The effect of oleic acid stabilizer on the surface properties of bimetallic PtNi catalysts.

A detailed study on the surface properties of oleic acid-stabilized PtNi nanoparticles supported on silica is reported. The oleic acid-stabilized PtNi nanoparticles were synthesized using NaBH4 as the reducing agent at various temperatures and oleic acid concentrations, prior to incorporation onto the silica support. X-ray diffraction studies of the unsupported oleic acid-stabilized PtNi particles revealed that the PtNi existed as alloys. Upon incorporation onto silica support, surface properties of the catalysts were investigated using H2-temperature reduction (H2-TPR), H2-temperature desorption (H2-TPD) and H2-chemisorption techniques. It was found that for the bimetallic catalysts, no oxides or very little oxidation occurred. Furthermore, these catalysts exhibited both Pt and Ni active sites on its surface though the availability of Ni active sites was dominant. A comparison of the surface properties of these materials with those prepared without oleic acid in our previous work [N. H. H. Abu Bakar et al., J. Catal. 265, 63 (2009)] and how they affect the hydrogenation of benzene is also discussed.

Virtual navigation for memory rehabilitation in a traumatic brain injured patient.

The use of 3D video games in memory rehabilitation has been explored very little. A virtual navigation task allows participants to encode the spatial layout of the virtual environment and activate areas involved in memory processing. We describe the rehabilitation of a 24-year-old man with traumatic brain injury presenting memory deficits, and evaluate the efficacy of a navigational training program measuring neuropsychological changes and fMRI modification cerebral activations. Memory improvement appears to be present both after navigational training and in follow-up testing. Furthermore, fMRI data suggest that this training may increase activation of the hippocampal and parahippocampal brain regions. The results suggest that intensive training in virtual navigational tasks may result in an enhancement of memory function in brain-damaged adults.

NiAg catalysts prepared by reduction of Ni2+ ions in aqueous hydrazine II. Support effect.

A series of bimetallic NiAg (Ni + Ag = 1% wt) catalysts supported on amorphous silica was synthesized via chemical reduction using hydrazine as the reducing agent at 353 K. Catalysts were prepared via impregnation or precipitation technique. It was found that the reduction of the Ni(2+) ions occurred only in the presence of silver, otherwise a stable blue [Ni(N(2)H(4))(3)](2+) complex was formed. Comparisons with similar NiAg catalysts supported on crystallized silica as prepared in our previous work indicated that the Ni(2+) ions weakly interacted with acidic crystallized silica on which they were readily reduced. For both supports, the combination of silver and nickel gave rise to a synergistic effect due to the existence of NiAg groupings. The surface and catalytic properties of the metal particles formed depended on the Ni:Ag ratio, method of preparation, and acidity of the support.

Study of Ni-Ag/SiO2 catalysts prepared by reduction in aqueous hydrazine.

We have studied bimetallic Ni-Ag (Ni + Ag = 1 wt%) catalysts supported on crystallized silica and prepared by aqueous chemical reduction with hydrazine at 353 K. Two protocols of reduction were used. Prepared catalysts were characterized by means of XRD, TEM, STEM, H2 chemisorption and H2-TPD. Their catalytic activity was studied in the gas-phase hydrogenation of benzene. The most important feature of the results obtained is the synergistic effect between Ni and Ag which led to improvement of dispersion and reactivity of nickel in the presence silver for precipitated catalysts. Silver is inactive in the test-reaction. Precipitated bimetallic catalysts give rise to total conversion from 373 K, a temperature at which conversion hardly reaches 30% for the impregnated catalysts. Dispersion and activity pass through a maximum of monotonically decrease with precipitated and impregnated catalysts, respectively. Deactivation was observed for bimetallic catalysts, particularly with precipitated samples. These results could be explained by the mechanism of metal reduction in the hydrazine media. As a result, various Ni-Ag species formed where Ni and Ag phases were separated clusters or interacted as heteroatomic groupings on the carrier surface. These grouping would be responsible of the high performances of the precipitated catalysts.

Study of nickel nanoparticles supported on activated carbon prepared by aqueous hydrazine reduction.

Nickel nanoparticles were obtained by the reduction in hydrazine aqueous media of nickel acetate as a precursor supported on activated carbon of high surface area. Classical catalysts using nickel acetate or nitrate were prepared for comparison. The catalysts were characterized by N(2) physisorption, H(2)-TPR, H(2)-adsorption, TPD, TEM, and XRD, and tested in the gas phase hydrogenation of benzene. Hydrazine catalysts were found much more active in benzene hydrogenation than corresponding classically prepared catalysts. Remarkably, their reactivity is comparable (turn-over frequency of 0.2001-0.2539 s(-1) at 393 K) to that of Pt classical catalysts supported on activated carbon in the same conditions. Evidence is given for the existence of the hydrogen spillover effect in benzene hydrogenation, not reported before in the literature. As a result of the hydrogen spillover effect, catalysts performances can be explained by a combination of surface metal atom reactivity, metal-support interaction strength, and specific surface area extent. Maximum effect is observed with hydrazine preparation method, for 1% Ni content and nickel acetate as a precursor. Unexpectedly, it was also found that hydrazine preparation increases the specific area of the catalysts.