Abstract
NaZSM-5 powder and membranes were hydrothermally prepared. Their (1) steam (H(2)O) adsorption properties and (2) the permeation and separation of gas and H(2)O were evaluated before and after the cation exchange of Na(+) to K(+) or Cs(+). The quantity of adsorbed H(2)O decreased as the size of the cation increased, indicating that the micropore volume and effective pore size of ZSM-5 decreased after cation exchange. The H(2) and N(2) permeances after cation exchange were less than 5% of the values before cation exchange, indicating a significant reduction in gas permeability. In contrast, the reduction of the H(2)O permeance values of the ZSM-5 membranes before and after K(+) or Cs(+) exchange was lower than that of H(2), resulting in improved H(2)O/H(2) separation performance. Compared with the NaZSM-5 membrane, the K(+)- or Cs(+)-exchanged ZSM-5 membranes exhibited superior H(2)O permselectivity, particularly at dilute H(2)O concentrations (<1 vol%).