Catalytic thermodynamic model for nanocluster adsorbates

We present an approach to study nanocatalysis using density functional theory (DFT), statistical mechanics, andthermodynamics. The analysis starts by using a coordination style approach, which is key to producing a me-soscale model free of arbitrary parameters for sizes of∼3nm <D< 100 nm. We apply DFT in a coordinationtype calculation of the nanocrystal binding energy and the adatom adsorption energy to give us a Hamiltonian ofthe nanocluster-adatom system. This is followed by informational statistical mechanical principles and ther-modynamics to complete the model. Carbon monoxide adsorbates are studied on gold clusters, hydrogen mo-lecules on palladium clusters, and oxygen radicals on platinum clusters. The data exhibits size effects for themeasured thermodynamic properties with cluster diameters between 3 and 9 nm. In spite of modeling threedifferent systems, wefind only small differences in the large-scale entropy (∼−70 J/K-mol) and enthalpy(∼−20 kJ/mol) of the nanoclusters. Shape effects are predicted to be greatest for nanoclusters of size∼10 nm.For the Pd-H2system, we use a cubic model which has close agreement with experimental data for Pd cubes. Thecomputationally efficient procedure we derive provides a theoretical scheme to determine the size and shapedependence of the entropy and enthalpy of nanocluster-adsorbate systems from sequential single molecule adsorption.status: Published onlin