Hydrogenation of carbon monoxide over vanadium oxide- promoted rhodium catalysts

The effect of vanadium oxide as support and promoter on supported rhodium catalysts on the CO hydrogenation has been investigated at 0.15 and 4.0 MPa. Rh/V,O, reduced at 723 K has a good selectivity toward oxygenated products, especially C,-oxygenates, but has a low activity added as a promoter to catalysts consisting and stability. Vanadium oxide of rhodium supported on silica and alumina showed a remarkable effect on the activity of these systems. For the silica-supported systems the activity increased by a factor of 40, the deactivation of these catalysts was low (2 % h-l) and the oxo-selectivity was very high (70 %I. Although the vanadium oxide blocks part of the active metal surface, as became evident from a suppressed chemisorption capacity, it also enhances the -rate of CO dissociation in those locations where reaction is still possible, The enhancement prevails over the blocking in the case of silicaand alumina-supported vanadium oxide-promoted catalysts, while blocking dominates for the vanadium oxide-supported catalyst after high temperature reduction. Experiments in which ethylene was added to a working catalyst, provided indications that the main promoter action of the vanadium oxide is to increase the CO dissociation, thereby increasing the activity of the catalyst. For the alumina-supported catalysts, most of the vanadium oxide is scavenged by the support and only at a high V/Rh ratio, the activity of the Rh/Al 0 catalyst is increased. The addition of vanadium oxide to the alumina-support$d3catalysts caused a suppression of the formation of ethers, covers the acidic The vanadium oxide probably hours of reaction no ether-forming sites of the alumina support. During the first acetic acid was observed for the alumina-supported catalysts due to a chromatographic effect. Initially, the acetic acid that was produced was adsorbed by basic sites of the support and only after prolonged reaction was acetic acid observed at the reactor outlet. INTRODUCTION The hydrogenation of carbon monoxide over rhodium catalysts produces a variety of products. The product distribution can be influenced by using different supports or promoters [l-11]. Since C2-oxygenates are desirable products from an economic point of view C121, much attention has been paid to improve catalyst activity and selectivity to C2-oxygenates. Vanadium oxide used as a support [9] or as a promoter [5,13,14] is reported to be of interest in this respect. In the preceding paper we reported the synthesis and characterization of such V203-promoted Rh/Si02 and Rh/Al203 systems C151. For the Rh/V203 catalyst, a 0166-9834/87/$03.50