface via a near-ambient pressure and low-temperature oxygen exposure and their oxidation reactivity with propylene via temperature programmed desorption spectra and polarization-modulated reflection-absorption infrared spectra. O₂ molecularly adsorbs at the (111) step sites of Au(997) surface while C₃H₆ adsorbs at both (111) step sites and (111) terrace sites. C₃H₆(a) adsorbed at the (111) step sites is more stable than at the (111) terrace sites and its oxidation reactions are dominant; meanwhile, O₂(a) is much more reactive than O(a) and prefers combustion reaction of C₃H₆(a). C₃H₆(a) adsorbed at the (111) step sites undergoes combustion reactions with O₂(a) to produce CO₂ and CO at low temperatures and partial oxidation reactions with O(a) to produce acrolein at high temperatures while C₃H₆(a) adsorbed at the (111) terrace sites undergoes combustion and partial oxidation reactions with O₂(a) to respectively produce CO₂/CO and acrolein at low temperatures. These results reveal site- and surface species-dependent reaction behaviors of propylene oxidation with molecular O₂ on Au surfaces and provide a complete fundamental understanding of oxidation reactions with molecular O₂ on Au surface.