CO Disproportionation on a Nanosized Iron Cluster

Abstract

First-principles electronic structure calculations, fully incorporating the effects of spin polarization and noncollinear magnetic moments, have been used to investigate CO disproportionation on an isolated Fe cluster. After CO dissociation, which occurs on a vertex between the facets, O atoms remain on the surface while C atoms move into the cluster as the initial step toward carbide formation. The lowest CO dissociation barrier found (0.77 eV) is lower than that on most of the studied Fe surfaces. Several possible paths for CO 2 formation were identified. The lowest reaction barrier was 1.08 eV.The carbon nanotubes (CNTs) are of great interest since they exhibit unique and useful chemical and physical properties related to toughness, electrical/thermal conductivity, and magnetism.1 The chemical vapor deposition (CVD) methods are widely used as a CNTs synthesis method since they open a way to highly controlled and continuous CNT production. [2][3][4][5] 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 will form carbon structures on the nanoparticles' surface. All properties, like diameter and chirality, of the nanotube are determined by the metal particle. In addition to the CNT synthesis, the metal nanoclusters with a size of less than 10 nm have attracted a great deal of attention due to their applications in magnetism, 6 electronics, 7 and catalysts. 8 The metal nanoparticles are widely used in several real-world catalytic applications, including the car exhaust catalysts, where reactions happen on 3-8 nm size Pt group metal particles. 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 is much higher than that on almost flat surfaces. Furthermore, the real nanoclusters have several unique active sites like facets and vertexes between the facets, which can have catalytic properties that differ drastically from the ones of almost flat surfaces. The research related to the active sites is mainly limited to atomic steps, and the nanosized clusters have received much less attention.9 Experimentally, many investigators have studied metal nanostructures using a wide range of surface science techniques, but these studies were done with rather a arbitrary size of clusters because it is very difficult to prepare fixed size clusters. 9 If we want to understand the active sites on clusters, we have to know which cluster we are studying. Even then, each cluster has several different active sites, and it is very difficult to know which of them is the most active one. For this reason, the computational approach, where precise sites can be studied, is very attractive.The present study is addressing the CO disproportionation CO (g) + CO (g) h CO 2(g) + C (s) on an iron nanocluster during the CVD method for the sy...

Mechanism study of floating catalyst CVD synthesis of SWCNTs

“…The obtained formation energy is +0.62 eV with a barrier of +1.04 eV. Considering that the particle morphology and reaction conditions are different, the calculated data are in reasonable agreement with the experimental results of Li et al 24 and earlier results by the authors 13. The experimentally measured barriers are in good agreement with experimental results for the Fe 2 O 3 catalysts used in modern industrial applications 25.…”

“…Subsequently, the particles were introduced into a heated ceramic tube reactor and mixed with a CO flow to induce CNT formation. This process differs significantly from the one presented in our previous studies in which the nanoparticle formation was based on thermal decomposition of ferrocene 13.…”

“…Iron has a large magnetic moment, and in the cluster geometry, the spin orientation is subtle. Therefore, we have fully incorporated the effects of spin polarization and collinear magnetic moments in our calculations 13. The adequacy of the computational parameters has been tested against the calculation of cluster geometry.…”

“…In our previous study 13, the reactivity of CO on a nanosized iron cluster has been tested using density functional theory (DFT) calculations with the PW91's generalized gradient approximation (GGA‐PW91) for the exchange and correlation functional 14. The calculations were performed with the Vienna ab initio simulation package (VASP code 15) with the projector augmented wave (PAW) method 16.…”

Influence of the diameter of single-walled carbon nanotube bundles on the optoelectronic performance of dry-deposited thin films

“…3. Both the decrease in the relative amount of amorphous material and the increase in L bundle were expected, since the catalytic activity of iron nanoparticles and diffusion rate of carbon are both more suitable for SWCNT production at higher temperatures [25–26]. This was also clearly evidenced by an increase in the reactor output concentration as confirmed with the DMA measurements: the number concentration ( NC ) increased steadily from NC 650 °C = 6 × 10 5 cm −3 at T set = 650 °C, with the corresponding geometric mean diameter GMD 650 °C = 45 nm, reaching NC 800 °C = 2 × 10 7 cm −3 and GMD 800 °C = 55 nm at T set = 800 °C.…”