Solvent-free Synthesis Of Iron-based Zeolites Promoted By Fenton's Reagent And Their Catalytic Performance In Hydroxylation Of Phenol

Hydroxylation of phenol is an important industrial reaction,in which dihydroxybenzene products?catechol and hydroquinone?can be used for different purposes.Moreover,ZSM-5,Beta and MOR molecular sieves are three kinds of important industrial related molecular sieves,which are widely used in catalytic fields such as petroleum processing,coal chemical industry and fine chemical industry.More importantly,iron-based molecular sieves have become a research hotspot in the field of catalytic synthesis because of its simple process,mild reaction conditions and green and pollution-free.Currently,there remains a great challenge to synthesize zeolites in an energy-saving and environmentally friendly manner.It is a green route to synthesize molecular sieves by solvent-free method without extra solvent,avoiding waste liquid and autogenous high pressure,and using"quasi solid conversion"mechanism to improve the effective utilization of raw materials and reduce costs.The addition of hydroxyl radicals into zeolite synthesis system by UV irradiation or Fenton reaction can significantly accelerate the nucleation of zeolite and its crystallization process.The purpose of this dissertation is to achieve the synthesis of Fe-ZSM-5,Fe-Beta and Fe-MOR molecular sieves with high crystallinity in a shorter period of high-temperature crystallization by an improved solvent-free method.The resultant materials were used as catalyst for hydroxylation of phenol.The main contents are as follows:1.A novel solvent-free route of synthesizing Fe-ZSM-5 zeolite was realized,which is featured by using Fenton's reagent as a promoter.The influences of crystallization time,amount of hydrogen peroxide and low-temperature pretreatment on the synthesis of Fe-ZSM-5 zeolite were investigated in detail.The results indicate that the combination of solvent-free synthesis with Fenton's reagent can facilitate the rapid crystallization of Fe-ZSM-5 zeolite.The resultant Fe-ZSM-5 zeolite was used as a catalyst for hydroxylation of phenol,and characterized by XRD,SEM,ICP-AES,N₂ physisorption and UV–Vis diffuse reflectance spectroscopy.Notably,it exhibits a much better catalytic performance as compared with the reference catalyst by conventional solvent-free method.The observed enhanced catalytic performance for this Fe-ZSM-5 catalyst is attributed to its larger BET surface area and mesoporous volume as well as enrichment towards phenol.2.Fe-Beta molecular sieve was synthesized by combining Fenton's reagent and solvent-free method.The effects of iron source,silicon source,high-temperature crystallization time,Fenton's reagent,low-temperature pretreatment temperature,the order of adding seeds and whether to add or not,and the type of ammonium salt on the synthesis of Fe-Beta molecular sieve were investigated in detail.The results show that Fe-beta molecular sieve with high crystallinity can not be synthesized in a shorter high temperature crystallization time,which may be due to the slow formation of TEA⁺species in the synthesis system.Seven representative samples were selected as catalysts to study the catalytic performance of hydroxylation of phenol,and characterized by XRD,SEM and N₂physisorption.Under the condition of 3 h reaction,the conversion rate of phenol was 39.50%and the selectivity of dihydroxybenzene was 98.16%for sample Fe₃-HP₀-LT₀-HT₇₂.Among the seven representative samples,the best performance was attributed to its large BET surface area.3.A novel solvent-free route of synthesizing Fe-MOR zeolite was realized,which is featured by using Fenton's reagent as a promoter.The effects of grinding method,iron source,high-temperature crystallization time,Fenton's reagent and low-temperature pretreatment temperature on the synthesis of Fe-MOR molecular sieve were investigated in detail.The results show that the Fe-MOR zeolite with high crystallinity can be synthesized in a shorter high temperature crystallization time.Two representative samples were selected as catalysts to study the catalytic performance of hydroxylation of phenol,and characterized by XRD and SEM.The results show that the poor catalytic performance may be attributed to the less Fe content in the two samples.