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

Abstract

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.

Synthesis of ultrasmall, homogeneously alloyed, bimetallic nanoparticles on silica supports

“…Electrostatic adsorption has been demonstrated for a host of single metals on many different supports (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17). Over composite oxide surfaces, pHcontrolled adsorption has been used to achieve selective metal adsorption onto one surface component or the other (18)(19)(20).…”