Synthesis of HZSM-5 coatings on the inner surface of stainless steel tubes and their catalytic performance in n-dodecane cracking Original Research Article

HZSM-5 zeolite coatings on the inner surface of stainless steel tubes (2 mm i.d., 350 mm length) were prepared by the secondary growth method and characterized by XRD, SEM and in situ FT-IR. The catalytic performance of the resulting HZSM-5 coatings was evaluated using the catalytic cracking of n-dodecane at 4 MPa and 525 °C (supercritical conditions) as a model reaction. With the repeated time of the secondary growth from 1 to 4, the mean thickness of HZSM-5 layers increased from 5.74 to 13.75 μm, together with an increase in the density. Over the zeolite coating of the third growth with suitable thickness (11.63 μm) and density, a high conversion of n-dodecane was achieved. The NaOH-treatment on HZSM-5 zeolite layers induced the creation of meso-pores in the HZSM-5 layer, thus enhanced its catalytic activity. These experimental findings demonstrated that a balance between the thickness and diffusivity of the HZSM-5 layer benefits its catalytic activity.