Katalitička svojstva La1-ySryCr1-xRuxO3 perovskita u oksidaciji ugljenmonoksida

The oxidation of CO over La1-ySryCr1-xRuxO3 perovskite type oxides with y=0.3 and 0 £x £0.100 have been studied. X-ray fluorescence analysis confirmed that content of elements in the bulk corresponds to the established nominal perovskite stoichiometry, indicating that no significant oxidation of ruthenium into volatile polyvalent oxides with their consequent escape from the sample occurred in air up to the temperature of 1000 ºC. According to X-ray diffraction analysis, all samples achieved the perovskite hexagonal with the presence of some SrCrO4. X-ray photoelectron spectroscopy analysis of ruthenium samples shows higher Ru and Sr surface concentrations than in the bulk. The binding energy for Ru3p is virtually the same in all samples and consistent with that of Ru4+ (463.6.464.3eV). Kinetic studies were performed in a differential recycle reactor with a recycling ratio 80. The results show that substitution of Ru4+ for Cr3+ in La1-ySryCrO3 leads to a significant increase in both the activity and the activation energy. The global CO oxidation rate, referred on the BET surface area, correlates with the surface Ru4+ atomic concentration. Hence, the activity reflect the surface enrichment in ruthenium. Moreover, an identical apparent activation energy E = 93 kJ/mol and the same specific rate per ruthenium surface ion were obtained for samples with a Ru content x ‡ 0.05 suggest that exposed Ru4+ ions mainly participate in the reaction.Predmet ovog rada je ispitivanje katalitičke aktivnosti mešanih oksida La1-ySryCr1-xRuxO3 strukture perovskita sa y = 0,3 i 0,025 £ x £ 0,100 u oksidaciji ugljenmonoksida. Visoka saglasnost unete i X-fluoroscentnom analizom nađene količine rutenijuma u uzorcima kalcinisanim na 100ºC u vazduhu, ukazuje na to da nije došlo do značajne oksidacije Ru do isparljivih polivalentnih oksida i njihovog otparavanja iz uzorka. Analiza difraktograma X-zraka je pokazala da je u svim uzorcima pored perovskitne faze prisutan i manji udeo SrCrO4 faze. Koncentracije Sr i Ru u površinskim slojevima, izračunate iz X-fotoelektronske spektroskopije, su veće u odnosu na njihovu koncentraciju u masi. Energija veze Ru3p je ista za sve uzorke i karakteristična je za Ru4+. Kinetika oksidacije ugljenmonoksida ispitivana je u diferencijalnom recirkulacionom reaktoru. Rezultati pokazuju da delimična zamena Cr3+ sa Ru4+ u La1-ySryCrO3 dovodi do znatnog porasta aktivnosti i energije aktivacije. Ukupna brzina oksidacija CO, obračunata po jedinici specifične površine, je skoro proporcionalna porastu atomske koncentracije Ru4+ na površini uzorka, odnosno Rux ‡ 0,05 dobivena je ista prividna energija aktivacije od E = 93 kJ/mol i ista specifična brzina oksidacije po površinskom jonu Ru4+,što ukazuje na to da su joni Ru4+ izloženi i da oni prevashodno učestvuju u reakciji

Characterization and carbon monoxide oxidation activity of La1-ySryCr1-xRuxO3 perovskites

The oxidation of CO over La1-ySryCr1-xRuxO3 perovskite type oxides with y=0.3 and 0 £ x £ 0.100 have been studied. X-ray fluorescence analysis confirmed that content of elements in the bulk corresponds to the established nominal perovskite stoichiometry, indicating that no significant oxidation of ruthenium into volatile polyvalent oxides with their consequented escape from the sample occurred in air up to the temperature of 1000°C. According to X-ray diffraction analysis, all sampls achieved the perovskite hexagonal with the presence of some SrCrO4. X-ray photoelectron spectroscopy analysis of ruthenium samples shows higher Ru and Sr surface concentraitions than in the bulk. The binding energy for Ru3p is virtually the same in all samples and consistent with that of Ru4+ (463.6-464.3eV). Kinetic studies were performed in a differential recycle reactor with a recycling ratio 80. The results show that substitution of Ru4+ for Cr3+ in La1-ySryCrO3 leads to a significant increase in both the activity and the activation energy. The global CO oxidation rate, referred on the BET surface area, correlates with the surface Ru4+ atomic concentraiton. Hence, the activity reflect the surface enrichment in ruthenium. Moreover, an identical apparent activation energy E = 93 kJ/mol and the same specific rate per ruthenium surface ion were obtained for samples with a Ru content x ³ 0.05 suggest that exposed Ru4+ ions mainly participate in the reaction

LaMO3 (M = Mg, Ti, Fe) perovskite type oxides: Preparation, characterization and catalytic properties in methane deep oxidation

Two new series of perovskite-type oxides LaMO3 (M = Mg, Ti, Fe) with different ratio Mg/Fe (MF) and Ti/Fe (TF) in the B cation site were prepared by annealing the precursor, obtained by the mechanochemical activation (MCA) of constituent metal oxides, at 1000 degrees C in air. In addition, two closely related perovskites LaFeO3 (LF) and LaTi0.5Mg0.5O3 (TM (50:50)) were synthesized in the similar way. Using MCA method, perovskites were obtained in rather short time and at room temperature. The samples were characterized by X-ray powder diffraction (XRPD), Xray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), temperature programmed desorption of oxygen (TPD), Mossbauer spectroscopy, BET surface area measurements and tested in methane deep oxidation. According to XRPD analysis all synthesized samples are almost single perovskite phase, with trace amounts of La2O3 phase. Data of Mossbauer spectroscopy identify Fe 31 in octahedral coordination. The activity of perovskite in methane deep oxidation increases in the order TM (50:50) LT MF series LT TF series. Higher activity of TF samples in respect to MF with similar Fe content can be related to the structural characteristic., mainly to the presence of predominantly most labile oxygen species evidenced by TPD at lowest temperature of oxygen evaluation. In used experimental conditions, the Fe substituted perovskite are thermal stable up to the temperature of 850 degrees C. The stability of Fe active sites is probably the most important parameter responsible for thermal stability of perovskite, but the atomic surface composition also should be taken into account

¿Ángeles en la batalla?: Representaciones de la enfermera en Champourcin y Urraca Pastor durante la guerra civil española

Durante la Guerra Civil Espanola (1936-39), tanto en el bando republicano como en el sublevado numerosas mujeres se ofrecieron como voluntarias para cuidar a los heridos, incluso careciendo de experiencia previa en cuestiones sanitarias. En palabras de Mary Nash, en la retaguardia y en las trincheras la enfermería era uno de los ámbitos más importantes de la movilización femenina (Rojas 215). Esto explica que desde el inicio del conflicto bélico la figura de la enfermera se mitificara, creándose romances y carteles en torno a ella (Greene 128). En opinión de Miriam Basilio, la imagen de la enfermera en h España republicana, junto con otras figuras femeninas tradicionales como las madres o las costureras, sirvió para contrarrestar las ansiedades masculinas producidas por la presencia de mujeres en el frente o en las fábricas (34)