Platinum methanol formation rate

Anhydrous, monomeric formaldehyde is not available commercially. The pure, dry gas is relatively stable at 80—100°C but slowly polymerizes at lower temperatures. Traces of polar impurities such as acids, alkahes, and water greatly accelerate the polymerization. When Hquid formaldehyde is warmed to room temperature in a sealed ampul, it polymerizes rapidly with evolution of heat (63 kj /mol or 15.05 kcal/mol). Uncatalyzed decomposition is very slow below 300°C extrapolation of kinetic data (32) to 400°C indicates that the rate of decomposition is ca 0.44%/min at 101 kPa (1 atm). The main products ate CO and H2. Metals such as platinum (33), copper (34), and chromia and alumina (35) also catalyze the formation of methanol, methyl formate, formic acid, carbon dioxide, and methane. Trace levels of formaldehyde found in urban atmospheres are readily photo-oxidized to carbon dioxide the half-life ranges from 35—50 minutes (36). 

We have seen that the process of oxidation of methanol involves the formation of chemisorbed fragments, predominantly COads and (probably) =C-OH. At lower potentials (E < 0.5 V), chemisorption of methanol on a clean platinum surface is faster than subsequent oxidation of the chemisorbed fragments to C02, but all investigators have reported that a steady-state can be established, in which a small residual current flows. It is less clear what the rate-limiting step is for this residual current, and intensive studies were first carried out by Bagotzky and Vassiliev [5] to attempt to distinguish the mechanism. For 1 M methanol/0.05 M H2S04 on smooth... 

The increase in the island dispersion, as it increases the ruthenium coverage, removes platinum sites that were present on the bimetallic surface before the experiment reported above was executed. In other words, the number of ensembles of Pt sites available,65,66 e.g., for chemisorption on the Pt sites of the Pt( 111 )/Ru surface was reduced. A typical case where this development is important is the process of dissociative chemisorption of methanol, as it requires as many as three adjacent sites for methanol dissociation (dehydrogenation) to chemisorbed CO65-67 As methanol oxidation to CO2 predominantly occurs via the CO formation process,67,68 the overall rate of methanol oxidation may be affected by an increase in ruthenium coverage at the expense of the number of collective Pt sites required for methanol decomposition to CO.65,66... 

The use of an infrared microscope enables the investigation of the surface of rather small electrodes. The resulting miniaturization of the necessary electrochemical cell allows its operation as a fiow cell in thin layer arrangement [242]. Combined with a rapid-scan FTIR spectrometer, acquisition of infrared spectra during electrode potential scans at a rate of d /dr = 200 mV-s are possible. The time resolution is equivalent to one complete spectrum recorded every 2.6 mV. The formation of various reaction intermediates of methanol oxidation in alkaline solution at a platinum electrode could be assigned to specific electrode potential ranges. 

Presently, the oxidation of methanol on pure platinum has more academic interest than practical application once DMFC universally employs platinum based materials having two or more metals as an anodic catalyst In absence of methanoUc inteimediate readsorption, the maximum reactiOTi rate for CO oxidation is 100-fold smaller than maximum reaction rate for CO adsorption from methanol dehydrogenation steps [11]. Indeed, the mechanism of methanol oxidation on platinum is expected to be equal to that on its alloys despite different kinetics which would result in a selection of pathway. In terms of complex activation theory, alloyed Pt is intend to lower the Ea barrier for CO adsorption, thus driving methanol oxidation to completion. As previously established [3], there are several factors that affect the calculated activation energy for the MOR at a given potential, such as coverage of methanoUc intermediates and anion adsorption from the electrolyte as well as pH and oxide formation processes. 

Figure 5 presents DBMS results for the oxidation of methanol on smooth polycrystalline platinum. Figure 5a shows the cychc voltammogram (CV), which is similar to CVs obtained in traditional electrochemical cells. Figure 5b corresponds to CO2 formation, which is monitored at miz = 44, while Fig. 5c presents the formation of methyl formate, which is detected at mIz = 60. We find that at an electrolyte flow rate of 5 pL/s, the average current efficiency for CO2 formation in a single potential cycle is only ca. 28%, and for methyl formate is about 0.5%. This suggests that over 70% of the Faradaic current results in other intermediates (likely formaldehyde and formic acid). Unfortunately, formaldehyde and formic acid in... 

Fig. 5 Simultaneously recorded CV (a), MSCV of CO2 at miz = 44 (b), and MSCV of methyl formate at mIz = 60 (c) on smooth polycrystalline platinum in 0.1 M methanol + 0.5 M H2SO4 solution. Scan rate 10 mV/s. Electrolyte flow rate 5 pL/s [10]...

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