Ag, Co3O4, Ag-Co3O4, and Ag/Co3O4 nanoparticles decorated mesoporous natural phosphate: effect of metal synergy and preparation method on the catalytic reduction reaction

Abstract

Addressed herein is a facile method for the preparation of cobalt-silver (Co-x-Ag-y) nanoparticles decorated mesoporous natural phosphate (m-NP). Various Co-x-Ag-y@NP nanocatalysts were prepared in different forms of Ag and Co3O4 including mono- and bimetallic active sites. The bimetallic nanocatalysts were prepared by two different preparation methods, namely in-situ (Ag-Co3O4) and ex-situ (Ag/Co3O4 core-shell). In the first step, colloidal Co-x-Ag-y nanoparticles were synthesized in solution and their formation was monitored by using UV-Visible spectroscopy. Furthermore, the obtained nanoparticles were characterized by XRD and IR spectroscopy. All nanoparticles were deposited on m-NP using a simple wetness impregnation method followed by a calcination at 500 degrees C. The prepared nanocatalysts were fully characterized by advanced analytical techniques including IR, XRD, XPS, SEM-EDX, FESEM, and TEM. The catalytic reduction of 4-nitrophenol was studied as a model reaction to investigate the effect of synergy created between the metals, oxidation state, catalyst structure, and preparation method on their catalytic activity. Accordingly, reaction kinetics and comparative study of various colloidal Co-x-Ag-y and m-NP supported nanocatalysts in the reduction of 4-nitrophenol was carried out. The optimized conditions were used to study the substrate scope of the catalytic reduction over various nitroarenes.