Low-Palladium-Content Iron(III) Nanocatalyst Supported on Zeolite-NaY for C-Cl Bond Activation

Abstract

A heterogeneous nanocatalyst comprising palladium (Pd/PdO) and iron(III) oxide (Fe2O3) in the dimension of 1-4 nm was synthesized using sodium-exchanged zeolite-Y or zeolite-NaY [a type of faujasite (FAU) zeolite having an aluminosilicate framework with a general formula of (Na-2)(3).5[Al7Si17O48].32H(2)O] as a support matrix. The catalyst was investigated as a true heterogeneous catalyst for activation of the robust C-Cl bond of aryl chlorides in the Suzuki-Miyaura cross-coupling (SMCC) reaction. The catalyst with very low Pd loading (0.0037 mol %) exhibited high reactivity in the SMCC reaction with various derivatives of aryl chlorides (Ar-Cl). Biaryl products were obtained with up to a 92% yield, high selectivity, and a good turnover number with this Pd/PdO-Fe2O3-Y catalyst. The catalyst exhibited good thermal stability and was highly recyclable. The reaction was found to be reliant on various parameters such as solvent system, temperature, time, and catalyst amount. A small aliquot of water (H2O) mixed with methanol (CH3OH) dramatically brought a substantial improvement in the product yield of the desired biaryl product. The role of zeolite-NaY was also investigated by comparing the results with various other synthesized catalysts. Different experimental studies indicated that the surface hydroxyl (-OH) groups of zeolite-NaY, modification of basic sites, and the ability to influence the reduction temperature of iron (Fe) and palladium (Pd) influenced the catalytic performance of the synthesized catalyst. The impact of Fe on the electronic structure and reactivity of Pd was analyzed through a density functional theory calculation. This study provided strong evidence for creation of a negative (-ve) charge on Pd with an increasing amount of Fe content and thereby favored the in situ transformation of Pd(II) to Pd(0) as required in the activation of the C-Cl bond.