Studies On Adhesion Strength And Chemical Modification Of ZSM-5Zeolite Films On Metallic Substrates

ZSM-5zeolite is a kind of solid acid catalyst with excellent catalytic performance, and recently structured catalytic reactors grown with ZSM-5zeolite films have been widespreadly investigated. Adhesion strength and catalytic performance are two important properties of ZSM-5zeolite films. On one hand, properties of zeolite films and metallic substrates are different, and zeolite films are easy to peel off, therefore the lifetime of ZSM-5films is shortened. On the other hand, pore size of ZSM-5zeolite is similar with some molecular, therefore the molecular diffusion in the pores is slow, thus the activity, the selectivity of ZSM-5catalyst are limited. In a conclusion, two important issues urgent to solve are how to increase the combination strength of zeolite films and substrate, and how to control the pore size of ZSM-5zeolite.The paper consists of two parts:(Ⅰ) the influence of the alkali treatment on the structure and the catalytic properties of ZSM-5zeolite films;(Ⅱ) the influence of the treatment of metal surface on the growth and the bonding strength between ZSM-5zeolite films and substrate. The details are discussed below:Firstly, ZSM-5zeolite films are coated on the wall of the capillary reactor, and then are treated in NaOH solution. These treated and untreated films are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and N2adsorption isotherm techniques. The results show that alkali treatment has a significant effect on the structure of the zeolite membrane. However, after being treated at65℃in0.2M NaOH solution for0.5h, there are no mesopores produced in ZSM-5zeolite films. On the contrary, high-resolution SEM and N2adsorption isotherm characterization results indicate that there are mesopores produced in ZSM-5zeolite powder which is also treated by NaOH solution.Second, desilicated ZSM-5zeolite films, which are coated in the inner wall of reacor using the in situ growth method and then treated in NaOH solution(treatment under65℃in0.2M NaOH solution for0.5h, are used in the catalytic cracking. The result shows that the alkali-treated zeolite films bring great improvement in several aspects such as the catalytic cracking of n-heptane for formation rate of gaseous products, conversion and product selectivity. And it also significantly lowers the initial cracking temperature of the decalin isomers cracking reaction.Thirdly, the influence of the treatment of metal surface on the bonding strength between ZSM-5zeolite films and substrate is investgated. And some methods measuring the bonding strength are discussed as well. The results indicate that films grown on the substrate which is treated at high temperature have high thermal shock resistance. However, while compared with those on the untreated substrate, the bonding strength of films on the treated substrate decreases. On the other hand, the bonding strength between the film and the substrate increases after the substrate being treated by hydrochloric acid or nitric acid resolution. Thermal shock method can be used to measure the bonding strength between the zeolite film and the substrate qualitatively; and indentation method can be used to measure the mechanical properties of ZSM-5films; and stretching method is one of the most intuitive way to evaluate the bonding strength of film-substrate interface, but the drawback is appropriate adhesive is not easy to obtain.