Synthesis And Catalytic Performances Of Iron-doped Hierarchically Porous SiO₂ Zeolite

The discovery of hierarchical molecular sieves solves the problem that material transport is difficult in the applications of industry,also solves the leaching of the active sites of macroporous molecular sieves.So far,the most of multi-hole zeolite catalysts are powdery.Although these materials have good activity in various reactions,but they have difficult in the separation from solution such as filtration and centrifugation,etc.So it causes the unnecessary economic consumption and energy waste in the industrial application.Hence,it is important to synthesize a molecular sieve with good activity and accessible material,which also makes it have better prospect in application of industry.In this paper,IRA-900 beads was as hard templating,tetrapropylammonium hydroxide organic alkaline solution was as alkali source,tetraethyl silicate was as silicon source,the source of iron was hexahydrate ferric chloride.By the processes of ion exchange,sol,hydrothermal polycondensation,high temperature calcination and so on.Finally,a hierarchical porous silica catalyst(Fe-ZSM-5)with MFI structure containing iron was prepared.The pore canal of target catalyst molecular sieve replicated perfectly the structure of IRA-900 hard template.The catalysts were characterized by scanning microscopy,X-ray diffraction,transmission microscopy,infrared,N2 adsorption/desorption and so on.The characterization results indicated that the surface of Fe-ZSM-5 molecular sieve was complete and regular.The pore size of Fe-ZSM-5 was about 30 nm.The particle size of Fe-ZSM-5 was 0.3 mm to 1.2 mm.Finally,UV showed that the most of iron species were four-coordinated structure in the target catalyst.For the catalytic oxidation of phenol,the conversion rate of phenol was 16%,and the selectivity rate of pyrocatechol was 79%.The degradation of methylene blue(MB)and phenol were the target reactions,and the catalytic performance of iron-doped hierarchical catalysts was investigated.The results showed that Fe-ZSM-5 exhibited good catalytic performance in degradation reaction.The degradation of MB solution only needed 2.5 h,and the degradation rate of MB closed to 100%.Similarly,for the degradation of phenol,the catalytic reaction only needed 3 h,and the degradation rate of phenol was close to 100%.The result is that the three-dimensional continuous multi-hole pores help to contact between the substance and the active site.Finally,through the leaching experiments and recycling test results,it further demonstrated that the Fe-ZSM-5 catalyst had a high stability,and after multiple catalytic reactions,there was no loss of effective active sites from target catalyst to solution.What's more,the catalyst separated from the reaction liquid without further centrifugation and filtration treatment,which showed great value for application in the industrial field.