کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5423860 | 1507947 | 2010 | 8 صفحه PDF | دانلود رایگان |
The adsorption and desorption of the system CO/Pt(111) and C6H6/Pt(111) at 300 K has been investigated with a pulsed molecular beam method in combination with a microcalorimeter. For benzene the sticking probability has been measured in dependence of the coverage θ. For coverages θ > 0.8 transient adsorption is observed. From an analysis of the time-dependence of the molecular beam pulses the rate constant for desorption is determined to be 5.6 sâ 1. With a precursor-mediated kinetic adsorption model this allows to obtain also the hopping rate constant of 95.5 sâ 1. The measured adsorption enthalpies could be best described by (199 â 77θ â 51θ2) kJ/mol, in good agreement with the literature values. For CO on Pt(111) also transient adsorption has been observed for θ > 0.95 at 300 K. The kinetic analysis yields rate constants for desorption and hopping of 20 sâ1 and 51 sâ1, respectively. The heats of adsorption show a linear dependence on coverage (131 â 38θ) kJ/mol between 0 â¤Â θ â¤Â 0.3, which is consistent with the desorption data from the literature. For higher coverage (up to θ = 0.9ML) a slope of â63 kJ/mol describes the decrease of the differential heat of adsorption best. This result is only compatible with desorption experiments, if the pre-exponential factor decreases strongly at higher coverage. We found good agreement with recent quantum chemical calculations made for (θ = 0.5ML).
Journal: Surface Science - Volume 604, Issues 23â24, November 2010, Pages 2098-2105