Preparation And Preliminary Study Of Dual-function Catalyst Pd/ZSM-5

As flight speed increases to the high supersonic and hypersonic regime, the temperature of the ram air taken on broad the vehicle becomes too high to cool the structure. Therefore it is necessary to utilize the fuel as the primary coolant. In this case, sensible heating of the fuel is not enough, and endothermic reactions like catalytic decomposition are needed.Catalytic cracking and dehydrogenation are the typical endothermic reactions. In this work, a dual-function catalyst Pd/ZSM-5 was prepared by depositing Palladium catalyst for dehydrogenation on the surface of zeolite ZSM-5 layer. Both cracking and dehydrogenation reactions were carried out on dual-function catalysts. In catalyst systems considered for aircraft application, the catalysts support techniques involved coating on plate-fin or directly on the wall of fuel passage are potential. Therefore, a study was conducted to prepare the dual-function catalysts coated on both stainless stain plate and stainless stain tube.Zeolites ZSM-5 were coated on the stainless steel plate and stainless steel tube by dip-coating and gas-assisted fluid displacement technology, respectively, and a silica-gel binding medium is used. An optimal coating technique and the composition of zeolite suspension were determined. The thickness of the coating was 7.5μm with 4.52mg/cm2 zeolites loaded on stainless steel plate, whereas, the thickness of the coating was 12.3~16.1μm with 5.0~6.0mg/cm2 zeolites loaded on stainless steel tube. Palladium was deposited on the coatings surfaces using electroless plating method. As a result, on the stainless steel plate and stainless steel tube 220μg/cm2 and 72μg/cm2~86μg/cm2 Palladium is deposited, respectively.By using n-Dodecane as model endothermic fuel, coating catalysts on stainless steel, the activity of various catalysts was measured in terms of heat sink, conversation, hydrogen product ratio, and major gas and liquid products distribution under supercritical conditions.With the zeolite ZSM-5 and dual-function catalyst Pd/ZSM-5, the total heat sink, conversion and hydrogen products ratio were remarkable increased. For cracking reaction at 640℃with Pd/ZSM-5 coated, compared to thermal cracking, the total heat sink was 3377kJ/kg, with the chemical heat sink was increased by 36%; the cracking ratio was 55.5%,increased by 22%, and the highest hydrogen production ratio was 3.1%,which was about five times of thermal cracking. For ZSM-5 coating, it increased to 3351kJ/kg, 53.4%, 1.4% in turn. In addition, study was carried out to research the catalyst lifetime. It was indicated that the catalyst lifetime was about 15 minutes.