Support Effects on the Activity of Ni Catalysts for the Propane Steam Reforming Reaction.

The catalytic performance of supported Ni catalysts for the propane steam reforming reaction was investigated with respect to the nature of the support. It was found that Ni is much more active when supported on ZrO2 or YSZ compared to TiO2, whereas Al2O3- and CeO2-supported catalysts exhibit intermediate performance. The turnover frequency (TOF) of C3H8 conversion increases by more than one order of magnitude in the order Ni/TiO2 < Ni/CeO2 < Ni/Al2O3 < Ni/YSZ < Ni/ZrO2, accompanied by a parallel increase of the selectivity toward the intermediate methane produced. In situ FTIR experiments indicate that CHx species produced via the dissociative adsorption of propane are the key reaction intermediates, with their hydrogenation to CH4 and/or conversion to formates and, eventually, to CO, being favored over the most active Ni/ZrO2 catalyst. Long term stability test showed that Ni/ZrO2 exhibits excellent stability for more than 30 h on stream and thus, it can be considered as a suitable catalyst for the production of H2 via propane steam reforming.

Solar light induced photocatalytic removal of sulfamethoxazole from water and wastewater using BiOCl photocatalyst.

The photocatalytic activity of bismuth oxychloride (BiOCl) toward sulfamethoxazole (SMX) elimination was investigated. BiOCl was synthesized according to a simple method using thiourea. Its physicochemical characteristics were determined by nitrogen physisorption, X-Ray diffraction, diffuse reflectance spectroscopy, scanning electron microscopy and transmission electron microscopy. Simulated solar irradiation and 1 g/L BiOCl, could effectively remove 0.5 mg/L SMX in less than 90 min. An increase in SMX concentration from 0.25 mg/L to 4 mg/L decreased the observed kinetic constant. Concerning the pH effect, it was found that under alkaline conditions SMX removal was slightly hindered. The water matrix's influence on SMX removal was explored, carrying out experiments in real water matrices, (bottled water (BW) and secondary effluent (WW)). Interestingly SMX removal was not practically altered in WW secondary effluent, but it was slightly hindered in BW bottled water. Experiments, performed in synthetic matrices, revealed that the presence of bicarbonates and chlorides slightly slowed down degradation kinetics, while humic acid enhanced SMX removal at concentrations up to 10 mg/L. Finally, an enhancement on SMX degradation was observed in the presence of persulfate. Quenching experiments of potential reactive species revealed that SMX degradation takes place mainly through reaction with hydroxyl radicals and photogenerated electrons.

Persulfate activation by modified red mud for the oxidation of antibiotic sulfamethoxazole in water.

Different pre-conditioning treatments were evaluated in order to stabilize red mud, a waste product from bauxite processing, for obtaining heterogeneous catalysts (named as B1-B3) that can be employed as suitable activators of sodium persulfate (SPS) for the degradation of sulfamethoxazole (SMX), a model antibiotic, in water. The presence of Fe3O4 in the composition of the catalysts was found to be a key factor for a suitable activation of SPS, according to the XPS measurements. The oxidation of SMX was successfully fitted to a pseudo-first-order kinetic model (r2 > 0.96), obtaining a 68% removal after 180 min when 0.8 mg/L of SMX was oxidized with 2 g/L of SPS and 2 g/L of catalyst B3. The presence of organic and/or inorganic constituents in the water matrix significantly hindered the degradation rate of SMX, the apparent kinetic constants being from 2 to 3 times lower than that determined in ultrapure water test. The use of ultrasound irradiation coupled to the addition of B3 catalyst improved importantly the SMX oxidation in real aqueous matrices, thus attaining values of removal which almost triplicated the ones obtained in absence of ultrasounds.

Synthesis and characterization of CoOx/BiVO4 photocatalysts for the degradation of propyl paraben.

Cobalt-promoted bismuth vanadate photocatalysts of variable cobalt content (0-1.0 wt.%) were synthesized and characterized with various techniques including BET, XRD, DRS, XPS and TEM. BiVO4 exists in the monoclinic scheelite structure, while cobalt addition improves the absorbance in the visible region although it does not affect the band gap energy of BiVO4. Cobalt exists in the form of well-dispersed Co3O4 nanocrystallites, which are in intimate contact with the much larger BiVO4 nanoparticles. Photocatalytic activity was evaluated for the degradation of propyl paraben (PP) under simulated solar radiation. The activity of pristine BiVO4 is significantly improved adding small amounts of cobalt and is maximized for the catalyst containing 0.5 wt.% Co. PP degradation in ultrapure pure water increases with increasing photocatalyst loading (100 mg/L to 1.5 g/L), and decreasing PP concentration (1600-200 µg/L). Experiments in bottled water, as well as in pure water spiked with bicarbonate and chloride ions showed little effect of non-target inorganics on degradation. Conversely, degradation is severely impeded in secondary treated wastewater. The enhancement of the photocatalytic activity of the synthesized catalysts is attributed to efficient electron-hole separation, achieved at the p-n junction formed between the p-type Co3O4 and the n-type BiVO4 semiconductors.

Photodegradation of ethyl paraben using simulated solar radiation and Ag3PO4 photocatalyst.

In this work, the solar light-induced photocatalytic degradation of ethyl paraben (EP), a representative of the parabens family, was studied using silver orthophosphate, a relatively new photocatalytic material. The catalyst was synthesized by a precipitation method and had a primary crystallite size of ca 70nm, specific surface area of 1.4m2/g and a bandgap of 2.4eV. A factorial design methodology was implemented to evaluate the importance of EP concentration (500-1500µg/L), catalyst concentration (100-500mg/L), reaction time (4-30min), water matrix (pure water or 10mg/L humic acid) and initial solution pH (3-9) on EP removal. All individual effects but solution pH were statistically significant and so were the second-order interactions of EP concentration with reaction time or catalyst concentration. The water matrix effect was negative (all other effects were positive) signifying the role of humic acid as scavenger of the oxidant species. Liquid chromatography-time of flight mass spectrometry revealed the formation of methyl paraben, 4-hydroxybenzoic acid, benzoic acid and phenol as primary transformation by-products; these are formed through dealkylation and decarboxylation reactions initiated primarily by the photogenerated holes. Estrogenicity assays showed that methyl paraben was more estrogenic than EP; however, parabens are slightly estrogenic compared to 17ß-estradiol.

Kinetics of ethyl paraben degradation by simulated solar radiation in the presence of N-doped TiO2 catalysts.

Ethyl paraben (EP), an emerging micro-pollutant representative of the parabens family, has been subject to photocatalytic degradation under simulated solar radiation at a photon flux of 1.3·10(-4) E/(m(2) s). Six nitrogen-doped titania catalysts synthesized by annealing a sol-gel derived TiO2 powder under ammonia flow and their un-doped counterparts, calcined in air at different temperatures in the range 450-800 °C, were compared under solar and visible light and the most active one (N-doped TiO2 calcined at 600 °C) was used for further tests. Experiments were performed at EP concentrations between 150 and 900 µg/L, catalyst loadings between 100 and 1000 mg/L, pH between 3 and 9, different matrices (ultrapure water, water spiked with humic acids or bicarbonates, drinking water and secondary treated wastewater) and hydrogen peroxide between 10 and 100 mg/L. For EP concentrations up to 300 µg/L, the degradation rate can be approached by first order kinetics but then shifts to lower order as the concentration increases. The rate increases linearly with catalyst loading up to 750 mg/L and hydrogen peroxide up to 100 mg/L. Near-neutral (pH = 6.5-7.5) and alkaline conditions (pH = 9) do not affect degradation, which is reduced at acidic pH. The presence of humic acids at 10-20 mg/L impedes degradation due to the competition with EP for the oxidizing species and this is more pronounced in actual wastewater matrices. UPLC-ESI-HRMS and HPLC-DAD were employed to follow EP concentration changes, as well as identify and quantify transformation by-products during the early stages of the reaction. Five such products were successfully detected and, based on their concentration-time profiles, a reaction network for the degradation of EP is proposed. Hydroxyl radical reactions appear to prevail during the initial steps as evidenced by the rapid formation of hydroxylated and dealkylated intermediates.