M. Chevrier

Diesel exhaust particles are taken up by human airway epithelial cells in vitro and alter cytokine production

The involvement of diesel exhaust particles (DEPs) in respiratory diseases was evaluated by studying their effects on two in vitro models of human airway epithelial cells. The cytotoxicity of DEPs, their phagocytosis, and the resulting immune response were investigated in a human bronchial epithelial cell line (16HBE14o-) as well as in human nasal epithelial cells in primary culture. DEP exposure induced a time- and dose-dependent membrane damage. Transmission electron microscopy showed that DEPs underwent endocytosis by epithelial cells and translocated through the epithelial cell sheet. Flow cytometric measurements allowed establishment of the time and dose dependency of this phagocytosis and its nonspecificity with different particles (DEPs, carbon black, and latex particles). DEPs also induced a time-dependent increase in interleukin-8, granulocyte-macrophage colony-stimulating factor, and interleukin-1beta release. This inflammatory response occurred later than phagocytosis, and its extent seems to depend on the content of adsorbed organic compounds because carbon black had no effect on cytokine release. Furthermore, exhaust gas posttreatments, which diminished the adsorbed organic compounds, reduced the DEP-induced increase in granulocyte-macrophage colony-stimulating factor release. These results suggest that DEPs could 1) be phagocytosed by airway epithelial cells and 2) induce a specific inflammatory response.The involvement of diesel exhaust particles (DEPs) in respiratory diseases was evaluated by studying their effects on two in vitro models of human airway epithelial cells. The cytotoxicity of DEPs, their phagocytosis, and the resulting immune response were investigated in a human bronchial epithelial cell line (16HBE14o-) as well as in human nasal epithelial cells in primary culture. DEP exposure induced a time- and dose-dependent membrane damage. Transmission electron microscopy showed that DEPs underwent endocytosis by epithelial cells and translocated through the epithelial cell sheet. Flow cytometric measurements allowed establishment of the time and dose dependency of this phagocytosis and its nonspecificity with different particles (DEPs, carbon black, and latex particles). DEPs also induced a time-dependent increase in interleukin-8, granulocyte-macrophage colony-stimulating factor, and interleukin-1β release. This inflammatory response occurred later than phagocytosis, and its extent seems to depend on the content of adsorbed organic compounds because carbon black had no effect on cytokine release. Furthermore, exhaust gas posttreatments, which diminished the adsorbed organic compounds, reduced the DEP-induced increase in granulocyte-macrophage colony-stimulating factor release. These results suggest that DEPs could 1) be phagocytosed by airway epithelial cells and 2) induce a specific inflammatory response.

Nitrogen dioxide effect in the reduction of nitric oxide by propane in oxidizing atmosphere

The role of nitrogen dioxide in the selective reduction of NO by propane over a Cu-MFI zeolite is investigated. NO2 and NO reductions were carried out under similar conditions of reaction. In the presence of oxygen, the reduction of NO by C3H8 does not differ significantly from that of NO2. In the absence of oxygen, the reduction of NO2 by propane occurs with a partial decomposition of the nitric dioxide molecule. Such a decomposition leads to the formation of oxygen, which is responsible for the increase in catalytic activity by comparison with the same reaction performed with NO. NO2 formed and released in the gas phase during the reduction of NO by propane in the presence of oxygen does not play a predominant role in the catalytic process.

Magnetic study of the interaction of hydrogen with a Pt/CeO2–Al2O3 catalyst: influence of the presence of chlorine

Abstract The influence of a chlorinated precursor on the redox properties of ceria was studied by comparing two Pt/CeO2–Al2O3 catalysts prepared from hexachloroplatinic acid and platinum acetylacetonate. In absence of chlorine, a dispersion value higher than 100% has been measured by irreversible hydrogen chemisorption. To interpret this result, the interaction of H2 with the support and the two catalysts were studied by magnetic measurements. The variations of the Ce3+ content have given evidence that different redox processes may occur. The hydrogen spillover is clearly observed in presence of platinum with the phenomenon being more pronounced for the ex-acetylacetonate catalyst. The limited amount of hydrogen irreversibly adsorbed at 294xa0K on the support for this free chlorine reduced catalyst is sufficient to explain the excessive value obtained for the platinum dispersion. The results show a fixation of chlorine on the supported ceria phase which inhibits the mobility of hydroxyl species responsible for the hydrogen spillover. Moreover, independently to the presence of chlorine, a reduction at 573xa0K seems to stabilise a significant fraction of Ce3+ ions against reoxidation under air at room temperature. This was not the case for bulk ceria and probably originates from ceria/alumina interactions occurring after reduction.

Preparation of alumina supported ceria. I: Selective measurement of the surface area of ceria and free alumina

In a general study of the role played by each component of three-way catalysts, a selective measurement of alumina and ceria surfaces area has been developed on model ceria-alumina supports. Three CeO2/Al2O3 solids (6.5, 13.4, 21 wt.% CeO2) were prepared by grafting Ce acetylacetonate on the surface of an alumina and calcination at 673 K. They were characterized by BET and X-ray diffraction measurements. The hydrogen temperature-programmed reduction (TPR) resulted in profiles similar to those of unsupported cerias, thus allowing an estimation of the equivalent surface area of ceria alone from the hydrogen uptake at low temperature. By adsorbing CO2 on the OH groups of the alumina surface, hydrogenocarbonates species were formed and the IR band at 1235 cm−1 was selected to determine quantitatively the unpertubed alumina surface. In that case, by comparison with the BET surface area, it was possible to deduce an other value of the ceria surface area. The two sets of values obtained by these independent methods were found in good agreement, thus giving a good support for the reliability of each method. They show that the unpertubed alumina surface decreases when increasing the cerium content. Only 20% of the original alumina surface is preserved in the support containing 21 wt.% CeO2.

Evolution of the ceria surface area of PtRh ceria-alumina catalysts submitted to hydrothermal aging at 1273 K

The accessible surface area of cerium oxide was measured on model ceria-alumina supported Pt and/or Rh catalysts submitted to an hydrothermal treatment at 1273 K (10% H2O in N2). Two distinct methods, developed for fresh catalysts, were utilized. They are based respectively on the hydrogen temperature programmed reduction (TPR) profiles and the infrared spectra of the specific adsorption of CO2 on the hydroxyl groups of alumina. After aging, the TPR curves have become flattened and it is difficult to have a good reliability in the deconvolution of the peak corresponding to the ceria surface reduction. On the support alone, the results of both methods are in agreement and indicate a decrease of the ceria surface area by a factor close to 4, whereas the total surface area is only divided by 2. It appears that cerium oxide sinters more rapidly than alumina. For the metallic catalysts, the calculated ceria surface areas values depend on the hypothesis done on the oxidation state of the precious metals before the TPR. If reliable results can be obtained in the case of rhodium with ORh=1.5, in presence of platinum, the mean oxidation state of platinum OPt=1 results in underestimated values. The ceria surface areas deduced from the infrared results are higher than those deduced from TPR. Although the former are uncertain, they are in good agreement with a lower coverage of the alumina surface by sintered cerium oxide particles.

Influence of the activation temperature on the metal accessibility in model three-way catalysts

Abstract The influence of the reduction temperature on the accessibility of the metallic surface was studied on model ceria-alumina supported platinum or rhodium catalysts. For a 0.5% Pt-Ce/Al solid, the H M values, deduced from hydrogen irreversible chemisorption, decrease deeply with Tr, the reduction temperature, from 60% at Tr = 300°C to 19% at Tr = 500°C. This can be attributed to strong interactions between ceria and platinum, since, the initial H2 chemisorption could be restored after reoxidation. The presence of BaSO4 in the support accelerates the loss of metallic area, because of sulfur poisoning of the platinum surface. For Tr = 300°C, the dispersion values were in agreement with those deduced from FTIR spectroscopy of adsorbed CO. In the case of rhodium, a 37% H/M dispersion was obtained, which did not change when Tr was increased from 300 to 500°C. For two industrial Pt-Rh three-way catalysts, the behaviour was found similar to that of platinum, the amount of chemisorbed hydrogen decreasing for Tr > 350°C. Thus, in the three-way catalysts characterization, the maximum metal accessibility is obtained after a reduction at 300°C.

Measurement of the ceria surface area of a three-way commercial catalyst after laboratory and engine bench aging.

ABSTRACT The ceria surface area of a commercial Pt-Rh three-way catalyst was determined after laboratory hydrothermal aging at 1173-1373xa0K and after 200xa0h on engine bench. It was measured by X-ray diffraction (XRD) line broadening analysis and by a method based on the exploitation of the hydrogen temperature programmed reduction (TPR) profiles. In this case, the hydrogen uptakes below about 900xa0K include the ceria surface reduction and that of the oxidized noble metals. They are analyzed and discussed, assuming two possiblities for the metals oxidation state. Compared to the fresh catalyst, the TPR profiles are deeply modified by the aging treatments. The ceria seems to sinter more than alumina, particularly between 1173xa0K and 1273xa0K. After aging at 1273-1373xa0K, the calculated ceria surface area is only 15-10 m 2 g −xa01 washcoat, which represents 20% of the BET area, instead of 40% initially. A stabilization treatment at 823xa0K under reactants leads to an additional ceria sintering, even for the more aged system. Finally, the measurements on the engine bench aged catalysts seem to indicate a better resistance of ceria to sintering in working conditions. The presence of a pollutant layer, containing phosphorus, zinc and calcium, did not modify the accessible ceria surface area measured by TPR.

Selective reduction of nitrogen oxide with hydrocarbons and hydrothermal aging of Cu-ZSM-5 catalysts

This paper deals with the hydrothermal deactivation, under an air + 10 vol. % H 2 O mixture between 923 and 1173 K, of Cu-MFI solids, catalysts for the selective reduction of NO by propane. Fresh and aged solids were characterized by various techniques and compared with a parent H-ZSM-5 solid. The catalytic activities were measured in the absence and in the presence of water. The differences between fresh and aged Cu-ZSM-5 catalysts (destruction of the framework, extent of dealumination...) were shown to be small in spite of the strong decreases in activity. Cu-ZSM-5 is more resistant to dealumination than the parent H-ZSM-5 zeolite. The rate of NO reduction into N 2 increases with the number of isolated Cu 2+ /Cu + ions. These isolated ions partially migrate to inaccessible sites upon hydrothermal treatments. At very high aging temperatures a part of the copper ions agglomerates into CuO particles accessible to CO, but these bulk oxides are inactive. Under catalytic conditions and in the presence of water, dealumination is observed at a lower temperature (873 K) than under the (air + 10 % H 2 O) mixture, because of nitric acid formation linked to NO 2 which is either formed in the pipes of the apparatus or on the catalyst itself.

Influence of the copper dispersion on the selective reduction of nitric oxide over Cu/Al2O3: Nature of the active sites

Cu/Al2O3 solids with various Cu loadings, between 0.3 and 6.4 wt %, are used for the reduction of NO by propane in the absence and in the presence of oxygen (up to 10 vol. %) in the 423–773 K temperature range. At a given temperature and for high Cu loadings, the introduction of oxygen induces a decrease in the activity in nitrogen formation. For low Cu loadings the activity increases with the oxygen content in the 1–2 vol. % range, then slightly decreases for higher oxygen amounts. The nature of the Cu species accessible to CO and NO is determined by infrared spectroscopy. High Cu loadings favor the formation of bulk oxides at the surface of the support whereas low Cu loadings favor the formation of isolated Cu species. The selective reduction of NO is thus related to the presence of these isolated copper species easily reduced and reoxidized.

Change in the redox properties of PdRh/CeO2-ZrO2 catalysts after ageing at 1323 and 1423 K

Hydrogen chemisorption and temperature programmed reduction were used to study the modification of the redox properties of a PdRh/CeO 2 -ZrO 2 catalyst after ageing at 1323 and 1423 K. In presence of Pd or Rh, large quantities of hydrogen are adsorbed at 295 K on the fresh catalysts. However, after ageing, H 2 chemisorption strongly decreases for the palladium catalyst and is practically no more observed in presence of rhodium. The quantification of H 2 uptakes at 295 K and during the TPR peaks show that in presence of Pd and/or Rh, the under-layers oxygen atoms of the CeO 2 -ZrO 2 solid solution have a reactivity close to that of the surface oxygen atoms. The number of layers reduced at 870 K is the highest after ageing at 1423 K and with the PdRh catalyst. It suggests that the oxygen mobility in the bulk increases with increasing the ageing temperature and is promoted by the presence of precious metals.