Effect of Iron Content in Alumina-Supported Palladium Catalysts and Their Reduction Conditions on Diclofenac Hydrodechlorination in an Aqueous Medium

Abstract

Iron oxide-modified 1Pd0.5Fe and 1Pd10Fe catalysts with a target content of 1 wt % Pd and 0.5 or 10 wt % Fe have been synthesized by the wet impregnation of Al₂O₃ with iron and palladium nitrates. The catalysts have been compared with each other and with a monometallic 1Pd catalyst in diclofenac (DCF) hydrodechlorination (HDC) in dilute aqueous solutions at 30°C in batch and flow reactors after high-temperature (320°C) and mild reduction (30°C), the latter being run in a batch or flow reactor. X-ray photoelectron spectroscopy (XPS) has revealed that, after reduction at 320°C, the catalysts contain mostly Pd⁰, Fe²⁺, and Fe³⁺. The Fe²⁺/Fe³⁺ ratio on the surface increases with a decrease in the iron content. The reduction of Pd²⁺ to Pd⁰ can occur even at 30°C; however, on the 1Pd0.5Fe surface, it is significantly less effective than that on 1Pd10Fe. According to XPS, temperature-programmed reduction, and diffuse reflectance infrared Fourier transform spectroscopy of adsorbed CO, modification with iron oxides leads to an increase in the palladium content on the surface compared with that on 1Pd, contributes to the formation of new Pd–O–Fe sites, and affects the reducibility of palladium. These effects enhance with an increase in the iron content. The iron-modified catalysts reduced at 320°C exhibit similar activity and stability in DCF conversion in flow and batch systems. The 1Pd10Fe catalyst, unlike 1Pd0.5Fe, is highly efficient and stable even after mild reduction at 30°C. Under flow conditions, it provides a DCF conversion comparable to that provided by 1Pd and a selectivity in the DCF HDC reaction that is higher than that provided by 1Pd, which is also active in hydrogenation.