Kinetics of Propene Desorption from Pd(111) Studied by Thermal Desorption Spectroscopy and Laser-Induced Thermal Desorption with Fourier Transform Mass Spectrometry

Thermal desorption spectroscopy (TDS) and laser-induced thermal desorption coupled with Fourier transform mass spectrometry (LITD/FTMS) are used to study the interaction of propene on Pd(111). TDS yields the exposure versus coverage dependence for propene adsorbed to Pd(111). A linear uptake from 0.1 to 1 L (corrected for ion gauge sensitivity) implies precursor mediated adsorption. Significant broadening and shifts to lower temperature occur in the TDS above about 0.26 L, which is assumed to be near saturation. Only propene (320 K) and hydrogen (300 and 500 K) desorb after heating a near-saturation exposure of propene. Propene mostly desorbs intact from the Pd(111) surface. TDS shows that no more than 10% of the near-saturation exposure of propene may decompose to surface bound carbon. Isothermal desorption data are acquired using LITD/FTMS at temperatures between 270 and 390 K. Rate constants are extracted from the data, and an Arrhenius plot yielded kinetic parameters (E a and A): E a = 79.2 ± 0.9 kJ/mol and, a preexponential, A = 1010.8±0.3/s (95% confidence level).