Alumina-supported palladium and palladium/copper catalysts: Characterization and use for selective hydrogenation of 1,3-butadiene
Furlong, Brian Keith
Hightower, Joe W.
Doctor of Philosophy
Butadiene is a normal deleterious contaminant that must be removed from C$\sb4$-olefin streams before being used in several industrial applications. While this impurity is substantially eliminated by selective catalytic hydrogenation, there is a considerable economic incentive to improve the currently employed palladium-based catalysts. The purpose of this research has been to investigate the effects of adding copper to alumina-supported palladium to enhance the selectivity of palladium for butadiene hydrogenation. 1,3-Butadiene semi-hydrogenation was studied in the presence of a 10:1 excess of 1-butene over supported bimetallic catalysts containing palladium in a vapor-phase atmospheric plug flow reactor in the temperature range 299-313 K. Copper addition to alumina-supported Pd increases its selectivity for converting butadiene to n-butenes without saturating or isomerizing the n-butenes. For example, with a Cu/Pd atomic ratio of two, the bimetallic catalyst selectively converts $>$99% of the diene to n-butenes while isomerizing or saturating less than 1% of the starting 1-butene. Under similar conditions, Pd alone maintains high n-butene selectivity to only about 50% conversion of the diene. Copper also promotes higher trans-2-butene selectivity at the expense of 1-butene production. The kinetics of 1,3-butadiene hydrogenation over the Pd and PdCu catalysts are first order in hydrogen and zero order in butadiene. Hydrogen sorption measurements show that copper addition decreases both surface adsorption and bulk absorption, suggesting surface decoration of Pd by Cu and possibly bulk Cu-Pd interactions in the supported bimetallic samples. Surface Cu-Pd mixing is confirmed by X-ray photoelectron spectroscopy (XPS) measurements. Extended X-ray absorption fine-structure (EXAFS) results reveal that oxidation of bulk palladium particles is slowed by the presence of copper. Probably copper surface mixing and/or decoration protects bulk palladium particles by suppressing oxygen diffusion. Combined, the results indicate that the bimetallic particles are present as bulk palladium particles with Cu-Pd mixing at the surface. These bimetallic catalysts containing Cu and Pd show promise for commercial use since they are considerably more selective than Pd-alone.
Chemical engineering; Organic chemistry; Engineering; Materials science