Evidence of an Oxidative-Addition-Promoted Pd-Leaching Mechanism in the Suzuki Reaction by Using a Pd-Nanostructure Design
ABSTRACT Nanocatalysts behave homogeneously: The structural changes of two rationally designed heterogeneous Pd-based nanocatalysts were examined in a Suzuki reaction. By taking advantage of additional nanostructural characteristics, direct evidence of the leaching of soluble Pd was obtained; hence, the catalysis is promoted by oxidative addition of aryl halides to the nanoparticles.
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ABSTRACT: We studied computationally the leaching of palladium from the ideal surface Pd(111) and its various structural defects at different coverages of CO, using density functional calculations on slab models. Accordingly, the energy required for leaching of a single Pd atom from a bare surface is quite large, at least similar to 270 kJ mol(-1). In a CO atmosphere at low density, PdCO is predicted to be the leaching species; this process was calculated to require at least 225 kJ mol(-1), somewhat less than the leaching of a bare metal adatom, 268 kJ mol(-1). The energies required for either leaching process (at low CO density), yielding single Pd atoms or PdCO subcarbonyl, correlate in a linear fashion with the coordination number of the Pd center to be leached. At high CO coverage, leaching of Pd subcarbonyl species, Pd(CO)(x) (x = 2, 3), was calculated to be thermodynamically favorable in several cases, providing direct theoretical evidence for the feasibility of Pd leaching in a dense CO atmosphere. In a qCatalysis Science & Technology 11/2012; 2(11-11). DOI:10.1039/C2CY20441J · 4.76 Impact Factor
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ABSTRACT: Alloy or core-shell Au-Pd bimetallic nanocrystals confined in silica nanorattles are prepared in order to enhancing their catalytic activity, selectivity and stability. The formation of the alloy or core-shell structure is controlled via tuning the reduction kinetics in a one pot hydrothermal solution. A kind of silane with alkylamino groups is chosen as the reducing agent and pre-encapsulated in the middle layer of hybrid solid silica nanospheres, which ensures that the Au-Pd bimetallic nanocrystals are prepared inside the silica nanorattles. The composition of the Au-Pd alloy core is easily tuned by changing the ratio of Au-Pd precursor concentration from 3 : 1, to 1 : 1, to 1 : 3. Suzuki cross-coupling reactions are chosen as model reactions to evaluate the catalytic ability of these nanocatalysts. The conversion and yield from highest to lowest for all catalyst are in the sequence: alloy Au3Pd1 > Au1Pd1 > Au1Pd3 > core-shell Au-Pd > Pd > Au. Notably, the alloy Au-Pd@SiO2 with the lowest Pd contentJournal of Materials Chemistry A 01/2013; 1(35-35):10382-10388. DOI:10.1039/C3TA11749A · 7.44 Impact Factor
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ABSTRACT: Ag–Pd bimetallic nanocrystals (NCs) with tunable compositions and narrow size distributions were produced by a one-pot synthesis. The NC growth process was investigated by time-dependent TEM, XRD, and UV–vis studies. In the hydrodechlorination of 4-chlorophenol, the AgPdx (x = 2, 4, 6, 9, 19) showed pronounced composition-dependent catalytic activities, leading to the AgPd9 catalyst with excellent activity.ACS Catalysis 06/2013; 3(7):1560–1563. DOI:10.1021/cs400282a · 7.57 Impact Factor