Effect of Particle Size and Support Type on Pd Catalysts for 1,3-Butadiene Hydrogenation

Pd nanoparticles supported on SiO 2 , Si 3 N 4 and Al 2 O 3 were studied to examine the effect of particle size and support type on the hydrogenation of 1,3-butadiene. Pd nanoparticles were produced using a reverse micelle method resulting in particles with a remarkably small particle size distribution (σ < < 1 nm). The support type and particle size were observed to affect both catalytic activity and product selectivity. All catalysts showed a decrease of their activity with time on stream, paired with an increase in selectivity to butenes (1-butene and cis/trans-2-butene) from a product stream initially dominated by n-butane. In situ XAFS demonstrated a correlation between the formation of palladium hydride and n-butane production in the early stages (~ 1 h) of reaction. The extent of palladium hydride formation, as well as its depletion with time on stream, was dependent on both particle size and support type. Metallic Pd was identified as the species selective towards the production of butenes

Reversible hydrogenation studies of NaBH4 milled with Ni-containing additives

NaBH4 has long been identified as a viable hydrogen-storage material due to a theoretical gravimetric H2 capacity of 10.6 wt %. Because of the high enthalpy of decomposition of 108 ± 3 kJ mol -1, thermal decomposition of the pristine material does not occur until at least 500 C, and thus NaBH4 has yet to be utilized in hydrogen-storage processes. In this study, NaBH4 has been milled with a variety of Ni-containing additives to investigate the effects on the temperatures required for thermal desorption of H2 by temperature-programmed desorption (TPD) measurements and the products characterized by powder X-ray diffraction (PXD). Ni-containing additives have been determined to significantly enhance the thermal desorption of H2 by at least 60 C (Ni (65 wt %) on Si/Al2O3). PCT cycling experiments have been conducted to ascertain their effects on the reversible hydrogenation of the milled NaBH4. PXD analysis indicates that Ni reacts with B evolved during thermal decomposition to form NixB y species including Ni3B, Ni2B, and Ni 3B4. A catalyst screening study of NaBH4 with a variety of nanoparticles, chlorides, borides, and mesoporous materials has also been conducted, the most effective of which has been found to be Pd nanoparticles, which have a desorption temperature of 420 C, a decrease of at least 85 C. © 2013 American Chemical Society