Adsorption energy of tert -butyl on Pt(111) by dissociation of tert -butyl iodide: Calorimetry and DFT

Document Type

Article

Publication Date

1-9-2014

Abstract

Dissociative and molecular adsorption of tert-butyl iodide on Pt(111) has been studied by single-crystal adsorption calorimetry (SCAC), photoelectron spectroscopy (XPS), reflection/adsorption infrared spectroscopy (RAIRS), and density functional theory (DFT) calculations. Up to a t-BuI total coverage of 0.07 ML, t-BuI adsorbs dissociatively at 100 K to form t-Buad plus Iad, with an integral heat of reaction of 223 kJ/mol. At higher coverage, up to a total coverage of 0.15 ML, t-BuI adsorbs molecularly directly to the Pt surface atoms with an average heat of adsorption of 91 kJ/mol. At 0.15 ML, the first layer is saturated. Between 0.15 and 0.38 ML, t-BuI adsorbs molecularly on top of the first layer with a constant heat of adsorption of 44.5 ± 1.9 kJ/mol. The standard enthalpy of formation of adsorbed tert-butyl on Pt(111) at 1/25 ML coverage is estimated from the heat measurements to be -168 ± 20 kJ/mol, giving a (CH3)3C-Pt(111) bond enthalpy of 216 ± 20 kJ/mol. DFT calculations were performed using the GGA-PBE and optB86b vdW density functionals to determine the heats of reaction and binding energies of relevant adsorbates. Comparison to the measured energies shows that optB86b vdW-DF is more accurate than GGA-PBE for describing the adsorption and bonding of t-buI and t-Bu on Pt(111) because these energies contain large contributions from dispersion forces. © 2013 American Chemical Society.

Publication Source (Journal or Book title)

Journal of Physical Chemistry C

First Page

427

Last Page

438

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