Preparation Of Cu-Based Mesocrystal Catalyst And Its Catalytic Performance In Si Hydrochlorination Reaction

Mesocrystals are non-classical crystals with a highly ordered nanoparticle superstructure,which are composed of aligned nanocrystals in crystallographic register.Because of their unique combination of nanoparticle properties and order with mesoscopic size allowing for novel collective and emergent properties,the mesocrystals possess promising applications and have received rapidly increasing interest.At present,the types of mesocrystal materials are relatively single,and their formation mechanism needs to be further studied.Therefore,it is particularly important to enrich the types of mesocrystals and explore the formation mechanism of mesocrystals.In addition,mesocrystal materials are mainly used in the fields of optoelectronics and biomedicine,and their applications in industrial catalytic reactions are rarely reported.The trichlorosilane（TCS）prepared by the Si hydrochlorination reaction is an important intermediate for the production of solar polysilicon,silane coupling agents and other organic silicon products.Improving the selectivity of trichlorosilane and reducing production costs are of great significance to the solar industry.If the mesocrystal structure can be integrated with Cu-based metal oxides to form a new type of mesocrystal material,it is very possible to greatly improve the catalytic performance of the Si hydrochlorination reaction.Based on this,the following research work is carried out in this thesis:（1）The core-shell-sructured Cu₂O@CuO mesocrystals with hexapod morphology were prepared by using solvothermal reaction followed by calcination.The formation mechanism of Cu₂O@CuO mesocrystal was revealed based on a series of time-dependent experiments.The mesocrystals are formed mainly based on the ordered assembly driven by the CH₃COOH molecule and the dipole-dipole interaction.At the same time,H⁺etching and further calcination are crucial to form the core-shell-structured mesocrystal with hexapod morphology.In addition,the prepared mesocrystal is used for the Si hydrochlorination reaction.The core-shell-structured Cu₂O@CuO mesocrystal catalyst system showed higher Si conversion,trichlorosilane selectivity and stability compared with the catalyst-free system and the core-shell Cu₂O@CuO nanoparticle catalyst system.This is due to the rough surface providing abundant active sites;the close contact and highly ordered arrangement between the Cu₂O core and CuO shell leads to the generation of the stronger electronic synergistic effect.In addition,the core-shell-structured mesocrystal catalyst is on the micrometer scale,thus improving its structural stability.（2）We successfully prepared Cu₂O mesocrystal by adjusting the ratio of DMF and H₂O in the reaction system.The dendritic core-shell Cu₂O@CuO mesocrystal material rich in defect sites is obtained through the calcination of the premade Cu₂O mesocrystal.The formation mechanism is inferred by collecting and analyzing the intermediate products of different reaction time periods.In this process,in addition to the driving effect of the CH₃COOH molecule and the dipole-dipole interaction,the change of solvent polarity is the key to the formation of dendritic morphology.In addition,the catalyst exhibits more excellent catalytic performance in the Si hydrochlorination reaction.In addition to the strong synergistic effect between the core and shell,the abundant defect sites on the surface are also conducive to the further improvement of catalytic performance.（3）We successfully prepared atomic Sn-doped bread-like Sn₁/CuO mesocrystal materials by using solvothermal reaction followed by calcination.It can be known that these factors have a greater impact on the morphology of the sample by adjusting the type and amount of precursor salt,the ratio of solvent and the type of acid.In addition,the formation mechanism of the material was explored combined with the time evolution experiments.When using Sn₁/CuO mesocrystal as a catalyst,the trichlorosilane yield has been significantly improved compared with Sn_x/CuO mesocrystal and Sn₁/CuO nanoparticles under the same experimental conditions,which is due to the active sites provided by the rough surface,the micrometer scale and the synergistic effect between Sn and CuO.