Traditional nanostructured design of cerium oxide catalysts typically focuses on their shape, size, and elemental composition. We report a different approach to enhance the catalytic activity of cerium oxide nanostructures through engineering high density of oxygen vacancy defects in these catalysts without dopants. The defect engineering was accomplished by a low pressure thermal activation process that exploits the nanosize effect of decreased oxygen storage capacity in nanostructured cerium oxides.

Experimental measurements of the conversion of m-cresol over Pt and Ru/SiO 2 catalysts show very different product distributions, even when the reaction is conducted at similarly low conversions and the same operating conditions (300 °C, 1 atm). That is, although ring hydrogenation to 3methylcyclohexanone is dominant over Pt, deoxygenation to toluene and C−C cleavage to C 1 −C 5 hydrocarbons prevail over Ru. For understanding the differences in reaction mechanisms responsible for this contrasting behavior, the conversion of mcresol over the Pt(111) and Ru(0001) surfaces has been analyzed using density functional theory (DFT) methods. The DFT results show that the direct dehydroxylation of m-cresol is unfavorable over the Pt(111) surface with an energy barrier of 242 kJ/mol. In turn, the calculations suggest that the reaction could proceed through a keto tautomer intermediate, which undergoes hydrogenation of the carbonyl group followed by dehydration to form toluene and water. At the same time, a low energy barrier for the ring hydrogenation path toward 3-methylcyclohexanone compared to the energy barrier for the deoxygenation path toward toluene over the Pt(111) surface is in agreement with the experimental observations, which show that 3methylcyclohexanone is the dominant product over Pt/SiO 2 at low conversions. By contrast, the direct dehydroxylation of mcresol becomes more favorable than the tautomerization route over the more oxophilic Ru(0001) surface. In this case, the deoxygenation path exhibits an energy barrier lower than that for the ring hydrogenation, which is also in agreement with experimental results that show higher selectivity to the deoxygenation product toluene. Finally, it is proposed that a partially unsaturated hydrocarbon surface species C 7 H 7 * is formed during the direct dehydroxylation of m-cresol over Ru(0001), becoming the crucial intermediate for the C−C bond breaking products C 1 −C 5 hydrocarbons, which are observed experimentally over the Ru/SiO 2 catalyst.

A combined experimental and theoretical comparative study of the hydrodeoxygenation (HDO) of anisole was conducted over Pt, Ru, and Fe metals. In the experimental part, an inert silica support was used to directly compare the catalytic activity and selectivity of the three metals at 375 ºC under H 2 flow at atmospheric pressure. In parallel, for density functional theory (DFT) calculations the close-packed Pt(111), Ru(0001), and Fe(110) surfaces were employed to compare the possible mechanisms on these metals. It was observed that over Pt/SiO 2 and Ru/SiO 2 catalysts, both phenol and benzene were the major products in a phenol/benzene ratio that decreased with the level of conversion. By contrast, over the Fe/SiO 2 catalyst, no phenol formation was detected, even at low conversions. The DFT results show that over all the three metal surfaces the dehydrogenation at the-CH 3 side group occurs before the CO bond breaking. This removal of H atoms from the-CH 3 group facilitates the activation of the aliphatic C alkyl-O bond. Therefore, it can be concluded that a common intermediate for the three metals is a surface phenoxy and the significant differences between the three metals is related to the reactivity of this surface phenoxy. That is, over Pt(111) and Ru(0001) the phenoxy intermediate is hydrogenated to phenol, which in turn, can undergo further HDO to form benzene. This result is in agreement with the experiments over Pt/SiO 2 and Ru/SiO 2 catalysts. Over these catalysts, both phenol and benzene are major products, with the selectivity to benzene increasing with conversion at the expense of phenol. In contrast, over the Fe(110) surface, the strong metal oxophilicity makes the direct cleavage of the CO bond in the surface phenoxy easier than

Patterned micro- and nanostructured surfaces have received increasing attention because of their ability to tune the hydrophobicity and hydrophilicity of their surfaces. However, the mechanical properties of these studied surfaces are not sufficiently robust for load-bearing applications. Here we report transparent nanocrystalline ZrO 2 films possessing combined properties of hardness and complete wetting behavior, which are expected to benefit tribology, wear reduction, and biomedical applications where ultrahydrophilic surfaces are required. This ultrahydrophilic behavior may be explained by the Wenzel model.

Nanostructurally stabilized zirconium oxide (NSZ) hard transparent films were produced without chemical stabilizers by the ion beam assisted deposition technique (IBAD). A transmission electron microscopy study of the samples produced below 150 °C revealed that these films are composed of zirconium oxide (ZrO2) nanocrystallites of diameters 7.5 ± 2.3 nm. X-ray and selected-area electron diffraction studies suggested that the as-deposited films are consistent with cubic phase ZrO2. Rutherford backscattering spectroscopy (RBS) indicated the formation of stoichiometric ZrO2. The phase identity of these optically transparent NSZ films was in agreement with cubic ZrO2, as indicated by the matching elastic modulus values from the calculated results for pure cubic zirconium oxide and results of nanoindentation measurements. Upon annealing in air for 1 h, these NSZ films were found to retain most of their room temperature deposited cubic phase x-ray diffraction signature up to 850 °C. Size effect and vacancy stabilization mechanisms and the IBAD technique are discussed to explain the present results.

Nanowires show great promise for development in many technological applications including electronics, photonics, and displays [1][2]. Due to the fine scale of nanowires, transmission electron microscopy (TEM) and atom probe tomography (APT) are among a limited number of techniques that can measure the crystallographic and chemical nature of these structures which ultimately define their performance.Individual nanowires have a nearly ideal geometry for (APT) analysis. When nanowires are synthesized with the proper length, orientation, and inter-wire separation spacings, nanowire APT analysis is relatively straightforward and has yielded reasonable results [3]. However, for many nanowire growth processes, it is difficult or undesirable to grow structures with these restrictions. One preparation technique demonstrated for APT analysis in such circumstances is a protected liftout method [4]. This research demonstrates two other methods for analysis of individual nanowires by APT. Previously developed techniques have demonstrated cross-correlative TEM and APT analysis on focused ion beam (FIB) prepared lift-out samples [5]. Performing TEM analysis of the sample before atom probe analysis is useful not only for obtaining complementary information about the crystal structure(s), but also for assisting in accuracy of the reconstruction. The radius, shank angle, layer thicknesses, and other structural information can be directly measured and incorporated into the atom probe reconstruction. This work expands the previously reported technique to both dispersed and substrate grown nanowires. This technique as applied to nanowires utilizes only the electron beam in order to avoid structural damage from the FIB column.In the first adaptation, the nanowires were removed from their substrate, suspended in ethanol, and then dispersed over a porous substrate. This geometry allows most of the nanowires to be retained on the surface suspended over the pore openings (Figure 1a). A nano-manipulator was placed in close proximity to the nanowire's base. A very small electron beam deposited platinum (e-beam Pt) weld was made at that location to provide just enough attachment to remove the wire from the porous substrate (Figure 1b). The nanowire was then moved to a TEM grid that had been sectioned such that a vertical portion of each grid bar extended beyond the horizontal grid bar. The nanowire was aligned with a vertical grid bar and securely welded with e-beam Pt. The nano-manipulator was then slowly drawn away from the nanowire until the initial small weld detached, leaving the nanowire mounted to the TEM half-grid (Figures 1c and 1d).In the second adaptation, the nanowires were left attached to the substrate on which they were grown. That substrate was mounted orthogonal to the nano-manipulator such that the nanowires were parallel with the nano-manipulator tip. A nanowire was securely welded, again using e-beam Pt, to the nano-manipulator which was then pulled away from the substrate to detach the nanowire (Figure 2). Omniprobe's ...

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The phase stability of nanocrystallites with metastable crystal structures under ambient conditions is usually attributed to their small grain size. It remains a challenging problem to maintain such phase integrity of these nanomaterials when their crystallite sizes become larger. Here we report an experimental-modelling approach to study the roles of nitrogen dopants in the formation and stabilization of cubic ZrO(2) nanocrystalline films. Mixed nitrogen and argon ion beam assisted deposition (IBAD) was applied to produce nitrogen-implanted cubic ZrO(2) nanocrystallites with grain sizes of 8-13 nm. Upon thermal annealing, the atomic structure of these ZrO(2) films was observed to evolve from a cubic phase, to a tetragonal phase and then a monoclinic phase. Our X-ray absorption near edge structure study on the annealed samples together with first-principle modelling revealed the significance of the interstitial nitrogen in the phase stabilization of nitrogen implanted cubic ZrO(2) crystallites via the soft mode hardening mechanism.