Preparation And Catalytic Performance Study Of Zeolite Analcime And LZ-276

As porous materials with regular channels and adjustable pore size,zeolites have a wide range of applications in the catalytic field because of their special microscopic morphology,abundant pores,large specific surface area and stable framework structure.Owing to the similar catalytic performance to the nobel metals,as well as low price and abundant reserves on the earth,copper-based nanomaterials have attracted great interests in catalysis field.Therefore,in this paper,zeolite-based catalyst was successfully prepared by combining copper nanoparticles?Cu NPs?and zeolites.Influences on product selectivity of styrene oxidation catalysized by the composite catalyst were further explored.Then,the cycloaddition reaction of CO₂ and epoxides was introduced.The two reactions above could combine into one-pot reaction.Moreover,a much stabler zeolite was prepared by hydrothermal synthesis and used for the one-pot synthesis of styrene carbonate.Main research contents in the thesis are as follows:1.Analcime ANA was prepared by hydrothermal synthesis method using tetrapropylammonium hydroxide?TPAOH?as organic template,silicic acid?SiO₂·nH₂O?as the silicon source and sodium aluminate?NaAlO₂?as the aluminum source.After the temperature rising in program stage,the crystallization sample was calcinated by high temperature.The Cu NPs/ANA composite catalyst was prepared by physical adsorption method and high temperature-pressure hydrogenation reduction process.The morphology,composition and structure of the sample were characterized by the scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?and temperature programmed reduction?H₂-TPR?.The composite catalyst was used in catalyzing the styrene oxidation reaction and it was found that the valence state of Cu NPs had a regulatory effect on the slectivity of the products.Then,considering that the product of styrene oxidation reaction,styrene oxide,can undergo cycloaddition reaction with CO₂ to achieve efficient use of CO₂,ANA was used in one-pot synthesis of styrene carbonate?SC?.After 10 h of reaction at 0.5 MPa and140?,the conversion of styrene was approximate to 100%,and the yield of styrene carbonate achieved to 78.2%.2.Using silicic acid as the silicon source,sodium aluminate and aluminum sulfate as the aluminum source,the zeolite LZ-276 was hydrothermally prepared without any templating agent.The zeolite sample was characterized by SEM,XRD,specific surface area and pore size analyzer,temperature-programmed desorption?TPD?and other means.LZ-276 and co-catalyst potassium iodide KI were applied to the oxidative carboxylation of styrene.The effects of oxygen source type,raw material ratio,reaction temperature,CO₂charging pressure and reaction time on the catalytic results were investigated.The optimum reaction conditions were as follow:the volume ratio V?styrene:tert-butyl hydroperoxide?=1:1,the pressure of CO₂ was 0.5 MPa and reacted at 140?for 10 h.Under this condition,the styrene conversion was close to 100%,and the yield of SC was77%.Compared with the previously reported literatures,the catalytic system had the advantage of ensuring high catalytic activity at lower pressure,and the molecular sieve catalyst exhibited good chemical stability in five cycles of reaction.In the five-cycle reaction,not only the yield of the target product is not significantly lowered,but also the structure of the catalyst remains intact.Based on these research work,the possible mechanism of LZ-276/KI catalyzing the oxidative carboxylation of styrene was proposed.One-pot synthesis method could be regarded as a two-step sequential reaction.At the same time,the?-carbon atom of styrene oxide was attacked by I^-,which led to the ring opening of styrene oxide.While the Si atom providing the alkaline site in LZ-276 could activate the CO₂ molecule.Then after the bond angle was less than 180°,it was inserted into the intermediate of the previous step to produce an alkyl carbonate compound.Finally,the target product styrene carbonate was obtained after removing the iodide ion from the intermediate alkyl carbonate compound and ring closure.In summary,both the zeolite catalysts showed excellent catalytic performance and stability in the study of catalytic reactions,which would provide new methods and ideas for the resource utilization of CO₂.Meanwhile,it also offered a promising opportunity of modifying zeolites with effective active substances.