Shape-controlled preparation of nano gold (Au), Au clusters, and Au single atoms based on layered double hydroxide with closo-dodecaborate and their utilization for selective nitrobenzene reduction

Abstract

Single-atom (SA) catalysts are superior in terms of catalytic activity, selectivity, and metal utilization. However, the complex preparation methods of SAs hinder their widespread application. Herein, layered double hydroxides (LDHs) with unique charge distributions were ingeniously combined with the dodecahydro-closo-dodecaborate anion [closo-B12H12]2−. We designed two different gold(Au) catalysts based on LDHs with closo-dodecaborate for the selective reduction of nitrobenzenes: composite dual-site Au SA/Au cluster catalysts (B12H12-MgAl-LDH-Au) were prepared using the anion exchangeability and spatial domain–limiting properties of LDH and the reducibility of [closo-B12H12]2−, and other Au nanoparticle catalysts (MgAl-LDH@B12H12@Au) were obtained using the reducibility of [closo-B12H12]2− immobilized on the LDH laminate. Up to 27 different nitrobenzene substrates can be selectively reduced to the corresponding azoxybenzenes (AOBs) with high efficiency at a wavelength of 450-nm radiation catalyzed by B12H12-MgAl-LDH-Au. However, large-size nanoparticles were more efficient in absorbing visible light energy. Therefore, 10 different AOB compounds were prepared using the MgAl-LDH@B12H12@Au system.