Discretization and Encapsulation of Palladium inside the Cavity of Crown Ether within the Interlayer of Layered Double Hydroxide for Enhanced Activity: A Case Study with Hydrogenation Reaction

The activity of the noble metal-based heterogeneous catalysts is limited by weak metal-support interactions, aggregation, and low surface to volume (S/V) ratio. The activity can be augmented in many ways. Among them, the discretization of the active sites and redistribution of electron density around the metal atom is an important one. In this work, these two phenomena are studied concerning a model reaction, hydrogenation of p-nitrophenol (p-NP). Herein, 1,4,7,10,13-pentaoxacyclopentadecane ether is introduced in the basal space of layered double hydroxide (LDH) to encapsulate noble Pd0 atom inside the cavity of the crown molecule strategically. The modified LDH (Pda-ECC-L0.10@in situ CoAl LDH) augments the properties, like, high S/V ratio and nonaggregation of active sites by forming nonagglomerative discrete catalytic (DNSC) sites within the cavity of crown ether in the basal space. The developed catalyst exhibits higher turnover frequency demonstrating the improved activity due to the formed DNSC sites and redistributes electron density around the Pd atoms by LDH layers and crown molecules. Thus, the present material synthesis route can be considered as a stand-alone method for preparation of the supported sub-nanometer noble metal catalyst with higher activity and can be exploited for reactions where noble metal catalyst are used.