Cr对Fe—Cr系高温变换催化剂的耐热性与还原性影响的研究

Effect of Cr on the Thermal Stability and Reduction Behavior of Industrial High Temperature Shift Fe-Cr Catalysts

利用热分析结合XRD、TEM、SEM、IR等对五种Fe-Cr系工业高温变换催化剂的热性能及还原活化进行了研究。结果发现,催化剂中的Cr除一般认为提高催化剂分散度、比表面和结构稳定性外,还具有提高还原温度,降低还原速度和还原度的性能,由此既可提高催化剂中Fe^(2+)/Fe^(3+)比例,又可防止其中Fe_3O_4过度还原。因而它就从一个侧面解释了助剂Cr的提高活性与耐热性的作用,还原气氛(干H_2湿H_2、CO和CO—/CO—CO_2),还原性气体浓度以及还原温度对催化剂的还原及还原后的性能有显著影响。一般宜用H_2还原,不宜直接用CO还原。催亿剂还原的难易程度及热稳定性与Fe_2O_3的晶型无明显对应关系,主要由催化剂的组成、制备工艺、结构等决定。因而不同催化剂有其各自适宜的还原活化条件。通过对催化剂的DTA及TG结果的仔细分析,得到了一些新的信息,据此可以解释并预测催化剂的活性与耐热性能。

Five industrial catalysts have been studied by means of thermal analysis(DTA, TG), TPR together with XRD, TEM, SEM and IR. The results indicate that the Cr present in the catalysts, besides ist well known promoting action, on dispersion, specific surface area and stability of structure, can also enhance: its reduction temperature and reduce its rate and total degree of reduction with the result of raising its Fe^(2+)/Fes^(3+) ratio and preventing Fe_3O_4 from over-reduction.The overall effect is higher activity and thermal stability.The kinds of reducing agents(dry H_2, wet H_2,CO and CO-CO_2)and their concentrations and reduction temperatures can affect nobably the reduction behavior, Hydrogen is generally suitable, but the direct use of CO is not, Ruduction property and thermal stability do not directly related to the Fe_2O_3 crystal habit, but depend on, catalyst composition, preparation and strueture. Naturally, diffrent catalysts will have their own proper reduction schedule. All of the above mentioned in formations are obtained by carefully analyzing DTA, TG and TPR data, from which their catalytic properties can be interpereted and predicted to some extent.