Research On The Preparation And Catalytic Performance Of Heptane Isomerization Of Metal Modified Mesoporous MCM-48 Catalyst

The sixth Gasoline standards of the state will be applied nationwide,and new gasoline standards claim to reduce sulfur,manganese and olefin content in gasoline with a great degree.Our country is short of gasoline resources with high octane number,therefore,alkanes isomerization technology must be developed to obtain gasoline harmonic components with high octane number.in order to make up the loss of octane number for low sulphur and no manganese.N-heptane isomerization reaction is one of important means to obtain gasoline with high octane number.MCM-48 has three-dimensional spiral channel structure,high specific surface area and adjustable aperture,which properties are in favor of mass transfer and the dispersion of active components,meanwhile,the adjustable aperture has shape-selective catalysis function.However,pure silica MCM-48 mesoporous molecular sieve is lack of active center and exhibits a poor thermal stability.Therefore,it is available to introduce metal with in-situ doping or loading method to improve heat and thermal stability which will add acid and base active center in molecular sieve.In this paper,different metal(Ni?Co?Zn)in-situ doping MCM-48 catalyst was prepared.The effects of metal on the structure,acidity and stability of MCM-48 were studied by means of X-ray diffraction(XRD),N2 adsorption-desorption,FT-IR,scanning electron microscope(SEM)and NH3 temperature programmed desorption(NH3-TPD)techniques.At the same time,Ni/M(Ni,Co,Zn)-MCM-48 bifunctional catalyst for n-heptane isomerization performance was studied.The central content in this paper were discussed as follows:1.Ni,Co,Zn modified mesoporous silica MCM-48 was prepared by in-situ doping hydrothermal synthesis.The influences of impurity atoms on the structure and property of mesoporous silica MCM-48 were discussed.The results show that mesoporous MCM-48 with better long-range order was prepared at the molar ratio of 0.98 TEOS: 0.558 CTAB: 0.469NaOH: 57.64 H2O: 0.02 M.Part of the metal take up skeleton of molecular and improved the acid properties of materials.2.Bifunctional Ni/M-MCM-48 catalysts were prepared by using different metal modified MCM-48 as the catalyst support and Ni as the active component with step impregnation method.The influences of metal content,reduction conditions and reactionconditions on n-heptane isomerization performance of Zn modified MCM-48 catalysts were studied.The results showed that when molar ratio of Zn to Si was 0.02,reduction time was 4h,reduction temperature was 400 oC,reaction temperature was 260 oC,WHSV was 5.1 h-1and hydrogen to hydrocarbon molar ratio was 2,n-heptane conversion and the selectivity of isoheptane reached 45% and 62%,respectively,at the preparation conditions of 4% Ni.