Invited Paper SS1-MoA3
Catalytic Reactivity of Mass Selected Nanoparticles

Monday, October 18, 2010, 2:40 pm, Room Picuris

It has recently been shown that for both the technologically important steam reforming process [1] and the methanation reaction [2] the rates are strongly dependent on the particles’ size. This is ascribed to the nature of the nanoparticles and in particular the presence of step and kink sites on the nanoparticles. The abundance of such sites is expected to be very dependent on the size and the synthesis procedure. In this work we have investigated the nature of mass selected Ruthenium nanoparticles and specifically their reactivity with respect to gasses relevant for the above mentioned processes. Ruthenium is known to be a very good catalyst for both processes, and in some situations it may be superior to the commonly used Nickel catalyst despite its much higher price. Nanoparticles of sizes relevant for the above mentioned processes (2-10 nm) are manufactured by a sputter magnetron and subsequently mass selected by a quadropole mass spectrometer. The nanoparticles are soft landed on various substrates (HOPG or SiO2) and the influence and the advantages of the substrates will be discussed. The nanoparticles have be characterized in situ by SEM, AES, ISS,TPD and STM while ex-situ TEM has been used. The surface area and the stability of the nanoparticles were initially determined by temperature programmed desorption, and their ability to dissociate CO was evaluated using isotopically labeled gasses. The nature of the CO bonding and dissociation will be correlated with similar investigations on purpose stepped single crystals of Ruthenium (Ru(0 1 54))] demonstrating how the activity can be evaluated as a function of size. The reactivity of such mass selected nanoparticles has also been measured in a newly developed micro reactor on a chip with a volume of only 235 nl. This small volume combined with the fact that all the reactants and products can be led directly into a quadropole mass spectrometer for analysis allows for a close correlation of size and overall reactivity at high pressure and temperature conditions.

References:

[1] G. Jones, J. G. Jakobsen, S. S. Shim, J. Kleis, M. P. Andersson, J. Rossmeisl, F. Abild-Pedersen, T. Bligaard, S. Helveg, B. Hinnemann, J. R. Rostrup-Nielsen, I. Chorkendorff, J. Sehested, and J. K. Nørskov, “First Principles Calculations and Experimental Insight into Methane Steam Reforming over Transition Metal Catalysts”, J. Catal. 259 (2008) 147-160.

82] M. P. Andersson, F. Abild-Pedersen, I. Remediakis, J. Engbaek, O. Lytken, S. Horch, J. H. Nielsen, J. Sehested, J. R. Rostrup-Nielsen, J. K. Nørskov, and I. Chorkendorff, “H2 Induced CO dissociation on nickel surfaces”, J. Catal. 255 (2008) 6-19.