Switch in Relative Stability between cis and trans 2-Butene on Pt(111) as a Function of Experimental Conditions: A Density Functional Theory Study

International audience; The adsorption of cis and trans 2-butenes on Pt(111) has been studied as a function of hydrogen coverage OH by means of calculations based on density functional theory (DFT) with the inclusion of dispersion forces. All hydrogen coverages have been considered, from 0 to 1.00 monolayer (ML). For each case, the di-sigma and pi adsorption geometries of the olefins have been compared at a surface coverage of theta(C4H8) = 0.11 ML. Calculations of the Gibbs free energies of these systems have identified the most stable 2-butene isomer (cis or trans) as a function of coverage, temperature, and pressure. In particular, focus was placed on two sets of conditions, namely, one with a pressure of 10(-7) Torr, a temperature of 80 K, and a gas ratio (P-H2/P-butene) of 25, similar to the conditions used in surface science studies, and a second with a pressure of 1 bar, a temperature range of 300-400 K, and a gas ratio (P-H2/P-butene) of 10, similar to catalytic hydrogenation conditions. With all selected functionals (PW91, PBE-TS, and optPBE), di-sigma bonding was found to be the most stable for both isomers of 2-butene and for all hydrogen coverages except for OH = 1.00 ML. At low pressures, 2-butene is physisorbed at low temperatures (