Synthesis Of RE/Al Composite Oxide By Spray Pyrolysis-Roasting Using Chloride Solution As Raw Material

Coprecipitation,alkoxide hydrolysis,hydrothermal synthesis and solo-gel meythod etc.are commonly used in the synthesis of RE/Al composite oxides.However,the processes are complex with long time and large amount of waste water.The spray pyrolysis method has none of these problems.Moreover,the theoretical temperature can be significantly reduced by preparing the precursor via spray pyrolysis before roasting.Aiming at the problem of waste water pollution and soil salinization in the production of rare earth complex oxides,the mechanism of direct thermal decomposition of rare earth chloride solution was mainly studied and the theory of synthesis of rare earth composite oxides via spray pyrolysis can be enriched,providing scientific reference for the development of spray pyrolysis synthetic technique of composite oxides from other metal chlorides.Therefore,industrial production line raw materials lanthanum chloride was selected as the raw material in this study.Based on the synthesis of RE/Al composite oxides by spray pyrolysis,a precursor thermal decomposition method was developed.In-depth studies were conducted according to the order of LaAlO3??-Al2O3/CeO2/LaAlO3?LaMn0.5xFe0.5xAl12-x-O19.via XRD,SEM,TG-DTA,H2-TPR,BET,H2-TPR and XPS.The catalytic properties of the prepared ?-Al2O3/CeO2/LaAlO3 and Mn and Fe doped lanthanum hexaaluminate were also investigated by means of CO reduction denitrification.A new synthesis of LaAlO3 method with Purity above 99.9%by the conditions of roasting at 800? for 2 h using the 2LaOCl·Al2O3 precursor prepared by spray pyrolysis.LaCrO3 and LaFeO3 were successfully prepared by using lanthanum chloride as raw material with the same method,and the versatility of the method was proved.When using aluminium chloride as crude material,different spray pyrolysis conditions were tested,and it was found that ?-Al2O3 could be prepared by one-step spray pyrolysis under 1000?,with the particles remaining at high temperature zone of pyrolysis furnace.Based on this result,?-Al2O3/CeO2 could be synthesized from aluminium and Cerium chloride solution by one-step spray pyrolysis.Then on the basis of low temperature preparation of LaAlO3 with the precursor synthesized by spray pyrolysis,and the accumulation of experimental experience,the method was proposed that the precursor was synthesized by spray pyrolysis,then the material was calcined subsequently to yield ?-Al2O3/LaAlO3.And this method is proved to be feasible.Different content CeO2/LaAlO3(?(CeO2)%=5%?15%,?(LaAlO3)=5%?15%)loaded?-Al2O3 was successfully prepared.This catalyst is a kind of hollow sphere with nano-scaled shell,and the content of active ingredient is 10%?12.5%.The light-off temperature of the catalyst is 190?,the NOx conversion rate reaches at a peak(100%)at 480?,then the catalytic activity of this catalyst remains constant with the increase of the temperature,which means good thermal stability,and meets the design requirement of the experiment.The method was proposed that preparing the precursor by spray pyrolysis,then the precursor was calcined at 1200? subsequently to yield Mn and Fe doped lanthanum hexaaluminate.When talking about lanthanum hexaaluminate,the ionic substitution of Fe and Mn would stimulate the generation of hexaaluminate.But the increase of substituted amount of Fe and Mn could enhance the crystallinity of hexaaluminate,which resulted in bigger grain size and smaller specific surface area than pure hexaaluminate.And it was discovered that the catalyst showed ideal catalytic activity when the substituted amount of Fe and Mn was 3.The LaAlO3 precursor prepared by citric acid was synthesized by controlling the dosage of organic chelating agent.On the basis of this experiment,LaAlO3 was prepared by twice calcination from relatively carbon-free precursor.And it is obvious that the products'specific surface area increased from 17.76 m2·g-1 to 32.62 m2·g-1.The BET specific surface area of ?-Al2O3/CeO2/LaAlO3(?(CeO2)%=12.5%,?(LaAlO3)=12.5%),which was synthesized by the precursor prepared by citric acid,increased from 69.65 m2·g-1 to 91.5 m2·g-1.And the BET specific surface area of LaMn3Al9O19,which was synthesized by the precursor prepared by citric acid,increased from 9.24 m2·g-1 to 13.46 m2·g-1.Due to the increase of specific surface area.the H2-TPR and CO catalytic reduction denitration properties were both promoted.