Preparing magnetic multicomponent catalysts via a bio-inspired assembly for heterogeneous reactions

Abstract

This article reports a facile synthetic approach for preparing magnetic porous catalysts, on which various inorganic compounds are alternately loaded using a pyrogallic acid (PG)-assisted layer-by-layer (LbL) coating. The PG forms an adhesion and reductive layer on the surface of hierarchically porous silica, and Pd, Al₂O₃, ZrO₂, or FeO_x can then be introduced on the surface of the material. Compared with the conventional impregnation method, the PG layer obviously improves the dispersion of catalysts and greatly reduces the blocking of the pores, which is caused by the formation of metal oxide catalysts. At the same time, the reduction properties of the layer help to reduce the diameter of the Pd nanoparticles to 5 ± 1.3 nm. The Fe³⁺ ions are partially reduced into Fe²⁺ by the PG layer to form Fe₃O₄, which endows the porous catalysts with a magnetic separation property. The synthesized multicomponent catalysts show excellent catalytic activity for various reactions, including the Suzuki Miyaura coupling, reduction, Knoevenagel condensation and Friedel–Crafts alkylation reactions. The TOF values show an improvement of 2 to 4 times over those of the catalysts prepared by the traditional impregnation method. The multicomponent magnetic catalysts also exhibit superior catalytic performance for many one-pot multistep cascade reactions.