We have performed kinetic simulations of the behavior of acetylene hydrogenation under ethylene rich conditions at a number of temperatures and feed gas compositions employing Pd and Pd/Ag alloy catalysts. The results of these simulations form a clear and consistent picture as to the origins of selectivity, thermal runaway, oligomer formation, the role of CO as a promoter of selectivity and inhibitor of oligomer formation, and the importance of proton transfer among carbonaceous species, The modeling gives insight into mechanistic details and provides an explanation for the influence of alloying catalyst on these phenomena.