A carbon matrix with pores of distinct diameters was gradually filled with LiBH 4 , and the corresponding nitrogen adsorption isotherms are presented. Four resins were prepared and characterized individually; micropores and mesopores of defined sizes (6, 10, 15, and 25 nm) were observed. Then, the four resins were mixed to obtain a material composed of micropores and four populations of mesopores of comparable volumes (0.18 cm 3 for micropores and 0.16 cm 3 for each mesopore, 0.82 cm 3 in total). This mixture was impregnated with LiBH 4 by melt impregnation at 10, 30, 50, 70, and 90 vol %, to determine how LiBH 4 fills a carbon matrix, especially how pores of distinct sizes compete with one another. We observed that all pores are filled concomitantly, but smaller pores are filled faster. After the formation of a thin film, the mesopores follow an axial filling (radially, the pores are filled or not) as no sensible modification of the pore diameter was observed during filling, while the pore volume decreased. Calorimetric and volumetric studies were performed for each material filled with LiBH 4 . Afterward, we determined how hydrogen release affected pore distribution and observed that inversely to LiBH 4 filling, LiH liberation affected pore diameters. Finally, we proposed a two-step pore filling protocol: the resins were filled with 10 vol % LiBH 4 and dehydrogenated before filling with 20, 40, and 60 vol % LiBH 4 to determine if the matrix can be efficiently doped with boron to improve its filling. This protocol also illustrates the inherent difficulties of the system that hinder its reversibility.
BACKGROUND: Advanced oxidation processes are an interesting alternative for wastewater treatment. The classic Fenton process, involving ferrous ions and hydrogen peroxide, requires strict pH adjustment and further iron removal. To overcome these difficulties, heterogeneous reaction with solid catalysts has been proposed. Until now, the solid catalysts have been employed as powders in agitated batch reactors. In this work, the application of structured catalysts for processes in flow is proposed. Nano-FeO x /Al 2 O 3 /cordierite monolithic catalysts were prepared making firstly an alumina coating, and then impregnation with aqueous solution of iron nitrate at various concentrations. The synthesized catalysts were characterized using various techniques and then they were studied for the dark Fenton reaction. RESULTS: The coating adherence in the structured catalysts was better than 93%. Also, high homogeneity of the coating was confirmed. From results of physicochemical characterization, it was deduced that the active phase would consist of oligonuclear (FeO) n nanoclusters highly dispersed on the surface of the alumina support. The catalytic activity was evaluated in phenol peroxidation in aqueous phase (without light, pH 3, 30°C), as a model reaction. The monolithic catalysts were active and chemically stable. The most active catalyst (phenol conversion > 90% at 80 min of reaction) was reused 12 times. CONCLUSIONS: The monolithic catalysts show a high potential for application in heterogeneous dark Fenton-type reactions. Then, wastewater treatment by means of advanced oxidation processes could be carried out in continuous mode without further operation to separate the catalyst.
Incipient wetness impregnation was employed to decorate two N-doped graphene-rich matrixes with iron, nickel, cobalt, and copper nanoparticles. The N-doped matrix was wetted with methanol solutions of the corresponding nitrates. After agitation and solvent evaporation, reduction at 800 °C over the carbon matrix promoted the formation of nanoparticles. The mass of the metal fraction was limited to 5 wt. % to determine if limited quantities of metallic nanoparticles catalyze the hydrogen capture/release of nanoconfined LiBH4. Isotherms of nitrogen adsorption afforded the textural characterization of the matrixes. Electronic microscopy displayed particles of definite size, evenly distributed on the matrixes, as confirmed by X-ray diffraction. The same techniques assessed the impact of LiBH4 50 vol. % impregnation on nanoparticle distribution and size. The hydrogen storage properties of these materials were evaluated by differential scanning calorimetry and two cycles of volumetric studies. X-ray diffraction allowed us to follow the evolution of the material after two cycles of hydrogen capture-release. We discuss if limited quantities of coordination metals can improve the hydrogen storage properties of nanoconfined LiBH4, and which critical parameters might restrain the synergies between nanoconfinement and the presence of metal catalysts.
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