Study Of Platinum-Gallium Catalysts For Propane Dehydrogenation To Propylene

Propane production costs continue to decline as shale gas extraction technology matures The production process of propane dehydrogenation to propylene using propane as raw material has become an investment hotspot due to its high product profit margin.At present,various propane dehydrogenation catalysts have been developed,but in actual industrial production,the use of Pt-based catalysts is still the mainstream.Gallium aluminum spinel（Ga₁Al_x）,gallium silicon molecular sieve(Ga₁Si₃₂-MFI)and lanthanum aluminum gallium perovskite(La Al₁Ga₃₂)support containing four-,six-,four-and six-coordinate Ga were designed and developed.The propane dehydrogenation study was carried out after the support was loaded with a low content of Pt（0.1 wt.%）,and the catalyst composition and structure in the reaction,that is,the coordination form of Ga and the synergistic effect of Pt-Ga,were investigated in the reaction.By ICP-AES,the loading of Pt are all about 0.1wt.%.According to HAADF-STEM statistics,the particle sizes of Pt/Ga₁Al₃₂,Pt/Ga₁Si₃₂-MFI,and Pt/La Ga₁Al₃₂ catalysts are all about 2 nm.It is found that the propane dehydrogenation performance of Pt/Ga₁Al₃₂with the ratio of gallium to aluminum is 1:32 is the best.In the presence of H₂,the conversion of propane increased from 12.6%of Ga₁Al₃₂ to 41.1%after loading Pt,and the selectivity of propylene was 96.4%.The propane conversion on spinel-supported Pt catalysts with too high or too low gallium aluminum ratio will decrease.Changes in the ratio of gallium to aluminum have little effect on the selectivity of propylene.Propane conversion was 24.3%and propylene selectivity was 62.3%over Pt/Ga₁Si₃₂-MFI catalyst.Propane conversion over Pt/La Ga₁Al₃₂ catalyst is only 2.1%and propylene selectivity is 94.7%.XPS verified that the coordination forms of Ga on the three catalysts meet the catalyst design requirements,and the loading of Pt helps to increase the surface Ga content.In addition to the difference in the Ga coordination form,there are also differences in the acidic properties of the catalyst surfaces.The order of acid content is:Pt/Ga₁Al₃₂>Pt/Ga₁Si₃₂-MFI>Pt/La Ga₁Al₃₂catalyst.The amount of catalyst acid does not correspond to propylene selectivity.The carbon deposition properties and content of the catalyst after the reaction were tested by TPO.Carbon deposits can be observed near Pt on Pt/Ga₁Si₃₂-MFI and Pt/La Ga₁Al₃₂.On Pt/Ga₁Al₃₂,due to the interaction between Pt and four-and six-coordinated Ga,Pt only plays the role of reverse overflow of hydrogen,so that Pt does not adsorb carbon deposits.The coordination form of Ga is the key factor leading to the excellent propane dehydrogenation performance of Pt/Ga₁Al_x.Appropriate Ga content can further improve the catalytic performance of the catalyst for propane dehydrogenation.When Ga/Al is 32,the catalyst can maintain high activity and good stability at the same time.