CO加氢反应过程中铁/硅沸石催化剂的表面性能

SURFACE CHARACTERISTICS OF Fe/SILICALITE CATALYST IN CO HYDROGENATION

高硅pentasil沸石载铁催化剂在CO加氢合成低碳烯烃的反应中表现有良好的性能.沸石载体不仅保证了活性组分的有效分散,同时也限制了加氢产物的链增长和二次加氢,产物烃基本在C_5以内,C_2—C_4烯烃选择性达60％以上.然而,合成沸石的晶粒大小和外观形貌会造成活性组分的分散不一,还原度不同也使表面相分布有较大差异.催化剂的性能与表面铁的相分布和价态密切相关.

Surface properties of Fe/silicalite catalyst in CO hydrogenation were studied by a combined method of temperature-programmed surface hydrogenation (TPSH), mass spectroscopy (MS) and MSssbauer spectro-scopy.It was found that lower hydrocarbons (mainly ethylene), a-Fe and H2O were the hydrogenation products of surface phases x-Fe5O2, Fe3+ and Fe3O4.There were two carbonifying centres on the surface of the catalyst, in which the first one (low temperature range) played an important role in maintaining of good activity, selectivity and stability of the catalyst.It was also found that a dynamic equilibrium existed on the catalyst surface in CO hydrogenation.The change of the surface phases was as follows:α-Fe + CO→Fe,C + Fe,O; Fe,C + H2→c-Fe+(-CH-)n;FerO+ H2→α-Fe+FeO+H2O;Fe3++H2→α-Fe;α-Fe+C(active)→FexC......