稀土元素对Mo-Bi系复合催化剂选择氧化异丁烯制甲基丙烯醛的影响

摘要

Mo-Bi composite oxide catalysts were prepared by co-precipitation method. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N2-physisorption (BET) techniques. The effects of the addition of rare earth elements (La, Ce, Pr or Sm) to the catalysts on the selective oxidation of isobutylene to methacrolein and methacrylic acid were investigated. The XRD results showed that the addition of Ce to the Mo-Bi complex oxide catalyst enhanced the intensity of bismuth molybdate phase, which could be due to the partial replacement of Bi ions with Ce ions. Besides, XPS results proved that the addition of Ce to the Mo-Bi composite oxide catalyst improved the amount of active oxygen (O2-) in the catalyst. With the addition of Ce as the promoter of Mo-Bi composite oxide catalyst, the catalytic activity was greatly enhanced, resulting in a higher selectivity of methacrolein and methacrylic acid. At the molar ratio of Mo to Ce of 12:0.5, the isobutene conversion was 99.6 %, the selectivity of methacrolein and methacrylic acid was 86.5 %, and the yield reached up to 85.5%.%采用共沉淀法制备了系列Mo-Bi系复合氧化物催化剂,利用X射线衍射(XRD)、X射线光电子能谱(XPS)和 N2物理吸附(BET)等表征手段对该系列催化剂的物理化学性质进行了表征,并考察了稀土元素(La,Ce,Pr 和Sm)的加入及Ce含量对异丁烯选择氧化制甲基丙烯醛和甲基丙烯酸反应的影响.结果表明,Ce的加入,提高了甲 基丙烯醛和甲 基丙烯酸选择性,当Ce和Mo的物质的量之比为0.5∶12时,催化剂活性较高,异丁烯转化率为99.6％,甲基丙烯醛和甲基丙烯酸总选择性为86.2％,总收率为85.5％.这是由于Ce的加入,使得Ce离子部分取代Bi离子,从而影响了催化剂中钼酸铁铋晶体,并使催化剂表面吸附活性氧O2-的含量增加,从而有利于提高甲基丙烯醛和甲基丙烯酸选择性.