The Preperation And Properties Investigation Of A New Type Lanthanum Zirconate Supported Catalyst Resisted To High-Temperature And Water Vaper Corrossion

Non-toxic monopropellant has potentially broad application in the filed of small space propulsion,because it has advantages of non-toxic,high density specific impulse,easy to store.Nevertheless,the adiabatic flame temperature of the Non-toxic monopropellants is extremely high.In addition,decomposition of the Non-toxic produces highly oxidizing species such as O2,acidic species such as HNO3,and water vapor that are highly corrosive to the catalyst bed.The traditional catalyst can hardly satisfy the application demands of the non-toxic monopropellant.Pyrochlore phase Lanthanum zirconate(La2Zr2O7,LZO)is a promising material of catalyst support for non-toxic monopropellant,because it has a good high-temperature,acid and water vapor resistence.In this work,LZO catalyst support was made from porous LZO using extrusion molding process.And on this basis noble metal Ir was successfully loaded on the LZO catalyst support by the multiple impregnation method,then Ir/LZO catalyst was prepared.The preparation processes of LZO catalyst support and Ir/LZO catalyst,the application performances were investigated systematacially.Influences of water powder ratio on extrusion molding process and properties of catalyst support was studied.The result shows that the optimal performance of LZO support and high-efficient extruding are obtained when the water powder ratio is 0.41g/g.Water powder ratio almost has no influence on mesoporous,but with the increasing of water powder ratio,macroporous reduce.Influences of calcination temperature and calcination time on crystal structure,compressive strength and pore structure was studied.The result shows that transformation of crystalline structure and sintering happen in the calcination process.In order to gain catalyst support with suitable surface area and compressive strength,the optimal calcination temperature is 1000 degrees,the optimal calcination time is 3 hours.The compositions,phases,surface charge performance and surface acidity of LZO catalyst support were investigated.Based on the results,the prepared LZO is pyrochlore phase,and the molar ratio of La to Zr is 0.94 to 1.The prepared LZO catalyst support has a surface area of 27.68m2/g,pore volume of 0.083cm3/g,average pore size of 21.34nm,and compressive strength of 26.2 MPa.The isoelectric point(IEPS)of LZO catalyst support is 9.0,and it is positively charged when pH is less than 9.0.The zeta point is up to its maximum 36.7V when pH is 3.8.If pH is greater than 9.0,it is negative charged,and the absolute value gets bigger along with the increase of pH.There are three kinds of acids on the surface of LZO catalyst support,they are week acid,medium-strong acid and strong acid,the acid contents respectively are 0.074mg/g,0.002mg/g and 0.009mg/g.LZO catalyst support gain a certain of surface acidity due to the existence of Zr,the increasing of acid species and strength result in the doping of La.Effects of calcination temperature and reduction temperature were investigated.In the calcination process,the chemical compositions and phases of LZO catalyst support are stable,Chloroiridic acid decomposes into Ir,IrO2 and IrCl3 accompanying with the sintering of Ir.The moderate calcination temperature for the prepared catalyst is 500?,at which gave the highest Ir dispersion.In the reduction process,reduction of irdium compounds and sintering of Ir happen at the same time.Therefore,the reduction should not higher than 550 degrees to guarantee the high dispersion of Ir.High-temperature resistence,thermal-shock resistence,and water vapor corrosion resistence of Ir/LZO catalyst were also investigated.At 1200 degrees,the chemical compositions and phases of Ir/LZO catalyst are stable,but the compressive strength increase 10.3%and the surface area decrease 25.3%as the result of sintering,Ir particles grown up from 1-2nm to about 10nm.Ir/LZO catalyst has a good the thermal-shock resistence,it is well preserved after experienced 10 times water quenching at 1200 degrees,but compressive strength decrease 20.3%as the result of the appearance of cracks.Meanwhile,sintering occurs,Ir particles grown up to 3p.m.In 1200 degrees water vapor environment,sintering and phase separation of LZO catalyst support carries out,sintering and oxidization also happens.As a result the surface area decreases 50.9%,and the compressive strength increase 30.5%.The catalytic performance for non-toxic monopropellant of Ir/LZO catalyst was investigated using a thermogravimetric experiment and a dropping experiment.The result suggests that the catalytic ignition time is 30ms,the reaction time is 205ms,and the ignition temperature is 52 degrees.LZO catalyst support also has certain catalytic activity because of the surface acidity.