The chemistry of mixed aromatic-alkyne systems on a metal surface is of general interest in many industrial processes. We use density functional theory (DFT) to investigate the chemistry of one such system (i.e., 1,4-diphenyl-butadiyne (DPB) in contact with Pd(110) and Pd(111) surfaces). Reaction pathways and the energetics of important processes are explored, including H-2 adsorption, dissociation and migration on the metal surface, the DPB-metal interaction, the energetics of H uptake, and the effects of impurities such as CO and CO2 on H chemistry. We find that (i) strong aromatic-metal interaction leads to significant binding strength of the DPB molecule to both Pd surfaces, especially the (110); (ii) H-2 molecules readily dissociate on the Pd surface into H-radicals, which get taken up by alkyne triple bonds; (iii) CO has strong binding to the metal surface, but interacts weakly with H radicals; and (iv) CO2 binds weakly to the metal surface, but could potentially lead to interesting chemical reactions with H.