Low temperature oxidation of CO over cluster-derived platinum-gold catalysts

In situ manipulation of the d-band center in metals for catalytic activity in CO oxidation

A combination of in situ XANES, temperature programmed oxidation, kinetic and density functional theory results demonstrate that the d-band centers (ε_d) of Au and Pt metals are upshifted when 39.9 V m^-1 of electric field is applied. This leads to the enhancement of the adsorption strength of CO on both metals, and, thus, results in the promotion (+15%) and the depression (-23%) of CO conversions on Au and Pt, respectively, in the CO oxidation.

Enhanced CO catalytic oxidation over an Au–Pt alloy supported on TiO2 nanotubes: investigation of the hydroxyl and Au/Pt ratio influences

The schematic illustrates the catalytic mechanism and reaction pathways of Au–Pt/TiO2 SNT catalysts with enhanced catalytic activity for CO oxidation.

Dendrimer-mediated synthesis of supported rhodium nanoparticles with controlled size: effect of pH and dialysis

Rh-dendrimer nanocomposites were synthesized in solution under different conditions and were subsequently used as precursors for the preparation of ZrO2-supported Rh nanoparticles. Elemental analysis, UV-vis, XPS, and STEM measurements were used to estimate the extent of the Rh-dendrimer interactions and to illustrate how the solution pH and dialysis affect the number of Rh atoms complexed with each dendrimer molecule, as well as the final size of the ZrO2-supported Rh particles. When the solution acidity was not controlled and the solution was not purified by dialysis, Rh particles with sizes in the 1-6 nm range were formed on the ZrO2 support. In contrast, the formation of nearly uniform Rh particles was observed when the synthesis was performed under controlled pH and dialysis conditions. Furthermore, the size of these Rh particles can be regulated by controlling the Rh/dendrimer ratio in the original solution.

H₂ production by renewables photoreforming on Pt-Au/TiO₂ catalysts activated by reduction

Bimetallic Pt-Au nanoparticles supported on reduced anatase nanocrystals represent a new class of promising photocatalysts with high activity in hydrogen production by photoreforming of aqueous solution of renewable feedstock, such as ethanol and glycerol. The catalysts are easily obtained by metal impregnation of commercial TiO₂, followed by a reductive treatment. Remarkably, deeper catalyst pre-reduction results in enhanced photoactivity. When ethanol is used as sacrificial agent, under both UV-A or simulated sunlight irradiation, H₂ is the most abundant product in the gas stream whereas, in the case of glycerol, significant amounts of CO₂ have also been detected, indicating a more efficient oxidation of the organic sacrificial agent. The presence of bimetallic Pt-Au nanoparticles and of Ti³⁺ sites/O²⁻ vacancies in the bulk structure of titania are two key parameters to maximize light absorption and feedstock activation, finally resulting in good photocatalytic performances.

The atomic structural dynamics of γ-Al2O3 supported Ir-Pt nanocluster catalysts prepared from a bimetallic molecular precursor: a study using aberration-corrected electron microscopy and X-ray absorption spectroscopy

This study describes a prototypical, bimetallic heterogeneous catalyst: compositionally well-defined Ir-Pt nanoclusters with sizes in the range of 1-2 nm supported on γ-Al(2)O(3). Deposition of the molecular bimetallic cluster [Ir(3)Pt(3)(μ-CO)(3)(CO)(3)(η-C(5)Me(5))(3)] on γ-Al(2)O(3), and its subsequent reduction with hydrogen, provides highly dispersed supported bimetallic Ir-Pt nanoparticles. Using spherical aberration-corrected scanning transmission electron microscopy (C(s)-STEM) and theoretical modeling of synchrotron-based X-ray absorption spectroscopy (XAS) measurements, our studies provide unambiguous structural assignments for this model catalytic system. The atomic resolution C(s)-STEM images reveal strong and specific lattice-directed strains in the clusters that follow local bonding configurations of the γ-Al(2)O(3) support. Combined nanobeam diffraction (NBD) and high-resolution transmission electron microscopy (HRTEM) data suggest the polycrystalline γ-Al(2)O(3) support material predominantly exposes (001) and (011) surface planes (ones commensurate with the zone axis orientations frequently exhibited by the bimetallic clusters). The data reveal that the supported bimetallic clusters exhibit complex patterns of structural dynamics, ones evidencing perturbations of an underlying oblate/hemispherical cuboctahedral cluster-core geometry with cores that are enriched in Ir (a result consistent with models based on surface energetics, which favor an ambient cluster termination by Pt) due to the dynamical responses of the M-M bonding to the specifics of the adsorbate and metal-support interactions. Taken together, the data demonstrate that strong temperature-dependent charge-transfer effects occur that are likely mediated variably by the cluster-support, cluster-adsorbate, and intermetallic bonding interactions.

Highly active mesostructured silica hosted silver catalysts for CO oxidation using the one-pot synthesis approach

A facile one-pot approach gave isolated silver nanoparticles anchored on a mesostructured silica matrix in a self-assembled way; these gave 100% CO conversion in CO oxidation at room temperature, which is higher than or comparable to the conversion obtained using noble metal catalysts.