Hydrocarbon combustion at high oxygen coverage on palladium: A model study on Pd(100)

Hydrocarbon combustion on Pd(100) was studied using temperature-programmed reaction spectroscopy (TPRS) at high oxygen coverages up to 1.1 oxygen atom per palladium atom. The hydrocarbons studied included both alkenes (propene, 1-butene, and 1,3-butadiene) and arenes (benzene, toluene, and styrene). Alkanes (pentane and cyclohexane) were also studied, but no reaction was detected. It was found that even at 1.1 O/Pd, efficient combustion reactions occur at 350-650 K for all the alkenes and arenes studied. It appears that higher chemisorption energies of hydrocarbon on the surface (butadiene > butene > propene; styrene > toluene > benzene) lead to lower activation energies and higher combustion yields. As the oxygen coverage increases from 0.25 O/Pd, the activation energies for the combustion reactions increase, and the combustion yields pass through a maximum, presumably due to a blocking effect of O(a) on hydrocarbon adsorption.