Pd-SnO2/Al2O3 heteroaggregate nanocatalysts for selective hydrogenations of p-nitroacetophenone and p-nitrobenzaldehyde
Pd-SnO 2 heteroaggregate nanocatalysts were synthesized by in-situ transformation of PdSn bimetallic nanoparticles on alumina. The PdSn bimetallic nanoparticles were prepared by co-reduction of Pd and Sn precursors. The obtained PdSn nanoparticles possibly have a core-shell like structure with Pd cores and Sn-rich shells due to the fast reduction of Pd precursors. The Pd-SnO 2 /Al 2 O 3 heteroaggreagte nanocatalysts were synthesized by calcination of PdSn/Al 2 O 3 in air followed by H 2 reduction. Various characterization techniques, such as HRTEM, XRD and XPS, were used to characterize the PdSn and Pd-SnO 2 . The Pd 3 -(SnO 2 ) 1 /Al 2 O 3 heteroaggreagte nanocatalysts with a ratio of Pd/Sn of 3/1 illustrated enhanced catalytic performances for p -nitroacetophenone and p -nitrobenzaldehyde hydrogenations relative to monometallic Pd nanocatalysts. Theoretical calculations using density functional theory suggested that Pd-SnO 2 facilitates the adsorption of reactants in a higher degree than that of products, thus enhancing the catalytic activity even with partial coverage of Pd surfaces with SnO 2 . The blockage effect of SnO 2 on Pd surfaces is speculated to enhance the catalytic selectivity for p -nitroacetophenone and p -nitrobenzaldehyde hydrogenations over Pd-SnO 2 heteroaggregate nanocatalysts.
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