Influence of Metal Deposition and Activation Method on the Structure and Performance of Carbon Nanotube Supported Palladium Catalysts.

The effects of the metal deposition and activation methods on metal particle size and distribution were investigated for carbon nanotube supported Pd catalysts. The Pd precursor was loaded by incipient wetness impregnation, ion adsorption, and deposition precipitation and was activated by thermal treatment under a nitrogen atmosphere or in the liquid phase by reduction by formaldehyde or sodium borohydride. Regardless of the metal precursor loading method, activation under a N2 atmosphere at 500 °C led to homogeneously distributed 4 nm Pd particles. Liquid-phase reduction by sodium borohydride provided a bimodal distribution with particle sizes of approximately 1 and >10 nm. A somewhat weaker reducing agent, formaldehyde, yielded particles approximately 1 nm in size. The activities of the catalysts for the hydrogenation of cinnamaldehyde correlated with the particle sizes.

Effects of the Functionalization of the Ordered Mesoporous Carbon Support Surface on Iron Catalysts for the Fischer-Tropsch Synthesis of Lower Olefins.

Ordered mesoporous carbon (CMK-3) with different surface modifications is applied as a support for Fe-based catalysts in the Fischer-Tropsch to olefins synthesis (FTO) with and without sodium and sulfur promoters. Different concentrations of functional groups do not affect the size (3-5 nm) of Fe particles in the fresh catalysts but iron (carbide) supported on N-enriched CMK-3 and a support with a lower concentration of functional groups show higher catalytic activity under industrially relevant FTO conditions (340 °C, 10 bar, H2/CO=2) compared to a support with an O-enriched surface. The addition of promoters leads to more noticeable enhancements of the catalytic activity (3-5 times higher) and the selectivity to C2-C4 olefins (≈2 times higher) than surface functionalization of the support. Nitrogen surface functionalization and removal of surface groups before impregnation and calcination, however, further increase the activity of the catalysts in the presence of promoters. The confinement of the Fe nanoparticles in the mesopores of CMK-3 restricts but does not fully prevent particle growth and, consequently, the decrease of activity under FTO conditions.

pH controlled adsorption of water-soluble ruthenium clusters onto carbon nanotubes and nanofiber surfaces.

Supported catalysts were prepared from water-soluble molecular clusters by pH controlled impregnations in order to probe the interactions occurring between the supports and the clusters and to maximize them. The PZC of different nano-carbon solids (nanotubes and nanofibers) was determined. The EpHL method of measuring the PZC could be successfully extended for the first time to these nano-carbon supports. When impregnating these nano-carbons with water-soluble Ru clusters by varying the pH, we found that two adsorption mechanisms were taking place. We postulate that interactions in the form of π-bond coordination or reactions with higher reactivity zones of the carbon surface occur at all pH values. Electrostatic interactions coexist with the latter and play a determining role, allowing or hindering maximal adsorption. Our water-impregnated samples exhibit smaller and better distributed nanoparticles in comparison to an organic-solvent-impregnated sample. Sintering of the particles at higher activation temperature led to nanoparticles with a bimodal size distribution on the nanofibers. The bimodal size distribution is a strong indication of two different adsorption mechanisms. The obtained Ru/nano-C catalysts present a valuable activity and selectivity in the hydrogenation of lactose into lactitol.