New insights of the initial processes of pyrene oxidation in the presence of Cu-based catalysts: Quantum-mechanical calculation and experimental evidence

Abstract

The oxidation and catalytic oxidation products of pyrene was analyzed by electron paramagnetic resonance (EPR), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF), Fourier-transform infrared spectroscopy (FT-IR), and gas chromatography-mass spectrometry (GC-MS). The in-situ transformation of Cu-based catalysts was analyzed. A qualitative model of pyrene oxidation with and without catalyst was built. CuO nanoparticles were in-situ formed as the active phases, and they decreased the polymerization and condensation of pyrene. The oxidation pathways of pyrene with and without CuO nanoparticles with the main product of 9-oxo-phenaleno-1-carbaldehyde were considered, which includes two elementary stages with the limiting Gibbs energy barrier of 227 kJ/mol. CuO increases the number of stages to three and reduces the Gibbs activation energy by 20 % of the limiting stage of pyrene oxidation. These findings provide new insights into the initial oxidation of pyrene and its catalysis. The proposed model and methods using Density functional theory (DFT) calculation offer a new theoretical approach for investigating hydrocarbon oxidation as well as designing catalytic systems for accelerating their oxidation.