Combustion synthesis of copper-doped perovskite SrFe1-xCuxO3-δ nanomaterials and its potential application on hydroxylation of anisole, a biomass model component

Abstract

A series of copper-doped strontium ferrites with a perovskite structure, SrFe1-xCuxO3-δ; x = 0–0.45 (SFCx), were successfully prepared via a combustion synthesis method using hexamine as fuel followed by heat treatment at 1000 °C for 3h. The obtained SFCx materials were characterized using various analytical and spectroscopic techniques. X-ray diffraction patterns of the perovskite exhibited a cubic structure with a Pm-3m (221) space group. The presence of Fe4+, Fe3+, Cu2+, Cu+, and oxygen vacancies was confirmed via X-ray photoelectron spectroscopy. The formation of nanoparticles was confirmed by scanning electron microscopy images of the perovskite phase. The surface area was investigated using the Brunauer–Emmett–Teller method. SFCx materials were systematically evaluated for catalytic hydroxylation of anisole using hydrogen peroxide, an environmentally benign oxidant, and acetonitrile as solvent. Effects of various reaction parameters, such as the catalyst concentration, H2O2/substrate molar ratio, solvent, reaction temperature, and time, were thoroughly studied. A maximum anisole conversion (76.9%) with 62.5% of guaiacol selectivity was observed in the presence of the SFC0.45 catalyst at 80 °C for 6 h using H2O2 as an oxidant. The proposed hydroxyl radical mechanism for catalytic hydroxylation of anisole is well supported by electron paramagnetic resonance (EPR) studies, where the quenching of signal corresponds to paramagnetic Cu(II) species by the introduction of hydrogen peroxide. Catalytic test results suggest that the synergistic effect of copper and oxygen vacancies facilitates anisole hydroxylation.