Effect of nanoparticle metal composition: mono- and bimetallic gold/copper dendrimer stabilized nanoparticles as solvent-free styrene oxidation catalysts

A range of mono- and bimetallic Au_mCu_n nanoparticles (NPs), with varying metal compositions, was prepared by using a third-generation diaminobutane poly(propylene imine) (G3 DAB-PPI) dendrimer, modified with alkyl chains, as a stabilizer. It was found that the length of the peripheral alkyl chain, (M1 (C₁₅), M2 (C₁₁), and M3 (C₅)), had a direct influence on the average nanoparticle size obtained, confirming the importance of the nanoparticle stabilizer during synthesis. The Au NPs showed the highest degree of agglomeration and polydispersity, whereas the Cu NPs were the smallest and most monodisperse of the NPs. The bimetallic NPs sizes were found to vary between those of the monometallic NPs, depending on the metal composition. Interestingly, the bimetallic NPs were found to be the most stable, showing very little variation in size over time, even up to 9 months. The DSNs were evaluated in the catalytic oxidation of styrene, using either H₂O₂ or TBHP as oxidant. Here, we show that the bimetallic DSNs are indeed the superior catalysts when compared to their monometallic analogues, under the same reaction conditions, since a good compromise between stability and activity can be achieved where the Au provides catalytic activity and the Cu serves as a stabilizer. These Au_mCu_n bimetallic DSNs present a less expensive and more stable catalyst with negligible loss of activity, opening the door to green catalysis.

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