The surface chemistry of crotonaldehyde and propene, primary and secondary reaction products in the aerobic selective oxidation of crotyl alcohol, has been studied by temperature-programmed reaction over Au/Pd(111) surface alloys. Gold strongly promotes desorption versus reaction at mole fractions > or = 0.3 (crotonaldehyde) and > or = 0.8 (C(3)H(6)); only approximately 5% of the chemisorbed aldehyde or alkene react over Au-rich alloys. Surprisingly, co-adsorbed oxygen strongly suppresses crotonaldehyde decomposition over both clean Pd(111) and alloy surfaces, while C(3)H(6) combustion, an important undesired side-reaction over unpromoted Pd(111), is also moderated by Au.