Hairy Foam: Thin Layers of Carbon nanofibers as Catalyst Support for Liquid Phase Reactions

Catalytic multiphase reactors are at the heart of many chemical industries.They allow efficient contact between gas and/or liquid reactant phases with solidcatalysts increasing reaction rates. In practice, the higher reaction rates can be takenadvantage of only under the condition that the transfer of mass (reactant and products)can keep up with the intrinsic activity of the catalysts used. In the case where masstransfer is relatively slow, concentration gradients will occur, especially in the poresystem of a heterogeneous catalyst. Concentration gradients will also induce loss inselectivity and byproducts are usually formed via reaction networks that often containparallel and consecutive reactions. Concentration gradients may thus prevent optimaloperation because the active catalytic sites experience different concentrations and atleast a part of the active sites operates under nonoptimal conditions. This problem ismost relevant when gases (e.g., hydrogen or oxygen) have to be dissolved in a liquid(e.g., water) resulting in low concentrations. This coupled with the low diffusivity ofgases in liquids cause concentration gradients to occur even more easily.Conventional multiphase reactors such as slurry phase reactor offers efficient masstransfer but the rate per unit volume of the reactor is low and the cost for catalystseparation is high. Whereas, trickle bed reactor pose mass transfer limitations,pressure drop and fluid maldistribution. Structured reactors, especially foam typeinternals exhibit low pressure drop and reduce fluid maldistribution. However,structured internals have low specific surface area and this can be improved bydeveloping thin layer of carbon nanofibers (CNFs) on the surface of the support. Thinlayer of CNFs offers high surface, high porosity and low tortuosity, maximizing themass transfer rate which is particularly important for heterogeneous catalytic reactionsin liquid phase. The research described in this thesis is focused on preparing a CNFlayer on a structured foam support (termed as ‘Hairy foam’) and then evaluating theperformance of hairy foam catalyst in comparison to conventional porous catalysts.