Ruthenium catalysts sulfur effects

This was assumed, because the contaminant content in the product was much lower compared with its content in the feed. After stopping the addition of sulfur dioxide, the catalyst recovered only sUghtl) 4.3 ppm hydrogen sulfide had a less dramatic effect on the ruthenium catalyst. The carbon monoxide content inthe product increased slightly... 

The effect of the types of alkah metal and alkaline earth metal salts on the activity for Ru-M (promoter)/AC with 4% of Ru is shown in Fig. 6.25. When the anions of metal salts are ah NO3 the effect of promoters follows the descending order as Ba(N03)2 >KNOs >Sr(NOs)2. When potassium as promoter and anion is SOJ, CO, N03 and OH, respectively, except for K2SO4 significantly reduces the activity due to the introduction of the sulfur, the influence of the rest anions on activity have little difference wherein nitrate salts are a few better. Obviously, sulfur is also a serious poison for ruthenium catalyst (Fig. 6.26). 

Alkenylation. Grabbs ruthenium catalyst was found to be an effective catalyst in the reaction of cyclic thioamides and dimethyl diazomalonate the desired enaminones were obtained in good yields (eq 49). Similar with the earlier reported reaction in the presence of [Rh2(OAc)4] (eq 39), this reaction may proceed via a sulfur ylide, which undergoes cyclization to yield an episulfide. Subsequent spontaneous desulfurization led to new C=C bond formation. 

Ruthenium(III) catalyses the oxidative decarboxylation of butanoic and 2-methylpropanoic acid in aqueous sulfuric acid. ° Studies of alkaline earth (Ba, Sr) metal alkoxides in amide ethanolysis and of alkali metal alkoxide clusters as highly effective transesterification catalysts were covered earlier. Kinetic studies of the ethanolysis of 5-nitroquinol-8-yl benzoate (228) in the presence of lithium, sodium, or potassium ethoxide revealed that the highest catalytic activity is observed with Na+.iio... 

The effect of suJfur poisoning on the coking tendency of alumina-supported ruthenium SNG catalyst has been studied. The clean KU/AI2O3 catalyst has exceptional coking resistance, and at 490 C and 25 atm, can tolerate steam to carbon ratios below stoichiometric (steam/carbori=0.6) with light naphtha before a continuous accumulation of carbon will occur. However, at this temperature (appropriate for SNG production), sulfur can adsorb on the active metal surfaces to a level which will cause a slow but steady accumulation of less reactive carbon. The critical sulfur coverage that adversely affected the steam to carbon ratio necessary to prevent continuous coking appears to fall just above one-half the maximum capacity of the catalyst. 

Several exothermic reactions may occur simultaneously within a methanation unit (Table 20.2). A variety of metals have been used as catalysts for the methanation reaction the most common, and to some extent the most effective methanation catalysts, appear to be nickel and ruthenium, with nickel being the most widely used (Seglin, 1975 Cusumano et al., 1978 Tucci and Thompson, 1979 Watson, 1980). The synthesis gas must be desulfurized before the methanation step since sulfur compounds will rapidly deactivate (poison) the catalysts (Cusumano et al., 1978). A problem may arise when the concentration of carbon monoxide is excessive in the stream to be methanated since large amounts of heat must be removed from the system to prevent high temperatures and deactivation of the catalyst by sintering as well as the deposition of carbon (Cusumano et al., 1978). To eliminate this problem, temperatures should be maintained below 400°C (750°F). 

Transition metal surfaces enriched with S, Se and Te, have been considered as candidates for DAFC cathode catalysts [112-115], For example, ruthenium selenium (RuSe) is a weU-studied electro-catalyst for the ORR [116, 117]. The ORR catalysis on pure Ru surfaces depends on the formation of a Ru oxide-like phase [118]. Ru is also an active catalyst for methanol oxidation. On the other hand, the activity of the ORR on RuSe is found not be affected by methanol [116]. RuS, has also been reported insensitive to methanol [119-122], DPT studies of model transition metal surfaces have provided with atomistic insights into different classes of reactions relevant to fuel cells operation, such as the hydrogen evolution [123], the oxygen reduction [124], and the methanol oxidation [125] reaction. Tritsaris, et al. [126] recently used DPT calculatimis to study the ORR and methanol activation on selenium and sulfur-containing transition metal surfaces of Ru, Rh, Ir, Pd, Co and W (Fig. 8.9). With RuSe as a starting point, the authors studied the effect of the Se on... 

Figure 4.28 Effect of 21 ppm sulfur dioxide on the activity of a ruthenium/alumina catalyst for the preferential oxidation of carbon monoxide the catalyst contained 1.6 wt.% ruthenium on alumina reaction temperature 150°C [338].

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