Chemisorption of ethanol

Shin J, Tomquist WJ, Korzeniewski C, Hoaglund CS. 1996. Elementary steps in the oxidation and dissociative chemisorption of ethanol on smooth and stepped surface planes of platinum electrodes. Surf Sci 364 122. 

Figure 31. Infrared reflectance spectra (EMtRS) of the adsorbates resulting from the chemisorption of ethanol on a platinum polycrystalline electrode in acid medium (0.5 M HCIO4, room temperature), (a) 10 M C2H5OH (b) 10 M C2H5OH.

Korzunov, V. A., Chuvylkin, I. Y, Zhidomirov, G. M., and V. B. Kazanskiy. 1981. Semi-empirical quantum-mechanical calculations of intermediate complexes in catalytic reaction. The stages of chemisorption of ethanol at the aluminum y-oxide. Kinetika i Kataliz. 22 930-936. 

The addition of Ni as the second or third element is claimed to increase the activity of Ft electrocatalysts. The main advantage of the introduction of this metal is the reduction of the ethanol oxidation potential, coupled with the rise in current density. A literature search reveals that Sn and Ni can introduce electronic modifications into Ft [50,51], in other words, these metals decrease the energy of the chemisorption of ethanol and its oxidation intermediates, such as CO. The participation of the Sn site in a bifunctional mechanism is also claimed, in order to explain the enhanced activity of the Ft-Sn/C catalyst [50,52]. The effect that Ni introduction has on Sn-sites must also be considered. The addition of a third metal boosts the oxophilic character of the surface, thus raising the... 

The reduction of acetaldehyde to ethanol could be explained by its chemisorption near rhodium particles and the action of spill over hydrogen. On Rh/La 0, Bell has observed that at low residence times acetaldehyde is the primary product whereas at longer residence times the formation of ethanol becomes the dominant process. They concluded that this pattern is characteristic of the sequential reaction process ... 

It has been found ]145] that the self-assembly of thiol molecules on Au(lll) from ethanolic solution depends significantly on the electrode potential. Especially at cathodic potentials, chemisorption of thiol molecules and the development of a highly ordered structure are slowed down significantly. 

It has often been pointed out that the electrical conductivity of sintered samples of ZnO and of other n-conducting oxides is frequently caused by the conductivity of thin layers near the surface, and not by the conductivity of the bulk (25-28). According to our present knowledge, these thin layers near the surface of oxides are caused by electron transfer from the layers to the chemisorbate during the chemisorption, and the amount of chemisorption may be related to the electronic properties of the gas molecules and of the solids. The dependence of the electrical conductivity of some semiconductors on the pressure of CO, COj, and on the vapor pressure of ethanol, methanol, acetone, and water, as observed by Ljaschenko and Stepko (29), can be explained by the same mechanism. The dependence of conductivity of some mixed oxides at high temperatures can be explained in a similar way (30). 

We have shown how hydroxyl groups on the silica surface act as active sites in the modification reaction. The amount of hydroxyls is controlled by the thermal pretreatment of the substrate. APTS molecules are physisorbed to the surface by hydrogen bonding of the amine group to a surface hydroxyl (H). Chemisorption of APTS to the silica surface, in dry conditions, involves the formation of siloxane bonds with release of ethanol (I). Water causes the hydrolysis of the ethoxy groups of the APTS, with formation of silane silanols. These silanols are more reactive than the original alkoxy groups. Siloxane bonds with other silane molecules or with the silica surface are formed with release of water (J). 

Parfitt and his co-workers pointed out (Day, Parfitt and Peacock, 1971) that there is an important difference between ethanol and isopropanol in their interactions with rutile. Whereas ethanol can displace water and undergo dissociative chemisorption to form the surface ethoxide, isopropanol is more readily adsorbed in the molecular form. This is consistent with the hydrophobic nature of ethanol-treated Ti02 and the autophobic nature of the ethanol monolayer. The latter effect is manifested in the form of a Type I isotherm, which is remarkably similar to that given by ethanol on alumina (see Figure 10.15). 

The electrocatalytic oxidation of ethanol has been investigated for many years on different platinum-based electrodes, including Pt/X alloys (with X = Ru, Sn, Mo, etc ), and dispersed nanocatalysts. Pme platinum smooth electrodes are rapidly poisoned by some strongly adsorbed intermediates, such as carbon monoxide, resulting from the dissociative chemisorption of the molecule, as shown by the first experiments in infrared reflectance spectroscopy (EMIRS). Both kinds of adsorbed CO, either linearly-bonded or bridge-bonded to the platinum surface, are observed. Besides, oth-... 

Since the transport in chromia is by electron transfer, chromia does not exhibit the Hall effect, photoconductivity, or carrier injection. Inconsistent results have been obtained from direct measurements of the diffusion of chromic ions in chromia 191,192). The dielectric constant was measured by Fang and Brower 193). The energy distribution curve of the photoelectrons emitted by chromia shows a spread of many electron volts 194), as is typical of insulators. The adsorption of gases such as ethanol shifts the limit of the photoeffect to longer wavelengths 195). Photoconductivity was not detected in chromia 196). Chemisorption of oxygen on chromia was not influenced by a previous nuclear irradiation in vacuo 189). 

J. V. Sinisterra, J. M. Marinas, and A. Llobura [Can. J. Chem., 61, 230 (1983)] employed an extended form of the Hammett equation to correlate data for esterification of ethanol with substituted benzoic acids in the gas phase over a solid AIPO4 catalyst. The focus of their efforts was correlation of values of the adsorption equilibrium constants and apparent rate constants. Use the information tabulated below to prepare a Hammett plot of experimental absorption equilibrium constants versus the corresponding values of the a parameters for the substituted benzoic acids indicated. Employ the a values in Table 7.2 of the text. In principle the intercept of the best straight line through these data should correspond to the adsorption equilibrium constant for benzoic acid. By how much does this value differ from the experimental value below What value of the parameter p characterizes the chemisorption of substituted benzoic acids ... 

The still warm electrode (about 80 C) was immersed into a 0.5 mM ethanol dye solution of Ru(NCS)2(dcbpy)2. Carboxyl groups are the commonly used anchoring groups for chemisorption of dye molecules onto TCO electrode surfaces [291]. The film remained in the above solution for up to 7 days. The sensitized film was stored in ethanol until required for use [358-362]. 

The observed distribution can be readily explained upon assuming that the only part of polymer framework accessible to the metal precursor was the layer of swollen polymer beneath the pore surface. UCP 118 was meta-lated with a solution of [Pd(AcO)2] in THF/water (2/1) and palladium(II) was subsequently reduced with a solution of NaBH4 in ethanol. In the chemisorption experiment, saturation of the metal surface was achieved at a CO/Pd molar ratio as low as 0.02. For sake of comparison, a Pd/Si02 material (1.2% w/w) was exposed to CO under the same conditions and saturation was achieved at a CO/Pd molar ratio around 0.5. These observations clearly demonstrate that whereas palladium(II) is accessible to the reactant under solid-liquid conditions, when a swollen polymer layer forms beneath the pore surface, this is not true for palladium metal under gas-solid conditions, when swelling of the pore walls does not occur. In spite of this, it was reported that the treatment of dry resins containing immobilized metal precursors [92,85] with dihydrogen gas is an effective way to produce pol-5mer-supported metal nanoclusters. This could be the consequence of the small size of H2 molecules, which... 

Chemisorption was accomplished by immersion for 12 hours in a 1 mM solution of either mercaptoethanol or hexadecylthiol the solvent was absolute ethanol. 

To study the promotion mechanism of Pt wire/FSM-16 in the PROX reaction, the Pt nanowires were extracted by HF/EtOH treatment from FSM-16, and the wires were again deposited on the external surface of FSM-16 from the ethanol solution. We found that the resulting external Pt wire/FSM-16 catalyst gave low TOFs (>35) and lower CO selectivity (>30%) in the PROX reaction [32]. This implies that the encapsulation of Pt wires in the silica channels of FSM-16 is a key to promote the selective CO oxidation in the PROX reaction. Furthermore, from the structural characterization by XANES, XPS and IR in CO chemisorption... 

The comprehensive investigation of the interactions of simple alcohols (methanol, ethanol, propan-l-ol, and butan-l-ol) with Fe203 powders (514) by a combination of surface analytical techniques and conversion measurements under high vacuum and at atmospheric pressure is an example of the attempts to establish correlations between surface structure and catalytic activity. IR and XPS data showed that methanol is chemisorbed mainly disso-ciatively, giving formate species, whereas molecular chemisorption prevails for higher alcohols, which form hydrocarbons as the major products. 

It has been shown that only those alcohols that form detectable surface alco-holate species on alumina undergo bimolecular dehydration with ether and water as reaction products (340). Thus, ether formation is the dominant reaction direction of methanol and ethanol at low temperatures, and the tendency toward ether formation is reduced as the chain length increases and chain branching occurs (28, 340). The same trends are observed for the stability and surface concentrations of the surface alcoholate species (27, 28, 47, 340). Alcoholate formation is due to a dissociative chemisorption step of the alcohol that occurs on A1—O pair sites (47, 340, 354-358). One is, thus, led to the conclusion that incompletely coordinated Al3+ ions and O2- ions are both important sites in the ether formation from alcohols and that their participation should be detectable by specific poisoning. 

In order to test the adsorption behaviors of this kind of macroporous materials, three colored materials Rhodamine B, indophenol, and methyl violet were chosen. The changes of concentrations of the solutions of dyes in a period were detected by UV-VIS spectrometer. The adsorption isotherms are shown in Figure 6. From the adsorption isotherms we can see that the adsorption behaviors of macroporous materials are not good. The reason may be (I) that the surface areas of macroporous materials are low ca. lOOmVg) and the active sites are few (II) the solvent ethanol was adsorbed by the hybrid materials. The adsorption isotherms of three colored materials were different. Methyl violet was an alkaline indicator and the adsorption of methyl violet and hybrid materials may correspond to a chemisorption. Acid indicator Rhodamine B was not adsorbed by the adsorbent and the solvent ethanol was adsorbed instead. Therefore, after reaction the concentration of the solution increased and the adsorption capacity appeared negative. Compared with the former two, indophenol molecule is smaller and is easy to be absorbed. Therefore, its adsorption behavior is stronger relatively. 

The well characterized and stable surface phases observed on the Sn-Pt(l 11) have provided researchers in the chemisorption and catalysis field with a substrate of great interest for studying the properties of bimetallic interfaces. Simple probe gases such as CO have been studied after adsorption on this system [45] as well as a variety of organic molecules such as acetylene [46], cyclohexane and benzene [47, 48], butane and isobutane [49], methanol, ethanol and water [50]. Several surface reactions of the above gases were also studied. 

---