Sulfur catalytic activity effect

The acid-catalysed hydrolysis of three iV-phenylalkanesulfinamides (49, R = i-Pr, t-Bu, 1-adamantyl) in aqueous mineral acids (HCl, HBr, H2SO4, HCIO4) was found to proceed via a slow spontaneous (uncatalysed) pathway, an A2 acid-catalysis pathway, and an acid-dependent nucleophilic catalysis pathway, the last of which predominates in hydrobromic and hydrochloric acid solutions (Scheme 16a). A mechanistic switchover from A2 to A1 (Scheme 16b) was detected for the isopropyl and t-butyl compounds in concentrated sulfuric acid. Order of catalytic activity, effect of added salts, Arrhenius parameters, kinetic solvent isotope, and solvent effects were all consistent with the proposed mechanisms. ... 

The effects of temperature, types and concentrations of adds were studied. The highest catalytic activity was achieved at 100°C in 1 - 3 M sulfuric add. 

D. Farcasiu and J. Q. Li, Preparation of sulfated zirconia catalysts with improved control of sulfur content, 111 effect of conditions of catalyst synthesis on physical properties and catalytic activity,... 

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... 

Cheekatamarla and Lane [62, 63] studied the effect of the presence of Ni or Pd in addition to Pt in the formulation of catalysts for the ATR of synthetic diesel. For both metals, a promotional effect with respect to catalytic activity and sulfur poisoning resistance was found when either alumina or ceria was used as the support. Surface analysis of these formulations suggests that the enhanced stability is due to strong metal-metal and metal-support interactions in the catalyst. 

It is now well established that the TMS are unique class of catalysts that are able to perform numerous hydrogenation and hydrogenolysis reactions in the presence of sulfur. In fact, they require sulfur for activity maintenance. The catalytic activity and selectivity of the TMS arises from the electronic and structural properties of the sulfides themselves. Support effects are secondary, improving sulfide dispersion and reducing metal cost in commercial catalysts. Fundamental effects can only be elucidated by studying TMS catalysts in their fully sulfided and catalytically stabilized states. Studies are of-... 

Activation of an M-CO bond for nucleophilic substitution in anion radical metallo-complexes appears to be quite a general effect (Kaim 1987 Mao et al. 1989,1992 Shut et al. 1995 Klein et al. 1996). Such activation seems to be the basis of metal-cluster catalytic activity. The iron-sulfur cluster (Bu4N)2Fe4S4(SPh)4 deserves to be mentioned here. The cluster is considered as a ferredoxin model (Inoue Nagata 1986) it catalyzes an electron transfer from //-butyl lithium or phenyl lithium to 5-phenyl thiobenzoate or phenylbenzoate (Inoue Nagata 1986). 

As is obvious, hydrogen sulfide active under current conditions is one of the reaction products. Its aggressiveness, the ability to interact with S02 even under natural conditions, promotes sulfur accumulation in the system, affects synthesis of condensation products and can alter their catalytic activity. Therefore, despite high effectiveness, oxidative catalytic dehydrogenation of ethylbenzene by sulfur dioxide may be found unacceptable for production management in relation to ecology and protection of the environment. 

The catalytic activities of the Fe203-I catalyst for the reaction of 2-propanol are shown as a function of calcination temperature of the catalyst in Fig. 2 (56). The maximum activity was observed with calcination at 300 and 450-500°C for the sample treated with sulfuric acid. It is considered that the former activity was due to the catalytic action by the mounted acid, but the latter one was based on acid sites created by strong interaction of the ion with the support. In the case of the sample treated with ammonium sulfate, the maximum activity was observed with calcination at 500°C, and the calcination at temperatures below 300°C did not give activity. The results seem to be reasonable judging from the absence of catalytic effect of ammonium sulfate. 

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