Platinum growth

High reaction temperatures in catalytic processes can lead to loss of active components by evaporation. This does not only occur with compounds that are known to be volatile (e. g., P2O5 in H3PO4, silica gel, HgCl2/activated carbon), but also by reaction of metals to give volatile oxides, chlorides, or carbonyls. In the oxidation of ammonia on Pt/Rh net catalysts (Ostwald nitric acid process), the catalyst reacts with the gas phase to form volatile Pt02- Furthermore, porous platinum growths are observed on the surface. This can be prevented by addition of rare earth oxides. 

Fig. 2.11 A distinct platinum growth mode on shaped gold nanocrystals (adapted from tef. [45])...

Other interesting thin-film studies using AES have included the growth of platinum on Ti02- and SrO-terminated (100) SrTiOs single-crystal substrates [2.154], of epitaxial niobium films on (110) T1O2 [2.155], the interaction of copper with a (0001) rhenium surface [2.156], and the characterization of radio-frequency (rf) sputtered TiN films on stainless steel [2.157]. 

Cisplatin, Pt (NH3)2Cl2, is a chemotherapeutic agent that disrupts die growth of DNA. If die current cost of Pt is 1118.0/troy ounce (1 troy oz = 31.10 g), how many grams of cisplatin can you make with three thousand dollars worth of platinum How many pounds ... 

There is little data available to quantify these factors. The loss of catalyst surface area with high temperatures is well-known (136). One hundred hours of dry heat at 900°C are usually sufficient to reduce alumina surface area from 120 to 40 m2/g. Platinum crystallites can grow from 30 A to 600 A in diameter, and metal surface area declines from 20 m2/g to 1 m2/g. Crystal growth and microstructure changes are thermodynamically favored (137). Alumina can react with copper oxide and nickel oxide to form aluminates, with great loss of surface area and catalytic activity. The loss of metals by carbonyl formation and the loss of ruthenium by oxide formation have been mentioned before. 

FIGURE 2-9 Repetitive cyclic voltanunograms illustrating the continuous growth of polyaniline on a platinum surface. 

Figure 9. Chronoamperometric curves for the growth of a polythiophene film on a stationary platinum disk electrode, from 0.1 M thiophene and 0.1 M LiC104 acetonitrile solutions, at different water contents (---) 0.04%, (--------) 0.14%,...

There is another method that has been sometimes employed in the vapor phase growth of eiystals. This method uses an evacuated eapsule as shown in 6.12.4., given on the next page. The eapsule is generally made from quartz, although platinum is sometimes used. Tlie capsule needs to be evacuated to remove any residual gas before heating is started. Otherwise, the internal pressure would build until the eapsule would explode. 

Figure 1 shows AES data for the oxidized titanium surface before and after deposition of 30 X of platinum with the substrate held at 130 K. The platinum thickness was calculated from the attenuation of the oxygen AES signal assuming layered growth of the metal. From the spectra It Is clear that the platinum was sufficient to completely attenuate the underlaying features of the titanium oxide. 

Jerkiewicz G, Vatankhah G, Lessard J, Soriaga MP, Park YS. 2004. Surface-oxide growth at platinum electrodes in aqueous H2SO4 Reexamination of its mecharusm through combined cyclic-voltammetry, electrochemical quartz-crystal nanobalance, and Auger electron spectroscopy measurements. Electrochim Acta 49 1451-1459. 

Chronoamperometric transients for CO stripping on polycrystalline platinum were measured by McCallum and Fletcher [1977], Love and Lipkowski [1988] were the hrst to present chronoamperometric data for CO stripping on single-crystalline platinum. However, they interpreted their data on the basis of a different model than the one discussed above. Love and Lipkowski considered that the oxidation of the CO adlayer starts at holes or defects in the CO adlayer, where OH adsorbs. These holes act as nucleation centers for the oxidation reaction, and the holes grow as the CO at the perimeter of these holes is oxidized away by OHads- This nucleation and growth (N G) mechanism is fundamentally different from the mean held model presented above, because it does not presume any kind of mixing of CO and OH [Koper et ah, 1998]. Basically, it assumes complete surface immobility of the chemisorbed CO. 

Figure 9.6 Visual representation of the platinum oxide growth mechanism, (a) Interaction of H2O molecules with the Pt electrode occurring in the 0.27 V < < 0.85 V range, (b) Discharge of 5 ML of H2O molecules and formation of 5 ML of chemisorbed oxygen (Ochem)- (c) Discharge of the second ML of H2O molecules the process is accompanied by the development of repulsive interactions between (Pt-Pt) -Ofi m surface species that stimulate an interfacial place exchange of Ochem and Pt surface atoms, (d) Quasi-3D surface PtO lattice, comprising Pt and moieties, that forms through the place-exchange process. (Reproduced with permission...

Bett JAS, Kinoshita K, Stonehart P. 1976. Crystallite growth of platinum dispersed on graphi-tized carbon black n. Effect of liquid environment. J Catal 41 124-133. 

Inaba M, Ando M, Hatanaka A, Nomoto A, Matsuzawa K, Tasaka A, Kinumoto T, Iriyama Y, Ogumi Z. 2006. Controlled growth and shape formation of platinum nanoparticles and their electrochemical properties. Electrochim Acta 52 1632-1638. 

---