The results of core-level photoemission indicate that Ni-CeO 2 (111) surfaces with small or medium coverages of nickel are able to activate methane at 300 K producing adsorbed CH x and CO x (x = 2,3) groups. Calculations based on density-functional 1 theory predict relatively low activation energy of 0.6−0.7 eV for the cleavage of the first C−H bond in the adsorbed methane molecule. Ni and O centers of ceria work in a cooperative way in the dissociation of the C−H bond at room temperature where a low Ni loading is crucial for the catalyst activity and stability. The strong electronic perturbations in the Ni nanoparticles produced by the ceria support of varying nature such as stoichiometric and reduced, result in a drastic change in their chemical properties towards methane adsorption and dissociation as well as the DRM reaction. The coverage of Ni had a drastic effect on the ability of the system to dissociate methane and catalyze the dry reforming process.

The transformation of methane into methanol or higher alcohols at moderate temperature and pressure conditions is of great environmental interest and remains a challenge despite many efforts. Extended surfaces of metallic nickel are inactive for a direct CH → CHOH conversion. This experimental and computational study provides clear evidence that low Ni loadings on a CeO(111) support can perform a direct catalytic cycle for the generation of methanol at low temperature using oxygen and water as reactants, with a higher selectivity than ever reported for ceria-based catalysts. On the basis of ambient pressure X-ray photoemission spectroscopy and density functional theory calculations, we demonstrate that water plays a crucial role in blocking catalyst sites where methyl species could fully decompose, an essential factor for diminishing the production of CO and CO, and in generating sites on which methoxy species and ultimately methanol can form. In addition to water-site blocking, one needs the effects of metal-support interactions to bind and activate methane and water. These findings should be considered when designing metal/oxide catalysts for converting methane to value-added chemicals and fuels.

Studies with a series of metal/ceria(111) (metal=Co, Ni, Cu; ceria=CeO ) surfaces indicate that metal-oxide interactions can play a very important role for the activation of methane and its reforming with CO at relatively low temperatures (600-700 K). Among the systems examined, Co/CeO (111) exhibits the best performance and Cu/CeO (111) has negligible activity. Experiments using ambient pressure X-ray photoelectron spectroscopy indicate that methane dissociates on Co/CeO (111) at temperatures as low as 300 K-generating CH and CO species on the catalyst surface. The results of density functional calculations show a reduction in the methane activation barrier from 1.07 eV on Co(0001) to 0.87 eV on Co /CeO (111), and to only 0.05 eV on Co /CeO (111). At 700 K, under methane dry reforming conditions, CO dissociates on the oxide surface and a catalytic cycle is established without coke deposition. A significant part of the CH formed on the Co /CeO (111) catalyst recombines to yield ethane or ethylene.

Cu clusters supported on β-Mo2C improve the selectivity towards methanol decreasing the amount of methane.

The visual limitation in keratoconus could be explained by different alterations that occur in these corneas and allowed development of a new grading system for this condition.

Methane is an extremely stable molecule, a major component of natural gas, and also one of the most potent greenhouse gases contributing to global warming. Consequently, the capture and activation of methane is a challenging and intensively studied topic. A major research goal is to find systems that can activate methane even at low temperature. Here, combining ultrahigh vacuum catalytic experiments followed by Xray photoemission spectra and accurate density functional theory (DFT) based calculations, we show that small Ni clusters dispersed on the (001) surface of TiC are able to capture and dissociate methane at room temperature. Our DFT calculations reveal that two-dimensional Ni clusters are responsible of this chemical transformation, evidencing that the lability of the supported clusters appears to be a critical aspect in the strong adsorption of methane. A small energy barrier of 0.18 eV is predicted for CH 4 dissociation into adsorbed methyl and hydrogen atom species. In addition, the calculated reaction free energy profile at 300 K and 1 atm of CH 4 shows no effective energy barriers in the system. Comparing with other reported systems which activate methane at room temperature, including oxide and zeolite-based materials, indicates that a different chemistry takes place on our metal/carbide system. The discovery of a carbide-based surface able to activate methane at low temperatures paves the road for the design of new types of catalysts towards an efficient conversion of this hydrocarbon into other added-value chemicals, with implications in climate change mitigation.

Objective: To evaluate the changes in correlations of higher order aberrations of the first corneal surface with halo phenomena, a form of image degradation, under night vision conditions measured objectively after successful LASIK (laser in situ keratomileusis) surgery. Methods: A prospective, observational, analytical study of 110 eyes that had undergone successful LASIK surgery for myopia and astigmatism. Preoperative sphere was (mean (SD)) 23.48 (1.70) D (0 to 28.00 D) and preoperative cylinder was 20.86 (0.87) D (0 to 24.00 D). Visual disturbance caused by halo phenomena was measured with the Starlights v1.0, and pupil size was measured with Colvard pupilometry after adaptation to a dark environment (0.17 lux). Corneal aberrations were computed for a corneal diameter representative of the eye's entrance pupil under night vision conditions. Results: The halo disturbance index increased in this study by a factor of 2.15 after successful LASIK surgery. Total root mean square for monochromatic higher order aberration displayed a significant correlation with halo disturbance index (r = 0.42; p,0.01). However, only secondary astigmatism (r = 0.36; p,0.01), coma (r = 0.25; p = 0.02) and spherical aberration (r = 0.40; p,0.01) were responsible for such behaviour, with the remaining corneal aberrations up to the sixth order not displaying any significant correlation when considered individually. Conclusion: Patients undergoing LASIK procedures display an increase of halo phenomena around lights in night vision conditions, even when the results of the surgery are considered entirely satisfactory according to current international standards of predictability, efficacy and safety. Secondary astigmatism, coma and spherical aberration are the higher order aberrations up to the sixth order that significantly correlated with halo disturbance index.

Water gas shift reaction catalyzed by Mo carbides surfaces and on Au supported thereon is studied by experiments and computational methods.