沉淀剂对铜锰复合氧化物组成结构及催化性能的影响

EFFECT OF PRECIPITATORS ON COMPOSITION STRUCTURE AND CATALYTIC PERFORMANCE OF COPPER-MANGANESE MIXED OXIDES

采用KOH和NaOH作沉淀剂,通过共沉淀法合成铜锰复合氧化物,运用XRD、TG-DSC、TPR、BET等对其进行了表征,并测定了其对变换反应的催化性能.研究结果表明,采用NaOH作沉淀剂时,沉淀物前驱体主要为Mn3O4和Cu2＋1O,而选用KOH为沉淀剂时,则主要为碱式硫酸铜Cu4＋2SO4（OH）6.2H2O;焙烧后两种沉淀剂所合成样品均转化为Cu1.5Mn1.5O4;用于变换反应后NaOH作沉淀剂的样品主体为Cu和MnO,而用KOH作沉淀剂的样品主体却为Cu、MnO与Mn.虽然KOH为沉淀剂所得沉淀终产物（前驱体）样品比表面积较大,但经过焙烧和反应后,NaOH为沉淀剂所得样品比表面积都要比相应的KOH为沉淀剂样品高50%以上.NaOH作沉淀剂所合成样品的TPR为只有一个还原峰的单一还原反应过程,而KOH作沉淀剂的样品TPR反应过程复杂,在150~900℃为多步反应过程,出现了多个反应峰.对于变换反应,以KOH作沉淀剂所制备样品失活速度极快,而以NaOH作沉淀剂所制备样品的催化活性显著高于以KOH作沉淀剂所制备样品,且具有良好的热稳定性.

Copper-manganese mixed oxides are synthesized by way of coprecipitation with KOH and NaOH used respectively as the precipitator.The as-synthesized samples are characterized by means of XRD,TG-DSC,TPR and BET and are tested in the water-gas shift reaction for determining their catalytic performance.It is proved that the end precipitates are mainly Mn3O4 and Cu2＋O for samples prepared with NaOH as the preciptator,whereas mainly Cu4＋2SO4（OH）6·2H2O is produced for samples prepared with KOH as the preciptiator.End precipitates prepared by use of either NaOH or KOH precipitator are all translated into Cu1.5Mn-1.5O4 after calcination.After water-gas shift reaction,the sample prepared with NaOH precipitator contains mainly Cu and MnO,while that with KOH precipitator contains mainly not only Cu,MnO but also Mn.Although the specific surface area of the KOH-precipitator prepared sample is quite large,after calcination and reaction,the specific surface area of the NaOH-precipitator prepared sample turns out to be larger than that of the KOH-precipitator prepared sample almost by 50% and over.The reductive process of the sample prepared with NaOH precipitator represents a simple process with only one exclusive reduction peak.However,the process of the sample prepared with KOH precipitator appears to be much more complex.Multistep reduction takes place in the range of 150 ℃ to 900 ℃.A number of reduction peaks are found.Under water-gas shift reaction conditions,the speed of deactivation of the KOH-prepared sample becomes very fast,while that of the NaOH-prepared sample is a lot lower.Conclusion is drawn that the NaOH-prepared sample exhibits obviously higher catalytic activity than the KOH-prepared sample,and its thermostability is considerable.