Study On Preparation Of Aluminum Nitride Supported Platinum-zinc Catalyst And Its Performance In Catalytic Dehydrogenation Of Isobutane

Covalent nitrides（typically such as boron nitride and aluminum nitride）are well-known high-temperature stable materials with excellent mechanical strength,corrosion resistance and thermal conductivity,and have potential application prospects in the field of heat-driven heterogeneous catalysis.In addition,the unique nitride surface can provide a new type of metal-support interaction,which provides a new way to replace traditional oxide supports to prepare supported catalysts,and it has always been a hot spot in the field of catalysis basic research.Diffierent from other covalent nitrides,the Al-N bond on the surface of aluminum nitride is easily hydrolyzed at room temperature（Al N+2H₂O→Al OOH+NH₃）,resulting in a large number of riveting sites that can disperse the active metal components,which is expected to solve the limitation of active metal dispersion on the nitride supports,providing new ideas for the development of highly dispersed and highly stable metal catalysts.This thesis focuses on the application background of the dehydrogenation of low-carbon hydrocarbons to olefins,that is,the reaction of isobutane dehydrogenation to isobutene.The synthesis and performance evaluation of aluminum nitride-based Pt alloy catalysts were carried out.Characterization methods such as spherical aberration electron microscopy,X-ray absorption spectroscopy,in-situ infrared revealed the intrinsic correlation between the catalyst microstructure and reaction performance,and explained the promotion effect of aluminum nitride support on the formation of the alloy phase and the promotion of the catalytic reaction performance.The main results are as follows:Nano-aluminum nitride（n-Al N）were used as a support to achieve high dispersion and stable loading of Pt species.Combined powder XRD,nitrogen physical adsorption,SEM test,Zeta potential measurement,mass spectrometry tracking roasting-reduction process and other methods revealed that the self-hydrolysis characteristics of aluminum nitride can promote the dispersion and immobilization of Pt active components.Combined with the evaluation of isobutane dehydrogenation performance,the influence of Zn promoter on the structure and catalytic dehydrogenation activity of Pt active components was investigated.The preferred Pt Zn/n-Al N catalyst,at 500℃,atmospheric pressure,WHSV=15.5 h^-1,and N₂ as the diluent gas.The initial conversion of isobutane was27.3%,and the corresponding isobutene selectivity is 92.4%.Four cycles of regeneration showed its good regeneration stability.Secondly,the microstructure of the Pt Zn/n-Al N catalyst was characterized in detail by in-situ XRD,spherical aberration electron microscopy,synchrotron radiation,CO-DRIFT,etc.The results showed that Pt Zn was present on the n-Al N surface in the form of～2 nm low-dimensional nanoclusters The fine structure was close to the Pt₃Zn₁ alloy phase.After the isobutane dehydrogenation reaction,the alloy phase gradually transformed into the Pt₁Zn₁ alloy phase.In the comparative Pt Zn/γ-Al₂O₃ catalyst,Pt mainly coexisted in the form of Pt nanoclusters and Pt₁Zn₁ alloy clusters.Under the test conditions of isobutane dehydrogenation at 500℃,atmospheric pressure,space velocity of 15.5h^-1 and N₂as the diluent gas,comparing the reaction performance of the two catalysts,Pt Zn/n-Al N catalyst showed two times isobutane conversion activity(5.5 vs 2.4 s^-1)higher than Pt Zn/Theγ-Al₂O₃catalyst,and the isobutene selectivity（92.4%）on the Pt Zn/n-Al N catalyst is also nearly 6%higher than that of the Pt Zn/γ-Al₂O₃ catalyst.Finally,based on the understanding of the characteristics of n-Al N and the unique dispersing ability of Zn species on its surface,a series of Zn O/n-Al N catalysts with different loadings were prepared,combined with XRD,nitrogen physical adsorption,and catalytic dehydrogenation testing.The effect of Zn loading on the catalyst structure and isobutane dehydrogenation performance was investigated,which provided research accumulation for the further development of non-noble metal low-carbon hydrocarbon dehydrogenation catalysts.