Preparation Of Pt/ZSM-5 Composite Catalyst Via Atomic Layer Deposition Technology For Catalytic Conversion Of N-butane

Light olefins and aromatics are important basic chemical raw materials with tight supply-demand relationship currently.The production of light olefins and aromatics by catalytic cracking of n-butane is one of the most important new technologies,which has a very broad application prospect in industry.Zeolites have shown better catalytic performance in catalytic cracking.Studies have illustrated that noble metals have good alkane dehydrogenation ability,which is very favorable for the catalytic conversion of alkane,and the chemical environmental states would make the catalytic performance very different.Using precious metal components with dehydrogenation function and molecular sieve with cracking capability,it is expected to prepare bifunctional catalysts with excellent catalytic conversion ability for n-butane.This thesis is dedicated to the preparation of high-performance noble metal-zeolite bifunction catalysts through atomic layer deposition technology,with acid sites and metal dehydrogenation sites working in synergy,and achieve to efficiently convert n-butane to produce light olefins and aromatics.ZSM-5 was used as the support,which also provides acid sites,and noble metal Pt species was deposited by atomic layer deposition technology.It could be found that the coordination state of Pt could be controlled by Si O₂ and Al₂O₃ on as-synthesized mAl/Pt/nSi/ZSM-5 bifunction catalyst.Combining with CO-DRIFTs and n-butane catalytic cracking results,it illustrated that Si O₂ and Al₂O₃ introduction can significantly change the coordination state of Pt,and enhance the ability to catalyze the conversion of n-butane.Comparing the results of n-butane conversion with different layers of deposited Si O₂ and Al₂O₃,it was found that 5Al/Pt/1Si/ZSM-5catalyst had the best n-butane catalytic cracking performance,its n-butane conversion could reach to 96%and yield of alkene with aromatics could reach to 63%at 550℃,significantly higher than other catalysts.On the basis of Pt/ZSM-5 bifunctional catalyst,in order to further improve the catalytic performance,a second noble metal Pd was further introduced by atomic layer deposition technology to prepare xPd-Pt/ZSM-5 series catalysts.With Pd added,better activity and stability of as-prepared samples could be found in n-butane catalytic cracking.As the content of Pd varied,xPd-Pt/ZSM-5 sample exhibited different catalytic performance.Under the same reaction conditions,the conversion rate of n-butane over Pt/ZSM-5 catalyst is 28%,and that on 30Pd-Pt/ZSM-5 catalyst could be up to 43%.The characterizations indicated that the increase of Pd content will affect the size of the metal particles and the coordination state of Pt,which may be the reason for the difference in catalyst performance.The work in this thesis provides new ideas for the construction of the active site in the atomic-level and regulate the distribution of the catalytic cracking products of light alkanes.