Selective Oxidation Of P-Xylene By M-MCM-41(M=Fe?Cu) And Cu-MOF

p-Xylene,as a cheap industrial raw material,is mainly used to synthesize terephthalic acid which was prepared polyester resins.However,other organic compounds containing oxygen groups were rarely synthesized by the oxidation of p-xylene.2,5-dihydroxy-terephthalic acid and 4-hydroxymethylbenzoic acid are widely applied to prepare materials,medicine,catalysis,energy,resulting in the rapid increase of their consumptions.However,current synthetic methods exists multiple reaction steps,high pressure and temperature,amounts of pollutants,and low yield.This is not suitable for the present the concept of environmental protection.In heterogeneous conditions,one step oxidation of p-xylene to the corresponding oxides is operational methods to solve these problems.MCM-41 and MOF materials have been widely used in catalysis because of their effective pore size and specific surface area.To solve these problems,series of M-MCM-41(M=Fe,Fe/Cu,Cu)materials and Cu-MOF as catalysts for selective oxidation of p-xylene to 2,5-dihydroxy-terephthalic acid and 4-hydroxymethylbenzoic acid were investigated.The main results are as following:(1)The catalytic performance of the catalyst using Fe-MCM-41(Fe:Si=1:100)as the model for the oxidation of p-xylene to 2,5-dihydroxy-terephthalic acid.It was found that using acetic acid and acetonitrile as mixed solvents are beneficial to the formation of 2,5-dihydroxy-terephthalic acid.The catalytic oxidation properties of Fe-MCM-41(Fe:Si=1:100),Fe-MCM-41(Fe:Si=1:50),Fe/Cu-MCM-41(Fe:Cu:Si=1:1:50),Cu-MCM-41(Cu:Si =1:50)and Cu-MCM-41(Cu:Si=1:100)were studied under mixed solvent.The generation of 2,5-dihydroxy-terephthalic acid and the transformation of p-xylene were both best using the Cu-MCM-41(Cu:Si=1:100)when acetic acid acetonitrile volume ratio was 3:1.(2)The hot filtration experiment of Fe/Cu-MCM-41(Fe:Cu:Si=1:1:50),Cu-MCM-41(Cu:Si=1:50)and Cu-MCM-41(Cu:Si=1:100)was investigated.The circulation experiment of Cu-MCM-41(Cu:Si=1:100)was also studied.All data showed that only Cu-MCM-41(Cu:Si=1:100)has no obvious deactivation.Under the optimum conditions,the conversion of p-xylene reached 21.7%and the selectivity of 2,5-dihydroxy-terephthalic acid was 73.0%.In the reaction system,4-hydroxy-methylbenzoic acid and p-benzoquinone-2,5-dicarboxylic acid.These by-products were easy to separate and purify from the reaction system.(3)Effects of reaction temperature,reaction time,solvents and their amounts were discussed for the selective oxidation of p-xylene to 4-hydroxymethylbenzoic acid using Cu-MOF as the catalyst.The data showed that the lower temperature is conducive to the transformation of p-xylene and the generation of 4-hydroxy methylbenzoic acid.The filtration and cycle experiments of Cu-MOF displayed the high activation of the catalyst.(4)Comparison of Cu-MOF,Cu-MCM-41(Cu:Si=1:50),Cu-MCM-41(Cu:Si=1:100),Cu-MCM-48(Cu:Si=1:50),Cu-MCM-4 8(Cu:Si=l:100),TCS-Cu-MCM-41(Cu:Si=1:50),TCS-Cu-MCM-41(Cu:Si=1:100),TS-Cu-MCM-41(Cu:Si=1:50),TS-Cu-MCM-41(Cu:Si=1:100),Cu-MOF-5,Cr-MOF,Cu-ZIF-8,Fe-MOF,3%Cu-M IL-125 and 5%CuO-TiO2 aerogel for selective oxidation of p-xylene to 4-hydroxy-methylbenzoic acid.All data verified that Cu-MOF was suitable for the preparation of 4-hydroxymethylbenzoic acid.In addition,it was found that Cu-MIL-125 may be an excellent catalyst for selective oxidation of p-xylene to 1,4-benzenedimethanol,while CuO-TiO2 aerogel may be a candidate catalyst for selective oxidation of p-xylene to 2,5-dihydroxy-terephthalic acid at low temperature.(5)The experimental conditions were optimized.30%H2O2(V):p-xylene(V)=3:1,CH3CN(V):p-xylene(V)=20:1,Cu-MOF(mg):p-xylene(mL)=30:1,30? and 5h are optimum conditions.The amplification experiment,even if enlarged 15 times,the reaction still exhibited excellent catalytic properties of p-xylene to 4-hydroxy-methylbenzoic acid,the conversion of p-xylene was 84.8%and the selectivity of 4-hydroxymethylbenzoic acid was 97.6%.(6)Through the analysis of FT-IR and XPS,it was found that Cu-MCM-41(Cu:Si=1:100)catalyst in the presence of Si-O-Cu-OH,indicating that the Cu(II)into the framework of MCM-41.According to the distribution of oxidation products,FT-IR,XPS and the oxidation of 2,5-methylphenol and terephthalic acid,the two stage oxidation mechanism was proposed.The mechanism was expected to open up a new avenue for non-Kolbe-Schmitt reaction to synthesize phthalic acid derivatives.(7)Through the analysis of FT-IR,XRD,BET,and XPS,it was found the structure properties of Cu-MOF before and after reaction was not changed.Moreover,the mechanism of the selective oxidation of p-xylene to 4-hydroxymethylbenzoic acid was proposed,according to the oxidation products and reported references.The proposed mechanism was guide to the application of MOFs in selective oxidation under mild conditions.