Novel mechanistic view of catalytic ozonation of gaseous toluene by dual-site kinetic modelling

Abstract

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractThe catalytic ozonation of VOCs is a promising approach for degradation of indoor VOCs, such as gaseous toluene. However, the mechanism and relevant kinetic steps involved in this reaction remain unclear. In this study, the catalytic ozonation of toluene over MnO 2 /graphene was investigated using the empirical power law model and classic Langmuir-Hinshelwood single-site (denoted as L-H s ) mechanism. The apparent activation energy determined using the power law model was 29.3±2.5 kJ mol −1 . This finding indicated that the catalytic ozonation of toluene over MnO 2 /graphene was a heterogeneous reaction, and the Langmuir-Hinshelwood mechanism was applicable. However, the L-H s mechanism did not fit the experimental data, suggesting that the reaction was non-single-site governed. A novel Langmuir-Hinshelwood dual-site (denoted as L-H d ) mechanism was then proposed to explain the experimental observations of the catalytic ozonation of toluene over MnO 2 /graphene through a steady-state kinetic study. This mechanism was based on the hypothesis that MnO 2 was responsible for ozone decomposition and toluene adsorption on graphene; these two types of adsorption were coupled by an adjacent attack. Furthermore, XPS results confirmed the presence of a strong connection between MnO 2 and graphene sites on the surface of MnO 2 /graphene. This connection allowed the adjacent attack and validated the dual-site mechanism. The L-H d model was consistent with the predicted reaction rate of toluene removal with a correlation coefficient near unity (r 2 = 0.9165). Moreover, the physical criterion was in accordance with both enthalpy and entropy of toluene adsorption constraints. Fulfillment of mathematical and physical criteria indicated the catalytic ozonation of toluene over MnO 2 /graphene can be well described by the L-H d mechanism. This study helps understand the catalytic ozonation of toluene over MnO 2 /graphene in a closely mechanistic view.

Simulation and optimization of the removal of toluene in air by ozonation with a catalytic open-cell foam

“…The fitted parameters are given in Table 2. The activation energy (61 kJ.mol -1 ) for toluene oxidation is in good agreement with available literature data in catalytic ozonation (44 kJ.mol -1 (Rezaei et al, 2013) and 48 kJ.mol -1 (Hu et al, 2017)). Behar et al (2015) reviewed the activation energy for toluene oxidation in thermocatalytic oxidation.…”

“…About the adsorption, the toluene adsorption enthalpy is highly negative and quite close to most of the literature data (ranging between -58 kJ.mol -1 (Hu et al, 2017) to -26 kJ.mol -1 (Hu, 2011), except one value of -271 kJ.mol -1 (Bedia et al, 2010)). It is also possible to determine the toluene adsorption entropy (ΔS toluene ) according to Eq.…”

“…J.mol -1 .K -1 , which respects the thermodynamic constraints given by Hu et al (2017). Actually, J o u r n a l P r e -p r o o f the loss of entropy in the adsorption of toluene onto the catalyst surface is higher than 41.9 J.mol -1 .K -1 but lower than the standard gas entropy of toluene (320.7 J.mol -1 .K -1 (Bedia et al, 2010)).…”

“…It is also possible to determine the toluene adsorption entropy (ΔS toluene ) according to Eq. (20) (Hu et al, 2017). It is -42.9…”

“…Actually, in a previous study about the use of the same type of catalytic glass foam for the removal of toluene by thermocatalytic oxidation (Lejeune et al, 2020b), the rate of oxidation reaches 0.12 g.m -3 .s -1 at 250°C and 1.0 g.m -3 inlet toluene concentration. Hu et al (2017) obtained a rate of toluene ozonation between 0.03 and 0.10 g.m -3 .s -1 with a MnO2/graphene catalyst at temperatures ranging from 22°C and 60°C. As previously highlighted, this comparison needs to be considered with caution because ruthenium is known to be more efficient than MnO2, but these results strengthen than the catalytic glass foam developed in this study can be competitive.…”