Investigation of reaction mechanism and kinetic modelling for the toluene total oxidation in presence of CoAlCe catalyst

Catalytic removal of toluene using MnO2-based catalysts: A review

Volatile organic compounds (VOCs) have serious hazard to human health and ecological environment. Due to its low cost and high activity, the catalytic oxidation technology considered to be the most effective method to remove VOCs. Toluene is one of the typical VOCs, hence its catalytic elimination is crucial for the regulation of VOCs. Manganese dioxide (MnO₂) has been extensively studied for its excellent redox performance and low-temperature operation conditions. In this review, we summarize the research progresses in the toluene catalytic oxidation of MnO₂-based catalysts, which contain single MnO₂, metal-doped MnO₂ and supported MnO₂ catalyst. In particular, we pay much attention on the relationship between the chemical properties and toluene oxidation performance over MnO₂ catalyst, as well as the catalytic reaction mechanisms. Moreover, the effects of different crystal forms and morphologies on the catalytic toluene reaction were discussed. And the perspective on MnO₂ catalysts for the catalytic oxidation of toluene has been proposed. We expect that the summary of these important findings can serve as an important reference for the catalytic treatment of VOCs.

Review of Emission Characteristics and Purification Methods of Volatile Organic Compounds (VOCs) in Cooking Oil Fume

Volatile organic compounds (VOCs) in cooking oil fumes need to be efficiently removed due to the significant damage they cause to the environment and human health. This review discusses the emission characteristics, which are influenced by different cooking temperatures, cooking oils, and cuisines. Then, various cooking oil fume purification methods are mainly classified into physical capture, chemical decomposition, and combination methods. VOCs removal rate, system operability, secondary pollution, application area, and cost are compared. The catalytic combustion method was found to have the advantages of high VOC removal efficiency, environmental protection, and low cost. Therefore, the last part of this review focuses on the research progress of the catalytic combustion method and summarizes its mechanisms and catalysts. The Marse-van Krevelen (MVK), Langmuir-Hinshelwood (L-H), and Eley-Rideal (E-R) mechanisms are analyzed. Noble metal and non-noble metal catalysts are commonly used. The former showed excellent activity at low temperatures due to its strong adsorption and electron transfer abilities, but the high price limits its application. The transition metals primarily comprise the latter, including single metal and composite metal catalysts. Compared to single metal catalysts, the interaction between metals in composite metal catalysts can further enhance the catalytic performance.

Highly efficient removal of toluene over Cu-V oxides modified γ-Al2O3 in the presence of SO2

Developing efficient catalysts with good resistance to complex flue gas is essential for VOCs removal in coal-fired flue gas. In this study, by exploring the effect of transition metal oxide additive, metal loading and bimetallic synergy on toluene oxidation in coal-fired flue gas, 10Cu-3V/γ-Al₂O₃ is identified as the optimal catalyst. It achieves 90% of CO₂ generation at 350 ℃, which is decreased by ca. 46 ℃ compared with 13Cu/γ-Al₂O₃. And it also exhibits good resistance to H₂O and good stability. ICP-OES, N₂ adsorption-desorption isotherms, XRD, TEM, XPS, EPR and H₂-TPR analyses were applied to characterize the catalyst composition and physicochemical properties. Doping V into 13Cu/γ-Al₂O₃ not only leads to better dispersity of CuO and homogeneous elements distribution that benefits to produce more active centers, but also constitutes the redox cycle of V⁵⁺ + Cu⁺ ↔ V⁴⁺ + Cu²⁺ which induces more surface chemical oxygen (O_sur). Moreover, since SO₂ is the main inhibiting factor in toluene oxidation, the SO₂ poisoning mechanism was illustrated by XPS, TG and in situ DRIFT analyses in depth.

Low-temperature oxidative removal of gaseous formaldehyde by an eggshell waste supported silver-manganese dioxide bimetallic catalyst with ultralow noble metal content

Under dark/low temperature (DLT) conditions, the oxidative removal of gaseous formaldehyde (FA) was studied using eggshell waste supported silver (Ag)-manganese dioxide (MnO₂) bimetallic catalysts. To assess the synergistic effects between the two different metals, 0.03%-Ag-(0.5-5%)-MnO₂/Eggshell catalysts were prepared and employed for DLT-oxidation of FA. The steady-state FA oxidation reaction rate (mmol g^-1 h^-1), when measured using 100 ppm FA at 80 °C (gas hourly space velocity (GHSV) of 5308 h^-1), varied as follows: Ag-1.5%-MnO₂/Eggshell-R (9.4) > Ag-3%-MnO₂/Eggshell-R (8.1) > Ag-1.5%-MnO₂/Eggshell (7.5) > Ag-5%-MnO₂/Eggshell-R (7.2) > Ag-1.5%-MnO₂/CaCO₃-R (6.8) > MnO₂-R (6) > Ag-0.5%-MnO₂/Eggshell-R (3.2) > Ag/Eggshell-R (2.6). (Here, 'R' denotes hydrogen-based thermochemical reduction pretreatment.) The temperature required for 90% FA conversion (T₉₀) at the same GHSV exhibited a contrary ordering: Ag/Eggshell-R (175 °C) > Ag-0.5%-MnO₂/Eggshell-R (123 °C) > Ag-5%-MnO₂/Eggshell-R (113 °C) > MnO₂-R (99 °C) > Ag-1.5%-MnO₂/Eggshell (96 °C) > Ag-3%-MnO₂/Eggshell-R (93 °C) > Ag-1.5%-MnO₂/Eggshell-R (77 °C). The eggshell catalyst outperformed the ones made of commercial calcium carbonate due to the presence of defects in the former. The MnO₂ co-catalyst enhances the catalytic activities through the capture and activation of atmospheric oxygen (O₂) with rapid catalytic regeneration. Also, MnO₂ favorably captures the hydrogen of the adsorbed FA molecules to make the oxidation pathway thermodynamically more favorable.

Gold and Ceria as Catalysts for VOC Abatement: A Review

Due to its excellent oxygen storage capacity, ceria is a well-known oxidation catalyst. However, its performance in the oxidation of volatile organic compounds can be improved by the introduction of gold. Depending on the type of VOC to be oxidized, the surface of gold nanoparticles and the gold/ceria interface may contribute to enhanced activity and/or selectivity. Choosing a proper preparation method is crucial to obtain optimal gold particle size. Deposition–precipitation was found to be more suitable than coprecipitation or impregnation. For industrial applications, monolithic catalysts are needed to minimize the pressure drop in the reactor and reduce mass and heat transfer limitations. In addition to the approach used with powder catalysts, the method employed to introduce gold in/on the washcoat has to be considered.

The Catalytic Oxidation of Formaldehyde by FeOx-MnO2-CeO2 Catalyst: Effect of Iron Modification

A series of FeOx-MnO2-CeO2 catalysts were synthesized by the surfactant-templated coprecipitation method and applied for HCHO removal. The influence of Fe/Mn/Ce molar ratio on the catalytic performance was investigated, and the FeOx-MnO2-CeO2 catalyst exhibited excellent catalytic activity, with complete HCHO conversion at low temperatures (40 °C) when the molar ratio of Fe/Mn/Ce was 2/5/5. The catalysts were characterized by N2 adsorption and desorption, XRD, H2-TPR, O2-TPD and XPS techniques to illustrate their structure–activity relationships. The result revealed that the introduction of FeOx into MnO2-CeO2 formed a strong interaction between FeOx-MnO2-CeO2, which facilitated the improved dispersion of MnO2-CeO2, subsequently increasing the surface area and aiding pore development. This promotion effect of Fe enhanced the reducibility and produced abundant surface-active oxygen. In addition, a great number of Oα is beneficial to the intermediate decomposition, whereas the existence of Ce3+ favors the formation of oxygen vacancies on the surface of the catalyst, all of which contributed to HCHO oxidation at low temperatures.

Comparative Study of Strategies for Enhancing the Performance of Co3O4/Al2O3 Catalysts for Lean Methane Combustion

Spinel-type cobalt oxide is a highly active catalyst for oxidation reactions owing to its remarkable redox properties, although it generally exhibits poor mechanical, textural and structural properties. Supporting this material on a porous alumina can significantly improve these characteristics. However, the strong cobalt–alumina interaction leads to the formation of inactive cobalt aluminate, which limits the activity of the resulting catalysts. In this work, three different strategies for enhancing the performance of alumina-supported catalysts are examined: (i) surface protection of the alumina with magnesia prior to the deposition of the cobalt precursor, with the objective of minimizing the cobalt–alumina interaction; (ii) coprecipitation of cobalt along with nickel, with the aim of improving the redox properties of the deposited cobalt and (iii) surface protection of alumina with ceria, to provide both a barrier effect, minimizing the cobalt–alumina interaction, and a redox promoting effect on the deposited cobalt. Among the examined strategies, the addition of ceria (20 wt % Ce) prior to the deposition of cobalt resulted in being highly efficient. This sample was characterized by a notable abundance of both Co3+ and oxygen lattice species, derived from the partial inhibition of cobalt aluminate formation and the insertion of Ce4+ cations into the spinel lattice.

Preparation of metal-doped Cu-Mn/HTS-1 catalysts and their mechanisms in efficient degradation of toluene

In order to study their synergistic catalytic effects in toluene degradation, CuMn₂O₄/HTS-1 (HTS-1 was a titanium silicon molecular sieve), Cu_0.7Mn₂Y_0.3O_x/HTS-1 and Cu_0.7Mn₂Ce_0.3O_x/HTS-1 catalysts were prepared by the impregnation method. The textural properties, redox properties and acidity of the catalysts were characterized by X-ray diffractometer (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), H₂ temperature-programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS), frustrated total internal reflection (FT-IR), ammonium temperature-programmed desorption (NH₃-TPD) and pyridine adsorption internal reflection (Py-IR) measurements. The potential roles of Lewis acid sites (activating dioxygen) were discussed, and the experimental results indicated that the most efficient route for toluene degradation over Cu_0.7Mn₂Ce_0.3O_x/HTS-1 (toluene conversion rate of 90% (T₉₉)=295°C) was ascribed to regulation of the synergistic effects of redox properties (activating molecular toluene) and Lewis acid sites (activating dioxygen). The Mars-Van-Krevelen (MVK) model was adopted to describe the reaction process of toluene oxidation, which gave an in-depth view into the toluene degradation over CuMn₂O₄/HTS-1, Cu_0.7Mn₂Y_0.3O_x/HTS-1 and Cu_0.7Mn₂Ce_0.3O_x/HTS-1. In addition, the synergistic effects between redox properties and Lewis acid sites were studied in detail.