Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

OP-II-2MONTE CARLO SIMULATION OF ADSORPTION ON SUPPORTEDNANOPARTICLESA.V. Myshlyavtsev 1,2 , P.V. Stishenko 11 Omsk State Technical University, Omsk, Russia2 Institute of Hydrocarbons Processing SB RAS, Omsk, RussiaIntroductionMost of commercial catalysts consist of nanometer scale particles (1-100 nm) depositedon a porous support. Experimental researches of catalytic processes are rather expensive andhard to conduct and often there is no way to make direct measurements of interestingparameters. For successful interpretation of obtained results suitable mathematical models arerequired [1].The computer model for simulation of metallic nanoparticles and adsorption on theirsurface has been developed. This model can be used for investigation of steady state ofsupported nanocrystals and adsorbate systems. The Metropolis algorithm is employed toarchive the configuration with minimal potential energy. Using this approach it is possible tosimulate bigger, than molecular dynamics allows, particles in a time period sufficient forputting the system in thermodynamic equilibrium. For evaluation of the system energy themodel can use the many-body potentials. Here we have chosen the tight-binding secondmoment approximation (TB-SMA) potential which shows rather good agreement withexperiments for fcc metals in case if sufficiently long interaction range is taken into account[2]. The model allows to simulate systems with up to several thousands atoms deposited inany type of crystal lattice. Type of adsorption can be specified by spatial configuration ofadsorbate, particle and support atoms given in internal coordinates. It is possible to simulateadsorption on different faces, sites or adsorption near different defects.ModelIn TB-SMA potential interaction between atoms depends on their type and distancebetween them. For metals it is reasonable to suppose that atoms can be located only in cells ofcrystal lattice and hence there is a finite set of all possible distances. So one can preliminarilycalculate terms of TB-SMA equation for all pairs of atom types and for all distances up to cutoff radius, where interaction values become vanishingly small. On that assumption we haveused the lattice gas model for representation of particle atoms spatial distribution. Thisallowed to significantly speed up interaction energy evaluation and neighbours enumeration –the most expensive parts of simulation in terms of computational resources. Because of lattice77