Thin layer of carbon-nano-fibers (CNFs) as catalyst support for fast mass transfer in hydrogenation of nitrite

CNF-foam 'hairy foam' and CNF aggregates supported Pd catalysts were studied for the reduction of aqueous nitrite solution and also compared with conventional catalysts. Relatively large Pd particle size and similar Pd particle size distribution on all the catalyst supports excludes any structure sensitive effects on reaction. Intrinsic rates over hairy foam catalysts were independent of CNF-layer thickness (8-28 mu m) and Pd loading (0.5-2 wt%), demonstrating the absence of any mass transfer limitations. When compared to conventional catalysts at comparable diffusion layers. CNF based catalysts showed at least three times higher rates of nitrite conversion per mole of surface palladium (TOF). Increased TOF is due to the improved mass transfer provided by macroporous structure of the entangled CNFs, which offers low tortuosity, provides accessibility to all the active sites. The intrinsic activity of graphite and CNF-supported Pd contributes significantly to the high activity for nitrite reduction. (C) 2010 Elsevier B.V. All rights reserved.