The in situ shape-controlled synthesis and structure-activity relationship of Pd nanocrystal catalysts supported on layered double hydroxide

The in situ and shape-controlled preparation of layered double hydroxide (LDH)-supported Pd nanocrystals (NCs) has been successfully achieved. A facile process involving the ion-exchange reaction and subsequently the reduction reaction and in situ growth of Pd NCs on the LDH sheet was introduced, and the main factors influencing the final shape of Pd NCs have been discussed. Specifically, the triangular Pd nanoplates anchored on the LDH can be selectively synthesized by manipulating the reduction kinetics of the reaction through synergistic effects of the oxidative etching of Pd(0) by the O-2-Cl- pair and the controlled release of PdCl42- in the PdCl42--LDH system. The catalytic performances of LDH-supported Pd nanocubes ({100} exposed facets), truncated octahedra ({100} and {111} exposed facets) and triangular nanoplates (mainly {111} exposed facets) were evaluated through the Suzuki cross-coupling reaction. The supported Pd nanocubes show the highest catalytic activity compared to the other two supported Pd NC catalysts, which can be attributed to the Pd {100}-oriented surface terminations having lower surface atom density, a higher degree of unsaturation for the crystal plane atoms and a stronger interaction with the LDH support than Pd {111} facets. In addition, the LDH-supported Pd nanocube samples present good reusability and high stability, which is of immense importance for the large-scale applications as supported catalysts in Suzuki reaction.