Synthesis And Catalysis Of Hierarchically Porous Ferrosilicate Beads

Hierarchically porous materials are widely used in catalysis, adsorption, ionexchange and other fields, because of their high hydrothermal stability and largespecific surface area. Most of porous materials are in form of nanosized particlesand they must go through the complex centrifugal separation process in order toachieve the reuse of the catalyst. The beads with macroscopic morphology canachieve straightforward separation from liquid medium, in which the complexity ofthe centrifugation process would be eliminated. From view of catalysis, this is ofgreat significance for the industrial applications of the catalyst.In our work, hydrothermal method was successfully used to synthesizehierarchically porous ferrosilicate beads (FeSil-HPB), which were characterized bySEM, XRD, FT-IR, UV-vis, XPS and N2adsorption-desorption measurement.Synthetic conditions have been widely studied, such as type and contention ofbase, resin content, iron source, the aging temperature and so on. Furthermore,FeSil-HPB was used to catalyze the hydroxylation of phenol and naphthol andbenzylation of benzene reaction. The characterization results showed that the beadswith hierarchical porosity could be successfully prepared in the media of TPAOH orTEAOH. The contention of the bases and content of resin have a big influence onthe shape and structure of the beads. Based on the characterization results of UV-visand XPS, it is concluded that the iron presence in the forms Fe3+and Fe2+and mostof them are tetrahedrally coordinated in the framework. The porous ferrosilicatebeads showed highly catalytic activity in both small and bulky substrates, forexamples in the hydroxylation of phenol and1-naphthol. The high activities aremainly due to the presence of hierarchically porosity with large mesopores, whichfavors mass transport of reactants. The beads could be recycled to an acceptedcontent after easy regeneration through room temperature washing in thehydroxylation of phenol, but loss of the active center still occurred. The ferrosilicatebeads also proved to be active in the benzylation of benzene. We found that thenature of iron coordinated environment and nano-iron oxide clusters might play animportant role in determining the reaction rate. More importantly, in the procedureof heterogeneous catalysis, the beads can remain the integrity of the structure and morphology during stirring. Therefore, the beads can achieve straightforwardseparation from the reaction mixture.