[en] Oxygen, present at high concentrations in water, is the main cause of corrosion in process equipment such as steam generators in power production and water-cooled stator windings in turbine generators. Thus, mitigating corrosion involves removal of oxygen by a method such as mechanical deaeration, chemical scavenging or catalytic recombination with hydrogen. Where hydrogen is already present in the water or that it can be conveniently provided, the catalytic recombination has become a preferred method because of its ability to remove oxygen to very low levels (a few ppb levels) without producing any undesirable by-products. Palladium supported on anion or cation exchange resins is the most common catalyst used in industry. Canadian utilities use sulfite-based resins to scavenge the oxygen in stator cooling water application. In the 1980's, AECL demonstrated the application of wetproofed catalysts for dissolved oxygen removal under an EPRI/AECL contract. The work reported here is focussed on further development of palladium- and platinum-based catalysts on inert styrenedivinylbenzene (SDB) polymer support for dissolved oxygen removal applications. The inert nature of the catalyst support is expected to be an additional benefit for this application. A lab-scale plug flow reactor, 19-mm diameter by 100-mm long, was used for the tests at water fluxes ranging from 400 to 900 mol·s^-1·m^-2 (4.3 to 9.6 bed volumes per minute) at ambient temperatures. The catalyst performance was characterized in terms of conversion efficiency based on dissolved oxygen concentrations at the inlet and outlet of the reactor and benchmarked against the commercial catalyst Lewatit OC1045 (marketed by Bayer). The effect of the type of precious metal (platinum or palladium), the catalyst support particle size distribution, the catalyst metal loading and the molar ratio of reactants (oxygen and hydrogen) on conversion efficiency was studied to optimize the catalyst performance. Also, the effect of the presence of boron, which is used as a corrosion inhibitor and poison for the nuclear reaction, on conversion efficiency was investigated. Dissolved oxygen concentrations as low as 13 ppb were measured at the lowest water flux used for the tests, and the catalyst performance profiles in terms of conversion as a function of water flux showed the ability to reduce dissolved oxygen concentration even further by increasing the residence time (decreasing water flux for a given bed size or increasing the bed size for a given water flux). Dissolved oxygen removal efficiency in excess of 97% over the complete range of water flux was achieved. An AECL proprietary catalyst with particle size distribution similar to that of the commercial catalyst demonstrated superior oxygen removal performance, but produced higher pressure-drop. The catalytic performance was strongly dependent on the particle size distribution of the catalyst, pointing to the need to give careful consideration to pressure-drop at the design stage. The recombination efficiency increased significantly when the dissolved hydrogen concentration was increased from stoichiometric to twice stoichiometric requirement for the reaction. Since the hydrogen required for the recombination is conveniently present in the stator cooling water through ingress from the generator hydrogen system, the catalytic reactor can be located in a suitable position in the cooling water recycle loop. Alternately, the sulfite resins used for deoxygenation may be replaced with the noble-metal catalyst, which will necessitate hydrogen addition to the water. For make-up water deoxygenation, the catalyst may be incorporated as part of the system with hydrogen addition. Boron at concentrations up to 1000 ppm had no major poisoning effect on AECL catalyst performance. A design equation for deoxygenation is derived from a simple analysis of catalyst performance. (author)

[en] After a single intravenous injection of [1-¹⁴C]-hexanoyl aldehyde sodium bi-sulfite (HASB), the blood radioactivity time course curve fitted well a two-compartment open model. The radioactivity distributed widely in the body, with the concentrations in liver and kidneys markedly higher than in blood and other tissues. Except in kidneys and liver, the radioactivities in tissues decreased to quite low levels 4 h after administration. The radioactivity in tumors were relatively lower. Thin layer chromatographic (TLC) analyses indicated that most of radioactivity in serum was in the form of unchanged ¹⁴C-HASB and the drug was metabolized rapidly after passing into some tissue cells in vivo. The major routes of elimination were found to be via expiration with 26.76% of the ¹⁴C recovered as carbon dioxide in 3 h and via urine with 14.6% of the ¹⁴C recovered in 24 h mainly in the form of metabolites

[en] Published in summary form only

[en] Structural changes occurring within non-conventional Dawson-type [α/β-Mo₁₈O₅₄(SO₃)₂]⁴⁻ polyanions in the form of tetrapentylammonium salts were studied by a combination of IR, Raman and visible spectroscopy at high temperature and high pressure. Evidence of the formation of bronze-type materials above 400 K and also upon pressurization to 8 GPa is presented. This conclusion is suggested to be a general result for polyoxometalate compounds subjected to extreme conditions and it opens opportunities for the design of new materials with interesting optical and electronic properties. - Graphical abstract: Structural changes occurring within non-conventional Dawson-type [α/β-Mo₁₈O₅₄(SO₃)₂]⁴⁻ polyanions in the form of tetrapentylammonium salts were studied by a combination of IR, Raman and visible spectroscopy at high temperature and high pressure. Evidence of the formation of bronze-type materials above 400 K and also upon pressurization to 8 GPa is presented. This conclusion is suggested to be a general result for polyoxometalate compounds subjected to extreme conditions and it opens opportunities for the design of new materials with interesting optical and electronic properties. Highlights: ► Spectroscopy studies of non-conventional Wells–Dawson polyoxometalates (POMs) at high temperature and high pressure. ► Discussion on the stability of two POM isomers. ► Local formation of bronze-like materials: possibilities for a new synthetic method at high pressure from POM precursors.

[en] Biological systems have evolved active sites containing [4Fe-4S]²⁺ clusters covalently linked to a mononuclear Fe or Ni or to a diiron cluster. Such structures have been found in sulfite reductase, carbonmonoxide dehydrogenases and most recently in [Fe]-hydrogenases. The link through a bridging ligand provides an exchange pathway that couples the spins of the two chromophores. In this contribution the spin physics of these systems as viewed from a standpoint of Moessbauer spectroscopy is discussed

[en] Depolymerization of polysulfide polymers with NaHS (I) and Na₂SO₃ (II) was studied. It is shown that polymers with 2.5, 3 and 4 atoms S per segment can be depolymerized without previous desulfurization. It is done with 0.5 mols of I and 2 mols of II per segment (for polymers S₂.₅ and S₃) and 3 mols of II (for S₄). The depolymerization of S₂.₅ and S₃ polymers is more efficient when the proportion of I is increased. When I:II=0.5:2, polymer S₂ gives a product of mol. wt. 710. The polymers S₂.₅, S₃ and S₄ yield product of mol. wts. 730, 1170 and 3300 resp. This shows that S,L2.₅ and S₃ can be simultaneosly depolymerized and desulfurized, provided that sufficient amounts of I and II are taken

[en] The possibility for obtaining energy based on oxidation of sulfide and sulfite ions while simultaneously solving an environmental problem is regarded. The catalysts used for the processes are shown. Different constructions of the fuel cells are studied. An analysis of the results so far is made, as well as possible future development. Key words: fuel cells, sulfides, sulfites

[en] Molybdenum is the only 4d metal found in almost all life. One such molybdenum-containing enzyme is sulfite oxidase, which also contains the dithiolene-molybdopterin ligand. Sulfite oxidase is essential in the degradation of sulfur-containing compounds such as cysteine and methionine. Past work has shown parallels in the chemistry of dithiolene-metal and diselenolene- metal complexes. Thus, in this present work, the oxygen atom transfer mechanism for a diselenolene sulfite oxidase biomimetic complex was investigated using computational tools, the results of which were compared to the analogous dithiolene biomimetic complex. From the results obtained, the molybdenum-diselenolene sulfite oxidase biomimetic complex is able to catalyse the oxygen atom transfer and does so with a marginally lower value of Δ_rG‡ than that for the analogous dithiolene complex. In particular, it was found that on average, the diselenolene complex had an activation energy 1.2 kJ mol^-1 lower in energy than the analogous dithiolene complex. However, the calculated value of Δ_rG suggests that the oxidation of sulfite is more favourable for the dithiolene complex where the average difference in reaction aqueous Gibbs reaction energy was -9.4 kJ mol^-1 relative to the diselenolene complex. It is noted that with the use of D3 and D3BJ corrections in combination with the B3LYP functional, the barrier for oxygen atom transfer is lowered by more than 30.0 kJ mol^-1 for both the diselenolene and dithiolene complexes. Such results suggest that to study such oxo-transfer reactions, the proper treatment of dispersion interaction is necessary. (author)

[en] Protohematin catalyzes the oxidation of sulphite. The optimum pH of the reaction is approximately 7 in the presence of a 0.05 M phosphate buffer. The oxidation of sulphite is not coupled to the reduction of protohematin to protohaem. Reagents able to form complexes with the iron of protohematin are inhibitors of its catalytic function. (authors)

[en] Some apparent contradictions about the role of O₂^- in the chain oxidation of sulfites by O₂ are explained. O₂^- may indeed initiate the chain. On the other hand, if, in the presence of OH scavengers, O₂^- has a leading part in the chain termination, in the absence of OH scavengers, its role is inhibited by a chain reaction which replaces O₂^- by OH radicals. (author)