Microwave-assisted catalytic oxidation of gaseous toluene with a Cu-Mn-Ce/cordierite honeycomb catalyst

Replacement of noble metal catalysts by CuMnOx/CeOx/CH catalyst in catalytic combustion of toluene

To verify the feasibility of replacing noble metal catalysts by transition metals-based catalysts, monolithic CuMnOx/CeOx/cordierite honeycomb (CH) catalysts were prepared by conventional impregnation method and applied in microwave catalytic combustion of toluene. The research suggested that CuMnOx/CeOx/CH catalysts, demonstrated strong microwave-absorbing ability due to first dielectric loss and secondary magnetic loss, exhibited higher catalytic activities under microwave heating than electric heating. This is probably attributed to high temperature "hot spots" of microwave, the abundant pore structure of active particles of CuMnOx/CeOx/CH catalyst, and oxygen vacancies and Oads on the catalysts' surface. The research also suggested that under the conditions of an initial toluene concentration of 1500 mg m-3, airflow of 0.18 m³ h-1 and gas hourly space velocity of 7000 h-1, toluene could be completely removed at a relatively low temperature of 276 °C and mineralized at 304 °C by microwave catalytic combustion. Compared with noble metal catalysts, CuMnOx/0.03CeOx/CH catalyst had a lower light-off temperature and nearly complete combustion temperature for toluene removal and mineralization under microwave heating, which confirms the possibility of replacing noble metal catalysts. Moreover, CuMnOx/0.03CeOx/CH catalyst exhibited excellent stability at a bed temperature of 300 ℃ after six cycles of a total of 960 min and achieved a 100 % removal and 94 % mineralization of toluene. This study also identified the key mechanism behind which is the electron transfers among Cu2+/Cu+, Mn4+/Mn3+/Mn2+, and Ce4+/Ce3+ that promoted the adsorption, activation, and transformation of gaseous oxygen. Hence, toluene is firstly adsorbed by active particles and then oxidized onto the hot spots by both Oads and Olatt which follows the L-H mechanism and the MvK mechanism, respectively. Therefore, this research work provides further technological support for the development of transition metals-based catalysts and the application of microwave catalytic combustion in treating industrial VOCs waste gas.

Recent advances in low-temperature nitrogen oxide reduction: effects of electric field application

This article presents a review of catalytic processes used at low temperatures to reduce emissions of nitrogen oxides (NOx) and nitrous oxide (N2O), which are exceedingly important in terms of their environmental impacts on the Earth. With conventional purification technologies, it has been difficult to remove these compounds under low-temperature conditions. By applying a catalytic process in an electric field for the three reactions of three-way catalysts (TWC), NOx storage reduction catalysts (NSR), and direct decomposition of N2O, we have achieved high catalytic activity even at low temperatures. By promoting ion migration on the catalyst surface, we have filled in the gaps in conventional catalytic technology and have opened the way to more efficient conversion of NOx and N2O.

Potential Strategy to Control the Organic Components of Condensable Particulate Matter: A Critical Review

More and more attention has been paid to condensable particulate matter (CPM) since its emissions have surpassed that of filterable particulate matter (FPM) with the large-scale application of ultralow-emission reform. CPM is a gaseous material in the flue stack but instantly turns into particles after leaving the stack. It is composed of inorganic and organic components. Organic components are an important part of CPM, and they are an irritant, teratogenic, and carcinogenic, which triggers photochemical smog, urban haze, and acid deposition. CPM organic components can aggravate air pollution and climate change; therefore, consideration should be given to them. Based on existing methods for removing atmospheric organic pollutants and combined with the characteristics of CPM organic components, we provide a critical overview from the aspects of (i) fundamental cognition of CPM, (ii) common methods to control CPM organic components, and (iii) catalytic oxidation of CPM organic components. As one of the most encouraging methods, catalytic oxidation is discussed in detail, especially in combination with selective catalytic reduction (SCR) technology, to meet the growing demands for multipollutant control (MPC). We believe that this review is inspiring for a fuller understanding and deeper exploration of promising approaches to control CPM organic components.

Synthetic effect of supports in Cu-Mn-doped oxide catalysts for promoting ozone decomposition under humid environment

The escalating levels of surface ozone concentration pose detrimental effects on public health and the environment. Catalytic decomposition presents an optimal solution for surface ozone removal. Nevertheless, catalyst still encounters challenges such as poisoning and deactivation in the high humidity environment. The influence of support on catalytic ozone decomposition was examined at a gas hourly space velocity of 300 L·g-1·h-1 and 85% relative humidity under ambient temperature using Cu-Mn-doped oxide catalysts synthesized via a straightforward coprecipitation method. Notably, the Cu-Mn/SiO2 catalyst exhibited remarkable performance on ozone decomposition, achieving 98% ozone conversion and stability for 10 h. Further characterization analysis indicated that the catalyst's enhanced water resistance and activity could be attributed to factors such as an increased number of active sites, a large surface area, abundant active oxygen species, and a lower Mn oxidation state. The catalytic environment created by mixed oxides can offer a clearer understanding of their synergistic effects on catalytic ozone decomposition, providing significant insights into the development of water-resistant catalysts with superior performance.

Current progress on catalytic oxidation of toluene: a review

Toluene is one of the pollutants that are dangerous to the environment and human health and has been sorted into priority pollutants; hence, the control of its emission is necessary. Due to severe problems caused by toluene, different techniques for the abatement of toluene have been developed. Catalytic oxidation is one of the promising methods and effective technologies for toluene degradation as it oxidizes it to CO₂ and does not deliver other pollutants to the environment. This paper highlights the recent progressive advancement of the catalysts for toluene oxidation. Five categories of catalysts, including noble metal catalysts, transition metal catalysts, perovskite catalysts, metal-organic frameworks (MOFs)-based catalysts, and spinel catalysts reported in the past half a decade (2015-2020), are reviewed. Various factors that influence their catalytic activities, such as morphology and structure, preparation methods, specific surface area, relative humidity, and coke formation, are discussed. Furthermore, the reaction mechanisms and kinetics for catalytic oxidation of toluene are also discussed.