Metal sulfides, enhancing hydrogen

Addition of hydrogen sulfide in solution was found to enhance the rate of this process albeit the efficiencies were generally low, partly due to concomitant precipitation of elemental sulfur during the photolytic experiments. The effects of reaction temperature, light intensity, and pH of the electrolyte were studied, and the photo-catalytic mechanism was discussed with reference to the theory of charge transfer at photoexcited metal sulfide semiconductors. 

Activity enhancement of mesoporous silicate FSM-16 by metal ion-exchange and sulfiding with hydrogen sulfide for acid-catalyzed reactions... 

The modification of mesoporous silicate FSM-16 by metal ion-exchange and sulfiding with hydrogen sulfide was studied through the isomerization of 1-butene, cis-2-butene and cyclopropane. It was revealed that the catalytic activities of MeFSM-16 were remarkably enhanced by sulfiding with hydrogen sulfide due to the formation of new Bronsted acid sites... 

Activity Enhancement of Mesoporous Silicate FSM-16 by Metal lon-exchange and 823 Sulfiding with Hydrogen Sulfide for Acid-catalyzed Reactions M. Sugioka, L. Andalaluna andJ.K.A. Dapaali... 

There have been only a few reports of mesostructured metal sulfides. Mesoporous cadmium sulfide was prepared from polyethylene oxide surfactants and cadmium salts exposed to hydrogen sulfide [35], A study of the effects of the counter-anion on the formation of CdS mesostructures led to the conclusion that the use of cadmium nitrate and perchlorate salts improved the degree of order of the mesostructure over the chloride, sulfate and acetate salts. This effect was attributed to the stronger acidity of conjugate acid by-products of the reaction in the case of nitrates that leads to the dissolution of high-energy defects and enhances structural order. 

To further enhance the visible light utilization of the metal sulfide solid solutions for hydrogen evolution, doping of metal sulfide solid solution with transition or alkaline metal ions has been extensively explored recently. As shown in Table 6.2, the metal sulfide solid solutions doped by Cu [147, 148], Ni [149, 150], Ag [151], Sn [152], and Bi [153] ions have been found to exhibit higher photocatalytic... 

Ma.nufa.cture. The preferred method for making nickel sulfate is adding nickel powder to hot dilute sulfuric acid. Adding sulfuric acid to nickel powder in hot water enhances the formation of H2S. Hydrogen sulfide always forms as a by-product upon reaction of metallic nickel and sulfuric acid. The hberated hydrogen is absorbed by the metal and then reduces the sulfate anion to H2S. 

Presulfide—A step in the catalyst regeneration procedure which treats the catalyst with a sulfur-bearing material such as hydrogen sulfide or carbon bisulfide to convert the metallic constituents of the catalyst to the sulfide form in order to enhance its catalytic activity and stability. 

In addition to transformation by corrodable metals (such as Fe° and Zn°), bimetallic combinations of a catalytic metal with a corrodable metal (such as Pd/Fe or Ni/Fe) have also been shown to transform a variety of contaminants. In most cases, rates of transformation by bimetallic combinations have been significantly faster than those observed for iron metal alone [26,96,135-139]. Not only have faster transformation rates been observed with bimetallic combinations, but, in some cases, transformation of highly recalcitrant compounds, such as polychlorinated biphenyls (PCBs), chlorinated phenols, and DDT has been achieved [24,140,141]. The mechanism responsible for the enhanced reactivity with bimetallic combinations is still unclear however, it has been suggested that electrochemical effects, catalytic hydrogenation, or intercalation of H2 may be responsible. A likely limitation to the full-scale application of bimetallic combinations to groundwater remediation is deactivation of the catalytic surface either by poisoning (e.g., by sulfide) or by formation of thick oxide films [136,142,143]. 

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