Ce助剂对Fe-K/Al_(2)O_(3)催化剂乙苯无水直接脱氢性能的影响

Effect of Ce Dopant on the Performance of Fe-K/Al_(2)O_(3)Catalyst Over Direct Dehydrogenation of Ethylbenzene Without Steam

比较了浸渍法、浸渍沉淀法及溶胶凝胶法制备的Fe-K-Ce/Al_(2)O_(3)催化剂催化乙苯无水直接脱氢反应的性能;考察了金属前驱体类型及Ce添加量对浸渍法制备的Fe-K-Ce/Al_(2)O_(3)催化剂性能的影响,并采用XRD、XPS、SEM、N_(2)物理吸附-脱附及H_(2)-TPR对催化剂进行表征。结果表明,在催化剂质量0.1 g、反应温度565℃、N_(2)体积流量10 mL/min、0.1 MPa的反应条件下,以Fe(NO_(3))3-Ce(SO_(4))_(2)为前驱体,用浸渍法制备的质量分数为1%Ce的Fe-K-Ce/Al_(2)O_(3)负载型催化剂,在乙苯直接脱氢制苯乙烯反应中表现出高的催化剂稳定性,且对苯乙烯的选择性保持在100%。在高温制备催化剂的过程中,Ce与Fe形成钙钛矿结构CeFeO_(3)化合物,铁酸盐的形成使得铁物种的还原温度大幅提高,因而催化剂的稳定性提高。XPS表征结果结合文献分析显示,钙钛矿结构的CeFeO_(3)不仅调变了催化剂的酸碱位点,而且所含非晶格氧的量更高,从而有利于提高苯乙烯的选择性。

This paper compares the performance of Fe-K-Ce/Al_(2)O_(3)catalysts prepared by impregnation,impregnation precipitation and sol-gel methods for catalyzing the direct dehydrogenation of ethylbenzene without steam,and investigates the effect of metal precursor type and Ce addition on the performance of Fe-K-Ce/Al_(2)O_(3)catalysts prepared by impregnation method.Moreover,the catalysts are characterized by means of XRD,XPS,SEM,N_(2)physical adsorption and desorption,and H_(2)-TPR.The results show that under the following reaction conditions:catalyst weight of 0.1 g,reaction temperature of 565℃,N_(2)flow rate of 10 mL/min and reaction pressure of 0.1 MPa,Fe-K-Ce/Al_(2)O_(3)loaded catalyst with 1%Ce by mass fraction prepared by impregnation method using Fe(NO_(3))_(3)-Ce(SO_(4))_(2)as the precursor exhibited a high catalyst stability in the direct dehydrogenation of ethylbenzene to styrene,and the selectivity of styrene was maintained at 100%.During the preparation of the catalyst at high temperatures,Ce and Fe formed a perovskite structured CeFeO_(3)compound,and the formation of ferrite greatly raised the reduction temperature of the iron species,so that the stability of the catalyst was improved.The XPS characterization results in combination with literature analysis show that the perovskite structured CeFeO_(3)not only modulated the acid-base sites of the catalyst,but also contained a larger amount of non-lattice oxygen,thus favoring the improvement of styrene selectivity.