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► IR spectra of Pt/ceria model catalysts monitor various surface sites. ► Regular and defect sites are identified. ► Metal-support interactions and oxygen spillover is probed.
...Vibrational spectroscopy of adsorbed CO is commonly used for the characterization of oxide-supported metal catalysts, in spite of persisting ambiguities concerning the band assignment. Here, we present reference data on well-defined Pt/CeO2(111)/Cu(111) model catalysts aiming at clear identification of the related features. Growth and morphology of the Pt particles are investigated by scanning tunneling microscopy (STM), the adsorption properties are probed by temperature programmed desorption (TPD), and the electronic structure has previously been studied by photoelectron spectroscopy (PES) and resonant photoelectron spectroscopy (RPES). Combining molecular beam (MB) methods and infrared reflection absorption spectroscopy (IRAS), we correlate this information to the interaction with CO.
Two types of defect adsorption sites are identified on the ceria support (2097cm−1, 2120cm−1), which are assigned to structural defects and reduced Ce3+ centers. The relative abundance of these sites changes upon thermal treatment. On the Pt nanoparticles, CO first adsorbs on-top at step and edge sites (2066cm−1), before adsorption on the (111) facets occurs in bridging (1875cm−1) and on-top (2080–2097cm−1) geometry. For the first time, we identify vibrational CO features, which arise from electronic metal-support interactions and from oxygen reverse spillover. On reduced CeO2−x(111), a red-shifted band at 2053cm−1 appears, which is attributed to increased π-backbonding from Pt to CO, as a result of a change in electronic metal-oxide interaction. Thermal treatment also activates oxygen reverse spillover from the support to the Pt nanoparticle, which gives rise to a blue-shifted feature in the CO spectrum (2090–2105cm−1) due to coadsorbed oxygen next to CO sites.
Adjustable morphology and degree of reduction represent desirable properties of model oxide substrates for heterogeneous catalysis. We investigate these properties in CeO2 (ceria) thin films on ...Cu(111) using scanning tunneling microscopy and photoelectron spectroscopy. We identify growth mechanisms of ceria on Cu(111): formation of incomplete oxide interfacial layer and formation of three-dimensional ceria pyramids by stacking of monolayer-high islands. Using these mechanisms, we control the coverage, the number of open monolayers, and the step density of ceria thin films on Cu(111). Annealing in vacuum allows us to control besides the morphology also the degree of ceria surface reduction. We find a correlation between surface reduction and morphological stability in annealed ceria layers. Oriented and stoichiometric thin films of ceria on Cu(111) can be prepared at temperatures as low as 150 and 250 °C. Both the morphology and the surface reduction of these films readily change with increasing temperature, which must be accounted for in considering temperature-programmed experiments with ceria on Cu(111).
Interaction of water with fully oxidized and partially reduced CeO₂(111) thin film model catalyst grown on a Cu(111) surface was investigated by photoelectron spectroscopy (PES), scanning tunneling ...microscopy (STM) and temperature programmed desorption (TPD). On the stoichiometric surface water adsorbs molecularly at low temperatures (≤120K) while on the reduced surface the adsorption is partially dissociative with formation of OH groups. STM indicates no morphology variation and a very sensitive Ce 4d–4f resonant photoelectron spectroscopy (RPES) no noticeable change of the oxidation state of ceria upon water adsorption and subsequent complete desorption. Formation of co-adsorbed phase of residual water with OH during molecular water desorption, on the other hand, leads to a substantial resonance of the Ce³⁺ photoemission state around 170K. We propose that this behaviour indicating ceria reduction is in this case an electronic effect of the Ce 4f charge accumulation and Ce 5d charge depletion.
Hypoxia is one of the major pathological factors affecting brain function. The aim of the present study was to describe the effect of neonatal hypobaric hypoxia on the behavior of rats and to analyze ...its effect on hippocampal neurodegeneration. Hypobaric hypoxia at a simulated altitude of 9000 m was induced for one hour in neonatal rat pups (PND7 and PND9) of both sexes. Subsequently, the rats underwent behavioral testing on PND25 and PND35 using a LABORAS apparatus to assess spontaneous behavior. Hypoxia did not cause any morphological damage in the hippocampus of rats. However, hypoxia on PND7 led to less horizontal locomotor activity both, in males (on PND25) and females (on PND35). Hypoxia on PND9 led to higher rearing in females on PND25. Hypoxic males exhibited higher grooming activity, while females lower grooming activity on PND35 following hypoxia induced on PND7. In females, hypoxia on PND9 resulted in higher grooming activity on PND25. Sex differences in the effect of hypoxia was observed on PND35, when hypoxic males compared to hypoxic females displayed more locomotor, rearing and grooming activity. Our data suggest that hypoxia on PND7 versus PND9 differentially affects locomotion and grooming later in adolescence and these effects are sex-dependent.
Laboratory mice in standard laboratory cages, besides horizontal and vertical locomotor activity, spontaneously display cage-bar related activities such as cage-grid climbing. Although, grid-climbing ...activity is one of the major components of spontaneous home-cage behavior of mice, its exact role is not fully understood. This study aimed to describe the sex-differences in coping with novelty and in spontaneous behavior of laboratory mice concerning the cage-climbing activity in an observer-independent open field test. Adult mice of both sexes (C57Bl/6NTac) underwent behavioral testing in LABORAS system. Female mice travelled significantly longer distance (by 30 %, p<0.05) and showed higher grid-climbing activity (by 50 %, p<0.05) than males. Based on our results, the grid-climbing is a sex-dependent activity of mice, however, its exact role remains to be elucidated.
Hypoxic-ischemic encephalopathy (HIE) is a neonatal condition that occurs as a consequence of perinatal asphyxia, which is caused by a number of factors, commonly via compression of the umbilical ...cord, placental abruption, severe meconium aspiration, congenital cardiac or pulmonary anomalies and birth trauma. Experimental studies have confirmed that male rat pups show a higher resistance to HIE treatment. Moreover, the long-term consequences of hypoxia in male are more severe in comparison to female rat pups. These sex differences can be attributed to the pathophysiology of hypoxia-ischemia, whereby studies are beginning to establish such gender-specific distinctions. The current and sole treatment for HIE is hypothermia, in which a reduction in temperature prevents long-term effects, such as cerebral palsy or seizures. However, in most cases hypothermia is not a sufficient treatment as indicated by a high mortality rate. In the present review, we discuss the gender differences within the pathophysiology of hypoxia-ischemia and delve into the role of gender in the incidence, progression and severity of the disease. Furthermore, this may result in the development of potential novel treatment approaches for targeting and preventing the long-term consequences of HIE.
A scanning tunneling microscopy/atomic force microscopy study is presented of a kinetically driven growth instability, which leads to the formation of ripples during Si homoepitaxy on slightly ...vicinal Si(0
0
1) surfaces miscut in 1
1
0 direction. The instability is identified as step bunching, that occurs under step-flow growth conditions and vanishes both during low-temperature island growth and at high temperatures. We demonstrate, that the growth instability with the same characteristics is observed in two dimensional kinetic Monte Carlo simulation with included Si(0
0
1)-like diffusion anisotropy. The instability is mainly caused by the interplay between diffusion anisotropy and the attachment/detachment kinetics at the different step types on Si(0
0
1) surface. This new instability mechanism does not require any additional step edge barriers to diffusion of adatoms. In addition, the evolution of ripple height and periodicity was analyzed experimentally as a function of layer thickness. A lateral “ripple-zipper” mechanism is proposed for the coarsening of the ripples.
Neonatal exposure to hyperoxia alters lung development in mice. We tested if retinoic acid (RA) treatment is capable to affect lung development after hyperoxic injury and to maintain structural ...integrity of lung. The gene of vascular endothelial growth factor A (VEGF-A) is one of the RA-responsive genes. Newborn BALB/c mice were exposed to room air, 40% or 80% hyperoxia for 7 days. One half of animals in each group received 500 mg/kg retinoic acid from day 3 to day 7 of the experiment. At the end of experiment we assessed body weight (BW), lung wet weight (LW), the wet-to-dry lung weight ratio (W/D) and the expression of mRNA for VEGF-A and G3PDH genes. On day 7 the hyperoxia-exposed sham-treated mice (group 80) weighed 20% less than the room air-exposed group, whereas the 80% hyperoxic group treated with RA weighed only 13% less than the normoxic group. W/D values in 80 and 80A groups did not differ, although they both differed from the control group and from 40 groups. There was a significant difference between 40 and 40A groups, but the control group was different from 40 group but not from 40A groups. The 80 and 80A groups had mRNA VEGF-A expression lowered to 64% and 41% of the control group. RA treatment of normoxic and mild hyperoxic groups increased mRNA VEGF-A expression by about 50%. We conclude that the retinoic acid treatment of newborn BALB/c mice exposed for 7 days to 80% hyperoxia reduced the growth retardation in the 80 % hyperoxic group, reduced the W/D ratio in the 40% but not in the 80 % hyperoxic group. Higher VEGF-A mRNA expression in the 80% hyperoxic group treated with RA was not significant compared to the 80% hyperoxic group.
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