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Abstract: In the catalytic hydrogenation of α,β-unsaturated aldehydes and ketones, highly selective allylic alcohol formation can be achieved by application of Au0 nanocolloids dispersed in amide solvents. The polyvinylpyrrolidone protected Au0 nanoparticles prefer Con over Cion and act as chemoselective quasihomogeneous metal catalysts in the hydrogenation of trans-2-butenal (crotonaldehyde), 2-methyl-2-propenal (methacrolein), 4-methyl-3-penten-2-one (mesityl oxide) and 3-methyl-3-penten-2-one. An extensive solvent screening revealed the superiority of amides as media for both synthesis and application of the Au0 nanocolloids. In comparison with the widely used alcohol solvents, amides offer enhanced colloidal stability for the Au0 nanosol and increased hydrogenation chemoselectivity. Control over the Au0 cluster formation provided the opportunity to investigate the size-dependency of the catalytic performance and to determine the optimum gold cluster size for a maximization of the allylic alcohol yields. The most successful Au0 clusters, with a typical diameter of 7nm and synthesized in N,N-dimethylformamide, lead to a crotyl alcohol selectivity of 73% at 93% crotonaldehyde conversion and a 58% allylic alcohol yield in the hydrogenation of mesityl oxide at a molar substrate/Au catalyst ratio of 200. Analogous Pt0 and Ru0 sols are more active than the Au0 nanosols, but substantially less chemoselective for allylic alcohols. The Au0 nanocolloids can be recycled efficiently by ultrafiltration over custom-made, cross-linked polyimide membranes. In the recycling experiments the gold nanodispersion was well retained by the solvent-resistant ultrafiltration membranes and the performance of the colloidal gold catalyst was satisfactorily preserved in successive hydrogenation runs. [Copyright &y& Elsevier]

Abstract: The activation of propane both in the absence and presence of gas-phase O2 or CO2 over a CuO–CeO2/γ-Al2O3 catalyst is investigated in a TAP reactor between 623 and 873K. Two different types of oxygen species are involved dependent on the mixture introduced: (1) lattice oxygen from the surface and bulk of the catalyst and (2) weakly adsorbed oxygen species produced either from gas-phase O2 or CO2. Both types of oxygen species participate in the total oxidation of propane. If pulses of pure propane are admitted, lattice oxygen from CuO and CeO2 is consumed, reducing these oxides to a certain extent. Apart from surface lattice oxygen from CuO and CeO2, also bulk lattice oxygen is involved in the activation of propane, demonstrating the high O mobility within the lattice of these metal oxides. Lattice oxygen of alumina is not available for reaction with propane. Introduction of O2 reoxidizes the reduced sites on CuO and CeO2, as expected for a Mars–van Krevelen mechanism. Also CO2 can replenish O vacancies in the active phase by dissociative adsorption on alumina and ceria. The adsorption on alumina is followed by reverse spillover of reactive O species to the active phase. The second type of oxygen consists of weakly adsorbed oxygen species, produced either from O2 on both CuO and CeO2, or from CO2 on CeO2, and enhances strongly the catalytic activity. In the presence of both O2 and CO2 in the propane feed, the predominant reaction pathways will only involve the two types of active species produced from O2, and not from CO2. [ABSTRACT FROM AUTHOR]

Abstract: Pure and N-doped TiO2 nanoparticles are obtained by a combination of wet and thermal procedures, starting from TiCl3 and alkoxide precursors; the N-source is both inorganic (NH3) and organic (triethylamine). Samples are characterized for their bulk, surface, optical and magnetic properties. Ab initio calculations of the electronic properties of the doped samples are performed. Sample thin films are tested for their photocatalytic activity, under UV and simulated solar irradiation, with respect to air pollutants ethanol and acetaldehyde. Both the disappearance of the molecule itself and the complete mineralization (CO2) are followed during the reaction time. FTIR/ATR analyses are performed on samples withdrawn during the course of the reaction to identify reaction intermediates. In the case of acetaldehyde, photocatalytic tests are also performed under visible light (λ >400nm). The photoactivity sequences of the N-doped samples under the different irradiation sources are discussed with reference to their surface/bulk properties, light absorption features, nature and amount of paramagnetic species. [Copyright &y& Elsevier]