Preparation Of Zirconia System Of Mesoporous Materials And Its Catalytic Butane Isomerization Activity,

Transition-metal oxides play an important role in catalysis.Among them,ZrO₂ has been paid much attention and has been used as acidic catalyst and catalyst support. As a strong acidic catalyst,SO₄^2-/ZrO₂ exhibits unique catalytic performance on catalytic reactions which require strong acidity,such as n-butane isomerization,in comparison with the catalysts Pt/Cl-Al₂O₃ or Pt/H-MOR used in industrial process. The latter suffer some drawbacks,e.g.corrosion,pollution,and relative low activity and stability.However,SO₄^2-/ZrO₂ has main disadvantages of loss of sulfur species and relative low surface area,which limits its industrial application.It is well known that tetragonal SO₄^2-/ZrO₂ has better catalytic activity than its monoclinic phase. However,with normal preparation methods the obtained ZrO₂ normally contains intercrystaUine pores.Also,tetragonal phase of ZrO₂ usually comes out with the appearing of monoclinic phase after calcination.Doping other metal species may stabilize tetragonal phase of ZrO₂ and increase its acidity strength.In this thesis,the research work was mainly focused on the preparation of ZrO₂,SO₄^2-/ZrO₂ and Al-and /or Ga-promoted SO₄^2-/ZrO₂ with intracrystaUine mesopores and the exploration of catalysts with high performance over n-butane isomerization.The major work may be summarized as the follows.SO₄^2-/ZrO₂ samples were prepared with sol-gel method by introducing water molecules through adding alcohol/water mixture and exposing in moisturized air.In the former method the amount of water added has great influence on phase of zirconia. Zirconia with higher surface area may be obtained with increasing aging time and temperature.However,the mesopores are mainly from intercrystalline pores.In the latter method the hydrolysis is relatively mild.Zirconia with intracrystalline mesopores was obtained although the surface area is not high.The pore size and thickness of pore wall may be varied with the change of template content.In order to improve the property of mesoporous zirconia,Al promoted zirconia and Al promoted sulfated zirconia was prepared with the methods by introducing water molecules through exposing in moisturized air and adding water stoichiometrically,respectively.With the former method the addition of Al may stabilize the tetrahedral phase of zirconia and increase its surface area.However,the product still contains considerable amount of intercrystalline pores and has wide pore size distribution.With the latter method the obtained Al promoted sulfated zirconia with strong acidity mainly contains intracrystalline mesopores with narrow pore size distribution.The method was further extended to prepare Al and Ga dual promoted sulfated zirconia.The characterization results show that the addition of metal promoters may stabilize the tetrahedral phase of zirconia.Although the addition of gallium does not affect the acidity of the product significantly,Al and Ga dual promoted sulfated zirconia has mainly intracrystalline mesopores with narrow pore size distribution.The amount of gallium promoter introduced is dependent on the way how gallium was introduced.In situ ¹³C MAS NMR was employed to the study of 1-¹³C-n-butane isomerization over mesoporous Al promoted sulfated zirconia and Al and Ga dual promoted sulfated zirconia.It was found that over all catalysts the isomerization of n-butane mainly follows the monomolecular reaction pathway at the initial reaction stage.However,the secondary Ga promoter may reduce the occurrence of the reaction through the bimolecular pathway at later reaction stage.This effect is significant at high Ga content.