In situ DRIFTS FT-IR and DFT study on Fe-V-W/Ti removal of NOx and VOCs

A High-Performance Mn/TiO2 Catalyst with a High Solid Content for Selective Catalytic Reduction of NO at Low-Temperatures

Mn/TiO2 catalysts with varying solid contents were innovatively prepared by the sol-gel method and were used for selective catalytic reduction of NO at low temperatures using NH3 (NH3-SCR) as the reducing agent. Surprisingly, it was found that as the solid content of the sol increased, the catalytic activity of the developed Mn/TiO2 catalyst gradually increased, showing excellent catalytic performance. Notably, the Mn/TiO2 (50%) catalyst demonstrates outstanding denitration performance, achieving a 96% NO conversion rate at 100 °C under a volume hourly space velocity (VHSV) of 24,000 h-1, while maintaining high N2 selectivity and stability. It was discovered that as the solid content increased, the catalyst's specific surface area (SSA), surface Mn4+ concentration, chemisorbed oxygen, chemisorption of NH3, and catalytic reducibility all improved, thereby enhancing the catalytic efficiency of NH3-SCR in degrading NO. Moreover, NH3 at the Lewis acidic sites and NH4+ at the Bronsted acidic sites of the catalyst were capable of reacting with NO. Conversely, NO and NO2 adsorbed on the catalyst, along with bidentate and monodentate nitrates, were unable to react with NH3 at low temperatures. Consequently, the developed catalyst's low-temperature catalytic reaction mechanism aligns with the E-R mechanism.

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.

Recent advances in simultaneous removal of NOx and VOCs over bifunctional catalysts via SCR and oxidation reaction

NOx and volatile organic compounds (VOCs) are two major pollutants commonly found in industrial flue gas emissions. They play a significant role as precursors in the formation of ozone and fine particulate matter (PM2.5). The simultaneous removal of NOx and VOCs is crucial in addressing ozone and PM2.5 pollution. In terms of investment costs and space requirements, the development of bifunctional catalysts for the simultaneous selective catalytic reduction (SCR) of NOx and catalytic oxidation of VOCs emerges as a viable technology that has garnered considerable attention. This review provides a summary of recent advances in catalysts for the simultaneous removal of NOx and VOCs. It discusses the reaction mechanisms and interactions involved in NH3-SCR and VOCs catalytic oxidation, the effects of catalyst acidity and redox properties. The insufficiency of bifunctional catalysts was pointed out, including issues related to catalytic activity, product selectivity, catalyst deactivation, and environmental concerns. Subsequently, potential solutions are presented to enhance catalyst performance, such as optimizing the redox properties and acidity, enhancing resistance to poisoning, substituting environment friendly metals and introducing hydrocarbon selective catalytic reduction (HC-SCR) reaction. Finally, some suggestions are given for future research directions in catalyst development are prospected.

Unravelling the impacts of sulfur dioxide on dioxin catalytic decomposition on V2O5/AC catalysts

Dioxins are high chlorine, toxic, and persistent organic pollutants that exert significant pressure on both human and the environment. From the analysis of current pollutant removal of the whole life cycle, such as integrated removal of NOx, SO2 and dioxins in a system, the dioxins oxidation activity as well as the distribution of oxidation products in the presence of SO2 are still a challenge. In this study, dibenzofuran (DBF) was regarded as a model dioxin compound, and V2O5/AC was used as a catalyst to investigate the impact of SO2 on degradation activity and the degradation path of DBF. Various characterization results showed that SO2 could promote the transformation of DBF to intermediates through a reaction with lattice oxygen and lower the apparent activated energy of DBF catalytic oxidation on V2O5/AC catalysts. The density functional theory (DFT) calculations confirmed that SO2 improved the oxidation ability of lattice oxygen on V2O5/AC. The ethyl hydrogen fumarate intermediate decreased and the small-molecule byproducts increased, providing further evidence that SO2 accelerates the degradation of DBF and its intermediates. However, the formation of VOSO4 would inevitably deteriorate the adsorption and oxidation abilities of V2O5/AC. A model is pioneered to describe the relationship between SO2 promotion and VOSO4 inhibition on DBF catalytic oxidation on a V2O5/AC catalyst. This study is expected to provide theoretical guidance for the collaborative abatement of multi-pollutants in flue gas.

A review on identification, quantification, and transformation of active species in SCR by EPR spectroscopy

Electron paramagnetic resonance (EPR) is the only technique that provides direct detection of free radicals and samples that contain unpaired electrons. Thus, EPR had an important potential application in the field of selective catalytic reduction of nitrogen oxide (SCR). For the first time, this work reviewed recent developments of EPR in charactering SCR. First, qualitative analysis focused on recognizing Cu, Fe, V, Ti, Mn, and free-radical (oxygen vacancy and superoxide radical) species. Second, quantification of the active species was obtained by a double-integral and calibration method. Third, the active species evolved because of different thermal treatments and redox-thermal processes under reductants (NH₃ and NO). The coordination information of the active species in catalysts and their effects on SCR performances were concluded from mechanism viewpoints. Finally, potential perspectives were put forward for EPR developments in characterizing the SCR processes in the future. After all, EPR characterization will help to have a deep understanding of structure-activity relationship in one catalyst.