title: Diffusion of hydrocarbons in the reforming catalyst: molecular modelling.
abstract: This is an analysis of the diffusion and adsorption of the model reagents involved in the reforming process (heptane, methylcyclohexane and toluene) in the support (gamma-Al2O3) and catalyst (Pt/gamma-Al2O3) made use of in this process. Since the properties of these catalytic systems are influenced by the interactions between the atoms of the catalyst structure (host) and the atoms of the reagents (guest), analysis was carried out at the molecular level, using advanced computer simulations (molecular dynamics and forced diffusion) implemented in the MSI Software. The virtual host-guest model constructed with this software enabled a simulation of the real reforming system (reforming catalyst-reagents) and analysis of the diffusion phenomenon in this system. The results show that the propensity of the reagents to adsorption and the host-guest interaction energy are correlated with the coefficients of diffusion. The diffusion coefficient values are lower in the catalyst than in the support, probably because of the increased adsorption at the active Pt centres. The decrease in pore diameter from 17 to 10A brings about a decrease in the diffusion coefficients not only due to steric hindrance, but also as a result of capillary condensation. The favourable influence of temperature is more distinct in models characterised by a larger pore size. This is so because molecular diffusion dominates over the mechanism of Knudsen diffusion, which increases the temperature-dependence of diffusion.
authors: Intitute of Chemistry and Technology of Petroleum and Coal, Wroclaw University of Technology, ul. Gdańska 7/9, 50-344, Wroclaw, Poland.
authors: Jerzy
authors: J
authors: Szczygiel
authors: Bartlomiej
authors: B
authors: Szyja
mesh_terms: D002384:Catalysis; D003198:Computer Simulation; D004058:Diffusion; D006838:Hydrocarbons / Q000737:chemistry*; D008958:Models, Molecular; D013696:Temperature
chemical_list: D006838:Hydrocarbons