Bilayered HZSM-5 zeolite Coatings with additional nonzeolite pores were synthesized on the inner surface of stainless steel tubes by a secondary growth method with the addition of ethanol, into the synthesis batch. The as-synthesized coatings were characterized by scanning electron microscopy and gas permeation, indicating that additional noneolitic pores Were. formed hi the presence Of ethanol. A remarkable greater than 1000-fold improvement in N-2 permeation was observed. Catalytic cracking of supercritical n-dodecane (500 degrees C, 4 MPa) over a series of bilayered HZSM-5 coatings showed that the HZSM-5 coatings with additional nonzeolite pores also exhibit a remarkable catalytic, activity improvement by ca. 150% and that the amount of nonzeolite porosity may play a determining role in the enhancement of the catalytic performance. According to. cracking products and the permeation test, the performance enhancement maybe attributed to the effective access of reactant to the acid sites in the zeolite pores due to the enhanced diffusion of supercritical n-dodecane in the zeolite coatings with the nonzeolite pores.