Core–shell Pd(0)@His-SiO2/CoFe2O4 nano-composite as a magnetically recoverable heterogeneous catalyst for the deprotection of oximes and Heck coupling†

Abstract

With the advent of nanotechnology, the rational engineering of core–shell nanostructure-based catalysts has received significant attention owing to their potential for exhibiting unique properties such as durability, structural flexibility, and porous shell adaptability. In this study, we designed a magnetic core–shell based heterogeneous nanocatalyst [Pd(0)@His-SiO₂/CoFe₂O₄] comprising a histidine functionalized silica supported cobalt ferrite core encapsulated with a Pd(0) nanoparticle shell. Cobalt ferrite was synthesized using a hydrothermal process and modified with silica to obtain homogeneous dispersion and a dense structure as well as to prevent self-agglomeration in the core. Further, the core moiety was functionalized using a non-toxic amine linker, i.e. histidine, which acts as a robust anchor for holding the Pd(0) shell. The catalytic activity of Pd(0)@His-SiO₂/CoFe₂O₄ was evaluated for the oxidative deprotection of oximes and Heck coupling, and excellent results were obtained with high recyclability of the catalyst. Comparative study showed that the Pd(0) nanoparticle shell is the active species and the cobalt ferrite core plays a promotional role. XPS showed the existence of synergism between the core and the shell, suggesting that the electron density was drifted from the cobalt ferrite core towards the Pd(0) shell, which could be the reason for its enhanced catalytic performance. VSM demonstrated high saturation magnetization in both fresh and reused catalysts, which facilitates the separation of the catalyst from the reaction mixture. Thus the proposed approach based on the core–shell nanostructure provides a useful platform for the fabrication of an active metal such as Pd(0) with easy accessibility, excellent activity and convenient recovery.