Heterogeneous Fenton-like reactions in natural soils and sediments at neutral pH with O2 as oxidant

International audienceHeterogeneous Fenton-like processes using O2 as oxidant and iron(II) minerals as substrate is a rapidly growing research field with important implications especially for in-situ organic pollutant degradation in natural media. These reactions can be conducted at neutral pH and several minerals are considered such as iron oxides [1], sulfides and clays. Autochthonous soil minerals have been also proposed as putative substrates for such heterogeneous Fenton-like reactions. However, the identity and efficiency of the reactive species produced upon air-oxidation reactions is still debated and may also depend on the mineral involved as well as on physicochemical conditions.We will present new spectroscopic results focusing on the identity and origin of reactive species produced upon oxygenation of a variety of natural soils and sediments at neutral pH. The air-oxidation protocol was performed on samples collected under anoxic conditions to preserve the reactivity of Fe(II) phases and X-ray absorption spectroscopy was used to monitor the changes in Fe speciation during the oxidation. Electron Paramagnetic Resonance (EPR) spin-trapping was used to investigate the identity and quantity of radicals yielded by these natural samples in the same air-oxidation experiments. Although hydroxyl radical was identified, our results yield strong evidences for the implication of another reactive species able to produce alkyl radicals in the presence of alcohols. Based on its significant dependence on the presence of Fe(II)-complexing ligands, this species is interpreted as the high-valent iron species Fe(IV) [2].[1] Ardo et al. Oxidative Degradation of Nalidixic Acid by Nano-Magnetite via Fe2+/O2-Mediated Reactions (2015), Environ. Sci. Technol. 49 (7), 4506–4514.[2] Morin et al. Phosphate boosts non-hydroxyl radical species production upon air-oxidation of magnetite and iron-sulfides at neutral pH. Submitted to The Journal of Physical Chemistry

Heterogeneous Fenton-like reactions in natural soils and sediments at neutral pH with O2 as oxidant

International audienceHeterogeneous Fenton-like processes using O2 as oxidant and iron(II) minerals as substrate is a rapidly growing research field with important implications especially for in-situ organic pollutant degradation in natural media. These reactions can be conducted at neutral pH and several minerals are considered such as iron oxides [1], sulfides and clays. Autochthonous soil minerals have been also proposed as putative substrates for such heterogeneous Fenton-like reactions. However, the identity and efficiency of the reactive species produced upon air-oxidation reactions is still debated and may also depend on the mineral involved as well as on physicochemical conditions.We will present new spectroscopic results focusing on the identity and origin of reactive species produced upon oxygenation of a variety of natural soils and sediments at neutral pH. The air-oxidation protocol was performed on samples collected under anoxic conditions to preserve the reactivity of Fe(II) phases and X-ray absorption spectroscopy was used to monitor the changes in Fe speciation during the oxidation. Electron Paramagnetic Resonance (EPR) spin-trapping was used to investigate the identity and quantity of radicals yielded by these natural samples in the same air-oxidation experiments. Although hydroxyl radical was identified, our results yield strong evidences for the implication of another reactive species able to produce alkyl radicals in the presence of alcohols. Based on its significant dependence on the presence of Fe(II)-complexing ligands, this species is interpreted as the high-valent iron species Fe(IV) [2].[1] Ardo et al. Oxidative Degradation of Nalidixic Acid by Nano-Magnetite via Fe2+/O2-Mediated Reactions (2015), Environ. Sci. Technol. 49 (7), 4506–4514.[2] Morin et al. Phosphate boosts non-hydroxyl radical species production upon air-oxidation of magnetite and iron-sulfides at neutral pH. Submitted to The Journal of Physical Chemistry

Heterogeneous Fenton-like reactions in natural soils and sediments at neutral pH with O2 as oxidant

International audienceHeterogeneous Fenton-like processes using O2 as oxidant and iron(II) minerals as substrate is a rapidly growing research field with important implications especially for in-situ organic pollutant degradation in natural media. These reactions can be conducted at neutral pH and several minerals are considered such as iron oxides [1], sulfides and clays. Autochthonous soil minerals have been also proposed as putative substrates for such heterogeneous Fenton-like reactions. However, the identity and efficiency of the reactive species produced upon air-oxidation reactions is still debated and may also depend on the mineral involved as well as on physicochemical conditions.We will present new spectroscopic results focusing on the identity and origin of reactive species produced upon oxygenation of a variety of natural soils and sediments at neutral pH. The air-oxidation protocol was performed on samples collected under anoxic conditions to preserve the reactivity of Fe(II) phases and X-ray absorption spectroscopy was used to monitor the changes in Fe speciation during the oxidation. Electron Paramagnetic Resonance (EPR) spin-trapping was used to investigate the identity and quantity of radicals yielded by these natural samples in the same air-oxidation experiments. Although hydroxyl radical was identified, our results yield strong evidences for the implication of another reactive species able to produce alkyl radicals in the presence of alcohols. Based on its significant dependence on the presence of Fe(II)-complexing ligands, this species is interpreted as the high-valent iron species Fe(IV) [2].[1] Ardo et al. Oxidative Degradation of Nalidixic Acid by Nano-Magnetite via Fe2+/O2-Mediated Reactions (2015), Environ. Sci. Technol. 49 (7), 4506–4514.[2] Morin et al. Phosphate boosts non-hydroxyl radical species production upon air-oxidation of magnetite and iron-sulfides at neutral pH. Submitted to The Journal of Physical Chemistry

Influence of the Preparation Procedure of Vanadium-Containing SiBEA Zeolites on Their Catalytic Activity in Propene Epoxidation

Two series of V-containing BEA zeolite catalysts, V<i>_x</i>SiBEA­(I) and V<i>_x</i>SiBEA­(II), were prepared by a two-step postsynthesis preparation procedure which consists, in the first step, in the dealumination of TEABEA zeolites by a treatment with nitric acid solution to obtain SiBEA zeolites with a Si/Al atomic ratio of 1000 and then, in the second step, in bringing SiBEA into contact with an aqueous NH₄VO₃ solution with different concentrations at a pH of 2.7. After 3 days, the solids were recuperated from the reaction mixtures: (1) on a sinter funnel and washed several times with distilled water to obtain the V<i>_x</i>SiBEA­(I) series and (2) in a rotating evaporator under vacuum via a membrane pump to obtain the V<i>_x</i>SiBEA­(II) series. The combined use of H₂-temperature-programmed reduction, diffuse reflectance (DR) UV–vis, Fourier transform infrared (FTIR), ⁵¹V magic-angle spinning (MAS) NMR, electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy allows determining the nature and environment of vanadium in both series of V-containing SiBEA zeolites after different treatments. The characterization of V<i>_x</i>SiBEA­(I) and V<i>_x</i>SiBEA­(II) series reveals the formation of various forms of vanadium species depending on the V content and conditions applied upon preparation of each series of V-containing SiBEA zeolites. As evidenced by DR UV–vis and ⁵¹V MAS NMR in the V<i>_x</i>SiBEA­(I) series, vanadium was present mainly as mononuclear framework pseudo-tetrahedral V­(V) species. In contrast, in the V<i>_x</i>SiBEA­(II) series, vanadium was present as mononuclear framework pseudo-tetrahedral and polynuclear extra-framework pseudo-octahedral V­(V) species. As shown by EPR, the oxidation state of V species easily changes upon calcinations in oxygen, outgassing under vacuum at 773 K and treatment with hydrogen at a high temperature (873 K). The presence of Brønsted and Lewis acidic centers was evidenced in both V<i>_x</i>SiBEA­(I) and V<i>_x</i>SiBEA­(II) series by FTIR spectroscopy with pyridine used as a probe molecule. The catalytic activity tests in propene epoxidation revealed that the highly dispersed mononuclear framework pseudo-tetrahedral V­(V) species are responsible for high selectivity to propene oxide, whereas polynuclear extra-framework pseudo-octahedral V­(V) species catalyzed mainly total oxidation. The V<i>_x</i>SiBEA­(I) series of catalysts with vanadium, present mainly as mononuclear framework pseudo-tetrahedral V­(V) species, show lower turn over frequency values than the V<i>_x</i>SiBEA­(II) series in which vanadium is present as both mononuclear framework pseudotetrahedral V­(V) species and polynuclear extra-framework pseudo-octahedral V­(V). It thus demonstrates that apart from highly dispersed isolated vanadium species, the availability of vanadium species to reagents also plays an important role in the gas-phase propene epoxidation