Hydrogen adsorption peaks

On K modified Ni(100) and Ni(lll)62,63 and Pt(lll)64 the dissociative adsorption of hydrogen is almost completely inhibited for potassium coverages above 0.1. This would imply that H behaves as an electron donor. On the other hand the peaks of the hydrogen TPD spectra shift to higher temperatures with increasing alkali coverage, as shown in Fig. 2.22a for K/Ni(lll), which would imply an electron acceptor behaviour for the chemisorbed H. Furthermore, as deduced from analysis of the TPD spectra, both the pre-exponential factor and the activation energy for desorption... 

Studies on the adsorption of hydrogen from the gas phase had provided strong evidence for the existenee of two forms of adsorbed hydrogen and the AC impedance studies were supported by the results of the new LSV and CV techniques. The early measurements using the voltammetry methods were hampered by the use of impure electrolytes which resulted in ill-defined hydrogen adsorption and desorption peaks but the realisation of the need for a clean electrochemical system soon resulted in the routine observation of the now familiar twin Hads peaks. 

Reduction in charge under hydrogen adsorption peaks. 

The current-potential behavior shown in Figure 5.22 is claimed to be characteristic of a clean platinum surface in a clean test solution,99 and can be used as a criterion of solution and electrode cleanliness in aqueous 0.5 M H2S04. The presence of organic material generally will cause a decrease in the hydrogen adsorption peaks and the appearance of new peaks. 

The addition of Re to the catalyst independent of the method of preparation resulted in increase of Hads (500 C) (Fig.4) and decrease ofHa (35°C) (Fig.5). The differential heats ofH2 adsorption were decreased under these conditions. The increase of activated extra additive adsorption of hydrogen occured mainly due to those forms of chemisorbed H2 that are desorbed at above 300°C. This tendency is the most significant for APRC(III). The peak of desorption of this form of chemisorbed H2 was shifted in the more high-temperature region (Fig.4c). Higher thermostability of Pt-Re-catalysts was displayed in the forms of activated Hj adsorption. For example, the decrease of H, amount (500°C) with the increase of temperature treatment from 500 to 700 C for APC(I) was 6.4 times, and for APRC(I) with 0.36 wt% Re content, the increase was 1.4 times. 

With this method, Andersson and Rosen [169] recently investigated the adsorption of hydrogen or deuterium and oxygen on neutral platinum clusters and discovered the catal3dic water formation on the free clusters. Figure 1.30 displays mass spectra obtained with different partial pressures of hydrogen and oxygen in the separate collision gas cells. Panel a in Fig. 1.30 shows a mass spectrum of pure Pt clusters with no reactive gas in the collision cells. The mass spectrum in panel b was sampled after the cluster ions passed reaction cell 1 filled with 0.14 Pa of O2. The additional peaks in the mass spectrum... 

The samples can be annealed at approximately 950°C in a helium atmosphere for 3 h, and afterward the temperature is varied to lower values linearly with time until room temperature after approximately 6 h [81]. Because of little contamination, no hydrogen adsorption peaks can be seen in the cyclic voltammetric runs. 

Plots of the rates of the uptake of hydrogen versus temperature can be seen in Figure 1, in which the first peak for the adsorption of hydrogen at about 320 K is not shown. For Li-FeZSM-5, five maxima are found approximately at 643 K, 723 K, 943 K, 984 K and 1002 K. While the former two maxima are also found with Na-FeZSM-5 at about 643 K and 723 K, the latter maxima are observed at 993 K, 1087 K and 1105 K. K-FeZSM-5 exhibits four peaks at 643 K, 723 K, 1109 K and above 1200 K. FezOa/Fe-AlZSM-S has only two clear peaks at 643 K and 723 K. Peaks at about 543 and 723 K are very small for all the ferrisilicates studied, while the area of the two peaks at about 643 and 723 K clearly Increases followed by an addition of the peak at 1105 K and peak shift towards high temperature after hydrothermal treatment. If the TPR for Na-FeZSM-5 is performed on the sample reoxidized at 823 K (curve e), only strong peaks at lower temperature are observed and the peaks at higher temperature almost disappear. 

V vs RHE(Reversible Hydrogen Electrode)) in Pt catalysts is well defined, while for PtRu catalysts it is less defined, because the adsorption/desorption hydrogen peaks are not developed on Ru. The double layer region of the PtRu/C catalysts is larger than for Pt/C, both because of the presence of more oxygenated species and also of a larger surface area due to a smaller particle size. Furthermore, the performance of the PtRu/C catalysts, for methanol oxidation, shows a superior activity as compared to the Pt catalysts in the... 

Analysis of the infrared spectra of octene hydrogenation products showed that double bond and skeletal isomerization of unreacted olefin takes place. Comparing the spectrum of pure octene-1 (Fig. 2) with the spectrum of the product from Experiment 1 (Fig. 3), it can be seen that the adsorption peak at 1800 cm. i decreases and the doublet at 900 and 980 cm. i is replaced by a peak at 980 cm. which formerly appeared as a shoulder on the 980 band. 

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