Olefin Purification and Selective Hydrogenation of Alkynes with Low Loaded Pd Nanoparticle Catalysts

Abstract

The catalytic performance of Pd-nanoparticle catalysts for the selective hydrogenation of alkynes at mild conditions (150 kPa and 303 K) was evaluated. A Lindlar commercial catalyst was also tested for comparison. The effects of acidity, amount of active sites and dispersion on the catalytic activity and selectivity were studied. At mild conditions, Pd-nanoparticle catalysts were considerably more active and slightly more selective than the Lindlar catalyst. The best synthesized catalyst for the purification of 1-pentene was Pd/Al2O3?Mg (r0= 41.1 mol gPd-1min-1, 94% selectivity). The activity and selectivity of Pd/CaCO3 were similar to those of the Lindlar catalyst. The smallest particle sizes (3-4.5 nm) favored the dissociative adsorption of hydrogen over Pd° active sites and a good catalytic behavior. The weaker acid centers (Lewis) of Pd/Al2O3?Mg and Pd/CaCO3 favored higher selectivities to the desired alkene. Pd/Al2O3 was the most active catalyst but also the least selective. This was due to strong acid sites, remnant Bronsted acid sites, which provide extra hydrogen that favors the alkyne hydrogenation rate and also the undesired overhydrogenation of the alkene and/or the isomerization.