Anderson, Marie L., Ford, Mark S., Derrick, Peter J. , Drewello, Thomas, Woodruff, D. P. and Mackenzie, Stuart R.. (2006) Nitric oxide decomposition on small rhodium clusters, Rh-n(+/-). Journal of Physical Chemistry A, Vol.110 (No.38). pp. 10992-11000. ISSN 1089-5639

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Abstract

The decomposition of nitric oxide on small charged rhodium clusters Rh-n(+/-)(6 < n < 30) has been investigated by Fourier transform ion cyclotron resonance mass spectrometry. For both cationic and anionic naked clusters, the rates of reaction with NO increase smoothly with cluster size in the range studied without the dramatic size-dependent fluctuations often associated with the reactions of transition-metal clusters. The cationic clusters react significantly faster than the anions and both exhibit rate constants exceeding collision rates calculated by average dipole orientation theory. Both the approximate magnitude and the trends in reactivity are modeled well by the surface charge capture model recently proposed by Kummerlowe and Beyer. All clusters studied here exhibit pseudo-first-order kinetics with no sign of biexponential kinetics often interpreted as evidence for multiple isomeric structures. Experiments involving prolonged exposure to NO have revealed interesting size-dependent trends in the mechanism and efficiency of NO decomposition: For most small clusters (n < 17), once two NO molecules are coadsorbed on a cluster, N-2 is evolved, generating the corresponding dioxide cluster. By analogy with experiments on extended surfaces, this observation is interpreted in terms of the dissociative adsorption of NO in the early stages of reaction, generating N atoms that are mobile on the surface of the cluster. For clusters where n < 13, this chemistry, which occurs independently of the cluster charge, repeats until a size-dependent, limiting oxygen coverage is achieved. Following this, NO is observed to adsorb on the oxide cluster without further N-2 evolution. For n = 14-16 no single end-point is observed and reaction products are based on a small range of oxide structures. By contrast, no evidence for N-2 production is observed for clusters n = 13 and n > 16, for which simple sequential NO adsorption dominates the chemistry. Interestingly, there is no evidence for the production of N2O or NO2 on any of the clusters studied. A simple general mechanism is proposed that accounts for all observations. The detailed decomposition mechanisms for each cluster exhibit size (and, by implication, structure) dependent features with Rh-13(+/-) particularly anomalous by comparison with neighboring clusters.

Item Type:	Journal Article
Subjects:	Q Science > QD Chemistry Q Science > QC Physics
Divisions:	Faculty of Science > Chemistry Faculty of Science > Physics
Journal or Publication Title:	Journal of Physical Chemistry A
Publisher:	American Chemical Society
ISSN:	1089-5639
Date:	28 September 2006
Volume:	Vol.110
Number:	No.38
Number of Pages:	9
Page Range:	pp. 10992-11000
Identification Number:	10.1021/jp062178z
Status:	Not Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
URI:	http://wrap.warwick.ac.uk/id/eprint/33026

Data sourced from Thomson Reuters' Web of Knowledge

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