Syntheses And Proton Conduction Properties Of FAU And LTA Type Zeolites

As typical inorganic microporous materials,zeolites have achieved rapid development since their artificial syntheses.In the fields of chemistry and chemical engineering,zeolites have been successfully applied as catalysts,adsorbents,and separation agents.According to the different framework elements of zeolites,they can be classified as aluminosilicate zeolites,silicoaluminophosphate zeolites,and aluminophosphate zeolites,etc.Moreover,there are also some heteroatom-containing zeolites,such as titanium-silicon zeolites,silicon-germanium zeolites and so on.In silicoaluminophosphate zeolites,the acid sites are produced due to the existence of silicon,thus,silicoaluminophosphate zeolites are often used as catalysts of preparing light olefins reaction.In the case of aluminosilicate zeolites,zeolites with a high silica-alumina ratio and strong acidity can be used in catalytic cracking of heavy oil and catalytic reduction of oxynitride;while,zeolites with low silicon-aluminum ratio are often used as adsorbents,desiccants and ion-exchanged reagents,such as X zeolite,3 A zeolite,4A zeolite and 5A zeolite.In recent years,the development of zeolites with new properties and new applications arouses more and more interest.Recently,the development of fuel cells has promoted the exploitation of proton conducting materials.In terms of most proton conducting materials,water usually plays a vital role in the proton condction.Zeolites have highly stable framework,good water adsorption capacity and ion-exchanged capacity,therefore they are the potential proton conducting materials.However,the relative researches of zeolites are rare.In this thesis,the aluminosilicate and silicoaluminophosphate zeolites,including FAU-type zeolites(NaX,NaY,SAPO-37)and the LTA-type zeolites(NaA)have been selected as targets to study their proton conduction properties.The main researches are summarized below:(1)In Na2O-Al2O3-SiO2-H2O system,FAU-type aluminosilicate zeolites with different Si/Al molar ratio have been synthesized.Based on this,we study the influencing factors of temperature,humidity,guest ions,stability and particle sizes on proton conduction properties of as-synthesized FAU zeolites.It suggests Na+ and water molecules in the pores or cages play an important role in proton conduction,which endow FAU zeolites with higher proton conductivity.Such FAU zeolites can exhibit high proton conductivity at high temperatures and reach 10-2 S cm-1(80℃,100%RH).Meanwhile,these FAU zeolites also have highly watery stability,thermal stability and acid/alkaline stability.After acid/alkali,boiling water as well as calcination treatments,their proton conductivity can still maintain 10-3 S cm-1.Furthermore,different Si/Al ratios,guest ions and crystal sitze have influence on the proton conduction property.(2)In Al2O3-P2O5-(TMA)2O-(TPA)2O-SiO2-H2O system,silicoaluminophosphate zeolite of SAPO-37(FAU-type)has been successfully synthesized.The as-synthesized SAPO-37 zeolite has regular morphology and particle size of 200-300 nm,which exhibits highly water-dependent proton conduction property.As a result,the proton conductivity of as-synthesized SAPO-37 can reach 10-3 S cm-1(40℃,in water).The templates of tetramethylammonium and tetrapropylammonium in the pores of SAPO-37 may further favor the proton conduction process.Furthermore,the SAPO-37@PVDF membranes have been prepared by spin coating method and the proton conduction properties have been explored.(3)In Na2O-Al2O3-SiO2-H2O system,LTA-type aluminosilicate zeolite NaA has been synthesized and its proton conduction property has been studied.The results show that the as-synthesized NaA zeolite has obvious temperature and humidity dependent proton conduction property.Under the conditions of 80℃ and 100%RH,the proton conductivity of as-synthesized NaA zeolite can reach 9.12×10-3 S cm-1.Moreover,we have synthesized LTA zeolites with different guest ions,such as Li A,KA,MgA,CaA and SrA by ion-exchanged method,their proton conduction properties have been further studied.(4)In Na2O-Al2O3-SiO2-H2O system,we utilize sodium hydroxide to activate diatomite to realize the synthesis of NaA zeolite under the condition of stirring and heating in a water bath.The as-synthesized NaA zeolite has a regular cubic morphology,and the molar ratio of Si/Al is about 1.There are lots of Na+ ions located in the pores/cages of as-synthesized.Such NaA zeolite exhibits good proton conduction property of 5.96×10-3 S cm-1 at 100%RH and 80℃.