Adsorption kinetics and thermodynamics from single crystal adsorption calorimetry

The interactions of CO, NO and O2 with Pt{111}, pt{211}, and Pt{411} have been investigated with Single Crystal Adsorption Calorimetry (SCAC). Coverage-dependent heat of adsorption and sticking probability data for 300 K are presented, and are discussed with respect to the kinetics and thermodynamics of adsorption and desorption. CO adsorption proceeds molecularly on both Pt{111} and Pt{411}, with initial sticking probabilities of 0.78 and 0.80, and initial heats of adsorption of 176 kJ mol-1 and 196 kJ mol-1, respectively. Both adsorbate layers are found to be non-localised, having identical pre-exponential factors of 2x1015 s-1. Discrepancies between isosteric and calorimetric heat of adsorption data at low coverage for CO/Pt{111} have been rationalised in terms of an entropy-driven localised/non-localised phase transition occurring above 300 K. Initial adsorption of NO occurs with a sticking probability of 0.84 on all three surfaces. The initial heat of adsorption for NO/Pt{411} indicates dissociative adsorption. The NO/Pt adsorbate layers are found to be highly localised, with pre-exponential factors in the range 1017 – 1020 s-1. This has been discussed in terms of desorption from highly compressed adsorbate layers in which co-operative effects are extant. O2 adsorption proceeds dissociatively on all three surfaces, with the initial heats of adsorption all above 300 kJ mol-1. Desorption occurs from localised adsorbate layers, with all systems having pre-exponential factors of 1018 s-1. A kinetic compensation effect has been observed for the data of this thesis, as well as that of the SCAC literature, and is discussed within the context of the chemisorption entropy-enthalpy compensation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo