Adsorption-desorption of hydrogen

Concerning to the TPR profiles (Figs. 2 and 3), in the case of catalyst B, a clear reduction peak of cerium oxide is observed at 495 C, which is not detected for catalyst A. Catalyst A presents the lowest Pd reduction temperature, followed by catalysts U and B. The presence of negative peaks at low temperatures (75 C) in the case of catalysts A and U can be tentatively explained by adsorption-desorption of hydrogen on the catalyst surface. Comparing the low temperature zone of the TPR profiles, it is observed that catalysts U and A show similar behaviour (reduction temperatures and hydrogen release), whereas the... 

One of the main disadvantages of the Damjanovic s scheme is that it does not consider possible weak adsorptions and the reversible adsorption/desorption of hydrogen peroxide at the interface. The mechanism proposed by Wroblowa et al. [104] considers the adsorption/desorption equilibrium either for the oxygen reactant or the hydrogen peroxide intermediate. They also proposed the chemical decomposition of the intermediate (1(4), besides the electrochemical reduction to water through k3 (Scheme 2.5). 

In this scheme, Bagotskii et al. [ 106] developed a parallel reaction pathway taking into consideration fast adsorption/desorption of hydrogen peroxide and negligible oxidation of the intermediate to oxygen (Scheme 2.6). 

The effective electroactive surface may be determined directly by the voltammogram in evaluating the quantity of electricity involved in the adsorption-desorption of hydrogen (region I). The quantity of electricity is obtained by the integration of the current-potential curves, because the potential varies linearly with time. The active surface area (S = 0.56 cm2) is then calculated from the charge under the hydrogen underpotential-deposited (UPD) peaks, which needs 210 pC cm 2, as follows ... 

The dissociative adsorption-desorption of hydrogen follows this rate expression ... 

The latest developments in the issue are indicating that the view based on the H adsorption model is subject of some revision. In References 23 and 24 the voltammetric contribution of some specifically adsorbed anions (acetate, oxalate, chloride and bromide) was studied in the case of Pt(lll) electrodes by means of experiments involving the displacement of the adsorbed species by CO in acidic medium. The conclusion of this study was that the usual states correspond to the reversible adsorption/desorption of hydrogen, whereas the so-called unusual states would correspond to the adsorption/ desorption of anions. 

Adsorption pseudocapacitance can come from two-dimensional surface reactions that involve faradaic desorption and adsorption of an electroactive species from the electrolyte at a metal surface [69], One good example is the adsorption/desorption of hydrogen (H) at Pt in the acid solution, following the reaction [41,69]... 

Zhao, X., Bo. Xiao, A.J. Fletcher, K.M. Thomas, D. Bradshaw, M.J. Rosseinsky, Hysteretic adsorption and desorption of hydrogen by nanoporous metal-organic frameworks. Science 306,1012,2004. 

Thomas KM. Adsorption and desorption of hydrogen on metal-organic framework materials for storage applications comparison with other nanoporous materials, Dalton Trans 2009, 2009,1487-1505. 

Sanyal A, Norsten TB, Uzun O, Rotello VM. Adsorption/desorption of mono- and diblock copol3Tners on surfaces using specific hydrogen bonding interactions. Langmuir 2004 20 5958-5964. 

Figure 10. Adsorption/desorption of fructose-catalyst species and its hydrogenation.

Fig. 11. Changes in specific magnetization of a supported nickel catalyst during adsorption and desorption of hydrogen at room temperature. [Selwood, P. W., J. Am. Chem. Soc. 78. 3893 (1956).]...

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