In our ongoing research into the catalytic conversion of biomass feedstocks into value added chemicals, we have found that reactant and product concentrations within porous catalyst supports, where reaction actually takes place, can be significantly different in comparison to bulk concentrations. Adsorption experiments were performed on activated carbon to explore this adsorption behavior, and a model to predict local concentrations in the pore has been developed. The reduction of individual acids, acid mixtures, and combinations of acids with their alcohol products were compared on carbon supported and unsupported ruthenium catalyst. On supported catalyst lactic acids(LA) reacts five times faster then propionic acid (PA) while on unsupported catalyst it is 15 times faster. This three fold increase matches the increase in local concentration on the carbon support.