Ruthenium loading, effect

Effect of Ruthenium Loading Two ruthenium concentrations (0.5% and 1.5%) were used to study the effect of ruthenium loading on syngas conversion over physically mixed Ru/Al-O-//ZSM-5 catalysts. The results are shown in Table II. The formation of C +C2 was greatly reduced from 40% w th 1.5% Ru to 25% with 0. % Ru. On the other hand, the higher ruthenium loading gave a coproduct of reduced end point (Ex. 2A and 2B). As expected, no difference in aromatics production was observed. 

The paper describes work on the preparation of Ru/AljOj catalyst containing different amounts of Ru and the effect of ruthenium loading on the removal of NOx vapours from air stream. The effect of residence time on the efficiency of removal is also discussed. The NOx analysis was carried out using spectrophotometer. The Phenol-di-sulphonic acid method was used for the estimation of nitrate. It was found that 1 wt% loading was the best for the removal of NOx comparison to 0.2 wt% and 2 wt% loadings and a higher residence time of... 

The effect of solvent. For these catalysts prepared by the impregnation methods, the solvent has direct influence on the loaded effect and loaded amount of active components of RuCls. The water, acetone, ethanol and tetrahydrofuran (THF) etc. can be used as the solvents of the RuCls solution. Table 6.20 shows the effect of four kinds of solvents on the dispersion, smface area and particle size of ruthenium. 

It is seen from Table 6.20 that different solvents have great effect on the loading effect of the active components. The dispersion of ruthenium is the highest when H2O is used as solvent, while with THF as solvent, the dispersion of ruthenium is the lowest and the catalytic activity is the worst. However, a lot of researchers considered that the effect of the acetones is better than that of the H2O, which is related probably with the surface characters of the activated carbons, especially the hydrophilicity. The surface of the ordinary activated carbons is hydrophobicity. 

Table 6.20 Effect of solvents on loaded effect of ruthenium...

Ruthenium catalysts, supported on a commercial alumina (surface area 155 m have been prepared using two different precursors RUCI3 and Ru(acac)3 [172,173]. Ultrasound is used during the reduction step performed with hydrazine or formaldehyde at 70 °C. The ultrasonic power (30 W cm ) was chosen to minimise the destructive effects on the support (loss of morphological structure, change of phase). Palladium catalysts have been supported both on alumina and on active carbon [174,175]. Tab. 3.6 lists the dispersion data provided by hydrogen chemisorption measurements of a series of Pd catalysts supported on alumina. is the ratio between the surface atoms accessible to the chemisorbed probe gas (Hj) and the total number of catalytic atoms on the support. An increase in the dispersion value is observed in all the sonicated samples but the effect is more pronounced for low metal loading. 

One of the drawbacks of DMFCs is the relatively slow rate of the anodic oxidation of methanol even on highly active platinum electrodes. It was shown that the Pt-Ru system is much more catalytically active than pure platinum (pure ruthenium is inert towards this reaction) (-> platinum-ruthenium -> electrocatalysis). The so-called bifunctional mechanism is broadly accepted to describe this synergistic effect, according to which organic species are chemisorbed predominantly on platinum centers while ruthenium centers more readily adsorb species OH, required for the oxidation of the organic intermediates. Usually the composition of such alloys is Pto.sRuo.s and the metal loading is 2-4 mg cm-2. 

Irrespective of the nature of the reaction intermediate, enolic type (11) or surface carbide (12), the dechne of the turnover number for the zeolites with higher Si/Al ratio can be explained as follows. For platinum (13) and palladium (14,15) loaded zeolites, support effects are known to exist. The higher the acidity (and the oxidizing power) of the zeolite, the higher will be the electron-deficient character of the supported metal. It also is well established now (16) that the average acidity of hydrogen zeohtes increases with the Si/Al ratio. This explains why the electron deficient character of ruthenium should increase with the Si/Al ratio of the zeolite, and a stronger interaction with adsorbed CO should be expected. Vannice (19,20) reported that the N value for CH4 formation decreases when the heat of adsorption for CO increases. All this explains why the tmnover number of the methanation reaction over ruthenium decreases when the Si/Al ratio of the zeolite support increases. 

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