Adsorption methanol

For potentials higher than 0.5 V vs. RHE, the formation of adsorbed oxygen species at Ru as well as at Pt will block the catalytic surface, leading to a decrease in the methanol adsorption kinetics. Therefore, in a potential range higher than 0.5 V vs. RHE, the kinetics of methanol oxidation is optimized at a Ru-poor catalyst, because methanol adsorption is not blocked and because the presence of Ru provides the extra oxygen atom needed to complete the oxidation of adsorbed CO to CO2. 

Figure 11.8 (a) SNIFTIR spectra of the species coming from methanol adsorption and oxidation at a Pt/C electrode 0.1 M HCIO4 + 0.1 M CH3OH 25 °C. (h) SNIFTIR spectra of the species coming from ethanol adsorption and oxidation on a Pt/C electrode 0.1 M HCIO4 + 0.1 M C2H5OH 25 °C. 

Figure 11.9 Intensities of the COl ( ) and CO2 ( ) bands as functions of potential, (a, b) From the spectra of the species coming from methanol adsorption and oxidation (0.1 M HCIO4 + O.IM CH3OH, 25 °C) (a) Pt/C electrode (b) Pto.g + RU0.2/C electrode, (c, d) From the spectra of the species coming from ethanol adsorption and oxidation (0.1 M HCIO4 + 0.1 M C2H5OH, 25 °C) (c) Pt/C electrode (d) Pto.pSno.i/C electrode. The dashed curves in (c) and (d) show I E).

Coutanceau C, Hahn F, Waszczuk P, Wieckowski A, Lamy C, Leger J-M. 2002. Radioactive labeling study and FTIR measurements of methanol adsorption and oxidation on fuel cell catalysts. Fuel Cells 2 153-158. 

Kazarinov VE, Tysyachnaya GY, Andreev VN. 1975. On the reasons for the discrepancies in the data on methanol adsorption on platinum. J Electroanal Chem 65 391-400. 

Sobkowski J, Wieckowski A. 1972. A new approach to the radiometric study of methanol adsorption on platinum. J Electroanal Chem 34 185-189. 

According to these results methanol adsorbate seems to consist of a mixture of (C, O) and (C, O, H) particles, the actual ratio depending on the concentration and total degree of coverage. This is in good agreement with coulometric determinations of the charge ratio for methanol adsorption, Qad, (see Eqs. 2.1 to 2.3) and adsorbate oxidation, Qox (see Eqs. 2.4 to 2.6) [14,47], These results will be discussed in Section 2.1.4. 

Charge measurements, as mentioned above, were also performed using the porous Pt electrodes required by the on-line MS technique. At low methanol concentrations (10 2 M), the charge ratio QaJQm, near 1 indicates that (C,0, H) must be the predominant adsorbate composition [14,47], This result is in good agreement with that of Heitbaum and co-workers [15] who used Eq. 1.2 to determine the number of electrons, n, per C02 produced from methanol adsorbate. They found for n a value of 3, which would be in agreement with reactions 2.1 or 2.2 for methanol adsorption. 

Fig. 4.5. Mass spectroscopic detection of carbon dioxide during methanol adsorbate oxidation and Sn(IV) injection. Porous Pt electrode, real area 12.3 cm2. Procedure after methanol adsorption at 0.4 V from 10 2 M 13CH3OH/0.5 M H2S04, the electrolyte was exchanged with 0.5 M H2S04, then potential step to 0J was applied and Sn(lV) was added. Dashed line no tin added.

Figure 3.31 Current/time curve for methanol adsorption. The methanol concentration was 0.5 M. Adsorption occurred after holding the potential at -I- 1.55 V for 20 ms, and then stepping the potential to 0.37 V. The step from 1.55 V to 0.37 V takes place 40 ms in from the right-hand edge. The x-nxis scale is 200 ms cm the y-axis scale is 3.33pAcm. After Bciglcr and Koch...

On the other hand, Bagotzky and Vassilyev (1967) also measured the charge passed during methanol adsorption at a potential in the double-layer region and the adsorbate oxidation. The results they obtained are given in Table 3.2 and strongly suggested that the adsorbate was COH (see equations (3.45) and (3.47)). 

Assume that the coverages of H, CO, and methanol are given by the Langmuir adsorption isotherm in which CO, H2, and methanol adsorption compete for the same sites, and the intermediates HjCO S are present in negligible quantities. 

The formation of silicon-flvxyride bonds on the surface of silica after treatment with hydrogen fluoride was never proven directly. However, there is a pronounced change in the adsorption and wetting properties. The silica becomes hydrophobic as was mentioned in a patent to Kimberlin (279a). Neimark and collaborators (279b) found a type V isotherm in the methanol adsorption on silica gel which had been treated with a solution of SiF in absolute alcohol. Wilska (280) obtained a water-repellent silica when solutions of HaSiPg were precipitated with ammonia. The Si—F bond is hydrolyzed only slowly. A considerable fluorine content of 7-10% F was reported in an older patent (281) for a silica that had been prepared by hydrolysis of SiF. ... 

Work Function Changes Following Methanol Adsorption on Clean Metals Monolayer Coverages)... 

Analogous methanol adsorption/desorption experiments conducted with the supported manganese pyrophosphate catalyst gave the following results 1) A single desorption peak centered at lOO C is observed (Figure 8). 2) Mass spectral analysis indicates the... 

TPRS experiments for this reaction step. The two hydrogens released in the methanol adsorption and the surface methoxy decomposition steps are eventually converted to water. Spectroscopic details about the formation of water are presently not available, but the formation of water most likely proceeds via the condensation of two surface hydroxyl groups. The reduced surface vanadia site is readily reoxidized back to vanadium (+5) by gas phase oxygen as shown by in situ Raman measurements.42... 

Among the early investigations of methanol adsorption and conversion on acidic zeolites, most of the H and C MAS NMR experiments were performed under batch reaction conditions with glass inserts in which the catalyst samples were fused. Zeolites HZSM-5 76a,204,206,264-272), HY 71,72), H-EMT 273), HZSM-12 274), HZSM-23 275), H-erionite 275), H-mordenite 271,272), and H-offretite 275,276), silicoaluminophosphates H-SAPO-5 271,274), H-SAPO-11 274), and H-SAPO-34 76,277,278), as well as montemorillonite 279) and saponite 279) were investigated as catalysts. 

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