Synthesis And Catalytic Performance Of Zr-Si Heteroatom Molecular Sieves

The main component of turpentine is ?-pinene,which is active in chemical properties,and can obtain numerous high-value-added fine chemicals or chemical intermediates through isomerization,oxidation,polymerization and other reactions.Zr-Si heteroatomic molecular sieving was prepared for the ?-pinene isomerization reaction in order to solve the problem of high product distribution and low yield of monocyclic terpenes in the current ?-pinene isomerization catalyst.The effects of preparation method,template type,preparation conditions and doping on the structure,morphology,pore diameter distribution and isomerization product distribution of Zr-Si hetero-atomic molecular sieve were discussed.Zr-Si heteroatomic molecular sieves were synthesized by hydrothermal method(DHT),dry glue method(DGC)and sol-gel method(Sol-Gel).Among them,the samples synthesized by hydrothermal method have obvious characteristic peaks and have a relatively high crystallinity,molecular sieves are dominated by micropores,with more acid centers and larger specific surface area.They show better activity and higher limonene selectivity in the ?-pinene isomerization reaction.The structure of Zr-Si molecular sieve was synthesized by hydrothermal method using cetyl trimethylammonium bromide(CTAB),tetrapropyl ammonium hydroxide(TPAOH),tetraethyl ammonium hydroxide(TEAOH)and methyl triethyl ammonium chloride(MTEA)as templates,and the influence of the types and amount of templates on the catalytic performance of molecular sieve was discussed.Zr-Si zeolite synthesized with tetrpropyl ammonium hydroxide(TPAOH)as template has Zr-MFI molecular structure,high crystallinity,small average particle size,and high catalytic activity.The amount of template affects the structure and catalytic performance of the molecular sieve.With the increase of the amount of template in the system,it is beneficial to the formation of molecular sieve framework zirconium to a certain degree.The molecular sieve samples prepared in proportion(n(TPAOH):n(Si)=0.25)have a more complete structure and more surface acid,which is conducive to the generation of monocyclic terpenes such as limonene and isosinolene.The crystallization temperature,crystallization time,calcination temperature,zirconium silicon ratio and other conditions affect the structure and catalytic performance of zeolite in the process of hydrothermal synthesis of zirconium siliconheteroatomic zeolite.The molecular sieves prepared when the crystallization temperature and time were 150? and 24 h respectively had good crystallinity,complete structure and good catalytic performance.At the same time,the calcination temperature affects the structure and performance of Zr-Si molecular sieve.The calcination temperature is 550? and the structure of the molecular sieve sample is complete.The prepared molecular sieve sample has high activity and the selectivity of monocyclic terpenes.When the content of zirconium is low,increasing the zirconium to silicon ratio is conducive to the formation of molecular sieve framework;when the content of zirconium is further increased,it is not conducive to the entry of zirconium atoms into the molecular sieve framework and the structural order is destroyed.Ti,Al,Na and Ni ions were doped with molecular sieve.Ti,Al and Ni ions could enter into the framework structure of molecular sieve and maintain the original structure.However,samples doped with Na ions had poor crystallinity and were not fully formed.Zr-Si zeolite catalysts doped with Ti,Al,Na and Ni ions all showed certain catalytic activity for the isomerization of ?-pinene,but the selectivity of the target product limonene was poor,and the products were basically ring-opening products.