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

Abstract

HZSM-5 zeolite coatings on the inner surface of stainless steel tubes (2mm i.d., 350mm 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 4MPa 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 13.75μm, together with an increase in the density. Over the zeolite coating of the third growth with suitable thickness (11.63μm) 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.