Adsorbates acetone

Infrared Studies. A gold residue from acetone was mixed with KBr and compressed to a pellet. Numerous IR scans were accumulated, and the spectrum indicated the presence of adsorbed acetone (mainly,... 

Removal of solvent allows the colloidal particles to grow to a film. However, strongly adsorbed acetone, and perhaps small amounts of acetone fragments or telomers as well, remain in the film affecting its electrical properties. 

Fig. 6 shows the IR-TPR of CsHb partial oxidation over Au/Ti0x-Si02. The interaction of Ar/C3He/H2/02 with the catalyst surface at 50 °C led to decrease in the band intensity of OH vibration at 3741 cm and the formation of a 1662 cm (C=0 of adsorbed acetone) band. Mass spec, results in Fig. 7 shows the reaction produced propionaldehyde, acetone, and CO2. The rate of product formation peaked at 140 °C. 

The H/D exchange between the methyl groups of adsorbed acetone molecules and the Bronsted acid sites of zeolite HZSM-5 was also observed upon adsorption of C-2-acetone on a deuterated catalyst (D,HZSM-5, nsi/ Ai = 21.5) at room temperature (Figs 20c and d). The " C MAS NMR spectrum of C-2-acetone adsorbed on zeolite D,HZSM-5 (Fig. 20e) consists of the carbonyl signal at 223 ppm with a featured sideband pattern and a methyl signal at 29 ppm. No significant... 

At moderate and low pressures, the Arrhenius plot of 32/ 26 calculated accord-ding to eqns. (33) or (35) shows a curvature below about 125°C . These complications observed at lower temperatures are, according to Ausloos and Steacie , due to a wall reaction in which a methyl radical reacts with an adsorbed acetone molecule producing methane. Other possible explanations have... 

It implies from the above discussion that "neutral" acetone complex previals at room temperature on the surface of H-zeolites if the coverage of OH groups is less than 100%. The domination of the acetone "neutral" species on the H-zeolite surfaces were also confirmed by the results of low temperature (125 K) measurements of MAS NMR of adsorbed acetone [8]. 

Since both albedo and gas adsorption depend on SSA, the climate response of the concentration of species adsorbed within the snowpack will be similar to that of albedo increase in regions where warming is accompanied by a change from HGM to QIM, such as the southern taiga and the warmer Alpine areas in the fall and decrease in the other regions. These effects will be modulated by the temperature increase, that will decrease the concentration of adsorbed species. For example, a temperature rise from -15 to -10 °C will desorb 40% of adsorbed acetone molecules, that have an adsorption enthalpy of 57 kJ/mol,, at constant SSA. The combined effect of warming and SSA change will then probably lead to a decrease in the concentration of adsorbed species in most areas. 

The first natural microporous aluminosilicate, i.e., natural zeolite, was discovered more than 200 years ago, and after long-term practical applications, the intrinsic properties of natural zeolites such as reversible water-adsorption capacity were fully recognized.13 41 By the end of the 19th century, during exploitation of ion-exchange capacity of some soils, it was found that natural zeolites exhibited similar properties some cations in natural zeolites could be ion-exchanged by other metal cations. Meanwhile, natural chabazite could adsorb water, methanol, ethanol, and formic acid vapor, but could hardly adsorb acetone, diethyl ether, or benzene. Soon afterwards, scientists began to realize the importance of such features, and use these materials as adsorbents and desiccants. Later, natural zeolites were also used widely in the field of separation and purification of air. 

At an early date it was observed that photodissooiation of adsorbed acetone 129) and biacetyl molecules 15) generated methyl radicals, which reacted with the surface of sublimed Bi or Sb, serving as adsorbents. From the spectral dependence of the metal erosion at the illuminated spot it could be ascertained that the maximum of the active spectral regions was markedly shifted to the red compared to that for the gas phase photodissociation. This implied a decrease of the required photon energy by an amount equivalent to about 1 ev, which was explained as a compensation effect, produced by the much stronger adsorption of the radicals, primarily formed (Section II, E). 

The decomposition of 2-propanol showed both similarities and differences among the surfaces. The most notable similarity is the fact that propene and acetone were produced at about the same ratio on all surfaces. Dehydrogenation to form acetone was the dominant reaction, as has been observed on ZnO powders ( ). The desorption temperatures of the reaction products, acetone, propene, and hydrogen were always higher than the temperature of desorption of the adsorbed acetone, propene, and hydrogen (hydrogen does not adsorb on ZnO under our conditions). Thus the evolution of acetone and propene are reaction limited in 2-propanol decomposition. 

Fig. 3. Phosphorescence spectra of acetone adsorbed on Vycor glass at 77 K in the absence (a) and presence of NO molecules (b-e) (amount of adsorbed acetone, 2.8 umol, amounts of added NO molecules (in Torn), b ...

The peaks resulting from acac-ligands are typically quite strong and they overlap with peaks from other species. Thus, other than acac-ligand species are difficult to identify at this stage. However, adsorbed acetone (bands at 1680-1670 cm and 1250-1240 cm [6, 7]) was not detected in any of the samples. The peak at 1460 cm can be due to acetate structures as the same peak was observed in the spectrum of HAc/alumina (not shown). The peak is strongest in the spectra of Hacac-treated samples. 

Methanol is oxidized to formate ions, acetone and acetaldehyde to acetate species. An enolic form of adsorbed acetone is seen, which accounts for rapid isotopic exchange of -OH. On O2 adsorption two bands at 1155 and 1020 cm are formed,which are however not assigned. Mixtures of CO plus O2 lead to the obvious formation of carbonates and bicarbonates. CO interaction with presorbed NH3 forms carbamate species. Oxidizing properties of the surface are shown by the reaction of trichloroacetone to trichloroacetate species. Nitriles are, however, hydrolysed to acetimidate species R-CNH . Similar reactions with surface -OH are shown by ethyl and phenyl isocyanate, which form urethanes by reaction with isolated -OH groups, and 1,3-diethylurea with -OH pairs. Reaction with surface -OH is also shown by trimethylchlorosilane, which, however, harshly attacks the surface and forms silicone species. ... 

Langmuir-Hinshelwood kinetics involving competetive adsorption of acetone molecules and hydrogen atoms were posmlated, and it was assumed that adsorbed acetone dominates. The SMSI effect is explained by the fact that the oxygen atom of the carbonyl group is more effectively activated than in conventional platinum catalysis. It is assmned that the oxygen atom is adsorbed on particularly active Ti " cen-... 

Certain solvents should be avoided with alumina or silica gel, especially with the acidic, basic, and highly active forms. For instance, with any of these adsorbents, acetone dimerizes via an aldol condensation to give diacetone alcohol. Mixtures of esters transesterify (exchange their alcoholic portions) when ethyl acetate or an alcohol is the eluent. Finally, the most active solvents (pyridine, methanol, water, and acetic acid) dissolve and elute some of the adsorbent itself. Generally, try to avoid going to solvents more polar than diethyl ether or methylene chloride in the eluent series (Table 19.2). 

The kinetics of acetone hydrogenation on Pt catalysts have been studied by Sen and Vannice (See Problem 7.9) [35]. To determine which bonding mode is more probable, the heat of adsorption for an on-top adsorbed acetone species was compared to that for a di-n-bonded i [x.2 species which had a C atom and the O atom interacting with a close-packed Pt(lll) surface. What are these two values Which species is favored ... 

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