Oxidative methanol reforming over supported copper catalysts for automotive fuel cell systems

Catalytic generation of hydrogen by the reaction of methanol with oxygen in the presence of steam over an industrial copper-zinc oxide catalyst was studied. Under differential oxygen conversion conditions, the catalyst remained in an oxidized state, and the main reaction was oxidation of methanol to carbon dioxide and water. The activity was proportional to the copper oxide surface area. The methanol consumption rate had a small positive order (0.18 th order) in methanol and oxygen and was suppressed by water. The catalyst deactivated with time on stream due to agglomeration of copper oxide. As the reactor temperature increased, the rate of methanol oxidation increased until thermal runaway occurred, and the oxygen conversion became very high. The catalyst away from the reactor entrance became reduced, and a significant rate of hydrogen production was observed. This thermal run-away phenomenon was examined for CuO/ZnO catalysts by time-resolved X-ray Absorption Spectroscopy during oxidative reforming of methanol. Under low oxygen conversion conditions, the presence of Cu+2 as the dominant copper species was confirmed while combustion of methanol to carbon dioxide and water was the primary reaction. After complete oxygen conversion, Cu+2 was reduced to Cu 0 while the principal activity of the catalyst was shifted to steam reforming, where the dominant product was hydrogen. Cu+ was observed as a transient species in the reduction of Cu+2 to Cu0 and no activity was attributed to it. Increasing the oxygen partial pressure decreased the rate of reduction of Cu+2. This observation was attributed to a heating effect associated with an enhancement of the combustion rate. Additional experiments showed that the catalyst could recover its original activity after a reduction/oxidation cycle.