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Author(s): Mathew D. Hughes [1]; Yi-Jun Xu [1]; Patrick Jenkins [1]; Paul McMorn [1]; Philip Landon [1]; Dan I. Enache [1]; Albert F. Carley [1]; Gary A. Attard [1]; Graham [...]

A series of MgO catalysts have been prepared by calcination of (MgCO3)4·Mg(OH)2 and these have been found to be effective for the transesterification of triglycerides with methanol at 200 °C. The calcination temperature controls the surface area, porosity and the surface structure and we observe that the optimal calcination temperature is in the range 550–700 °C as this provides a balance between high surface area, and hence high concentration of active sites, and the pore structure which permits access of the reactants. Using appropriate conditions conversions in excess of 98% could be obtained. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

CeO2has been prepared from an acetate precursor by an antisolvent precipitation technique using supercritical CO2. The supercritically synthesized ceria support was used to prepare Au–Pd based catalysts for the selective oxidation of alcohols in solvent-free conditions using molecular oxygen as oxidant. The supercritically precipitated catalyst demonstrated high activity for alcohol oxidation, and it was much more active than catalysts prepared using a CeO2support derived from the acetate through a non-supercritical synthesis route. The bimetallic Au–Pd supported catalyst was considerably more active than monometallic catalysts containing Au and Pd only. HAADF imaging and STEM–XEDS mapping showed that both Au and Pd metallic components were intimately mixed and uniformly highly dispersed over the supercritical nanocrystalline CeO2support spheres. In contrast, the Au–Pd catalyst on the non-supercritical CeO2support showed discrete uniform Au–Pd alloy particles with a size range of 50 to 150 nm. The homogeneous alloy particles were Au-rich and Pd-deficient as compared with the preparation ratio and a low number of highly dispersed Pd was also associated with the support. XPS data for the ceria supported catalysts confirmed the differences of metal dispersion and identified that in both cases the surface species present were Au0and Pd2+. On extended re-use the non-supercritical Au–Pd/CeO2catalyst showed sequential deactivation. On the contrary, the supercritical Au–Pd/CeO2catalyst showed a significant increase of activity, and it was only during the third re-use that the activity was marginally lower than the fresh catalyst. After use the spherical morphology of nanocrystalline supercritical CeO2started to increasingly break down, until the morphology started to resemble the CeO2prepared by the non-supercritical route. Simultaneously there was an increase of the metal particle size on the supercritically prepared CeO2support, as discrete Au-rich and Pd-rich bimetallic particles were formed, and there was a decrease of the metal content. XPS confirmed the loss of metal on use and showed that there was reduction of the ceria surface during use. The increase of activity with a corresponding loss of metal components indicates that the fresh catalyst contains Au and Pd in inactive forms, whilst the active sites have extremely high turnover frequencies. [ABSTRACT FROM AUTHOR]

The oxidation of benzyl alcohol to benzaldehyde has been investigated in the absence of solvent using zeolite-supported Au and Au–Pd catalysts. Three zeolites were investigated, ZSM-5, zeolite β and zeolite Y, and these were contrasted with the titanoslicalite TS-1 and TiO2 as supports. For the Au catalysts the best results are obtained with zeolite β as the support and the conversions were comparable or better than those observed with TiO2 in terms of turn over frequencies. However, the selectivities observed with the acidic zeolites were lower than the non-acidic TS-1 and TiO2. This is due to the subsequent reaction of benzaldehyde via acid catalysed reactions to give benzyl benzoate and its dibenzyl acetal, and, in some cases dibenzylether. Initial catalysts were evaluated with a gold loading of 2 wt% and increasing this to 4 wt% showed the expected increase in activity, indicating that there is scope to improve the performance of these catalysts. The most active catalysts were prepared by impregnation and catalysts prepared by deposition precipitation were considerably less active. Introduction of Pd into the catalyst improved the activity without significantly affecting the selectivity. [ABSTRACT FROM AUTHOR]

The oxidation of alcohols to aldehydes with 02 in place of stoichiometric oxygen donors is a crucial process for the synthesis of fine chemicals. However, the catalysts that have been identified so far are relatively inactive with primary alkyl alcohols. We showed that Au/Pd-TiO[sub 2] catalysts give very high turnover frequencies (up to 270,000 turnovers per hour) for the oxidation of alcohols, including primary alkyl alcohols. The addition of Au to Pd nanocrystals improved the overall selectivity and, using scanning transmission electron microscopy combined with x-ray photoelectron spectroscopy, we showed that the Au-Pd nanocrystals were made up of a Au-rich core with a Pd-rich shell, indicating that the Au electronically influences the catalytic properties of Pd. [ABSTRACT FROM AUTHOR]

The effectiveness of Mg as a promoter of Co-Ru/γ-Al2O3 Fischer-Tropsch catalysts depends on how and when the Mg is added. When the Mg is impregnated into the support before the Co and Ru addition, some Mg is incorporated into the support in the form of MgxAl2O3+x if the material is calcined at 550°C or 800°C after the impregnation, while the remainder is present as amorphous MgO/MgCO3 phases. After subsequent Co-Ru impregnation MgxCo3-xO4 is formed which decomposes on reduction, leading to Co(0) particles intimately mixed with Mg, as shown by high-resolution transmission electron microscopy. The process of impregnating Co into an Mg-modified support results in dissolution of the amorphous Mg, and it is this Mg which is then incorporated into MgxCo3-xO4. Acid washing or higher temperature calcination after Mg impregnation can remove most of this amorphous Mg, resulting in lower values of x in MgxCo3-x O4. Catalytic testing of these materials reveals that Mg incorporation into the Co oxide phase is severely detrimental to the site-time yield, while Mg incorporation into the support may provide some enhancement of activity at high temperature. [ABSTRACT FROM AUTHOR]