Kinetics on platinum

Akoshima, S., Oishi, M., Yashiro, K., Sato, K., Mizusaki, J. (2010). Reaction kinetics on platinum electrode/yttrium-doped barium cerate interface under H2—H2O atmosphere. Solid State Ionics, 181, 240—248. 

Sheng W, Gasteiger HA, Shao-Hom Y (2010) Hydrogen oxidation and evolution reaction kinetics on platinum acid vs alkaline electrolytes. J Electrochem Soc 157(11) B1529-B1536. doi 10.1149/1.3483106... 

A pletliora of different SA systems have been reported in tire literature. Examples include organosilanes on hydroxylated surfaces, alkanetliiols on gold, silver, copper and platinum, dialkyl disulphides on gold, alcohols and amines on platinum and carboxyl acids on aluminium oxide and silver. Some examples and references can be found in [123]. More recently also phosphonic and phosphoric esters on aluminium oxides have been reported [124, 125]. Only a small selection out of tliis number of SA systems can be presented here and properties such as kinetics, tliennal, chemical and mechanical stability are briefly presented for alkanetliiols on gold as an example. 

Purely parallel reactions are e.g. competitive reactions which are frequently carried out purposefully, with the aim of estimating relative reactivities of reactants these will be discussed elsewhere (Section IV.E). Several kinetic studies have been made of noncompetitive parallel reactions. The examples may be parallel formation of benzene and methylcyclo-pentane by simultaneous dehydrogenation and isomerization of cyclohexane on rhenium-paladium or on platinum catalysts on suitable supports (88, 89), parallel formation of mesityl oxide, acetone, and phorone from diacetone alcohol on an acidic ion exchanger (41), disproportionation of amines on alumina, accompanied by olefin-forming elimination (20), dehydrogenation of butane coupled with hydrogenation of ethylene or propylene on a chromia-alumina catalyst (24), or parallel formation of ethyl-, methylethyl-, and vinylethylbenzene from diethylbenzene on faujasite (89a). 

In this section, we summarize the kinetic behavior of the oxygen reduction reaction (ORR), mainly on platinum electrodes since this metal is the most active electrocatalyst for this reaction in an acidic medium. The discussion will, however, be restricted to the characteristics of this reaction in DMFCs because of the possible presence in the cathode compartment of methanol, which can cross over the proton exchange membrane. 

Antoine O, Bultel Y, Durand R. 2001. Oxygen reduction reaction kinetics and mechanism on platinum nanoparticles inside Nafion . J Electroanal Chem 499 85-94. 

Macia MD, Campina JM, Herrero E, Feliu JM. 2004. On the kinetics of oxygen reduction on platinum stepped surfaces in acidic media. J Electroanal Chem 564 141 -150. 

Zinola CF, AM Castro Luna, Arvia AJ. 1994. Temperature dependence of kinetic parameters related to oxygen electroreduction in acid solutions on platinum electrodes. Electrochim Acta 39 1951-1959. 

Hsueh KL, Gonzalez ER, Srinivasan S. 1983. Electrolyte effects on oxygen reduction kinetics at platinum—A rotating-ring disk electrode analysis. Electrochim Acta 28 691-697. 

Hence, it appeared that the story was complete and the adsorption of hydrogen on platinum understood. However, considerable controversy was arising even as the definitive experiments were being performed. In 1959, Schuldiner carried out kinetic measurements on the H2-evolution reaction... 

Figure 4.10 Secondary ion intensities of ethylidyne, =CCH3, on platinum(l 11) during reaction with D2 at 383 K. Curves a-d are the measured SIMS intensities of CH + fragments at 15-18 amu, respectively. Curves e-h represent a kinetic simulation for a consecutive reaction via two intermediates (adapted from Creighton et al. [30]).

EELS has been used to study the kinetics of relatively slow surface reactions, such as the hydrogen-deuterium exchange in benzene adsorbed on platinum [54], In... 

Kinetics of Ethylidyne Formation on Platinum(lll) Using Near-Edge X-ray Absorption Fine Structure... 

Hence, the rate would be reduced at higher pressure px. The reaction of CO and 02 on platinum follows such a kinetics. 

H. A.-Kozlowska, J. Klinger, and B. E. Conway, /. Electroanal. Chem. 75, 45 (1911). Fukuda and A. Aramata, The kinetic study of adsorption processes of the phosphate species on platinum)111) in aqueous acidic solutions, J. Electroanal. Chem., in press (1997). 

Guisnet, M. and Eouche, V. (1991) Isomerization of n-hexane on platinum dealuminated mordenite catalysts II. Kinetic study. Appl. Catal, 71, 295-306. 

In addition to the presence of these elements in ores, they are also available from recycled feeds, such as catalyst wastes, and as an intermediate bulk palladium platinum product from some refineries. The processes that have been devised to separate these elements rely on two general routes selective extraction with different reagents or coextraction of the elements followed by selective stripping. To understand these alternatives, it is necessary to consider the basic solution chemistry of these elements. The two common oxidation states and stereochemistries are square planar palladium(II) and octahedral platinum(IV). Of these, palladium(II) has the faster substitution kinetics, with platinum(IV) virtually inert. However even for palladium, substitution is much slower than for the base metals so long as contact times are required to achieve extraction equilibrium. 

On Pt-Sn, assuming that ethanol adsorbs only on platinum sites, the first step can be the same as for platinum alone. However, as was shown by SNIFTIRS experiments [37], the dissociative adsorption of ethanol on a PtSn catalyst to form adsorbed CO species takes place at lower potentials than on a Pt catalyst, between 0.1 and 0.3 V vs RHE, whereas on a Pt catalyst the dissociative adsorption of ethanol takes place at potentials between 0.3 and 0.4 V vs RHE. Hence it can be stated that the same reactions occur at lower potentials and with relatively rapid kinetics. Once intermediate species such as Pt-(COCH3)adsand Pt-(CO)ads are formed, they can be oxidized at potentials close to 0.3 V vs RHE, as confirmed by CO stripping experiments, because OH species are formed on tin at lower potentials [39, 40] ... 

The kinetics of the electrochemical oxidation of ammonia on platinum to dinitrogen in basic electrolytes has been extensively studied. In the widely supported mechanism originally suggested by Gerischer and Mauerer[ll], the active intermediate in the selective oxidation to N2 is a partly dehydrogenated ammonia adsorbate, NH2 ads or NHaatomic nitrogen adsorbate N ag, which is apparently formed at more positive potentials, is inactive toward N2 production at room temperature. Generally, only platinum and iridium electrodes exhibit steady-state N2 production at potentials at which no sur-... 

Detailed investigations on the kinetics and mechanisms of reactions of square planar palladium (II) complexes are largely lacking. However, enough data exist to show that the reactions of palladium (II) complexes are much faster than those of platinum (II), and that the two systems react by the same type of mechanism. Some of the data available are given in Table VIII along with the same information on platinum (II) and nickel (II) for comparison (3). The results show an approximate relative order of reactivity for analogous complexes of the triad as follows ... 

Ertl, G. (1989). The oscillatory catalytic oxidation of carbon monoxide on platinum surfaces. In Spatial inhomogeneities and transient behaviour in chemical kinetics, (ed. P. Gray, G. Nicolis, F. Baras, P. Borckmans, and S. K. Scott), ch. 37, pp. 563—76. Manchester University Press. 

---