Diffusion, Sorption and Reactions in Micro- and Mesopores

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Diffusion in micro- and mesopores is in many cases limiting for mass transfer and reaction rates in porous natural or synthetic materials. Accessibility and reactivity of micro- and mesopore domains should be a function of the pore sizes as well as pore polarities. In natural porous media both parameters can be assumed to show a distribution, depending on the type of the porous material. Moreover, educts and products of a reaction may show different polarities resulting in a distribution of diffusivities with an impact on overall reaction rates. The objective of this work is the synthesis and characterization of well-defined porous materials with different pore sizes and polarities containing catalytically active sites, and study their accessibility with various methods. The catalytic hydrodehalogenation of chlorinated hydrocarbons (trichloroethylene (TCE) and chlorobenzene) and the hydrogenation of benzene serve as model reactions resulting in different product distributions in terms of polarity and molecular size. The use of well-characterized model solids should allow to relate diffusion rates and reactivities of the different materials to pore sizes and pore polarities. It is expected that the results will lead to a better understanding of naturally occurring abiotic degradation processes in water saturated natural porous media. Results could also have an impact on the development of tailired porous catalytic acti materials for the clean up of ground water contaminated with organic hydrcarbon compunds.