Hydrogen on platinum

E. Lamy-Pitara, S.E. Mouahid, and J. Barbier, Effect of anions on catalytic and electrocatalytic hydrogenations and on the electrocatalytic oxidation and evolution of hydrogen on platinum, Electrochim. Acta 45, 4299-4308 (2000). 

Adsorption of Reaction Components In many cases, adsorption of a reactant is one of the hrst steps in the electrochemical reaction, and precedes charge transfer and/or other steps of the reaction. In many cases, intermediate reaction products are also adsorbed on the electrode s snrface. Equally, the adsorption of reaction products is possible. The example of the adsorption of molecular hydrogen on platinum had been given earlier. Hydrogen adsorption is possible on the platinum electrode in aqueons solntions even when there is no molecular hydrogen in the initial system at potentials more negative than 0.3 V (RHE), the electrochemical reaction... 

Bewick, A. and Russell, J. W. (1982) Structural investigation by infra-red spectroscopy of adsorbed hydrogen on platinum. J. Electroanal. Chem., 132, 329-344. 

Peremans A, Tadjeddine A. 1994. Vibrational spectroscopy of electrochemically deposited hydrogen on platinum. Phys Rev Lett 73 3010-3013. 

Some characteristics of ignition of hydrogen on platinum catalyst (title only translated). 

Analogous studies of the chemisorption of 14C-labeled benzene on copper powder and on platinum powder showed no chemisorption on the former, and the establishment of a low surface coverage over a range of temperature on the latter (Fig. 1). Again the surface coverage of hydrogen on platinum appeared to be about three times that achieved by benzene. 

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... 

In the presence of Pb(II) ions in sulfuric acid, potential oscillations have been observed for galvanostatic oxidation of hydrogen on platinum electrode [129]. This behavior has been attributed to ad-sorption/oxidation/desorption processes of lead on the platinum surface. Lead at high values of coverage is oxidized to insoluble PbS04, which blocks the Pt surface. 

Our article has concentrated on the relationships between vibrational spectra and the structures of hydrocarbon species adsorbed on metals. Some aspects of reactivities have also been covered, such as the thermal evolution of species on single-crystal surfaces under the UHV conditions necessary for VEELS, the most widely used technique. Wider aspects of reactivity include the important subject of catalytic activity. In catalytic studies, vibrational spectroscopy can also play an important role, but in smaller proportion than in the study of chemisorption. For this reason, it would not be appropriate for us to cover a large fraction of such work in this article. Furthermore, an excellent outline of this broader subject has recently been presented by Zaera (362). Instead, we present a summary account of the kinetic aspects of perhaps the most studied system, namely, the interreactions of ethene and related C2 species, and their hydrogenations, on platinum surfaces. We consider such reactions occurring on both single-crystal faces and metal oxide-supported finely divided catalysts. 

In this example the exclusion of the intermediates could be effected, essentially in one way only, since the column of stoichiometric numbers ( (2) is obtained from the column (2) by multiplication by an arbitrary factor this holds for any other suitable column of stoichiometric numbers. However, this is not always the case—even when the reaction is described by one overall equation. Thus, a possible mechanism of oxidation of hydrogen on platinum is (25)... 

The concepts which we develop above were used in the dissertation by Buben, written under the guidance of Frank-Kamenetskii at the Institute of Chemical Physics in 1940. As Buben showed, together with the difference between D and n, also significant is the role of thermal diffusion which acts, as a rule, in the same direction, i.e., increasing Tr compared to (9) in the case when the light component is deficient, DZ > k so that in accordance with (9) Tr > Tc. In contrast, when Tr < Tc anyway, thermodiffusion decreases the flow of the heavy component to the heated surface and causes further decrease of Tr. Direct experiments by Buben, who studied the oxidation of hydrogen on platinum wires, showed that for a content of 2-5% H2 in air,... 

It should be said that at present the available literature concerning the kinetic models which account for the topochemical character of catalyst surface processes is limited, but reference can be made to refs. 119 and 120. In ref. 119, a kinetic model for the oxidation of hydrogen on platinum is... 

Organodiazenes show a somewhat richer chemistry. Many years ago it was demonstrated that coordinated phenyldiazene can be catalyti-cally hydrogenated on platinum(O) according to Eq. (59) (268, 216). 

Maxted and Hassid (858), and later Kwan (859), found the heat of sorption of hydrogen on platinum to be independent of the amount that was taken up. It is quite probable that, at the temperatures they used in their investigations, hydrogen penetrates the surface layers of the metal. 

The Nature of the Pt-H Bonding for Strongly and Weakly Bonded Hydrogen on Platinum... 

The nature of the Pt-H bonding for strongly and weakly bonded hydrogen on Platinum... 

M.K. Oudenhuijzen, J.H. Bitter and D C. Koningsberger, The Nature of the Pt-H bonding for strongly and weakly bonded hydrogen on Platinum. A XAFS spectroscopy study of the Pt-H antibonding shaperesonance and Pt-H EXAFS , J. Phys. Chem. B, 105 (2001), 4616-4622. 

Figure 26 Sq for D2 ( ) on Pt(5 3 3) as a function of E at T = 300 K and i = 0° [63]. The dashed line represents the contribution of direct sticking on the (111) terraces of Pt(5 3 3). Subtraction of this function from the data ( ) provides an estimate of the (1 0 0) steps contribution ( ). A polynomial fit (dotted line) is included to guide the eye. The solid curve is a hard cube calculation of the sticking probability of phy si sorbed hydrogen on platinum.

However, for some electrocatalytic reactions, such as the electrooxidation of alcohols, aldehydes or acides, and also the electro reduction of oxygen, lead adatoms can exhibit a promoting effect (3-7). Moreover, lead can change the selectivity in the case of electrocatalytic reductions of nitrocompounds (8), whereas it inhibits the adsorption of hydrogen on platinum (9,10),... 

Chemisorption of hydrogen on platinum metals is a reversible process as demonstrated by the symmetry of the cyclic voltammetric curves (- voltammetry). The voltammetric behavior of these systems depends on the... 

Ru(bpy)3 transfer between water and 1,2-dichloroethane (Ding et al., 1996) Absorption/desorption of hydrogen on platinum electrodes (Will and Knorr, 1960). 

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