载体对钒铬氧化物催化剂结构及催化3-甲基吡啶氨氧化反应活性的影响

通过等体积浸渍法制备了Nb₂O₅,MgF₂,TiO₂和SiO₂负载和未负载的钒铬氧化物催化剂,并应用X射线衍射、N₂吸附-脱附、H₂程序升温还原和NH₃程序升温脱附对催化剂进行了表征. 结果表明,催化剂比表面积较大时有利于CrVO₄-I(单斜)的生成,比表面积较小则有利于CrVO₄-III(斜方)的生成. 在310-400℃下3-甲基吡啶氨氧化制备3-氰基吡啶反应中,具有较高催化活性的催化剂与V物种还原性较高和表面活性位数量较多有关; 而高的3-氰基吡啶选择性则与催化剂表面较低的酸性密切相关. 升高反应温度可大幅度提高催化剂的活性,且其选择性基本不变.

Effect of supports on the structure and activity of vanadium-chromium oxide catalysts for ammoxidation of 3-picoline

Bulk and Nb₂O₅-, MgF₂-, TiO₂-, and SiO₂-supported vanadium-chromium oxide catalysts were prepared by the incipient wetness impregnation method and investigated for the ammoxidation of 3-picoline to nicotinonitrile at 310-400 ℃. The physical and chemical properties of the catalysts were assessed by X-ray diffraction, N₂ adsorption-desorption, H₂-temperature-programmed reduction, and NH₃-temperature-programmed desorption. The surface area of the supports influenced the formation of the active components of the catalysts: high surface area encouraged the formation of monoclinic CrVO₄ whereas low surface area favored the formation of orthorhombic CrVO₄. The high reducibility of vanadium in the catalyst and the large number of surface active sites resulted in higher 3-picoline conversion efficiencies. The high selectivity was attributed to the low surface acidity of the catalysts. Reaction temperature showed a positive effect on the catalytic performance for it could increase 3-picoline conversion and maintain nicotinonitrile selectivity.