Preparation, Characterization And Catalytic Properties For Cracking Of Zeolitic Film Catalysts Supported On Metallic Mesh

With the development of technology in Aero-Space field, high energy density fuels and endothermic hydrocarbon fuels are two main aims in fuels development. The new conception of zeolitic film supported on metallic mesh using as catalytic cracking catalysts has been submitted, in order to increase the heat-absorbing capacity of endothermic hydrocarbon fuels and improve ignition and combustion behaviors of high energy density fuels. For these reasons, preparation, characterization and catalytic properties for cracking of zeolitic film catalysts supported on metallic mesh have been researched by us in this thesis. The results which were got by us from our research are as below:(1) Synthesis of submicron sized zeolite Y has been studied without the presence of organic templates. The size of zeolite NaY crystals is influenced by n(Na2O)/n(SiO2) of the synthesis mixture. The size of NaY zeolite crystals decreases initiallyand then increases with increasing n(Na2O)/n(SiO2). The n(Si)/n(Al) ratio of Y zeolite crystals decreases initially and then almost keeps constant with increasing n(Na2O)/n(SiO2). The n(Si)/n(Al) ratio of the Y crystals is about 2.0 at n(Na2O)/n(SiO2)≥1.04. Silica source is another factor influencing the particle size. The zeolite crystals which are synthesized from silica sol and nano silica have uniform size distribution, and the average sizes of the crystals are 300nm and 500nm, respectively. When sodium silicate is used as silica source, the particle size appears a dual mode distribution (big particles are about 1000nm while small particles are around 100nm). When n(SiO2)/n(Al2O3) of synthesis mixture is changed from 25 to 5, zeolite Y particles with the size of 50nm-100nm are obtained. Microwave heating can accelerate the formation rate of NaY crystals compared with conventional heating, but it has no influence on the particle size.(2) Clear solutions were optimized for crystallization of FAU-type zeolite. The clear solution was also used for preparation of FAU-type zeolite coatings on the grids made of FeCrAl alloys. Crystal seeds are beneficial to produce continuous and uniform coatings on grids. Seeds can also increase the amount of the crystals on grids. The ageing of the synthesis mixture is considered as another important factor. The as-synthesized FAU coatings have catalytic activities with the initial conversion of about 13.2% for JP-10 cracking at 500℃, while the conversion of thermal cracking is 4.4%. Unfortunately, the catalytic activity decreases rapidly with time on stream.(3) FAU coatings with higher catalytic activities are obtained by modification of rare earth ions. The order for ion exchange is important. NH4+ ions in zeolite can be replaced by Ce3+ ions easily, whereas it is very difficult to exchange H+ ions by Ce3+ ions. The concentration of the rare earth salt solution has little influence on the catalytic cracking of n-octane over FAU zeolite coatings. There is almost no difference in the catalytic activities between Ce3+ and La3+ ions-exchanged FAU coatings.(4) Catalytic cracking of JP-10 has been investigated over many types of zeolite. Pore size of zeolite is an important factor influencing JP-10 cracking. The yield of gas products is higher over HY, HUSY and Hβcatalysts than that on HZSM-5. In order to improve the catalytic properties of HZSM-5, HZSM-5-OH and HZSM-5-H were prepared by treating HZSM-5 crystals in basic and acidic solutions, respectively. The average conversions of JP-10 cracking are 67.15%,75.86% and 71.74% for HZSM-5,HZSM-5-OH and HZSM-5-H catalysts, respectively. The gaseous cracking products for each catalyst are mainly consisted of ethylene, propane, propylene and iso-butane. Their yields depend on the catalyst preparation method. The magnitude of these four components of gas products follows propylene>ethylene>iso-butane >propane for each catalyst. The yield of gas products decreases over HZSM-5-OH catalyst while the yield of liquid products increases. The yield of gas products increases over HZSM-5-H catalyst while the yield of liquid products decreases.(5) ZSM-5 coatings on stainless steel foils were synthesized by hydrothermal synthesis. The influence of support surface pretreatment was studied on the adhesion strength between zeolite crystals and stainless steel support. The results have shown that high-temperature pretreatment has more favorable effect on adhesion strength of zeolite coatings compared to acid treatment or cleansing with detergent, the degree of which depends on the temperature. ZSM-5 coatings with the highest coverage and the strongest adhesion strength were achieved on stainless steel support that was pretreated at 850℃for 5h. The immersion of high-temperature pretreated support in the synthesis solution also imposes influence on surface coverage and adhesion strength of zeolite coatings, the degree of which depends on pretreatment temperature.