Hydrogenation of 1,3-butadiene on Pt(111)

The adsorption of butadiene was realized under low pressure,p=10−7 Torr and studied by Auger Electron Spectroscopy (A.E.S.). The reaction of butadiene hydrogenation was then investigated on Pt(111) under quasiatmospheric pressure. The surface was characterized by low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) before and after each catalytic test. It was shown that the surface quickly reached a first saturation state equivalent to one butadiene molecule per 2 to 3 platinum atoms which did not reduce its catalytic activity. A mechanism was proposed involving butadiene as the most abundant surface species and the hydrogenation of C4H7 as the rate determining step. The influence of sulphur adsorbed in controlled quantities, θs<1 was also investigated. Sulphur did not change the mechanism of the reaction but slightly improved the selectivity in butenes. Total poisoning occurred for θs=0.5. Finally, a short review of the results concerning the hydrogenation of butadiene on the three low index faces of platinum is given. The most important result was an increase of the activity with increasing surface roughness.