CO dissociation and CO+O reactions on a nanosized iron cluster

Abstract

Catalysis over metal nanoparticles is essential for the growth of carbon nanotubes and all the properties of the resulting nanotube, such as diameter and chirality, are affected by the metal particle. Thus, it is very important to understand the carbon chemistry taking place on nanometer size metal particles. Here we present the fi rst ab initio computational study of chemical reactions on a nanosized iron cluster. The clusters have reaction sites, such as edges and vertexes between the facets, Which have not been studied before. First principles electronic structure calculations, fully incorporating the effects of spin polarization and non-collinear magnetic moments, have been used to investigate CO disproportionation on an isolated Fe 55 cluster. After CO dissociation, O atoms remain on the surface while C atoms move into the cluster, presumably as the initial step toward carbide formation. Here we show that the lowest CO dissociation barrier found on the cluster (0.77 eV) is lower than on most previously studied Fe surfaces. This dissociation occurs on a vertex between the facets. Several possible paths for CO 2 formation were identifi ed. The calculated lowest reaction barrier is 1.08 eV, which is comparable to the barrier of 0.65 eV obtained by experiment. KEYWORDSNanoparticle, density functional theory (DFT), mechanism, synthesis Since their discovery, carbon nanotubes (CNTs) have been the object of very intensive research. CNTs are of great interest since they exhibit unique and useful chemical and physical properties related to toughness, electrical/thermal conductivity, and magnetism [1]. Several different techniques have been introduced to synthesize CNTs [2 5] but among the various routes, carbon vapor deposition (CVD) methods have attracted widespread interest since they open a way to highly controlled and continuous CNT production on designed architectures [5 9]. In these processes, metal nanoparticles are produced in a mixed flow of carbon precursors and other gases (e.g., hydrogen) and the growth process is driven by cleaving the carbon atoms from the precursors and these atoms then form carbon structures on the surface of the nanoparticles. The metal catalyst nanoparticle is essential for CNT growth. All properties, like diameter and chirality, of the nanotube are determined by the metal particle. The ability to control the properties of CNTs is essential for their use in technological applications [10]. Thus, it Nano Research 661 Nano Res (2009) 2: 660 670 is very important to understand the carbon chemistry taking place on the nanometer size metal particles. I n a d d i t i o n t o t h e C N T s y n t h e s i s , m e t a l nanoclusters with a size less than 10 nm have attracted a great deal of attention due to their applications in magnetism [11], electronics [12], and catalysis [13]. Often the good catalytic activity can be related to catalytic sites, like atomic size steps, on the cluster. Due to the high curvature of the clusters, the special site density and distribution are much hi...

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