Action of Co-Mo-Bi-Fe-Sb-K catalysts in the partial oxidation of propylene to acrolein: 1. The composition dependence of activity and selectivity

The role of various components of a multiphase oxide catalytic system in the partial oxidation of propylene to acrolein is investigated. Catalytic activity is studied for the Co6-8Mo12Fe2-3Bi0.5-0.75Sb0.1K0.1Ox catalyst, which is taken to be the reference, and for catalysts in which the amount of some component is progressively reduced down to zero. The results obtained provide insights into the role of the components of the catalyst. CoMoO4 forms the structural framework of the catalyst. Iron molybdate can be stabilized on CoMoO4 as beta-phase. As its content is increased, the catalyst gains activity but its selectivity declines. Bismuth molybdate is responsible for the selectivity of the process. When present in small amounts, MoO3 raises the selectivity, binds free oxides, and converts reduced molybdates into their oxidized forms. Excess molybdenum trioxide causes a dramatic fall in the catalytic activity. Potassium and antimony decrease the catalytic activity, but even small amounts of these elements raise the selectivity of the catalyst. Chromium can substitute for iron atoms in the multicomponent catalyst. Ni, Mn, and Mg substitute for Fe in iron molybdate to decrease the catalytic activity.