Two different techniques (precipitation with ammonia and hydrothermal synthesis with ethylene glycol, both followed by autoclave aging) were employed for the synthesis of CeO2-ZrO2 mixed oxides on a 80-20 wt.% basis. Aging parameters, such as time and temperature, were systematically investigated in order to determine the optimal conditions to maintain high surface area and oxygen mobility of the prepared solids. Different loadings ofnickel and cobalt (3, 6, 12 and 18 wt.%) were subsequently deposited via homogeneous deposition precipitation method. Calcined bimetallic catalysts were characterized by N2 adsorption-desorption, XRD, H2-TPR, TPO-TGA and FE-SEM methods, and tested for activity, selectivity and stability in the reforming of equimolar CH4-CO2 gas streams. During temperature programmed methane reforming tests, syngas with a H2/CO ratio between 0.3 and 0.79 was produced. Growth of carbon nanofilaments over the catalyst does not lead to deactivation, but can cause reactor plugging. Two conditions are vital and must be fulfilled simultaneously to avoid excessive carbon deposition: strong interaction between the NiCo bimetallic particles and CeZr support, which exists only at NiCo loadings up to 6 wt.%, as well as high oxygen mobility within the highly defective CeO2-ZrO2 crystalline lattice for timely carbon oxidation.
COBISS.SI-ID: 5011482
Catalytic wet-air oxidation (CWAO) of aqueous solutions of bisphenol A (BPA) was investigated in a trickle-bed reactor at temperatures up to 230°C and oxygen partial pressure of 10.0 bar over TiO2 and Ru/TiO2 solids. It was observed that in the given range of operating conditions BPA undergoes both noncatalyzed and catalyzed oxidation routes. The employed Ru/TiO2 catalyst containing 3.0 wt % of metallic phase enabled complete removal of BPA and morethan 96% of TOC removal at temperatures of 200°C and above. No catalyst deactivation occurred that could be attributed to the dissolution of active ingredient material. At these conditions, no carbonaceous deposits were accumulated on the catalyst surface. The acute toxicity of end-product solutions to organisms from different taxonomic groups and estrogenicity determined by the genetically modified yeast, compared with those of the feed solutions, was significantly reduced by CWAO treatment over the Ru/TiO2 catalyst. For comparison, oxidative destruction of BPA was also investigated in this study by means of either photolytic or heterogeneous photocatalytic oxidation. A commercial TiO2 photocatalyst illuminated by UV light enabled complete removal of BPA; however, lower decrease of toxicity and estrogenicity in the treated solution was observed.
COBISS.SI-ID: 4835098
Bisphenol A (BPA) is a well known endocrine disruptor. Significantly less is known about its ability to induce antioxidant defense and oxidative stress in aquatic organisms. This is an interesting subject because BPA can act both as a prooxidant (induces the formation of reactive oxygen species) and an antioxidant. The aim of the present study was to elucidate if BPA induces changes in the activities of antioxidant enzymes catalase (CAT) and glutathione S-transferases (GSTs) and the level of lipid peroxidation in crustacean Daphnia magna. These biomarkers were followed after acute (48 h) and chronic (21 d) exposure period. Interestingly, CAT and GSTs were changed in the same manner after both exposure durations. The most observable change in daphnids was the increase of GSTs activities, measured with 1,2-chloro-4-dinitrobenzene as a substrate. No GSTs activities with ethacrynicacid and 1,2-dichloro-4-nitrobenzene as substrates were detected. The activity of CAT and the level of lipid peroxidation remained unchanged in daphnids exposed to sublethal concentrations of BPA. The reproduction rate wasconsiderably affected already at 1.73 mg/L while the growth was only affected at the highest concentration (13.8 mg/L), where also significant mortality was observed.
COBISS.SI-ID: 5094170
Wet hydrogen peroxide catalytic oxidation (WHPCO) is one of the most importantindustrially applicable advanced oxidation processes (AOPs) for the decomposition of organic pollutants in water. It is demonstrated that manganese functionalized silicate nanoparticles with interparticle porosity act as a superior Fenton-type nanocatalyst in WHPCO as they can decompose 80% of a test organic compound in 30 minutes at neutral pH and room temperature. By using X-ray absorption spectroscopic techniques it is also shown that the superior activity of the nanocatalyst can be attributed uniquely to framework manganese, which decomposes H2O2 to reactive hydroxyls and, unlike manganese in Mn3O4 or Mn2O3 nanoparticles, does not promote the simultaneous decomposition of hydrogen peroxide. The presented material thus introduces a new family of Fenton nanocatalysts, which are environmentally friendly, cost-effective, and possess superior efficiency for the decomposition of H2O2 to reactive hydroxyls (AOP), which in turn readily decompose organic pollutants dissolved in water.
COBISS.SI-ID: 4863514
Effects of four different nanocrystalline CeO2-based catalysts on crustaceans Daphnia magna and early-life stages of zebrafish Danio rerio were studied. Pure CeO2 and CuO-CeO2 mixed oxides with a nominal 10, 15 and 20 mol. % CuO content were tested. Pure CeO2 provoked no effects, but CuO-CeO2 mixed oxides induced some sublethal effects on fish and affected daphnidsć survival. The most pronounced effects were found on fish body growth, which was reduced at 10 mg/L in case of CuCe20 and 50 mg/L in cases of CuCe10 and CuCe15. Daphnidsćsurvival was affected above 80 mg/L of CuCe20, while CuCe10 and CuCe15 did not affect daphnids. None of the materials was highly toxic to daphnids and fish in comparison to some other environmental pollutants. Differences in effects between the materials could not be explained by their specific physicochemical properties. This work indicates that more attention should be placed at potential toxicity of nanostructured materials, such as nanocrystalline mixed-oxides.
COBISS.SI-ID: 4936474