Production of hydrogen by partial oxidation of methanol over Cu/ZnO catalysts prepared by microemulsion technique Original Research Article

Production of hydrogen by partial oxidation of methanol, using air as oxidant, has been studied over a series of Cu/ZnO catalysts prepared by microemulsion technique. The catalytic activity was compared to that of a reference catalyst prepared by conventional co-precipitation. The BET surface areas of the microemulsion catalysts (30–70 wt.% Cu) ranged from 22 to 36 m2/g and were considerably lower than that of the reference (60 m2/g). Nevertheless, the microemulsion catalysts were more active in the partial oxidation reaction and exhibited high hydrogen and carbon dioxide selectivities. At a molar O2/CH3OH ratio of 0.1, hydrogen production was initiated at about 185°C over the microemulsion catalysts. Over the reference, hydrogen production began at 215°C under the same conditions. The catalytic activity was found to be strongly dependent on the partial pressure of oxygen, which also plays an important role in determining the product distribution. By increasing the O2/CH3OH ratio, the methanol conversion and carbon dioxide selectivity increase, while production of water occurs at the expense of hydrogen. By TEM and TPR, it was observed that Cu is less well-dispersed in the microemulsion catalysts than in the reference. The higher catalytic activity is not expected considering the lower number of exposed Cu sites, i.e. the turnover frequencies are substantially higher over the microemulsion catalysts. It is possible that, a strong interaction between a small part of CuO and the ZnO lattice is responsible for the higher turnover frequencies of the microemulsion catalysts, or that particular crystallographic Cu planes or surface imperfections are the active sites of the reaction.