Kinetics of the catalytic oxidation of toluene over Mn,Cu co-doped Fe2O3: Ex situ XANES and EXAFS studies to investigate mechanism

Abstract

In this study, the catalytic mechanism of Mn,Cu-Fe2O3 catalyst was directly determined through reaction kinetics coupled with surface characterization. The impact of operating conditions on the catalytic performance of Mn,Cu-Fe2O3 nanocomposite for toluene oxidation in a continuous fixed-bed reactor was investigated. It was found that Mn,Cu-Fe2O3 catalyst gave the best catalytic performance in toluene removal when the initial concentrations of toluene and oxygen were at 165 ppmv and 10% at a flow rate of 200 mL min−1, respectively. Subsequently, Power-law, Mars-van Krevelen, and Langmuir-Hinshelwood models were developed to describe the kinetics of the total toluene oxidation for both toluene- and oxygen-dependent mixtures in a range of temperatures. According to the results, the basic Power-law model could not properly represent the kinetics of toluene oxidation over the catalyst. Meanwhile, the Mars-van Krevelen model allows for determining the kinetic mechanism under the variation of C7H8 concentration. The Langmuir-Hinshelwood model is attainable to express the kinetics of the oxygen-involved reaction mechanism. Moreover, the change in the structure of Mn,Cu-Fe2O3 catalyst after the catalytic reaction was characterized by X-ray Absorption Near-edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) measurements to confirm the catalytic mechanism determined through reaction kinetics. The achieved results suggest the possibility of using various models to justify the correlation between model-simulated and experimental data for VOCs oxidation in a continuous-flow catalytic reactor.