Synthesis Of ZSM-5 Zeolites In PAM/GO Hydrogel And Their Catalytic Performance In MTO Reaction

Aluminosilicates molecular sieve ZSM-5 with MFI framework has large surface area,high thermal stability,strong acidity and good molecular shape selection performance.ZSM-5 as an effective catalyst for methanol-to-olefin(MTO)reaction,its catalytic performance is inseparable from its morphology.It is important to develop synthetic strategies to control the morphology of ZSM-5 molecular sieve.Polyacrylamide(PAM)and graphene oxide(GO),as commonly used additives,can control the morphology of ZSM-5 molecular sieve when they are used alone.PAM can interact with GO through the functional groups on their surface,PAM/GO hydrogel have influence on the morphology of ZSM-5 molecular sieve.In this paper,hierarchical pores ZSM-5 molecular sieves with different morphology were successfully synthesized in PAM/GO hydrogel by hydrothermal method.The effects of the amount of PAM and GO,the interaction of in-situ PAM and finished PAM with GO on the morphology and MTO catalytic performance of ZSM-5 molecular sieves were investigated.In this thesis,ZSM-5 molecular sieves were synthesized in in-situ PAM,GO,in-situ PAM/GO hydrogel respectively.The addition of appropriate amount of PAM changed the growth direction of ZSM-5 molecular sieves,making it grow along the caxis.With the increase of the amount of PAM,the length of the c-axis gradually increased,forming a coffin-shape ZSM-5 molecular sieves.The adsorption energy of the GO is different from different facets,thus influence the morphology of ZSM-5molecular sieves.ZSM-5 molecular sieves were synthesized in PAM/GO hydrogel,with the increase of GO content,the growth of(101)facet was promoted,and the coffin-shaped ZSM-5 molecular sieves were obtained.Compared with the samples synthesized in PAM hydrogel,the c-axis was longer and the coffin-shaped was more obvious.The samples synthesized in GO have(001)facet,the(001)facet disappear when synthesized in PAM/GO hydrogel.Through TG,FT-IR and XPS characterization shown that PAM and GO may interact with hydrogen bonds,the addition of GO can limit the movement of polymer,and improve the cross-linking between monomer,forming a more uniform network structure and changing the morphology of ZSM-5 molecular sieves.Next,this paper further explored the effects of finished PAM and PAM/GO composite hydrogel on ZSM-5 molecular sieves.The ZSM-5 molecular sieves synthesized in the original formula with the addition of finished PAM did not have fixed morphology.Nano-sized ZSM-5 molecular sieves were synthesized in the new formula,hexagonal ZSM-5 molecular sieves were synthesized by adding finished PAM,and ellipsoidal ZSM-5 molecular sieves were obtained in the PAM/GO composite hydrogel.The FT-IR result shown that hydrogen bonds may exist between finished PAM and GO.Finally,the acidity and MTO catalytic performance of the ZSM-5 molecular sieves were investigated.When only in-situ PAM or GO were added,the MTO catalytic performance was slightly improved and the life of the ZSM-5 molecular sieves was short.ZSM-5 molecular sieves synthesized in in-situ PAM/GO hydrogel have excellent MTO catalytic performance due to its more suitable weak acid and strong acid content.The life of the catalytic,the conversion of methanol and the selectivity of light olefins were significantly improved.When the amount of in-situ PAM is 5% and the amount of GO is 15 mg,the selectivity of light olefins was the best.The selectivity of light olefins was 78.7% and the life was over 35 h.Similarly,ZSM-5 molecular sieves synthesized in finished PAM/GO hydrogel shown the best selectivity of light olefins and the life of catalytic.The selectivity of light olefins was stable at about 65.0%,and the life was 23 h.When the amount of GO was too much,the life of ZSM-5 molecular sieves was shortened,and the selectivity of light olefins was reduced,so the amount of GO should be appropriate.