Zinc Oxide Supported Modified ZSM-5 Catalyst For Propane Dehydrogenation Research

The oxidative dehydrogenation of propane breaks through the limitation of the kinetic equilibrium of direct dehydrogenation of propane.The use of mild CO₂ as an oxidant is a promising route for propane dehydrogenation.It is well known that carbon dioxide as a greenhouse gas has caused global temperatures to rise and disrupted the global ecological balance.It is a urgent need to look for rational routes to reduce the emission of CO₂ and ease the process of global warming.Zinc oxide is considered to be an environmentally friendly catalyst and has become a promising catalyst for propane dehydrogenation due to its low cost.However,the zinc oxide active sites are likely to agglomerate to generate larger zinc oxide nanoclusters on the surface of the catalyst,but large particles of zinc oxide nanoclusters exhibited poor catalytic performance for propane dehydrogenation.It is generally believed that ZSM-5 molecular sieve is also widely used as a catalyst support due to its low price.Meanwhile,ZSM-5 catalysts are widely alkane cyclized and partially alkane dehydrogenated.However,the C-C bond will be deeply cleaved due to the strong acidic sites on the surface of the ZSM-5 molecular sieve,resulting in declined surface area and severe carbon deposit.This case hinders the exposure of active sites and reduces catalytic performance of alkane dehydrogenation.This work aims to synthesize a novel zinc oxide supported modified ZSM-5molecular sieve catalyst by modifying the active site of ZSM-5 supported zinc oxide.Our strategy is to reduce the acidity and basicity of the molecule and the active site dispersion of zinc oxide by removing aluminum from the ZSM-5 molecular sieve and by tuning it with magnesium.For ZSM-5 molecular sieve catalysts with relatively small acid content,we use aluminum nitrate to dealuminate aluminum to generate aluminum vacancies on the surface of ZSM-5,and then transfer the active sites of zinc to the molecular sieve framework to regulate the molecular sieve cell volume and catalytic performance.It can be seen that 7Zn/DEZSM-5 catalyst exhibits excellent catalytic performance with a propane conversion of 55%and a selectivity of 81%.7Zn/DEZSM-5 catalyst exhibits well stability and remains better stability after experiencing six regeneration cycles with less carbon deposits.At the same time,the effects of precursors with different active sites and different reaction conditions on the activity of ZSM-5 catalysts supported by zinc oxide were also investigated.Additionally,for the ZMS-5 molecular sieve catalyst with large amount of acidity,the approach we adopted is to change the acidity and alkalinity of the surface of the ZSM-5 molecular sieve through different levels of magnesium precursors,and adjust the zinc active site through the different amount of magnesium content on the molecular sieve.It is clear that the activity of magnesium-modified ZSM-5 molecular sieve catalyst is roughly positively correlated with the magnesium content.The size of zinc active sites can be well cut by magnesium species,and large zinc oxide nanoclusters can be cut into small zinc oxide micro-nanoclusters.The synthesized catalysts were measured by XRD,Raman,XPS,BET,²⁷Al solid nuclear magnetic resonance,NH₃-TPD.The research on this subject provides a promising strategy to improve the catalytic activity of ZSM-5 supported ZSM-5 molecular sieves,and has excellent application prospect.