Ni/HZSM-5催化剂的结构及其催化山梨醇水相加氢合成烷烃性能

采用浸渍法制备了Ni/HZSM-5双功能催化剂,考察了焙烧温度对催化剂结构及其催化山梨醇水相加氢合成C5～C6烷烃性能的影响.结果表明,在金属中心和酸性载体的协同作用下,通过山梨醇中C-O键加氢和异构化高选择性合成了C5～C6烷烃.经500°C焙烧的Ni/HZSM-5催化剂上山梨醇水相加氢的活性最高,山梨醇转化率为62.0%,戊烷和己烷的总选择性为76.4%,其中异己烷选择性达45.4%.对催化剂进行N2物理吸附、X射线衍射、NH3程序升温脱附和H2程序升温还原等表征后发现,经500°C焙烧催化剂的有效比表面积和孔体积均明显增大,HZSM-5负载的硝酸镍分解成较小晶粒的NiO,表面酸量适中,且Ni物种与载体相互作用较强,较易被H2还原,Ni还原度达100%.这是其催化活性最高的原因.

Structure of Ni/HZSM-5 Catalyst and Its Catalytic Performance for Aqueous Phase Hydrogenation of Sorbitol to Alkanes

A bifunctional Ni/HZSM-5 catalyst was prepared by the conventional impregnation method.The effects of calcination temperature on the structure properties of the catalyst and its catalytic performance for aqueous phase hydrogenation of sorbitol were studied.The results showed that C5～C6 alkanes were effectively obtained by the hydrogenation of the C-O bond in sorbitol and the following isomerization due to the synergism of the metal center and acid support.Moreover,the catalyst calcined at 500 °C exhibited a maximum value of 62.0% for sorbitol conversion and 76.4% of selectivity for pentane and hexane in comparison with other catalyst samples,wherein the isohexane selectivity was about 45.4%.The catalyst samples were characterized by N2 physical adsorption,X-ray diffraction,NH3 temperature-programmed desorption,and H2 temperature-programmed reduction.It was found that the surface area and pore volume of the catalyst calcined at 500 °C were obviously increased.Smaller grains of NiO can be formed from the decomposition of nickel nitrate on the surface of HZSM-5,which can provide with the appropriate amounts of acid and the interaction between the nickel species and acid support for easier hydrogen reduction with the Ni reducibility of 100%.All these factors are closely related to the highest catalytic performance of Ni/HZSM-5 catalyst for aqueous phase hydrogenation of sorbitol.