Preparation Of Pt-based And Al-based Catalysts And Their Applications In Propane Dehydrogenation

With the increasing demand for low-carbon olefins and continue enhancement in the proven reserves of natural gas and shale gas,the technology of anaerobic propane dehydrogenation to increase propylene production to replace traditional steam cracking and catalytic cracking technology has important economic value.However,the current commercial catalysts still have some problems including high-temperature sintering of the active components,which leads to deactivation,and the catalyst preparation cost is relatively high,etc.Therefore,there is an urgent need to develop high-performance PDH catalysts with long service life,good recycling,or use earth abundant,non-toxic,and low cost raw material for fabrication.Based on this,this thesis work mainly starts from two aspects.On the one hand,the mesoporous channel structure of the microporous TS-1 carrier were modified to confine the highly active PtSn nanoparticles and promote gas-solid contact-separation.On the other hand,we explored the structure and catalytic mechanism of the coordinated unsaturated active site neighboring the oxygen vacancies on the cheap reduced alumina,which provides a theoretical directions for further preparation of cheap and efficient PDH oxide catalysts.（1）The PtSn/TS-1 catalysts with multi-stage pore structure were synthesized by the method of desiliconization,which were investigated the effect on of long time reaction stability,cycle regeneration stability and propylene formation rate.The effect of carrier structure（titanium-silicon framework structure,surface acidity,etc.）and the valence state of PtSn active center on catalytic performance was investigated by FT-IR,UV-Vis,NH₃-TPD,XRD,XPS,N₂physical adsorption and desorption,etc.TEM,TG and Raman characterization techniques were used to explore the relationship between multi-stage pore structure and the dispersion of PtSn particles and sintering degree,coke formation and carbon deposition type.It is found that the multi-stage pore structure obviously reduces the total amount of carbon deposition,but the carbon deposition type has almost no change.Proper desiliconization and pore expansion is beneficial to the disperse of PtSn particles and effectively restrain its sintering.The diffusion law of propylene/propane molecules in the hierarchical porous structure was studied by ZLC（zero length column method）.The results show that the prepared hierarchical porous structure can increase the interface between active components and reactants,promote the desorption and diffusion rate of propylene,reduce the formation rate of carbon deposition,and improve the catalytic activity and stability of the catalyst.（2）Through the controllable reduction ofγ,δ,θ,α-Al₂O₃nanocatalysts,the quantitative relationship between the oxygen vacancy（the corresponding coordinately unsaturated Al-O acid-base pairs）and propane dehydrogenation activity was explored.Using O₂pulse oxidation experiment,it was found that there was a linear relationship between the number of oxygen vacancies in the reduced alumina and the propylene formation rate.Via the characterization of physical and chemical adsorption of NH₃-TPD,C₃H₈-TPD and C₃H₆-TPD,we deeply understand the formation process of coordinately unsaturated Al cations(Al_cus)sites and dynamic surface structure changes of alumina catalysts during PDH reaction.