Removal of NOX Using Hydrogen Peroxide Vapor over Fe/TiO2 Catalysts and an Absorption Technique

Oxidation-absorption process for simultaneous removal of NOx and SO2 over Fe/Al2O3@SiO2 using vaporized H2O2

3% Fe/Al₂O₃ and 3% Fe/Al₂O₃@SiO₂ were prepared to investigate the performance in simultaneous removal of NO_x and SO₂ using vaporized H₂O₂. Certain paraments were changed to explore the activity of catalysts, including temperature, H₂O₂ concentration, GHSV and coexistence gases component. A 24-h durability test was conducted on 3% Fe/Al₂O₃@SiO₂. Moreover, a series of characterizations were employed to analyze the physical and chemical properties of catalysts, including XRD, BET, SEM, TEM, FTIR and XPS. Compared with 3% Fe/Al₂O₃, 3% Fe/Al₂O₃@SiO₂ exhibited more excellent catalytic activity, which could achieve the peak removal efficiency of 100% for SO₂ and 93.76% for NO_x. Moreover, 3% Fe/Al₂O₃@SiO₂ kept stable simultaneous removal efficiency in a 24-h test. The characterization results indicated that the BET area was greatly improved and the core-shell structure was synthesized with the formation of more micropores and mesopores by the coating of SiO₂, which could improve the activity of catalyst at high temperature and high SO₂ concentration. Besides, the mechanism of SO₂ molecules on simultaneous removal was investigated. On one hand, a part of H₂O₂ was consumed by SO₂ molecules without catalyst, which resulted in the drop of NO_x removal by the decrease of oxidants. The main products were sulfites and bisulfites, which were broken down into SO₂ over the catalyst. On the other hand, the presence of SO₂ was beneficial for NO_x removal by increasing oxygen vacancies on the catalyst surface and facilitating the absorption of NO₂ by NaOH solution.

Oxidation of NO x Using Hydrogen Peroxide Vapor over Mo/TiO2

xMo/TiO₂ catalysts (x = 1, 2, 3, and 4%) were prepared using the coprecipitation method in the present study. The coprecipitation method was used in the thermal catalytic decomposition of H₂O₂ steam to treat NO _x at a low temperature range (80-160 °C). Several characterization techniques have been employed, such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller measurements, transmission electron microscopy (TEM), scanning electron microscopy and energy-dispersive X-ray spectrometry (SEM-EDXS), and Fourier transform infrared spectroscopy. The activity tests showed that the incorporation of molybdenum into TiO₂ led to a significant increase in the catalytic oxidation of NO, and under the condition of H₂O₂/NO = 6:1 (molar ratio), the NO _x removal rate of 2% Mo/TiO₂ is the highest, reaching 92.56%. XRD, TEM, and SEM-EDXS analyses showed that Mo was well dispersed on the surface of an anatase-phase TiO₂. XPS analysis indicated that Mo mixed with slag mainly existed in the form of Mo⁶⁺. Moreover, in comparison with the mostly reported SCO catalysts, used for the elimination of NO, the prepared Mo/TiO₂ catalyst showed excellent stability and sulfur resistance.

Research on NO and SO2 removal using TiO2-supported iron catalyst with vaporized H2O2 in a catalytic oxidation combined with absorption process

Simultaneous removal of NOx and SO₂ is carried out by an oxidation-absorption process, which NO oxidized by active hydroxyl radicals (·OH) derived from catalytic decomposition of vaporized H₂O₂ over Fe₃O₄/TiO₂ and then adsorbed by NaOH solution along with SO₂. Fe₃O₄/TiO₂ synthesized by wet impregnation method with an additional reduction under H₂ atmosphere was characterized by XRD, FTIR, BET, XPS, and VSM analysis. Effects of H₂O₂ concentration, H₂O₂ injection rate, reaction temperature, gas flow rate, and flue gas component on simultaneous removal were investigated. The experimental results show that NO can be effectively oxidized by highly reactive ·OH radicals generated from H₂O₂ decomposition over Fe₃O₄/TiO₂ catalyst, and removal efficiencies of 93.31% for NO, 85.90% for NOx, and 100% for SO₂ were obtained. The surface zero-valent iron (Fe⁰) and divalent iron (Fe²⁺) are the key factors of the catalytic oxidation with hydroxyl radical. H₂O₂ adsorption and dissociation mechanism on catalyst surface was studied using DFT calculation. The calculation results demonstrate that H₂O₂ prefers to dissociate on iron containing surface, and ·OH radicals generation follow by Haber-Weiss (H-W) mechanism. The stable oxidative product of HNO₂ and HNO₃ were generated through NO/NO₂ and H₂O₂ co-adsorption on the FeO/TiO₂ (0 0 1) surface.

Radical-induced oxidation removal of multi-air-pollutant: A critical review

Sulfur dioxide (SO₂), nitric oxide (NO) and elemental mercury (Hg⁰) are three common air pollutants in flue gas. SO₂ and NO are the main precursors for chemical smog and Hg⁰ is a bio-toxicant for human. Cooperative removal of multi-air-pollutant in flue gas using radical-induced oxidation reaction is considered as one of the most promising methods due to the high removal efficiency, low cost and less secondary environmental impact. The common radicals used in air pollution control can be classified into four types: (1) hydroxyl radical (OH), (2) sulfate radical (SO₄^-), (3) chlorine-containing radicals (Cl, ClO₂, ClO, HOCl^-, etc.) and (4) ozone. This review summarizes the generation methods and mechanism of the four kinds of radicals, as well as their applications in the removal of multi-air-pollutant in flue gas. The reactivity, selectivity and reaction mechanism of the four kinds of radicals in multi-air-pollutant removal were comprehensively described. Finally, some future research suggestions on the development of new technique for cooperative removal of multi-air-pollutant in flue gas were provided.