Tuning the catalytic activities of supported metal nanoparticles can be achieved by manipulating their structural properties using an appropriate design and synthesis strategy. Each step in a catalyst synthesis method can potentially play an important role in preparing the most efficient catalyst for a particular chemical reaction. Here we report the careful manipulation of the post-synthetic heat treatment procedure, together with control over the the amount of metal loading, to prepare a highly efficient 0.2 wt.% Pt/TiO2 catalyst for the chemoselective hydrogenation of 3nitrostyrene. We found that for Pt/TiO2 catalysts with 0.2 and 0.5wt.% loading levels, reduction alone at 450 °C induces the coverage of Pt nanoparticles by TiOx through a strong metal support interaction which is detrimental for their catalytic activities. However, this surface coverage can be avoided by combining a calcination treatment at 450 °C with a subsequent reduction treatment at 450 °C allowing us to prepare a exceptionally active Pt/TiO2 catalyst with the optimum Pt distribution. Detailed characterisation of these catalysts has revealed that the peripheral sites at the Pt metal/TiO2 support interface are the most likely active sites for this hydrogenation reaction.

Heterogeneous palladium catalysts modified by N-heterocyclic carbenes (NHCs) are shown to be highly effective toward the direct synthesis of hydrogen peroxide (H 2 O 2 ), in the absence of the promoters which are typically required to enhance both activity and selectivity. Catalytic evaluation in a batch regime demonstrated that through careful selection of the N-substituent of the NHC it is possible to greatly enhance catalytic performance when compared to the unmodified analogue and reach concentrations of H 2 O 2 rivaling that obtained by state-of-the-art catalysts. The enhanced performance of the modified catalyst, which is retained upon reuse, is attributed to the ability of the NHC to electronically modify Pd speciation.

The solvent-free selective hydrogenation of nitrobenzene was carried out using a supported AuPd nanoparticles catalyst, prepared by the modified impregnation method (MIm), as efficient catalyst >99% yield of aniline (AN) was obtained after 15 h at 90 °C, 3 bar H2 that can be used without any further purification or separation, therefore reducing cost and energy input. Supported AuPd nanoparticles catalyst, prepared by MIm, was found to be active and stable even after four recycle experiments, whereas the same catalyst prepared by SIm was deactivated during the recycle experiments. The most effective catalyst was tested for the chemoselective hydrogenation of 4-chloronitrobenzene (CNB) to 4-chloroaniline (CAN). The activation energy of CNB to CAN was found to be 25 kJ mol−1, while that of CNB to AN was found to be 31 kJ mol−1. Based on this, the yield of CAN was maximized (92%) by the lowering the reaction temperature to 25 °C.

D´eborah De Masi opened the discussion of the paper by Laura Prati: Can you explain why you have better results with ruthenium nanoparticles than with bimetallic RuAu NPs? Is it due to a change of the crystallinity of Ru when it is on the surface of Au? Laura Prati replied: There is not a direct explanation but we experienced that the synergistic eff ect is not always positive. It depends on the structure, on the electronic distribution, on the matching between reactant, etc. Aldiar Adishev asked: Can you explain how the introduction of gold aff ects reactions tested with bimetallic systems? Or do you have future plans to further study the eff ect of gold? Laura Prati answered: We have seen that Au can have an eff ect on both electronic or geometric eff ects. However the balance between these two factors depends on the structures of the bimetallic particles you are synthesizing. In the case of Pd, for example, we have shown that the eff ect of gold mainly aff ects the O2 interaction with the catalyst thus in turn reducing the occurrence of Pd-O species. Baldassarre Venezia remarked: In this work it has also been emphasized how the Pd/AC and AuPd/AC catalyst were selective in the oxidation of benzyl alcohol to benzaldehyde. However, might this result be due to the low concentration of benzyl alcohol (0.3 M in cyclohexane) employed in the oxidation reaction? The low amount of benzyl alcohol in the autoclave might have hindered the disproportionation reaction of benzyl alcohol into toluene and benzaldehyde, whose kinetics is generally proportional to benzyl alcohol concentration and reaction temperature. Laura Prati responded: Actually we used quite dilute solution (0.3 M). Of course this could have an impact on the selectivity of the reaction. However we established that in the case of AuPd compared to pure Pd there is a decreased adsorption of oxygen on the catalyst surface which can explain a diff erent selectivity. Please refer to previous work in ref. 1 and 2.

Abstract:Selective hydrogenation of nitrobenzene was carried out under solvent-free conditions using supported AuPd nanoparticles catalyst, prepared by modified impregnation method (M Im ), as efficient catalyst. >99% yield of aniline (AN) was obtained after 15 hours at 90 °C, 3 bar H 2 that can be used without any further purification or separation, therefore reducing cost and energy input. Supported AuPd nanoparticles catalyst, prepared by M Im , was found to be active and stable even after 4 recycle experiments whereas the same catalyst prepared by S Im deactivated during the recycle experiments.The most effective catalyst was tested for the chemoselective hydrogenation of 4-chloronitrobenzene (CNB) to 4-chloroaniline (CAN). The activation energy of CNB to CAN was found to be 25 kJ mol -1 , while that of CNB to AN was found to be 31 kJ mol -1 . Based on this, the yield of CAN was maximized (92%) by lowering the reaction temperature to 25 °C.