制备条件对异丁烯选择性氧化催化剂性能的影响

Influence of preparation conditions on the properties of catalysts in the selective oxidation of isobutylene

通过正交实验设计,改变钼酸铵溶液的质量分数、pH值和催化剂焙烧温度,利用共沉淀法制备了一系列Mo Bi Co Fe Ce Cs K复合氧化物催化剂。借助于BET、TG DSC、XRD等分析方法对催化剂的物理化学性质进行了表征。在常压连续流动固定床反应器中,系统地考察了上述三种制备条件对复合氧化物催化剂催化异丁烯选择性氧化生成甲基丙烯醛反应性能的影响。结果表明,大比表面积的催化剂具有较高的活性,而平均孔径小的催化剂选择性较差。催化剂的最佳制备条件为:钼酸铵溶液的质量分数10%、pH值2～3、焙烧温度500℃。在异丁烯∶空气=6∶94(体积比)、GHSV=3600h-1和360℃条件下,异丁烯转化率87.2%,甲基丙烯醛选择性72.0%,甲基丙烯醛收率62.7%。

A series of catalysts composed of Mo-Bi-Co-Fe-Ce-Cs-K were prepared by orthogonally varying the three key factors, the concentration of ammonium paramolybdate solution, pH value and calcination temperature. The physico-chemical properties of the catalysts were characterized by BET, TG-DSC and XRD. The catalytic performance for selective oxidation of isobutylene to methacrolein was studied by using a continuous fixed bed micro-reactor under atmospheric pressure. The results indicated that the activity of the catalysts increased with surface area increasing, and the selectivity decreased with pore diameter decreasing. The optimum preparation conditions of the catalysts were that the concentration of ammonium paramolybdate solution was 10%, pH ranged from 2 to 3 and calcination temperature was 500?℃. For the catalyst prepared at the optimal preparation conditions, the experimental results showed that isobutylene conversion was 87.2%, selectivity to methacrolein was 72.0% and the yield of methacrolein was 62.7% at the experimental conditions of isobutylene∶air=6∶94, GHSV=3?600?h^(-1) and reaction temperature=360?℃.