We report a convenient excess anion modification and post-reduction step to the impregnation method which permits the reproducible preparation of supported bimetallic AuPd nanoparticles having a tight particle size distribution comparable to that found for sol-immobilization materials but without the complication of ligands adsorbed on the particle surface. The advantageous features of the modified impregnation materials compared to those made by conventional impregnation include a smaller average particle size, an optimized random alloy composition, and improved compositional uniformity from particle-to-particle resulting in higher activity and stability compared to the catalysts prepared using both conventional impregnation and sol immobilization methods. Detailed STEM combined with EDX analyses of individual particles have revealed that an increase in anion concentration increases the gold content of individual particles in the resultant catalyst, thus providing a method to control/tune the composition of the nanoalloy particles. The improved activity and stability characteristics of these new catalysts are demonstrated using (i) the direct synthesis of hydrogen peroxide and (ii) the solvent-free aerobic oxidation of benzyl alcohol as case studies.
All bound up: Au‐Pd nanoparticles having a mean particle size of 3–4 nm and supported on titania (see figure; scale bar 2 nm) exhibit high activity in the selective oxidation of aromatic hydrocarbons using tert‐butyl hydroperoxide as an oxidant. The supported nanoparticles stabilize surface‐bound radicals.
In a new experimental system synchrotron radiation from the SRS (Daresbury, UK) has been used to photoionise Ar at threshold and to produce an electron beam with an energy resolution of about 3.5 meV (FWHM). The authors have observed the variation of the total scattering cross section of O2 in a supersonic beam over the energy range 0.1-1.3 eV. Rotational effects are strongly apparent and the results suggest that there are important contributions to the scattering from the higher partial waves l=4 and 6 as well as l=2. This apparatus shows the potential to open up the field of electron-molecule scattering at rovibrational resolution to a large variety of molecules.
In the solvent free oxidation of benzyl alcohol, using supported gold-palladium nanoalloys, toluene is often one of major by-products and it is formed by the disproportionation of benzyl alcohol. Gold-palladium catalysts on acidic supports promote both the disproportionation of benzyl alcohol and oxidative dehydrogenation to form benzaldehyde. Basic supports completely switch off disproportionation and the gold-palladium nanoparticles catalyse the oxidative dehydrogenation reaction exclusively. In an attempt to provide further details on the course of these reactions, we have utilized in situ ATR-IR, in situ DRIFT and inelastic neutron scattering spectroscopic methods, and in this article we present the results of these in situ spectroscopic studies.
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