Preparation And Perfoemance Study Of Hierarchical TS-1 For Hydroxylation Of Benzene

Titanium silicate molecular sieves have excellent catalytic activity in the hydroxylation of benzene under mild conditions,which has attracted widespread attention of researchers.However,its narrow pore size limits the diffusion of reaction substrates,and carbon deposition easily blockages the pore and causes catalyst deactivation.Its framework titanium content is low,framework titanium is the main active center,which limits the catalytic activity.In recent years,due to the advantages of hierarchical zeolite molecular sieves with both microporous molecular sieves and mesoporous molecular sieves,researchers in the field of porous materials have focused on the preparation of hierarchical zeolite molecular sieves.However,the methods for synthesizing hierarchical titanium-silicon molecular sieves reported in the literature generally have problems such as complicated preparation process and high cost,which is not conducive to their industrial application development.The biggest challenge facing phenol and hydroquinone production industry is how to find a cleaner,safer and more environmentally friendly new process to replace the traditional production methods.Benzene can be directly hydroxylated with hydrogen peroxide as oxidant.The final product can be obtained from raw materials by one step chemical reaction,which accords with the view of green chemistry.In this paper,we mainly solve these problems,such as:the narrow pore size limits the diffusion of the substrate of the reaction substrate,the contact with the active titanium site,and the low content of the framework titanium.A series of hierarchical Ti-rich TS-1 zeolites were prepared by low-cost nonionic surfactant Triton as mesoporous template,ammonium carbonate as crystallization modifier,and hydrothermal synthesis method.The effect of chain length on the formed catalyst is intended to increase the activity and stability of the catalyst.The main research contents and conclusions are as follows:?1?A new route to synthesis hierarchical Ti-rich TS-1 with uniform intracrystalline mesopores,uniform crystal size and the higher Ti content has been developed by using the environmental-friendly and cheap surfactant Triton X-100 as the assisted template agent and?NH₄?₂CO₃ as crystallization-mediating agent.In this way,the surface area and pore volume of the resulting materials can be adjusted by the TritonX-100 content.The catalytic properties of the Nano-size hierarchical Ti-rich TS-1 were investigated by hydroxylation of benzene to phenol with H₂O₂ as oxidizing agent and deionized water as solvent.Due to the combination of hierarchical pores and high titanium content,the hierarchical Ti-rich TS-1 shows improved catalytic activity in the oxidation of benzene,the yield of phenol increased from about 18%to about 27.7%,and the stability was good,and no deactivation occurred after repeated use for 5 times.?2?The Triton series with different chain lengths was used as a mesoporous template to systematically study the effects of different lengths of Triton on the structural properties and catalytic properties of the catalyst.As the chain length increases,the particle size of the hierarchical titanium silicalite gradually decreases and the surface becomes rough.The results of nitrogen adsorption and desorption showed that the use of Triton,which has different numbers of ether bonds,utilizes the difference in hydrophilicity to achieve controllable pore size of the hierarchical TS-1 and controllable specific surface area.The catalytic performance evaluation results show that the optimal hydrophilic chain length of hierarchical TS-1 for catalyzing the hydroxylation of benzene to phenol is 30,and the phenol yield is increased from 16.7%to 37.2%.