Oxidized cobalt nanoparticles

Oxidized cobalt nanoparticles have been prepared from side-chain cobaltoce-nium containing ROMP block copolymers [79]. ROMP of either an all-organic... 

FIG. 10 Hysteresis magnetization loops obtained at T = 3 K. (A) Diluted liquid solution of cobalt nanoparticles in hexane. (B) Cobalt nanoparticles deposited onto freshly cleaved graphite (HOPG) and dried under argon to prevent oxidation. Substrate parallel (—) and perpendicular (—) to the field. 

Another difference between Co and Fe is their sensitivity towards impurities in the gas feed, such as H2S. In this respect, Fe-based catalysts have been shown to be more sulfur-resistance than their Co-based counterparts. This is also the reason why for Co F-T catalysts it is recommended to use a sulphur-free gas feed. For this purpose, a zinc oxide bed is included prior to the fixed bed reactor in the Shell plant in Malaysia to guarantee effective sulphur removal. Co and Fe F-T catalysts also differ in their stability. For instance, Co-based F-T systems are known to be more resistant towards oxidation and more stable against deactivation by water, an important by-product of the FTS reaction (reaction (1)). Nevertheless, the oxidation of cobalt with the product water has been postulated to be a major cause for deactivation of supported cobalt catalysts. Although, the oxidation of bulk metallic cobalt is (under realistic F-T conditions) not feasible, small cobalt nanoparticles could be prone to such reoxidation processes. 

Toupin M., Brousse T., Belanger D. Influence of microtexture on the charge storage properties of chemically synthesized manganese dioxide, Chem Mater 2002 14 3946-52. Wu N.L. Nanocrystalline oxide supercapacitors. Mater Chem Phys 2002 75 6-11. Delpeux S., Szostak K., Frackowiak E., Bormamy S., Beguin F. High yield of pure multiwalled carbon nanotubes from the catalytic decomposition of acetylene on in-situ formed cobalt nanoparticles. J. Nanosc. Nanotech. 2002 2 481-4. 

The Pauson-Khand reaction has also been carried out under different conditions, such as the use of chiral ligands, including PuPHOS, CamPHOS, and camphorsultam the use of aldehydes as the carbon monoxide source > the use of solid-supported cobalt catalyst to enhance purification, such as the dry-state adsorption the use of colloidal cobalt nanoparticle and the use of metallic cobalt supported on mesoporous silica prepared by decomposing Co2(CO)8 on mesoporous silica supports (SBA-15 and MCM-41) in the refluxing toluene solution.Other modifications include different promoting methods, such as photo-irradiation, microwave irradiation, molecular sieves, TEMPO,A-oxides, and supercritical fluids. Furthermore, the cycloaddition between allene and carbon monoxide under similar conditions is known as the allenic Pauson-Khand reaction,27,41 jjjg reaction among alkyne, carbodiimide, and CO is referred to as the aza-Pauson-Khand reaction. ... 

Wang, Q., and Yun, Y. (2012). A nanomaterial composed of cobalt nanoparticles, poly(3,4-ethylenedloxythiophene) and graphene with high electrocatal5dic activity for nitrite oxidation, Microchim Acta, 177, pp. 411-418. 

In situ structural studies can also provide considerable insight into material properties and formation pathways. Koziej and co-workers have employed X-ray absorption spectroscopy (XAS) and diffraction for this purpose and have studied the formation of cobalt and cobalt oxide nanoparticles from a benzyl alcohol route.Here, the importance of the reaction temperature on the reactivity of the cobalt isopropoxide starting material with benzyl alcohol was noted. The first report of cobalt nanoparticles from a benzyl alcohol route via the reduction of Co " was established for reaction temperatures of 180 °C. Meanwhile, lower reaction temperatures (80 °C) lead to oxidation and afford cubic C03O4 nanoparticles. The in situ studies have been carried out on samples prepared at 140 °C in an effort to understand the mechanism behind such a complex reaction scheme. It was found that at this temperature both processes occur simultaneously reduction to Co° and oxidation to C03O4, followed by reduction to CoO. Studying the assembly of nanoparticles in detail can also provide an insight into how these processes could be potentially manipulated. 

FIGURE 2.5 Transmission electron microscopy images of polystyrene-coated cobalt nanoparticles with particle diameter of 32 nm after oxidation for 1 week. (Reprinted with permission from Keng, P.Y. et al., 2009, ACS Nano, 3, no. 10, 3143-3157. Copyright 2009 American Chemical Society.)... 

Shi Z-Q, Dong Z-P, Sun J, Zhang F-W, Yang H-L, Zhou J-H, Zhu X-H, U R. Filled cobalt nanoparticles into carbon nanotubes as a rapid and high-efficiency catalyst for selective ep-oxidation of styrene with molecular oxygen. Chem Eng J 2014 237 81-7. 

Figure 1.21 Transmission electron micrograph of a cobalt nanoparticle wrapped in graphitic sheaths. Such graphitic sheathing gives the particles considerable stability toward oxidation without affecting their magnetic properties. (From Seshadri, R. etal., Cham. Rhys. Lett., 231, 1308, 1994. With permission.)...

---