Some commercially important chemicals are produced in trickle bed reactors where gaseous and liquid reactants flow cocurrently down through a fixed catalyst bed. An important feature of such three-phase system is that the catalyst pellet may exposed to an extremely nonuniform environment because the flowing liquid may only partially contact (wet) the pellet surface. Partial wetting can enhance or retard the rate of a reaction depending on whether the reaction is gas reactant limiting or liquid reactant limiting. The purpose of the proposed work is to devise a meachanism which will enable reactor designers to predict how the intrinsic catalytic selectivity is altered by the multiphase transport associated with partial wetting. The PIs plan to do both experimental as well as modelling work for this system. Initially, a single pellet reactor is to be constructed and reaction rates will be measured. Then four spherical pellets will be put together to simulate packing conditions in a large fuel scale reactor. In this setup liquid pockets can be created and their effect on the reaction rate evaluated. Facilities will thus exist to measure directly the relationship between the overall reaction rates (selectivity) and the wetting efficiency.