THE PERFORMANCE OF TITANIA-SUPPORTED WACKER CATALYSTS IN THE OXIDATION OF 1-BUTENE

The kinetics of l-butene oxidation over titania-supported catalysts ha s been investigated. The reaction rate shows a first-order dependence on I-butene and water coverage at low partial pressures. At higher par tial pressures of water in the feed the reaction rate first strongly i ncreases and then levels off, when the water coverage exceeds a monola yer, probably due to partial dissolution of PdSO4. The concentration o f dioxygen in the feed has a slight positive influence on the activity up to 15 kPa. Heterogeneous Wacker catalysts consist of a palladium s alt deposited on a vanadium pentoxide layer on a support material such as titania. The composition of the catalyst appears to be of major in fluence on its performance. For palladium acetate-based catalysts the activity shows a first order in the palladium coverage. The activity o f the catalysts decreases with increasing vanadium oxide coverage. Tem perature programmed reduction (TPR) shows that the reduction temperatu re of the vanadium oxide overlayer increases with increasing coverage. The easiness of reducibility of the titania-supported catalysts in co mparison to the alumina-based ones is directly related to the one orde r of magnitude higher activity of the tinania-based catalysts. On oxid izing 1-butene to butanone, the activity of titania-supported catalyst s decreases by approximately 60% during the first 100 h of operation. After this initial deactivation, the activity and selectivity of the c atalyst remains stable for more than 700 h. TPR and high resolution el ectron microscopy (HREM) show that this deactivation is mainly caused by a slight sintering of the vanadium oxide layer.