Book of Abstracts Book of Abstracts - Universität Konstanz

B - 16
54
Reactivity of Size-Selected Gas-Phase Transition Metal Carbide and
Sulfide Clusters
James Lightstone 1 , Melissa Patterson 1 , Robert J. Beuhler 2 1, 2
, Michael G. White
1 Department of Chemistry, Stony Brook University, Stony Brook, NY 11974, USA
2 Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973, USA
We have recently constructed a cluster deposition apparatus which employs a magnetron
sputtering source for generating gas-phase cation clusters of pure metals and metallic
compounds. The focus is on generating clusters of the early transition metal compounds
(carbide and sulfides), which are known in their bulk form to be active catalysts for a wide
range of heterogeneous reactions [1,2]. In many cases, metal carbides offer distinct advantages
over the parent metal in selectivity and resistance to poisoning, and for certain reactions their
catalytic behavior is similar to that of the Group 8-10 noble metals [2,3]. Very recent theoretical
calculations also suggest that small carbide clusters, i.e., the Ti8C12 Met-Car and Ti14C13
nanocrystallite, are more reactive than bulk TiC surfaces [4]. The work reported here examines
the gas-phase reactivity of small transition metal carbide and sulfide clusters as a first step
towards investigations of model catalysts prepared by size-selected deposition.
Ion beams containing a wide array of transition metal compound clusters, TxMy + (T ≡ Ti,
Mo, Zr, Nb; M ≡ C, S), were generated using a magnetron sputtering source, including “magic”
number species such as the Ti8C12 + Met-Car. The gas-phase reactivity of mass-selected TxMy +
clusters was studied using a hexapole collision cell, into which reactive gases were introduced,
and a second quadrupole mass filter for product detection. Results will be presented for the
adduct formation and reactions of the Ti8C12 + Met-Car with a variety of sulfur containing
molecules, such as OCS shown in the accompanying figure below. In addition, we will also
present results on the reactivity of MoxSy + clusters and future plans for size-selected cluster
deposition. This work was supported by the U.S. Department of Energy, Office of Basic Energy
Sciences, Division of Chemical Sciences under contract No. DE-AC02--98CH10886
Figure 1. Mass spectrum of the reaction
products resulting from collisions between
Ti8C 12 + and OCS at 300K. .
References
500 600 700 800 900 1000
[1] J.G. Speight, The Chemistry and Technology of Petroleum, second ed., New York, McGraw-Hill,
1991.
[2] Chen, J. G., Chem. Rev. 1996, 96, 1477; Oyama, S. T., Catal. Today 15, 179 (1992).
[3] Levy, R. L.; Boudart, M., Science 181, 547 (1973).
[4] H. Hou, J. T. Muckerman, P. Liu and J. A. Rodriguez, J. Phys. Chem. 107, 9344 (2003); P. Liu and
J. A. Rodriguez, J. Chem. Phys. 119, 10895 (2003).
Intensity
1.20E-008
1.00E-008
8.00E-009
6.00E-009
4.00E-009
2.00E-009
0.00E+000
Ti 8 C 12
Ti 8 C 12 + S
Ti 8 C 12 + SCO
Ti 8 C 12 + S(SCO) 3
Mass
Ti 8 C 12 + S(SCO) 5