Platinum deposition

Catalytic processes frequently require more than a single chemical function, and these bifunctional or polyfunctional materials innst be prepared in away to assure effective communication among the various constitnents. For example, naphtha reforming requires both an acidic function for isomerization and alkylation and a hydrogenation function for aromati-zation and saturation. The acidic function is often a promoted porous metal oxide (e.g., alumina) with a noble metal (e.g., platinum) deposited on its surface to provide the hydrogenation sites. To avoid separation problems, it is not unusual to attach homogeneous catalysts and even enzymes to solid surfaces for use in flow reactors. Although this technique works well in some environmental catalytic systems, such attachment sometimes modifies the catalytic specifici-... 

The platinum electrode is also very convenient for investigating various adsorption phenomena in electrochemical systems. The surface of platinum is very stable and reproducible. As will be shown in what follows, the true working area can be determined with high accuracy for platinum surfaces with appreciable roughness and even for electrodes with highly dispersed platinum deposits. It is comparatively easy to clean the surface of adsorbed impurities and to control the state of the surface. 

It was found in the 1960s that disperse platinum catalyst supported by certain oxides will in a number of cases be more active than a similar catalyst supported by carbon black or other carbon carrier. At platinum deposits on a mixed carrier of WO3 and carbon black, hydrogen oxidation is markedly accelerated in acidic solutions (Hobbs and Tseung, 1966). This could be due to a partial spillover of hydrogen from platinum to the oxide and formation of a tungsten bronze, H WOj (0 < a < 1), which according to certain data has fair catalytic properties. 

Figure 3. Scanning electron microscopy images of gold electrodes coated by the nanostructured TMPP/C12 monolayer after the electrochemical platinum deposition. The deposition charge was 41 and 160Cm for the left and right images, respectively. (Reprinted from Ref [18], 2005, with permission from Wiley-VCH.)...

Hj concentration as a function of time for various alcohols as electron donor. In the presence of primary and secondary alcohols the rates of Hj generation are equal although the induction periods at the start of illumination are different. In the presence of a tertiary alcohol the rate of formation is substantially lower. As mentioned in section 4.2 alcohols are not strongly adsorbed at the TiO particles and therefore do not react with the positive holes before they are trapped. The main scavenger in this system is the platinum deposit which scavenges electrons and catalyses the reduction of hydrogen ions 2 e" -I- 2 —> H2- A surprising observation was that the H2... 

Zhou W-P, Lewera A, Bagus PS, Wieckowski A. 2007. Electrochemical and electronic properties of platinum deposits on Ru(OOOl) Combined XPS and cyclic voltammetric study. J Phys ChemC 111 13490. 

The catalytic properties of a Pt/Sn combination were observed on different kinds of electrode materials alloys [90], electro co-deposits of Pt and Sn [89, 90], underpotential deposited tin [42] or a mixture of tin oxide and platinum deposited on glass [95], All different materials present a marked influence on methanol electrooxidation. 

The catalyst employed consisted of platinum deposited on the external surface of 1/8 x 1/8 in. cylindrical alumina pellets. The data below were obtained in run C-127S. Determine the composition at the exterior surface of the catalyst. 

Aris A process for the hydrocatalytic isomerization of C8 fractions. Developed by Leuna-Werk and Petrolchemische Kombinate Schwedt in 1976. The catalyst is platinum deposited in a mixture of alumina and natural mordenite. 

Platinum deposition techniques, 79 157 Platinum dichloride, 79 655 Platinum-divinyltetramethyldisiloxane complex, in silicone network preparation, 22 563 Platinum films, 79 658 Platinum gauze catalyst, 77 180-181 Platinum-group metal compounds, 79 635-667 analysis of, 79 637 economic aspects of, 79 635-636 health and safety factors related to, 79 658... 

Recent studies performed with deactivated anodes show [55] that electroless or electrolytic platinum deposition on failed anodes, not only lowered the polarisation behaviour of these anodes (see Fig. 5.20), but also demonstrated an equivalent lifetime as that of a new anode in accelerated life tests in the sulphuric acid solution (see Fig. 5.21). These results unequivocally demonstrate that the deactivation of anodes, for which the Ru loading is still high, is a direct consequence of the depletion of Ru from the outer region of the anode coating. Note that this process of surface enrichment by conducting electroactive species will not lead to reactivating a failed anode, if there is a TiC>2 build-up at the Ti substrate/coating interface. 

B. Sun, A.V. Vorontsov, P.G. Smirniotis, Role of platinum deposited on Ti02 in phenol photocatalytic oxidation, J. Phys. Chem. B 19 (2003) 3151-3156. 

Platinum deposited on Nafion shows long lasting catalytic activity for methanol oxidation3i-32, because the membrane stabilizes Pt2+. which oxidize methanol. ... 

Herrmann, J.M., Disdier, J., Pichat, P. 1986. Photoassisted platinum deposition on TiO, powder using various platinum complexes. J Phys Chem 90 6028-6034. 

Fig.5 Atomic Force Microscopy (AFM) picture of platinum deposition (CVD) on activated HOPG...

Table 2 Operating conditions and mean ] a silica support particle size of platinum deposition obtained on ...

For obvious reasons related to the necessary reduction of the amount of catalyst used in fuel cells, ORR has been studied on thin films of platinum deposited onto glassy carbon or titanium [73, 79] and on small metal particles on carbon [80-82]. The reduction of the Pt film thickness (<1 nm), as well as of the size of the particles (diam. < 3 nm), induces a moderate loss of activity attributed to differences in the adsorption of O2 on the metal surface. 

Effect of platinum content. Since a beneficial role of platinum deposited on titania had been reported for the photocatalytic oxidation of some organic compounds (refs 6, 7), several catalysts, from 0.5 to 10 wt % Pt with a constant particle size, were prepared and studied. The variations of the initial rate of formation of cyclohexanone as a function of Pt contents are shown in Fig. 2. There is not only no beneficial effect of Pt as mentioned in refs.(6, 7) but a... 

Fig. 2. Effect of the percentage of platinum deposited on Ti02 on the initial formation rate of cyclohexanone.

Chromium [10,39], niobium [42], titanium [13], and 90% titanium/10% tungsten [58] have been used as adhesion layers for platinum deposition. Chemical etching procedures based on H202/ethylenediamine tetraacetic acid (EDTA)/ NH4OH have been described for removal of interfering titanium [13] or tita-nium/tungsten [58] adhesion components from the surface of platinum electrodes. The procedure was shown to be effective for more than 24 h after treatment,... 

The catalyst contained 10% platinum deposited on activated carbon. This high platinum content (20 times more than in the commercial catalyst) made the activity of the catalyst more stable, thus facilitating the studies of kinetics. The surface of platinum in 1 g of the catalyst measured by hydrogen chemisorption was 2 m2. Since the concentrations of H2 and NO in the... 

Fig. 11.2 Schematic representation of a photoirradiated semiconductor particle loaded with small amounts of platinum deposits.

Levels of lactate in buttermilk and yoghurt (and blood) were estimated using disposable sensors formed from screen-printed graphite laminated between two polymer sheets [18]. Platinum (deposited by sputter-coating) was the transducing surface. Layers of Nation were added to reduce interference and were surmounted by lactate oxidase in a mixture of polyethyleneimine and poly (carbamoyl) sulphonate hydrogel. The samples were measured in stirred buffer. A good correlation between biosensor results and those obtained with an enzyme kit was claimed but the data had a considerable amount of scatter—if the enzyme kit is taken as the reference method then a more severe analysis of the biosensor results [33] would not have shown them in a... 

Courbon H, Herrmann JM, Pichat P. Effect of platinum deposits on oxygen adsorption and oxygen isotope exchange over variously pretreated, UV-illuminated powder Ti02. J Phys Chem 1984 88 5210-5214. 

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