Synthesis of supported Pd nanocluster catalyst by spontaneous reduction on layered double hydroxide

Abstract

A feasible method for spontaneous in situ reductions on layered double hydroxides (LDHs) to prepare supported catalysts with Pd sub-nanoparticles is proposed. In this process, the reductive sites for the Pd2+ are introduced into the LDHs laminates in a highly dispersed distribution, and a series of reductive supports (such as CoAl-LDHs, CoNiFe-LDHs, FeAl-LDHs) are prepared. The obtained reductive support is directly used to reduce Pd precursor without the addition of a reducing agent. HRTEM images show that metallic Pd is successfully reduced and evenly distributed on the support. Moreover, hexadecyl trimethyl ammonium chloride (CTAC) is introduced to improve the dispersion of Pd. HAADF-STEM results illustrate that metallic Pd particles are prepared in the form of a sub-nanometer size. XPS analysis show that Co and Pd species undergo a redox reaction and have an electronic interaction with CTAC. The factors affecting the nucleation and growth of Pd sub-nanoparticles in CTAC-modified support spontaneous in-situ redox are also discussed. The obtained PdMI/CoAl-LDHs (prepared by modified support spontaneous in situ redox method (MI)) is applied to the selective oxidation of benzyl alcohol. It is found that the selectivity is 91% at a conversion of 92%, and turnover frequency (TOF) of PdMI/CoAl-LDHs is 2.2 times higher than that of PdD/MgAl-LDHs prepared by the common dipping method. Furthermore, PdMI/CoAl-LDHs shows excellent stability in 5 times reusability and 150 h use, demonstrating the Oswald ripening of Pd particles can be effectively prevented.