Gas-phase acetoxylation of 1,3-butadiene over palladium catalysts. Part 3: Effects of addition of alkali metal salts to Pd-Sb-V catalyst and catalytic properties of Pd-Sb-V-CsCl-KOAc catalyst

Abstract

Pd-Sb-V-KOAc catalyst suffers from a short life-time in the gas—phase acetoxylation of 1,3-butadiene (BD), and the effects of addition of various metal salts to Pd-Sb-V catalyst were studied. The activity and the selectivity were enhanced with an increase in the amount of acetate and a decrease in the electronegativity of the alkali metal in the acetates. Acetates may be effective increasing the AcO− concentration, which did not improve the life-time of the catalyst. Catalysts containing an alkali metal halide instead of an acetate had no activity. Pd-Sb-V-CsCl-KOAc catalyst, however, had a considerably improved life-time and selectivity retaining the high activity of Pd-Sb-V-KOAc catalyst. The addition of CsCl resulted in an increase in the reaction order with respect to PBD. This increase may mean that the addition of CsCl leads to an enhancement of the electron density of Pd. The following mechanism is suggested: (1) Pd in the CsCl-doped catalyst would have a high electron density; (2) the BD concentration on the catalyst would be decreased because of the reduced interaction of BD with Pd; (3) the polymer and coke formation due to adsorbed BD molecules were suppressed; and (4) this suppression caused the improvement in the life-time and selectivity.