Probing the structural role of Cr in stabilized tannery wastes with X ray absorption fine structure spectroscopy

The effective stabilization of tannery sludge wastes is explored using X Ray Absorption Fine Structure XAFS spectroscopies. Solidification of the Cr rich waste was realized via vitrification of the incinerated sludge with silica and flux agents. It is demonstrated that the effective reduction of Cr VI and the structural role of Cr are strongly modulated by the chemical composition of the waste. Eskolaite microcrystallites are embedded in the silica matrix of all vitrified samples and the extent of microcrystalline formation is strongly related to the glass basicity. Both Cr VI and Cr III species are identified, corresponding to Cr VI O4 glass formers and Cr III O6 network modifiers. The toxic Cr VI prevails only in the glasses with the highest basicity index and lowest waste content, nevertheless it is safely incorporated and immobilized in the silica matrix. However, the detected abundance of Cr VI increases glass basicity and as a result, glass polymerization is hindered. Thermal treatment, a process that leads to glass ceramics transforms almost all Cr VI to Cr III , while eskolaite formation is promoted concurrently. Nevertheless, microcrystalline growth proceeds mainly via depletion of Cr III from the silica matrix and not from the reduced Cr VI ; yet, Cr removal from the glass matrix does not impair the chemical stability of the devitrified product

Direct Reduction in Greenhouse Gases by Continuous Dry (CO2) Reforming of Methane over Ni-Containing SHS Catalysts

The world of energy is on the cusp of profound transformation. Hydrogen or hydrogen-containing fuel mixtures in the form of synthesis gas, as carriers of clean energy, will be in the short term among the most efficient solutions to pressing environmental problems, reducing the amount of greenhouse gases as well as pollution of cities and dependence on oil-based fuels. Carbon dioxide conversion of methane is the most promising method for the production of synthesis gas due to the simultaneous consumption of two greenhouse gases and, accordingly, a successful solution to environmental problems. Ni/Mn-based catalysts have been prepared by self-propagating high-temperature synthesis (SHS) for this process. The samples were characterized by X-ray diffraction, scanning electron microscopy, and nitrogen porosimetry. The effects of the catalysts’ composition on activity, selectivity, and product yield were investigated. The influence of the content of Ni, Mn on the behavior of catalysts has been established. Comparison of spinels with different component ratios showed that they have a defective structure. Non-stoichiometric spinels with highly defective catalyst structures were obtained due to very high heating and cooling rates during SHS. They work as active sites, which underlies the high activity of the catalysts