Research On The Preparation And Catalytic Performance Of M-MCM-48(M=Pr,Nd) Catalyst For N-Heptane Hydroisomerization

Praseodymium and neodymium modified mesoporous silica MCM-48,Pr-MCM-48 and Nd-MCM-48 were prepared by in-situ doping hydrothermal synthesis method,using TEOS as the silicon source,CTAB as the template,sodium hydroxide as the alkali source,praseodymium nitrate hexahydrate as praseodymium source or neodymium nitrate hexahydrate as neodymium source.The effect of crystallization temperature,crystallization time,calcined temperature,calcined time and the molar ratio of M?Pr or Nd?/Si were investigated.The mesoporous zeolites of the optimum synthesis conditions were characterized by means of XRD,N₂adsorption-desorption,SEM,TEM,NH₃-TPD and FT-IR techniques.Nickel supported on the Pr-MCM-48 and Nd-MCM-48 was evaluated in fixed bed microreactor by hydroisomerization of n-heptane.The effects of catalyst preparation and reaction conditions were investigated by the performance of hydroisomerization.The following results were obtained:?1?The Pr-MCM-48 and Nd-MCM-48 with better long-range order were crystallized at120? for 72 hours and calcined at 550? for 4 hours,Pr/Si molar ratio of 0.02 or Nd/Si molar ratio of 0.04,respectively.The acidity of pure silica MCM-48 was improved by introducing praseodymium or neodymium into MCM-48.?2?The optimum synthesis conditions of Ni/Pr-MCM-48 and Ni/Nd-MCM-48 were reduced at 400? and 3%Ni supported,respectively.The better performance of hydroisomerization of Pr-MCM-48 and Nd-MCM-48 were reacted at 280?,respectively.?3?The conversion order of n-heptane of Ni/MCM-48,Ni/Pr-MCM-48 and Ni/Nd-MCM-48 was:Ni/Nd-MCM-48>Ni/Pr-MCM-48>Ni/MCM-48;The isomerization selectivity order of i-heptane was:Ni/Pr-MCM-48>Ni/Nd-MCM-48>Ni/MCM-48.The introducing of praseodymium and neodymium into pure silica MCM-48 promoted the conversion and isomerization of n-heptane.The conversion and isomerization selectivity of Ni/Nd-MCM-48 were 56.4%and 68.5%,respectively,and the conversion and isomerization selectivity of Ni/Pr-MCM-48 were 47.2%and 77.1%,respectively.The yield of isoheptane of Ni/Nd-MCM-48 was relatively higher than that of Ni/Pr-MCM-48,which showed that Ni/Nd-MCM-48 was more suitable for the isomerization of n-heptane.