PROMOTER EFFECT OF PD IN HYDROGENATION OF 1,3-BUTADIENE OVER CO-PD CATALYSTS

Addition of a second metal or metal oxide often improves the selectivi ty of a supported catalyst for the hydrogenation of 1,3-butadiene impu rities in commercial n-butene streams. This research has explored the effect of adding Pd to cobalt supported on alumina. Catalysts containi ng 5 wt% Co and varying amounts (0.1 to 1.0 wt%) of Pd were prepared a nd characterized by X-ray diffraction, X-ray photoelectron spectroscop y, chemisorption of CO and H-2, and temperature-programmed reduction a fter having been subjected to a variety of carefully controlled pretre atments. Activities and product selectivities were tested for hydrogen ation of pure 1,3-butadiene and butadiene in a mixture with 1-butene a t room temperature. The presence of Pd increased the reducibility of t he Co, and separate aluminate, Co, and Pd-Co bimetallic surface phases were identified following various pretreatments. Increasing the Co/Pd ratio decreased the formation of n-butane at room temperature relativ e to the rate of butadiene conversion, although the improved selectivi ty was achieved at the expense of increased olefin isomerization and d eactivation due to accumulation of carbonaceous residues on the surfac e. It was not possible to determine unequivocally whether the observed modifications were due to electronic effects or selective poisoning o f the separate Co sites. (C) 1995 Academic Press, Inc.