The Effect of Promoters Ca、Sr and Ba to CO Oxidation on the Co/γ Al₂O₃ Catalyst（Ⅱ）

A series of Co-M /γ-Al₂O₃ catalysts （M =Ca、Sr and Ba, Co₃O₄/Al₂O₃= 8wt%,M/Co = 15mol%） were prepared by wetness impregnation method. The alumina was impregnated with solution of Co（NO₃）₂. 6H₂O and M（NO₃）₂（M = Ca、Sr or Ba） and was calcined at 750℃ for 3h and at 900℃ for 2h rcspectively. The oxidation activity of CO was determined in a gas flow system. The effect of promoters Ca、Sr and Ba was studied by XRD、XPS、DTA、TPR and SET surface measurements. As a result, the temperature of coversion 100% of CO decreased about 20-60℃ on the samples contained Ca、Sr and Ba. The order of promotive effect is Ca＞Sr＞Ba. The samples calcined at 750℃ and 900℃ were less active than that at 400℃ and 600℃, the main reason is Co-γ-Al₂O₃ interaction became stronger with the calcination temperature increased. The experimental result indicated that the main active phase was the surface Co²⁺ Al³⁺ interaction phase which was more difficult to reduce than Co₃O₄. All promoters Ca、Sr and Ba existed as oxides which segregated on the surface and occupied some surface sites. The segregation order is Ba＞Sr＞Ca, this is connected with the catalytic activity.