Methanol oxidation silver

The methanol oxidation silver process employs an autothermal reactor since the exothemtic heat of the reaction maintains the catalyst bed temperature at 650-725°C. The catalyst bed consists of a thin layer of metallic Ag particles (99.99%) on a gauze substrate. The reaction is conducted with excess methanol. 

Methanol oxidation on Ag polycrystalline films interfaced with YSZ at 500°C has been in investigated by Hong et al.52 The kinetic data in open and closed circuit conditions showed significant enhancement in the rate of C02 production under cathodic polarization of the silver catalyst-electrode. Similarly to CH3OH oxidation on Pt,50 the reaction exhibits electrophilic behavior for negative potentials. However, no enhancement of HCHO production rate was observed (Figure 8.48). The rate enhancement ratio of C02 production was up to 2.1, while the faradaic efficiencies for the reaction products defined from... 

GP 4] [R 11] For methanol oxidation over sputtered silver catalyst, conversion is higher when using micro channels of smaller diameter (8.5 vol.-% methanol balance oxygen 510 °C 4—27 ms sHghfly > 1 atm) [72]. For two channels of the same width, but different depths (70 pm, 130 pm), concentration differences of nearly 10% at the same residence time were detected, all other parameters being equal. 

Similar size effects have been observed in some other electrochemical systems, but by far not in all of them. At platinized platinum, the rate of hydrogen ionization and evolution is approximately an order of magnitude lower than at smooth platinum. Yet in the literature, examples can be found where such a size effect is absent or where it is in the opposite direction. In cathodic oxygen reduction at platinum and at silver, there is little difference in the reaction rates between smooth and disperse electrodes. In methanol oxidation at nickel electrodes in alkaline solution, the reaction rate increases markedly with increasing degree of dispersion of the nickel powders. Such size effects have been reported in many papers and were the subject of reviews (Kinoshita, 1982 Mukerjee, 1990). 

An extension of the research on silver complexes with Lewis base-functionalized mono(A-heterocyclic carbene) ligands has been made toward the better-studied and stronger coordinating phosphine systems. The reaction of a diphenylphosphine-functionalized imidazolium salt with silver oxide in dichloromethane affords a trinuclear silver carbene complex 50, as confirmed by electrospray-ionization mass spectrometry.96,97 Metathesis reaction of 50 in methanol using silver nitrate gives 51 in 33% yield. The crystal structures of 51 were found to be different when different solvents were used during crystallization (Scheme 12).97 One NO3- anion was found to be chelated to... 

Reactions alcohols, 29 36-49 adsorption, 29 36-37 clean surfaces, 29 37-38 ethanol oxidation, 29 44—48 methanol oxidation, 29 38-44 oxidation on copper and silver, 29 38-48 oxidation reaction, silver, 29 48-49 base-catalyzed, of hydrocarbons, 12 117 free radical mechanism in, of hydrogen peroxide, 4 343... 

Robb, D. A. and P. Harriott. 1974. The kinetics of methanol oxidation on a supported silver catalyst. J. Catal. 35 176-183. 

The higher decomposition points were obtained when adrenochrome methyl and ethyl ethers were prepared by oxidation of the appropriate catecholamine in methanol with silver oxide. The BOlid aminochromes were then obtained as microcrystalline solids on addition of dry ether and cooling the resultant solution to — 80°. The slightly less pure products were obtained when the oxidation was carried out in acetonitrile. [R. A. Heacock and B. D. Scott, loc. cit. (footnote c )]. 

Thus, Hickinbottom17 was able to prepare methyl a-D-glucopyranoside (in approximately 70% yield) by reaction of 3,4,6-tri-0-acetyl-2-0-tri-chloroacetyl-/3-D-glucosyl chloride in methanol, with silver oxide as catalyst and acceptor for hydrogen chloride. 

The nature of the working silver catalyst was different during methanol oxidation and ethene oxidation reactions as a result of variations in the reaction conditions (Wachs, 2002). In methanol oxidation (at 600 °C), H 2 was a major by-product, and Raman spectroscopy showed that the silver catalyst was essentially reduced and contained only trace amounts of atomic oxygen in the subsurface. During ethene oxidation (at ca. 230 °C), H2 was not formed as a byproduct. The absence of H2 and the lower reaction temperature during ethene oxidation result in a silver surface with atomic oxygen species. 

Cao et al., 2006 recently used microfabricated reactors with online GC for a Raman investigation of silver catalysts during methanol oxidation catalysis. Their results are consistent with those described above. 

For many catalysts, the major component is the active material. Examples of such unsupported catalysts are the aluminosilicates and zeolites used for cracking petroleum fractions. One of the most widely used unsupported metal catalysts is the precious metal gauze as used, for example, in the oxidation of ammonia to nitric oxide in nitric acid plants. A very fast rate is needed to obtain the necessary selectivity to nitric oxide, so a low metal surface area and a short contact time are used. These gauze s are woven from fine wires (0.075 mm in diameter) of platinum alloy, usually platinum-rhodium. Several layers of these gauze s, which may be up to 3 m in diameter, are used. The methanol oxidation to formaldehyde is another process in which an unsupported metal catalyst is used, but here metallic silver is used in the form of a bed of granules. 

Platinum and silver gauze are used in ammonia and methanol oxidation to nitric oxide and formaldehyde, respectively. The gauze consists of fine wire mesh of O.Smm diameter, supported as layers within the reactor. Activation that pits" the metal wire is necessary to enhance the active surface area. ... 

In the following we will investigate the methanol oxidation process over silver, copper and heteropoly molybdates in order to identify the occurrence of the possible reaction pathways from Schemes 2 and 3 on polycrystalline surfaces and at atmospheric pressure. The main emphasis in these experiments will be on the source of active oxygen. This focus was chosen to better understand the involvement of bulk and sub-surface [10,48] chemistry in selective oxidation catalysis. Such an understanding is required when the catalytic performance is compared between series of chemically different systems which are chosen to investigate only one surface property such as acidity. These experiments will naturally only cover a small selection of the problems discussed with the reaction Schemes. 

The selective oxidation of methanol to give formaldehyde is in practice performed in two different processes, one using metallic silver, the other using iron molybdate as catalyst. Vanadium oxide has been shown to be a good selective catalyst in a variety of oxidation processes (refs. 1-2) and we have previously shown that it is also selective for methanol oxidation (refs. 3-5) when the V Og is applied as a very thin layer (monolayer) on different supports the support can have a significant influence on the activity and selectivity of these monolayer catalysts, as was shown by Roozeboom (ref. 6). In a previous paper (ref. 5), it was shown that both the type of support (A Og or TiC ) and the crystal structure of the TiO have an influence on the selectivity of the catalyst for the production of formaldehyde in general, production of the formaldehyde increases with a decrease in the reducibility of the vanadia. 

Oxidation of 3-acyl-4-hydroxy-2H-l,2-benzothiazine 1,1-dioxide (9) in methanol by silver carbonate or terf-butyl hypochlorite produced 3-methoxy-4H-l,2-benzothiazin-4-one 1,1-dioxide (35),32 apparently by a free radical mechanism with participation of solvent. 

Computational results showed that if silver was positively charged, Lewis acid-base interaction between methanol and silver would be strengthened, and methanol can undergo a stable chemisorbed form on silver surface, which is the key step in the oxidation of methanol to formaldehyde. Also, the further oxidation of formaldehyde was inhibited and the selectivity of the partial oxidation of methanol to formaldehyde was thus enhanced over the positively charged silver catalyst. ... 

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