Process polyol

Figure 9. Schematic representation of the polyol process exemplified with Pt. TEM (left) shows a narrow particle size distribution (ca. 3 nm). (Reproduced from [223], 2000, with permission from Elsevier Science.) Experimental XPS curves (right) fit sufficiently well with the Pt(0) standard. (Reprinted from Ref [53], 2007, with permission from Wiley-VCH.)...

A subtle control of the particle morphology and size can also be brought about using Fievet s Polyol process for catalyst preparation. The main advantage here is the easy access to nanoparticulate metals at any normally equipped laboratory bench without the restrictions imposed by anaerobic working conditions [224]. It is clear... 

The reduction of metal hydroxides or oxides powder by polyol was first reported by Figlarz and co-workers, which gave rise to fine powders of Cu, Ni, Co and some noble metals with micrometer sizes (polyol process) [32,33]. The polyol process was first modified for the preparation of PVP-protected bimetallic and monometallic nanoclusters such as Pt/Cu, Pd/Pd, Pt/Co, Pt, Pd, etc. [34-38]. The previous results definitely revealed that Pt, Pd, Cu and Co in these PVP-protected metal or alloy nanoclusters were in a zero-valent metallic state. 

Wan, J., Cai, W., Meng, X. and Liu, E. (2007) Monodisperse water-soluble magnetite nanoparticles prepared by polyol process for high-performance magnetic resonance imaging. Chemical Communications, (47), 5004—5006. 

Li, D.S. and Komarneni, S. (2006) Microwave-assisted polyol process for synthesis of Ni nanoparticles. Journal of the American Ceramic Society, 89 (5), 1510-1517. 

Cheng, W.T. and Cheng, H.W. (2009) Synthesis and characterization of cobalt nano-particles through microwave polyol process. AIChEJournal, 55 (6), 1383-1389. 

Tanase, M. and Laughlin, D. (2004) Polyol process synthesis ofmonodispersed FePt nanoparticles. Journal of Physical Chemistry B, 108 (20), 6121-6123. 

In 1996, Liu et al. reported the selective hydrogenation of cinnamaldehyde, an a,/ -unsaturated aldehyde, to cinnamyl alcohol, an a,/ -unsaturated alcohol, by means of PVP-protected Pt/Co bimetallic colloids prepared by the polyol process [111]. The colloids were obtained as a dark-brown homogeneous dispersion in a mixture of ethylene glycol and diethylene glycol, and characterized by TEM and XRD. These authors prepared different samples of nanoparticles with Pt Co ratios of 3 1 and 1 1, the mean diameters of which measured 1.7 and 2.2 nm, respectively. These colloidal systems were also compared with the single metal-... 

Pristine CNTs are chemically inert and metal nanoparticles cannot be attached [111]. Hence, research is focused on the functionalization of CNTs in order to incorporate oxygen groups on their surface that will increase their hydrophilicity and improve the catalyst support interaction (see Chapter 3) [111]. These experimental methods include impregnation [113,114], ultrasound [115], acid treatment (such as H2S04) [116— 119], polyol processing [120,121], ion-exchange [122,123] and electrochemical deposition [120,124,125]. Acid-functionalized CNTs provide better dispersion and distribution of the catalysts nanoparticles [117-120],... 

When we consider the metals of nanoscopic size, fine metal particles from micrometer to nanometer size can be synthesized by both physical and chemical methods. The former method provides the fine metal particles by decreasing the size by addition of energy to the bulk metal, while in the latter methods, fine particles can be produced by increasing the size from metal atoms obtained by reduction of metal ions in solution. Since chemical reactions usually take place in homogeneous solution in any case, this chapter includes most of the cases of synthesis and growth of fine metal particles. However, the polyol process, reaction in microemulsions, and formation in the gas phase are omitted, since they are described in later chapters by specialists in those fields. 

Monodisperse Metal Powders Preparation by the Polyol Process and Characterization... 

Table 9.2.2 Chemical Analysis (wt%) of Some Noble Metal Powders Obtained by the Polyol Process...

Polymer-protected, monodisperse, nanoscale silver particles (Fig. 9.2.1c and d) have been obtained through spontaneous nucleation by the polyol process as follows (23). PVP (1-25 g) and AgNOj (50-3200 mg) were dissolved in EG (75 mL) at room temperature. Then the solution was heated up to 120°C at a constant... 

Ag-Pd Alloy Powders (7,27). Bimetallic colloids, namely, Ag-Pd and Au-Pt, can be obtained by the polyol process. The composition Ag7oPdx> is of particular interest to make the internal electrodes of multilayer ceramic capacitors (MLCC). Polymer-protected, monodisperse, nanoscale Ag70Pd30 particles have been obtained... 

For each noble metal it appears that reaction parameters such as the nature of the precursor, temperature, and time have to be optimized. Recently a study of the electrochemical reduction of noble metals species in EG was undertaken by Bonnet et al. (28). Belter control of the experimental conditions leading to the preparation of monodisperse particles in the nanometer, submicrometer, and micrometer size range for various noble metals is expected from knowledge of the electrochemical fundamentals of the polyol process. 

Table 9.2.4 Chemical Analysis of Two Cobalt Powders Obtained from the Same Parent Hydroxide by Solid-Gas Reduction and by the Polyol Process (Main Impurities/ Cobalt Ratios in ppm by Weight)...

CofOH) (precursor) Co (solid-gas reduction) Co (polyol process)... 

Thus, monodisperse Co-Ni powders can be obtained by the polyol process in the whole composition range including pure Co or Ni powders. The particle size can be varied over a wide range, which can reach three orders of magnitude. 

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