Oxygen

About: Oxygen is a research topic. Over the lifetime, 48149 publications have been published within this topic receiving 1113788 citations. The topic is also known as: O & Oxygen.

Designed oxygen carriers from macroporous LaFeO3 supported CeO2 for chemical-looping reforming of methane

Abstract: Chemical-looping reforming of methane (CLRM) offers an effective approach for coproducing syngas and pure hydrogen. In this work, CeO2 nano particles (2–3 nm) are well dispersed on the wall surface of three-dimensional ordered macroporous (3DOM) LaFeO3, obtaining a highly efficient oxygen carrier for the CLRM technology. The physical and chemical properties of the oxygen carriers were characterized by SEM, TEM, H2-TPR, XPS, XRD, CH4-TPR and CH4-TPD techniques. It is found that the presence of CeO2 on LaFeO3 results in the formation of Ce3+ and Fe2+ due to the CeO2-LaFeO3 interaction. The coexistence of Ce3+ and Fe2+ irons induces abundant oxygen vacancies on the mixed oxides, which strongly improves the reducibility, oxygen mobility and reactivity for methane oxidation. The presence of CeO2 also improves the resistance towards carbon deposition formation, and this allows the CeO2/LaFeO3 materials own high available oxygen storage capacity (available OSC, the maximum amount of oxygen consumed by methane reduction without the formation of carbon deposition). It is also noted that the agglomeration of CeO2 nano particles would reduce the reactivity of oxygen carriers. Among all the obtained samples, the 10% CeO2/LaFeO3 sample exhibits the highest yields of syngas (9.94 mmol g−1) and pure hydrogen (3.38 mmol g−1) without the formation of carbon deposition, which are much higher than that over the pure LaFeO3 sample (5.73 mmol g−1 for syngas yield and 2.00 mmol g−1 for hydrogen yield). In addition, the CeO2/LaFeO3 oxygen carrier also showed high stability during the successive CLRM testing either in the activity (yields of syngas and pure hydrogen) or structure (macroporous frameworks) aspect.

On the Reasons for High Activity of CeO2 Catalyst for Soot Oxidation

Abstract: The present work has demonstrated the reasons why CeO2 becomes an active catalyst for diesel particulate (soot) abatement, which attracts recent worldwide attention in the development of clean diesel automobiles. Four typical fluorite-type oxides, CeO2, ZrO2, Pr6O11, and a CeO2−ZrO2 solid solution have been studied as model catalysts for soot oxidation in conjunction with the redox property and the reactivity of solid oxygen species. It was found that the redox property measured in terms of oxygen storage/release capacity was not the sole determining factor for the observed catalytic activity decreasing in the order of CeO2 ≫ Pr6O11 ≈ CeO2−ZrO2 > ZrO2. The reactivity of oxygen species involved in the redox cycles would rather be important. The ESR measurement showed that admission of O2 to the pre-reduced CeO2 surface generated superoxide ions (O2−). Such reactive oxygen species were less abundant on CeO2−ZrO2 and were not detected on ZrO2 and Pr6O11. The labeled and unlabeled O2 pulse experiments demonst...

Adsorption of sulfur dioxide on hematite and goethite particle surfaces

Abstract: The adsorption of sulfur dioxide (SO2) on iron oxide particle surfaces at 296 K has been investigated using X-ray photoelectron spectroscopy (XPS). A custom-designed XPS ultra-high vacuum chamber was coupled to an environmental reaction chamber so that the effects of adsorbed water and molecular oxygen on the reaction of SO2 with iron oxide surfaces could be followed at atmospherically relevant pressures. In the absence of H2O and O2, exposure of hematite (α-Fe2O3) and goethite (α-FeOOH) to SO2 resulted predominantly in the formation of adsorbed sulfite (SO32−), although evidence for adsorbed sulfate (SO42−) was also found. At saturation, the coverage of adsorbed sulfur species was the same on both α-Fe2O3 and α-FeOOH as determined from the S2p : Fe2p ratio. Equivalent saturation coverages and product ratios of sulfite to sulfate were observed on these oxide surfaces in the presence of water vapor at pressures between 6 and 18 Torr, corresponding to 28 to 85% relative humidity (RH), suggesting that water had no effect on the adsorption of SO2. In contrast, molecular oxygen substantially influenced the interactions of SO2 with iron oxide surfaces, albeit to a much larger extent on α-Fe2O3 relative to α-FeOOH. For α-Fe2O3, adsorption of SO2 in the presence of molecular oxygen resulted in the quantitative formation of SO42− with no detectable SO32−. Furthermore, molecular oxygen significantly enhanced the extent of SO2 uptake on α-Fe2O3, as indicated by the greater than two-fold increase in the S2p : Fe2p ratio. Although SO2 uptake is still enhanced on α-Fe2O3 in the presence of molecular oxygen and water, the enhancement factor decreases with increasing RH. In the case of α-FeOOH, there is an increase in the amount of SO42− in the presence of molecular oxygen, however, the predominant surface species remained SO32− and there is no enhancement in SO2 uptake as measured by the S2p : Fe2p ratio. A mechanism involving molecular oxygen activation on oxygen vacancy sites is proposed as a possible explanation for the non-photochemical oxidation of sulfur dioxide on iron oxide surfaces. The concentration of these sites depends on the exact environmental conditions of RH.