Multiple societally important chemical reactions rely on catalytic processing in aqueous conditions, including biomass processing, electrochemical energy conversion, fertilizer production, and water purification. Often, these applications use expensive transition metal catalysts, such as platinum. A goal of our work is to understand the molecular-level ways in which these catalysts function, so that we may design less expensive catalysts for chemical reactions that occur in aqueous conditions. Experiments and simulations have uncovered a variety of ways in which water influences catalytic phenomena. For example, it alters reaction intermediate and transition state energies, co-catalyzes certain reaction steps, and controls which catalytic pathways are followed. However, a comprehensive picture about how H2O molecules influence catalytic behavior, including their influence on catalytic thermodynamic and kinetic quantities, remains unresolved. In this work, we use density functional theory (DFT) with both implicit and explicit solvation, ab initio molecular dynamics (AIMD), and force-field molecular dynamics (ffMD) to examine how interfacial water influences Pt-catalyzed conversions of methanol, glycerol, and ammonia. Specifically, we provide details about how the structure of liquid water influences the adsorption of aqueous phase molecules, the energies of catalytic surface intermediates and transition states, and the frequency factors and activation barriers of catalytic reactions. We highlight the role of hydrogen bonding in these phenomena and make general hypotheses about how catalytic mechanisms play out in aqueous phase.