Research Of The Novel Microporous Polymers Immobilized Mo-Based Catalysts Preparation And Its Catalytic Properties

Metal-organic frameworks(MOFs)are composed of metal ions and organic ligands via coordinative assembly and then to formed high crystalline materials with a periodic network structure.Hyper-crosslinked polymers(HCPs)are a series of amorphous polymers which are entirely made up of organic molecules by covalent bond.They both have been widely researched and applied in the fields of catalysis,gas storage,separation and so on because of their porosity,tunable cavity sizes,large surface areas and thermal stability.In this paper,two kinds of MOFs with free amino on their ligands,MIL-53-NH2(Al)and MIL-101-NH2(Al),were treated with a two-step postsysthetic modification(PSM),respectively,to synthesize two kinds of heterogeneous catalysts with molybdenum acetylacetonate(MoO2(acac)2)loaded which was the active component.In addition,a novel HCPs named SNW-1 which is synthesized based on Schiff base chemistry,was also used as the support to synthesize the novel MoO2(acac)2@SNW-1 catalyst.The catalytic performances of the three kinds of catalysts were tested in the epoxidation of soybean oil.Meanwhile,these catalysts were characterized by various analytical and spectroscopic techniques.For MIL-53-NH2(AI),the two-step PSM process was as follows:the amine groups were reacted with salicylaldehyde to produce a salicylidene(R-N=C-C6H4OH)moiety,then the moiety act as Schiff-base ligand was coordinated with MoO2(acac)2,thus the MIL-53-NH2-SA-Mo catalyst was obtained.The as-prepared catalyst had good catalytic activity in the epoxidation of soybean oil in the tert-butyl hydroperoxide(TBHP)/toluene system The experimental results showed that the soybean oil conversion and the epoxided soybean oil(ESBO)yield reached 85.1%and 65.3%,respectively,under the optimal reaction conditions(Reaction temperature=110?,n(TBHP):n(double bond)=1.2:1,0.1 g catalyst and reaction time=4 h).The catalyst is stable and can be reused at least three cycles.The characterization results of FT-IR,XRD,UV-Vis-DRS and XPS indicated the imine bone was generated and MoO2(acac)2 coordinated with the azomethine nitrogen in the MIL-53-NH2-SA-Mo catalyst.Moreover,the PSM treatment didn't destroy the original structure of MIL-53-NH2(Al)and the active centers of molybdenum complexs were highly dispersed in the micro channels of MIL-53-NH2(Al).The PSM of MIL-101-NH2(Al)was similar to that of MIL-53-NH2(Al)as mentioned above.Under the optimized conditions,the soybean oil conversion and the ESBO yield reached 89%and 67.4%,respectively,using MIL-101-NH2-SA-Mo as the catalyst.The catalytic activity remained unchanged even after three recycling reactions.The results of FT-IR,UV-Vis-DRS and XPS confirmed the imine bone and coordination of Mo species existed in the MIL-101-NH2-SA-Mo catalyst.However the signals of these bones were weak.From the XRD and N2 adsorption results,it could be concluded that the crystalline structure of MIL-101-NH2(Al)was well kept after the MoO2(acac)2 species were introduced,and the catalyst possessed a large specific surface area.Considering the amount of the Mo species loaded was higher,it could be speculated that there were two kinds of Mo species in the MIL-101-NH2-SA-Mo catalyst,that is,one is the MoO2(acac)2 species coordinated with Schiff-base ligand,the other is the MoO2(acac)2 species encapsulated in the micropores of MIL-101-NH2 suport.The MoO2(acac)2@SNW-1 catalyst was prepared by a special toluene solvent-internal reflux method.The obtained catalyst showed high catalytic performance in the epoxidation of soybean oil.The soybean oil conversion was 90.1%and ESBO yield was 70.7%using the 57.5%(w)MoO2(acac)2@SNW-1 as the catalyst.From the FT-IR,SEM,and N2 adsorption characterization results,it could be concluded that the pores of SNW-1 were mainly microsize and the the active MoO2(acac)2 species were highly dispersed in the micropores of SNW-1,which led to the obvious decrease in the specific surface areas and pore volume.