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

The 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 MnO2/graphene was investigated using the empirical power law model and classic Langmuir-Hinshelwood single-site (denoted as L-Hs) 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 MnO2/graphene was a heterogeneous reaction, and the Langmuir-Hinshelwood mechanism was applicable. However, the L-Hs 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-Hd) mechanism was then proposed to explain the experimental observations of the catalytic ozonation of toluene over MnO2/graphene through a steady-state kinetic study. This mechanism was based on the hypothesis that MnO2 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 MnO2 and graphene sites on the surface of MnO2/graphene. This connection allowed the adjacent attack and validated the dual-site mechanism. The L-Hd model was consistent with the predicted reaction rate of toluene removal with a correlation coefficient near unity (r2 = 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 MnO2/graphene can be well described by the L-Hd mechanism. This study helps understand the catalytic ozonation of toluene over MnO2/graphene in a closely mechanistic view

Activated carbon surface chemistry: Changes upon impregnation with Al(III), Fe(III) and Zn(II)-metal oxide catalyst precursors from NO3− aqueous solutions

[EN] Because of the relevance in heterogeneous catalysis, the changes produced in the surface chemistry of activated carbon (AC) upon impregnation with the Al3+, Fe3+ and Zn2+ ions from aqueous solution of NO3 salts at pH 2.91 for Al3+, 1.54 for Fe3+ and 5.16 for Zn2+ in two successive soaking and oven-drying steps are studied. The samples (A120, F120 and Z120) were analyzed in terms of elemental composition and by energy dispersive X-ray analysis (EDX), FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS), and measurement of pH of the point of zero charge (pHpzc). The process yield was 102 wt% for A120, 114 wt% for F120, and 103 wt% for Z120. Chromene, pyrone and ether type structures are by far predominant in AC. The hydrolysis of metal ions markedly influences the pH of the impregnation solution and thereby the oxidation of surface functional groups of AC by O2 and NO3 dissolved in such a solution. The degree of AC oxidation is larger with the Fe3+ solution than with the Al3+ and Zn2+ solutions. Carboxylic acid groups for F120 and phenolic hydroxyl groups for Z120 and especially for A120 are formed from reducing structures of AC. The nitrogen content is higher by Z120 > A120 >F120 > AC. pHpzc is 10.50 for AC, 5.20 for A120, 4.00 for F120 and 6.30 for Z120. 2016 The Authors. Published by Elsevier B.V. on behalf of King Saud University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)