Elimination des NOx issus de sources fixes (réduction par les hydrocarbures en C3 en présence de SO2)

Ce travail a consisté à étudier la réduction des NOx par les hydrocarbures en C3 afin d'examiner l'influence du SO2 sur des catalyseurs à base de métaux nobles dans le domaine de température 200- 400C en présence de CO2, H2O et en excès d'oxygène. L'étude en fonction de la richesse du milieu montre que la conversion des NOx est totale à la stœchiométrie en absence de SO2 et que le catalyseur à base de Pt/ZrAl est le plus résistant au soufre. Les performances de divers métaux (Pt, Pd, Rh, Ag, Ir, Sn) supportés sur différents oxydes (Al, K-Al, Ce-Al, Ti-Al, Zr-Al, Ce-Zr, Si, C) en réduction des NOx par le propène (1000ppm) ont montré que le catalyseur Pt/ZrAl est le plus actif. La pré-sulfatation des catalyseurs augmente généralement leur activité en présence de SO2 et diminue la sélectivité en N2O. Enfin une disparition de NO a été observée en présence de propane et absence de ce réducteur. Ceci est lié à la formation d'acide nitrique via la formation de NO2 et non à la réduction des NOx.In the present work the NOx reduction with C3 hydrocarbons has been examined. The objective is to study the influence of SO2 on metal based catalysts with an oxygen excess in the presence of CO2 and H2O, in a temperature range from 200 to 400 C. The NOx are totally converted under stoechiometric conditions in the absence of sulfur dioxide and the most sulfur resistant catalyst is Pt/ZrAl. A series of different metals (Pt, Pd, Rh, Ag, Ir, Sn ) supported on several oxides (Al, , K-Al, Ce-Al, Ti-Al, Zr-Al, Ce-Zr, Si, C) were tested for NOx reduction with 1000 ppm propylene and the Pt/ZrAl was found to be the most active catalyst. The sulfation of the catalysts, generally leads to an increase of their activity in the presence of SO2, and conversely to a decrease of the N2O selectivity. Finally, the NO consumption has been observed in both the presence and the absence of propane. This phenomenon has been associated with the nitric acid formation via NO oxidation and not with NOx reduction.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

TET2-mediated 5-hydroxymethylcytosine induces genetic instability and mutagenesis

International audienceThe family of Ten-Eleven Translocation (TET) proteins is implicated in the process of active DNA demethy-lation and thus in epigenetic regulation. TET 1, 2 and 3 proteins are oxygenases that can hydroxylate 5-methylcytosine (5-mC) into 5-hydroxymethylcytosine (5-hmC) and further oxidize 5-hmC into 5-formylcytosine (5-fC) and 5-carboxylcytosine (5-caC). The base excision repair (BER) pathway removes the resulting 5-fC and 5-caC bases paired with a guanine and replaces them with regular cytosine. The question arises whether active modification of 5-mC residues and their subsequent elimination could affect the genomic DNA stability. Here, we generated two inducible cell lines (Ba/F3-EPOR, and UT7) over-expressing wild-type or catalytically inactive human TET2 proteins. Wild-type TET2 induction resulted in an increased level of 5-hmC and a cell cycle defect in S phase associated with higher level of phospho-rylated P53, chromosomal and centrosomal abnormalities. Furthermore, in a thymine-DNA glycosylase (Tdg) deficient context, the TET2-mediated increase of 5-hmC induces mutagenesis characterized by GC > AT transitions in CpG context suggesting a mutagenic potential of 5-hmC metabolites. Altogether, these data suggest that TET2 activity and the levels of 5-hmC and its derivatives should be tightly controlled to avoid genetic and chromosomal instabilities. Moreover, TET2-mediated active demethylation might be a very dangerous process if used to entirely demethylate the genome and might rather be used only at specific loci