Hydrogen trapping: Synergetic effects of inorganic additives with cobalt Sulfide absorbers and reactivity of cobalt polysulfide
Résumé
The biphasic product CoS2 + Co(OH)(2) obtained by oxidation of cobalt sulfide is known to trap hydrogen at room temperature and low pressure according to a balanced reduction equation. Adding various inorganic compounds to this original absorber induces their reduction by hydrogen in the same conditions at a significant rate: (i) excess cobalt hydroxide is reduced to metallic cobalt; (ii) nitrate ions are reduced to ammonia; (iii) sulfur and sodium thiosulfate are reduced to H2S or NaHS and Na2S, respectively. Without a hydrogen absorber these inorganic compounds are not reduced by H-2, suggesting synergetic effects involving H-2 and the hydrogen absorber. Amorphous cobalt polysulfide, CoS5, is also reduced by hydrogen at room temperature and releases H2S gas. In the presence of a base to neutralize H2S gas, the reaction rate is initially slower than with the CoS2 + Co(OH)(2) mixture due to the higher stability of polysulfide chains but the H-2 trapping yield is improved, making CoS5 a good candidate for H-2 trapping.