In-Situ Observation of Hydrogenation of Ethylene on a Pt(111) Surface under Atmospheric Pressure by Infrared Reflection Absorption Spectroscopy

Hydrogenation of ethylene on a Pt(111) surface in the presence of gaseous ethylene and hydrogen in the 103 Pa range was investigated by infrared reflection absorption spectroscopy (IRAS). The IRA peaks assigned to di-σ-bonded ethylene and ethylidyne were observed on Pt(111) under the flow of 1.3 × 102 Pa of ethylene and 6.5 × 103 Pa of hydrogen at 200−300 K, and the apparent activation energy of ethylene hydrogenation was estimated to be 37 ± 5 kJ mol-1 from the rate of temperature-dependent ethane production. The ethylene hydrogenation on ethylidyne-covered Pt(111) was also examined under the same condition. The peak due to the di-σ-bonded ethylene was not observed on ethylidyne-covered Pt(111), although the similar rate of hydrogenation and the similar activation energy (39 ± 5 kJ mol-1) were obtained as those on clean Pt(111). The π-bonded ethylene, which has been previously proposed as an intermediate by the sum−frequency generation (SFG) experiment under the catalytic hydrogenation condition and by I...