Synthesis of meso-microporous SAPO-11by hard template method and its catalytic application for long-chain alkanes hydroisomerization

Key words:  SAPO-11  meso-microporous structure  hard template  carbon material  hydroisomerization

Abstract:

Hierarchically SAPO-11zeolite with meso-microporous structures (meso-SAPO-11) was synthesized by adding carbon black as a hard template in crystallization process of traditional hydrothermally prepared method. The effect of different amounts of carbon addition on the mesoporous volume and acid property was evaluated. N_2adsorption/desorption isotherm, XRD, TEM and Py-FTIR characterization were employed to identify the crystalline structures, pore properties, and acid types. Catalytic hydroisomerization performances of Meso-SAPO-11catalysts with 0.5% Pt loading were evaluated by using n-C₁₂ as a model compound. It is found that the mesoporous volume shows a parabolic tendency with the increasing amount of carbon addition, and the volume reaches the highest at the 10% addition of carbon. No significant change on crystalline structure is observed by XRD pattern, and obvious mesoporous structure is presented by TEM images. The results of hydroisomerization test demonstrate that the catalytic performance is related to the mesoporous volume and acid property of SAPO-11zeolite:on one hand, increasing the mesoporous volume in microporous SAPO-11can increase the speed of mass transfer, as well as expose more activated microporous pores to enhance the isomerization activity; on the other, raising the ratio of Brnsted acid to Lewis acid can also enhance the hydroisomerization activity. Reaction temperature investigation shows that isomer products selectivities remarkably decrease with the increase of the reaction temperature.