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 selectivity of a supported catalyst for the hydrogenation of 1,3-butadiene impurities in commercial n-butene streams. This research has explored the effect of adding Pd to cobalt supported on alumina. Catalysts containing 5 wt% Co and varying amounts (0.1 to 1.0 wt%) of Pd were prepared and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, chemisorption of CO and H-2, and temperature-programmed reduction after having been subjected to a variety of carefully controlled pretreatments. Activities and product selectivities were tested for hydrogenation of pure 1,3-butadiene and butadiene in a mixture with 1-butene at room temperature. The presence of Pd increased the reducibility of the 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 relative to the rate of butadiene conversion, although the improved selectivity was achieved at the expense of increased olefin isomerization and deactivation due to accumulation of carbonaceous residues on the surface. It was not possible to determine unequivocally whether the observed modifications were due to electronic effects or selective poisoning of the separate Co sites. (C) 1995 Academic Press, Inc.