Morphologically tailored facet dependent silver nanoparticles supported α-Al2O3 catalysts for chemoselective reduction of aromatic nitro compounds

Abstract

The nanoparticles surface area, intrinsic sites, exposed microcrystal shapes and lattice planes are some of the key factors in nanocatalysis. The influence of nanoparticles shape dependent had been profound effect on its catalytic activity. This study is focused on the synthesis of morphologically shape-controlled silver (Ag) nanoparticles supported on α-Al2O3 catalysts were performed. The correlation of Ag NPs with varied facets and lattice planes on the catalytic activities in chemoselective reduction of nitro compounds was investigated. Engineering the silver nanoparticles with different shapes and facets i.e., nanocubes (AgNCs), nanowires (AgNWs) and nano spheres (AgNSPs) were synthesized by using modified polyol method. It is demonstrated that there is a significant difference in their activities with respect to the shape and nanocrystal facets. The evolution of nanoshapes and the structural properties of Ag nanoparticles were analysed by SEM, TEM, HR-TEM and P-XRD techniques. From XRD, Ag nanocubes exhibited high percentage of low index (100) facets which are favourable active centers than (111) plane in nitro reduction. We observed that the silver nanocubes selectively exposed (100) facets, which are highly favorable for the enhanced catalytic activity in nitro reduction. The reaction rate of nitro phenol to amino phenol over different Ag nanoshapes are 35.01 × 10−3 min−1 (AgNCs/Al2O3), 8.28 × 10−3 min−1 (AgNWs/Al2O3), 0.65 × 10−3 min−1 (AgNSPs/Al2O3), respectively. The calculated thermodynamic parameters of the Ea values 23.6, 28.6 and 29.4 for the AgNC, AgNWs and AgNSP respectively.