Methanol, decomposition of

The influence of the presence of sulfur adatoms on the adsorption and decomposition of methanol and other alcohols on metal surfaces is in general twofold. It involves reduction of the adsorption rate and the adsorptive capacity of the surface as well as significant modification of the decomposition reaction path. For example, on Ni(100) methanol is adsorbed dissociatively at temperatures as low as -100K and decomposes to CO and hydrogen at temperatures higher than 300 K. As shown in Fig. 2.38 preadsorption of sulfur on Ni(100) inhibits the complete decomposition of adsorbed methanol and favors the production of HCHO in a narrow range of sulfur coverage (between 0.2 and 0.5). 

K. Franaszczuk, E. Herrero, P. Zelenay, A. Wieckowski, J. Wang, and R.I. Masel, A comparison of electrochemical and gas-phase decomposition of methanol on platinum surfaces, J. Phys. Chem. 96(21), 8509-8516 (1992). 

Acid-base reactivity is an important property of oxide catalysts, and its control is of interest in surface chemistry as well as being of importance in industrial applications. The exposed cations and anions on oxide surfaces have long been described as acid-base pairs. The polar planes of ZnO showed dissociative adsorption and subsequent decomposition of methanol and formic acid related with their surface acid-base properties[3]. Further examples related to the topic of acid-base properties have been accumulated to date[ 1,4-6]. 

Hsiao, M.C., Merritt, B.T., Penetrante, B.M. et al. (1995) Plasma-assisted decomposition of methanol and trichloroethylene in atmospheric pressure air streams by electrical discharge processing, J. Appl. Phys. 78, 3451-6. 

Catalytic production of hydrogen from methanol has been studied for the last 30-40 years and decomposition of methanol to CO and H2 (Equation 6.5) has been utilized commercially in the steel industry for decades as a method for providing carbon monoxide for the carbonization of steel. 

Fig. 25. Proposed mechanism of the side-chain alkylation of toluene by methanol on basic zeolites (a) and the surface species formed during the decomposition of methanol on basic zeolites (b).

Methanol can be converted to hydrocarbons over acidic catalysts. However, with the exception of some zeolites, most catalysts deactivate rapidly. The first observation of hydrocarbon formation from methanol in molten ZnCl2 was reported in 1880, when decomposition of methanol was described to yield hexamethylbenzene and methane.414 Significant amounts of light hydrocarbons, mostly isobutane, were formed when methanol or dimethyl ether reacted over ZnCl2 under superatmo-spheric pressure.415 More recently, bulk zinc bromide and zinc iodide were found to convert methanol to gasoline range (C4-C13) fraction (mainly 2,2,3-trimethyl-butane) at 200°C with excellent yield (>99%).416... 

A comparative study with various types of zeolite showed that Cs-exchanged X and Y zeolites were active for toluene alkylation but primarily catalyzed the decomposition of methanol to CO.431 L and Beta zeolites, in turn, were less active and required higher reaction temperature but were much more selective, providing only very little CO. Adding boron to Cs-exchanged zeolites promotes the alkylation reaction 432 It appears that boron reduces the decomposition of methanol to CO without inhibiting active sites for side-chain alkylation. 

The reaction may be considered as a combination of the endothermic decomposition of methanol ... 

To improve process economics, further work is needed to improve catalyst lifetimes. A more stable system employed a noble metal-loaded potassium L-zeolite catalyst for the condensation of ethanol with methanol to produce a 1-propanol and 2-methyl-l-propanol (US patent no. 5,300,695) (18). However, yields were small compared with the large amounts of CO and C02 produced from the methanol. More recently, Exxon patented a noble metal-loaded alkali metal-doped mixed metal (Zr, Mn, Zn) oxide (US patent nos. 6,034,141 and 5,811,602) (19,20). The catalyst was used in a syngas atmosphere. As with other catalysts, the higher temperatures resulted in decomposition of methanol. Changes in catalyst composition were noted at higher temperatures, but the stability of the catalyst was not discussed. Recently, compositions including Ni, Rh, Ru, and Cu were investigated (21,22). 

By 7-irradiation, charge carriers are generated in the bulk of A1203 and Si02. By diffusion of the charge carriers to the surface of the solids, the decomposition of methanol is enhanced 63). 

The dehydrogenation (decomposition) of methanol to give CO and H2 on supported catalysts has attracted much attention because of its practical relevance for methanol-fueled vehicles or heat-recovery techniques... 

Hwu, H.H. et al.. Potential application of tungsten carbides as electrocatalysts. 1. Decomposition of methanol over carbide-modified W(H1), J. Phys. Chem. B, 105, 10037, 2001. 

This result shows that the product is obtained upon the decomposition of methanol to CO and hydrogen (Eq. 11.16). 

The product distribution is summarized in Table 4. The potentials given in the table are IR-free potentials. Under a nitrogen atmosphere, hydrogen was found to be the only product. This is due to the decomposition of methanol. On both electrodes, the main product was CO. Methyl formate was also formed. Insignificant amounts of hydrocarbons were produced. Comparing the two electrodes, InP has higher activity for COj reduction. 

We compared our novel catalysts with a commercial methanol synthesis catalyst Cu-Zn-A1 (Cu-Zn-Al=42 45 13, in atomic ratio). As shown in Fig.la, although the conversion of CO2 for the Cu-Zn-Al/HY composite catalyst was the highest (30.5%), the selectivity of hydrocarbons was the lowest (6.3%) in our study. The decomposition of methanol to CO at high temperatures accounts for the remarkable decrease in the selectivity of hydrocarbons. Moreover, because olefins are easily hydrogenated into paraffins over Cu-based catalysts [7], no olefins and only a trace of iso-butane appeared in the products. The Fe-Zn-Zr (1 1 1)... 

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