CeO_2乙苯脱氢催化剂的XRD、XPS研究

XRD and XPS Study on the CeO_2 Catalyst for Dehydrogenation of Ethylbenzene

利用XPS中的Ar+溅射技术,发现CeO2是一种Ce3+和Ce4+共存的混合价态氧化物,其表面Ce3+/Ce4+比是0.1.在乙苯脱氢条件下,CeO2催化剂表面存在如下动态平衡:CeO2■CeO2-x(0<x<0.3),CeO2和CeO2-x存在于同一晶体中,CaF2型晶体结构并没有发生改变.实验表明,稳定的苯乙烯收率与表面CeO2-CeO2-x稳定物相密切相关,乙苯催化脱氢的活性相可能是CeO2-CeO2-x.CeO2催化剂表面Ce3+/Ce4+比值下降,其副产物(苯和甲苯)含量随之减少,乙苯脱氢选择性随之提高.

Using the Ar^＋ sputtering technology,we found that the CeO2 catalyst was a mixed valence oxide,which contained Ce^3＋ and Ce^4＋ , with the Ce^3＋/Ce^4＋ ratio at the surface being 0. 1. Under the reaction condition of ethylbenzene dehydrogenation, the dy namic equilibrium CeO2H2、CO→←H2OCeO2-x（0〈x〈0.3）took place at the surface of CeO2 catalyst. CeO2 and CeO2-x coexisted in the same crystallite and both took the same CaF2 crystal structure. The experiment indicated that the stable yield of styrene was closely related to the stable composition of CeO2-CeO2-x at the catalyst surface,and therefore the active phase could be CeO2-CeO2-x for catalytic dehydrogenation of ethylbenzene. Furthermore,it was found that the byproducts （B and T） decreased and the selectivity of ST increased with the decrease of the Ce^3＋/Ce^4＋ ratio at CeO2 catalyst surface.