Oxygen-modified

Surface modifications and surfiice roughness Cu, Mo, and Be laser mirrors atomic oxygen modified (corroded) surfaces and films, and chemically etched surfaces. 

On the contrary, on oxygen-modified metal surfaces where secondary reactions between the adsorbed oxygen and ethylene decomposition products can easily occur, the effect of oxygen on the adsorptive capacity of the... 

Successful applications of the oxygen-modified CNFs are reported on immobilization of metal complexes ]95], incorporation of small Rh particles [96], supported Pt and Ru CNFs by adsorption and homogeneous deposition precipitation ]97, 98], Co CNFs for Fischer-Tropsch synthesis ]99], and Pt CNFs for PEM fuel cells [100]. 

When extra oxygen species are coadsorbed with methanol, some modifications of the reaction steps are needed. Although a promotion effect of adsorbed oxygen atoms on formation of methoxy from methanol molecule has been reported on some oxygen-modified metal surfaces ... 

In order to elucidate the results of the CO TPD experiment, the detailed structure of the oxygen-modified Mo(l 12) surfaces and the adsorption sites of CO on these surfaces have been considered. Zaera et al. (14) investigated the CO adsorption on the Mo(l 10) surface by high-resolution electron-energy-loss spectroscopy (HREELS) and found vatop sites. Francy et al. (75) also found a 2100 cm loss for CO on W(IOO) and assigned it to atop CO. Recently, He et al. (16) indicated by infrared reflection-absorption spectroscopy that at low exposures CO is likely bound to the substrate with the C-0 axis tilted with respect to the surface normal. They, however, have also shown that CO molecules adsorbed on O-modified Mo(l 10) exhibi Vc-o 2062 and 1983 cm L characteristic to CO adsorbed on atop sites. Thus it is supposed that CO adsorbs on top of the first layer Mo atoms. 

Figures. TPD of CO from oxygen-modified Mo(l 12). Adapted from Ref. 6.

On the clean and oxygen-modified surfaces, adsorbed methanol first dissociates into... 

The results presented here indicate that a new methanol dehydrogenation reaction path is opened when the Mo(l 12) surface is modified by a p(lx2) oxygen layer. The result of the CO adsorption experiment suggests that main electronic effect of oxygen modifier is restricted to the metal atoms directly bonded with the oxygen atoms. TTiis leads to a concept of the selective blocking of the surface atoms to create new active structures, which can provide a powerful mean to control catalytic reaction paths. 

Ab initio pseudopotential study of dehydrogenation of methanol on oxygen-modified Ag(llO) surface has been described by Sun et al. [277]. 

In this paper, the results of the isomerization of hexane, heptane and octane over a Mo2C-oxygen-modified-catalyst, a Mo03-carbon-modified catalyst and a Pt//l-zeolite catalyst, at atmospheric pressure, are presented. Also, the results for a conventional Pt/Al203 catalyst are presented for the isomerization of hexane. Then, the effect of pressure on the isomerization of heptane and octane over the molybdenum catalysts and the Pt//l-zeolite catalyst is shown. Finally, the ability of the molybdenum catalysts to catalyse the isomerization reaction at high conversion with high selectivity even with hydrocarbons larger than hexane is demonstrated this is not possible over the Pt catalysts. The differences between the catalysts are discussed in terms of the reaction mechanisms. 

Figure 20.5 Activation period for n-hexane isomerization over Mo2C-oxygen-modified at atmospheric pressure (623 K, p(C6) = 5 Torr).

The effect of pressure on the isomerization of n-heptane and n-octane was determined over the Pt//l-zeolite, Mo2C-oxygen-modified and M0O3-carbon-modified catalysts. The weight hour space velocity (WHSV) was changed with the pressure to keep the conversion at a similar level, enabling the effect on the isomerization selectivity and the product distributions to be seen. Other conditions were kept constant. 

The results for the isomerization of n-heptane are presented in Table 20.5. Over all the catalysts the main products are again the 2-methyl (M2H) and 3-methylhexanes (M3H), with a significant contribution from the dimethylpentanes of 12-13% over the platinum and Mo2C-oxygen-modified catalysts, and 21% over the Mo03-carbon-modified catalyst. 3-Ethylpentane always contributes around 3% to the isomer distribution and almost no cyclic products are observed. Increasing the pressure over the... 

Pt// -zeolite, Mo2C-oxygen-modified and Mo03-carbon-modified catalysts leads to a decrease in the ratio of the M2H/M3H isomers of 1.10 to 1.02, 0.92 and 0.87 to 0.71 respectively. 

Figure 20.9 Pseudo-Arrhenius plots for the isomerization of n-heptane (6 bar, H2/n-C7 = 30) (a) Pt/jS-zeolite (b) MoO -carbon-modi ficd (c) Mo2C-oxygen-modified.

Mc C-oxygen modified Mo03-carbon modified Pt//i-zeolite... 

The results for the isomerization of n-heptane and n-octane over the molybdenum oxycarbides show that similar isomerization selectivities are obtained at low conversion ( 25% conversion gives 90-95% selectivity) to those over the platinum catalyst. However, on increasing the conversion, the isomerization selectivity obtained over the Mo2C-oxygen-modified and... 

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