沉淀剂对铜锰复合氧化物变换催化剂构效的影响

Effect of precipitator on the texture and activity of copper-manganese mixed oxide catalysts for the water gas shift reaction

以CuSO4.5H2O和MnSO4.H2O为原料,KOH和NaOH为沉淀剂制备了铜锰复合氧化物,考察了其变换反应催化性能,利用XRD、低温氮气吸附法、TG、H2-TPR等对所合成样品进行了表征。以KOH和NaOH为沉淀剂所得沉淀终产物的物相组成和织构明显不同,分别为层状结构碱式硫酸铜Cu4SO4(OH)6.H2O及无定形锰氧化物和Cu2+1O和Mn3O4混合物。两种物相组成和织构完全不同的沉淀终产物焙烧后都生成Cu1.5Mn1.5O4固熔体,在变换反应条件下均转化为Cu和MnO,但其催化性能却有明显差异。以NaOH为沉淀剂,得到以Cu2+1O和Mn3O4复合体为主的沉淀终产物,焙烧及还原后保持了较高的织构稳定性,提高了样品的活性和热稳定性。而以KOH为沉淀剂得到以层状结构碱式硫酸铜Cu4SO4(OH)6.H2O和无定形锰氧化物为主的沉淀终产物,在焙烧过程发生的演变极其复杂,削弱了铜锰组分协同效应,造成其活性和热稳定性极差。研究结果表明,NaOH作沉淀剂所制备样品的织构稳定性、催化活性显著高于以KOH作沉淀剂所制备样品,且热稳定性良好。

Copper-manganese mixed oxides were synthesized by co-precipitation with either KOH or NaOH as precipitators from CuSO4·5H2O and MnSO4·H2O as starting materials.The as-synthesized samples were tested for the water gas shift reaction and characterized by XRD,low temperature N2 absorption/desorption,TG and TPR.The obtained end precipitate consists mainly of Mn3O4 and Cu2＋1O for samples prepared using NaOH as the precipitator whereas Cu4SO4（OH）6·H2O is obtained for the samples using KOH as the precipitator.Both the end precipitates prepared with NaOH and KOH as precipitators are converted to Cu1.5Mn1.5O4 after calcination,and reduced to Cu and MnO after the water gas shift reaction.Drastic differences are observed in their catalytic properties for the water gas shift reaction.The dry samples are composed of Mn3O4 and Cu2＋1O when using NaOH as a precipitator and these samples maintain a relatively high texture stability and composition uniformity which ensure higher activity and thermal stability.However,for the layered structure of Cu4SO4（OH）6·H2O and the amorphous manganese oxide,the composition of the dry samples prepared with KOH as a precipitator shows that the samples undergo a complex evolution during calcination resulting in a weakening of the synergistic effect between copper and manganese.Therefore,under the water gas shift reaction conditions the stability of the texture and composition uniformity of the KOH precipitated sample decrease greatly,which leads to a decrease in activity and thermal stability.The present comprehensive study results show that the Cu-Mn mixed oxide prepared using NaOH as a precipitator has significantly higher texture stability and catalytic activity than that prepared using KOH as a precipitator,and present excellent thermal stability.