Effect of interparticle interaction on the low temperature oxidation of CO over size-selected Au nanocatalysts supported
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Catalysis Letters, Vol. 113, Nos. 3–4, February 2007 (Ó 2007) DOI: 10.1007/s10562-007-9027-7
Effect of interparticle interaction on the low temperature oxidation of CO over size-selected Au nanocatalysts supported on ultrathin TiC films Luis K. Ono and Beatriz Rolda´n-Cuenya* Department of Physics, University of Central Florida, Orlando, FL 32816, USA
Received 5 November 2006; accepted 21 December 2006
This work aims to get insight into the influence of interparticle interactions on catalysis. The low temperature CO oxidation is used as a model reaction. A strong dependence of the catalytic activity and stability of gold nanoparticles uniformly dispersed on polycrystalline TiC films was observed as a function of the interparticle distance. Two samples with similar height distributions (2 nm), but with different average interparticle distances (30 and 80 nm), were synthesized using diblock copolymer encapsulation. Their chemical reactivity was investigated by temperature programmed desorption (TPD), and reactive coarsening and subsequent deactivation was observed for the sample with the smallest interparticle distance. The system with the largest average interparticle distance showed higher stability towards agglomeration and longer lifetime. KEY WORDS: catalysis; Au nanoparticle; diblock copolymer; sintering; CO oxidation; interparticle interaction; size effects; XPS; TPD; AFM.
1. Introduction The heterogeneous catalytic chemistry of supported gold nanoparticles is a topical subject [1]. Haruta et al. [2] demonstrated that the catalytic activity and selectivity of gold changes drastically when small nanoparticles are considered. Highly dispersed Au nanoparticles were found to be excellent catalysts for a multitude of technological and environmentally important reactions including propene epoxidation [3], water–gas shift reactions [4], hydrogenation of CO2 and CO [5], the reduction of nitrogen oxides [6,7], and other air purification applications [8,9]. In the last two decades, considerable effort has been dedicated to the systematic investigation of the influence of the nanoparticle preparation method [10–19], size [2,20], shape [2], and nanoparticle-metal oxide support interaction [2,21] on catalytic performance. In order to get more in-depth knowledge of possible deactivation mechanisms [22–24], special attention has been devoted to the investigation of the dynamic character of a catalyst’s surface under ‘‘real-world’’ reaction conditions [25,26]. Furthermore, the stability of catalysts has been systematically monitored by using differently spaced metal nanostructures and size–shape-confining prefabricated supports [27–39]. In situ scanning tunneling microscopy (STM) studies conducted in Goodman’s group [27] revealed modifications in the size and substrate distribution of gold and silver nanoparticles evaporated on TiO2(110) upon *To whom correspondence should be addressed. E-mail: [email protected]
exposure to CO/O2 (2:1) and O2 at high pressure (13.33 mbar) and room temperature (RT). Because both gas dosing
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