Methanol diffusion studies

Gas-phase methylation of catechol by methanol was studied on y -AI2O3 modified by the basic elements K, Li, Mg and Ca. Addition of 7.5 at.% Mg to y-AljOa was optimal and increased the 3-methyl catechol selectivity from 0.26 to 0.65. X-ray diffraction experiments showed the diffusion of Li and Mg cations into the y -AI2O3 bulk. This induces a change in the surface species (XPS data) and the surface acid-base properties (TPD experiments). Ca and K addition to y-alumina was ineffective due to formation of basic oxide layers on the sur ce. 

Wang et al240 reported the electrooxidation of MeOH in H2S04 solution using Pd well-dispersed on Ti nanotubes. A similar reaction was studied by Schmuki et al.232 (see above), but using Pt/Ru supported on titania nanotube which appear a preferable catalyst. Only indirect tests (cyclic voltammetry) have been reported and therefore it is difficult to understand the real applicability to direct methanol fuel cell, because several other aspects (three phase boundary to methanol diffusivity, etc.) determines the performance. 

Every, H. A., Hickner, M. A., McGrath, J. E. and Zawodzinski, T. A. 2005. An NMR study of methanol diffusion in polymer electrolyte fuel cell membranes. Journal of Membrane Science 250 183-188. 

The most widely studied conducting polymer support is polyaniline (PANl), which has been shown to decrease the poisoning of Pt by COads [88]. Gharibi et al. have recently explored the factors responsible for the enhanced formic acid oxidation activity of Pt supported on a carbon/PANI composite [89]. They concluded that improvements in both electron and proton conductivities, as well as the increased methanol diffusion coefficient and decreased catalyst poisoning, could be involved. A carbon nanotubes/PANI composite [90], poly(o-methoxyaniline) [91], and polyindole [92] have recently been reported as effective supports for formic acid oxidation at Pt nanoparticles, while polycarbazole [93] has also been used to support PtRu nanoparticles. 

Babu et al. carried out Pt and C NMR and electrochemical experiments on commercial Pt—Ru alloy nanoparticles and compared the results with those on Pt-black samples having similar particle sizes, and concluded that alloying with Ru reduces the total density of states at the Pt sites, in accord with conclusions drawn from synchrotron X-ray absorption studies ofPt-Ru electrocatalysts [199]. The COj,d diffusion studied by C electrochemical NMR spectroscopy in the temperature range 253—293 K revealed that CO surface diffusion is too fast to be considered as the rate-Hmiting factor in methanol oxidation. The NMR experiments also demonstrated that the addition of Ru to Pt increases the surface diffusion rates of CO, and a... 

In the methanol permeation study using a diffusion cell set-up, the positioning of the working elechode is very important. Attaching the working electrode on the membrane enhances methanol oxidation current detection. Even a small distance away from the membrane surface can affect the results because the methanol oxidation current may not be detected. The best way is to attach the working electrode on the membrane or to prepare it on the membrane by a suitable method, such as elecholess deposition. 

Another study on the preparation of supported oxides illustrates how SIMS can be used to follow the decomposition of catalyst precursors during calcination. We discuss the formation of zirconium dioxide from zirconium ethoxide on a silica support [15], Zr02 is catalytically active for a number of reactions such as isosynthesis, methanol synthesis, and catalytic cracking, but is also of considerable interest as a barrier against diffusion of catalytically active metals such as rhodium or cobalt into alumina supports at elevated temperatures. 

Photolysis at 254 nm of phenylbutazone (220) in aqueous solution raised to pH 8 to 9 with sodium hydroxide gave a mixture of ring-opened products. Reisch etal. identified samples of aniline, the malonamides (221) and (222) and the 2-oxohexanamide (225). When the solution was basified with diethylamine, the amino diamide (223) was produced in addition to (222) and (225). In methanol solution the malonamides (221) and (224) were obtained [132]. In an older study by Pawelczyk and Wachowiak, a 20% solution (pH 10.5) of phenylbutazone sodium was kept in a clear glass bottle in diffused daylight for 2 years. 

In another study (40) we found that protonation of pyridine is diffusion-controlled with a one-to-one solute-methanol complex as the reactive species. Thus, while methanol plays essentially no role in the proton transfer to dipicrylamine in the first study, it is indeed intimately involved in the proton transfer to pyridine. 

Coughlin and Canevari (1%9) have published experimental data on two systems at a variety of operating conditions the extraction of xylene from polypropylene and the extraction of methanol from polypropylene. These studies were conducted in a single screw extruder at low pressures and w was assumed to be small in comparison with w. Coughlin and Canevari developed a model which they used in conjunction with their experimental data to obtain a value for the diffusion coefficient. The values that they computed were of the order of 10 mVsec, which obviously means that the model is incorrect. Coughlin and Canevari also computed values for the mass transfer coefficient and found it to be independent of screw speed. This observation is particularly noteworthy since they saw no evidence of bubble formation. 

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