Development of catalyst system for selective combustion of hydrogen

The selective catalytic combustion of hydrogen in ion-exchanged ZSM-5 was investigated at 823 K and one atmosphere in this research. The results of TPR and hydrogen combustion in MeZSM-5 (Me represents the exchanged metal ion) showed that the sequence of reducibility following the order: CuZSM-5>FeZSM-5>NiZSM-5, was the same as that of reaction activity. It is concluded that, the greater the reducibility of these catalysts, the higher the catalytic activity for hydrogen combustion. The method of chemical vapor deposition of silicon alkoxide on CuHZSM-5 was used to modify the catalyst pore opening size, and to prepare a series of novel catalysts (SiCuHZSM-5). From the adsorption measurements, and the combustion of a reactant mixture (containing isobutane, hydrogen and air) over these catalysts, it was demonstrated that some SiCuHZSM-5 possessed reactant shape selectivity due to an effective pore blocking. Therefore, during combustion reactions, hydrogen was selectively oxidized within the ZSM-5 pores containing copper ion catalysts; in contrast, isobutane was not, because of a diffusion limitation into the pores. (C) 1997 Elsevier Science B.V.