DFT calculations and Monte Carlo simulations of the co-adsorption of hydrogen atoms and ethylidyne species on Pt(111)

A grandcanonical Monte Carlo (MC) simulation is described for calculating s urface coverages of adsorbed hydrogen atoms and ethylidyne species on Pt(11 1) as a function of temperature and partial pressures of ethane and hydroge n. The MC simulation is based on self-consistent, gradient-corrected densit y functional theory (DFT) calculations of the energies of adsorption of H a toms and ethylidyne species at various positions on a periodic Pt(111) slab . DFT calculations of lateral interaction energies between pairs of adsorba tes at various distances of separation on the Pt(111) slab are reported. Th e MC simulation results are in agreement with results from microcalorimetri c measurements at 300 K and 573-673 K of the heats of hydrogen adsorption v ersus adsorbate coverage on two silica-supported Pt samples and on Pt powde r. The MC simulation results for the coadsorption of H atoms and ethylidyne species on Pt(111) are used to develop analytical expressions that describ e the surface coverages by these species over a wide range of temperatures and pressures (i.e., hydrogen pressures from 1 to 101 kPa, ethane pressures from 0.1 to 10 kPa, and temperatures from 550 to 750 K). The application o f these results is discussed for modeling the kinetics of ethane hydrogenol ysis over Pt catalysts.