Tailoring Nanochannel in ZSM-5 Membranes via Al Distribution Control

The effects of Al distribution on the permeation and separation properties of the ZSM-5 membranes were investigated. Two types of ZSM-5 membranes with different Al distributions were prepared via secondary growth methods using pentaerythritol (PET) or tetrapropylammonium cation (TPA + ) as organic structure-directing agents. The results of 27 Al-NMR and UV–vis–DRS suggested that the distribution of Al in ZSM-5 membranes can be largely controlled in the channels or intersections using PET or TPA + . Membrane properties were evaluated by conducting hydrocarbon vapor permeation tests in unary systems and a separation test for the methanol/H 2 binary mixture. Significant differences were observed in the permeation behavior of the n -alkane hydrocarbons through the two Na-ZSM-5 membranes. The activation energies for the permeation of n -hexane through ZSM-5 membranes in which Al was mainly located in the channels and intersections were 46.8 and 18.7 kJ mol –1, respectively, indicating that Na + in narrow pores would disturb n -hexane permeation. In addition, the separation performance for the methanol/H 2 mixture considerably depended on the Al distribution. The separation factor was massively improved by the maldistribution of Al in the channels, possibly because methanol adsorbed on Na + paired with Al in the channels blocked H 2 permeation, resulting in high methanol selectivity.