Deep oxidation of NO via catalytic ozonation

In addition to selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) which are available to remove NOx from flue gas, oxidation method is receiving more and more attention because this method makes it possible to remove NOx and SO2 from flue gas simultaneously by wet scrubbing. O3 as a strong oxidant has a high oxidation capacity and it can oxide NO to N2O5 which has a higher water solubility compared with NO2. However, it needs a long reaction time and the escape of unreacted ozone may cause secondary pollution. In this study, FeMnCo/Al2O3 catalyst and FeMnCe/Al2O3 catalyst were prepared and applied to enhance the deep oxidation of NOx with ozone and reduce O3 slip. Effects of various operating parameters such as O3/NO ratio, gas residence time, and operating temperature were evaluated, and the results demonstrate that N2O5 began to generate when O3/NO ratio was higher than 1.0 and increased with increasing O3/NO ratio. Little residual O3 was formed in the presence of catalyst, while 350 ppm O3 was measured at the outlet gas when O3/NO ratio was controlled at 2.0. The N2O5 conversion efficiency increased with increasing gas residence time and operating temperature, and the highest N2O5 conversion efficiency was achieved at 100°C. Furthermore, the conversion efficiency remained around 90% during 20 h operation over FeMnCe/Al2O3 catalyst with an O3/NO ratio of 1.73, a gas residence time of 1.2 s, and a temperature of 100°C. On the other hand, the N2O5 conversion efficiency remained around 80% during 3 h operation over FeMnCo/Al2O3 catalyst. Overall, FeMnCe/Al2O3 catalyst reveals good potential for deep oxidation of NO by O3 and can be further developed as a viable catalyst for reducing NO emission from industries.Implications: In this study, FeMnCo/Al2O3 catalyst and FeMnCe/Al2O3 catalyst were applied to enhance the deep oxidation of NO into N2O5 with O3. The catalysts can improve the conversion of NO into N2O5, shorten the reaction time and reduce the unreacted O3 slip, which are beneficial to reduce the size of the reactor required and cost of APCDs (air pollution control devices) in practical application. This method can make it possible to simultaneously remove NOx and SO2 from flue gas by wet scrubbing for reducing NO emissions from industries, especially small and medium scaled industries, to meet increasingly stringent emission standards.

Effect of the Modification of Catalysts on the Catalytic Performance

Changing the composition and structure of a catalyst to obtain a positive impact on its performance is challenging [...]

A Review of Noble Metal Catalysts for Catalytic Removal of VOCs

Volatile organic compounds (VOCs) are important precursors for the formation of secondary pollutants, such as fine particulate matter (PM) and ozone (O3), which will lead to severe atmospheric environmental problems to restrict the sustainable development of the social economy. Catalytic oxidation is a safe, eco-friendly, and simple method for eliminating VOCs, which can be converted into CO2 and H2O without the generation of other harmful substances. The fabrication and development of catalysts are very crucial to enhance the catalytic oxidation efficiency of the removal of VOCs. The noble metal catalyst is one of the commonly used catalysts for the catalytic oxidation of VOCs because of the high reaction activity, good stability, poisoning-resistant ability, and easy regeneration. In this review, the research progress of noble metal (Pt, Pd, Au, Ag, and Ir) catalysts for the removal of VOCs in recent years was summarized with the discussion of the influence factors in the preparation process on the catalytic performance. The reaction mechanisms of the removal of VOCs over the corresponding noble metal catalysts were also briefly discussed.

Cobalt- and Copper-Based Chemiresistors for Low Concentration Methane Detection, a Comparison Study

Methane is a colorless/odorless major greenhouse effect gas, which can explode when it accumulates at concentrations above 50,000 ppm. Its detection cannot be performed without specialized equipment, namely sensing devices. A series of MOX sensors (chemiresistors type), with CoO and CuO sensitive films were obtained using an eco-friendly and low-cost deposition technique (sol-gel). The sensing films were characterized using AFM and SEM as thin film. The transducers are based on an alumina wafer, with Au or Pt interdigital electrodes (IDE) printed onto the alumina surface. The sensor response was recorded upon sensor exposure to different methane concentrations (target gas) under lab conditions (dried target and carrier gas from gas cylinders), in a constant gas flow, with target gas concentrations in the 5-2000 ppm domain and a direct current (DC) applied to the IDE as sensor operating voltage. Humidity and cross-sensitivity (CO2) measurements were performed, along with sensor stability measurements, to better characterize the obtained sensors. The obtained results emphasize good 3-S sensor parameters (sensitivity, partial selectivity and stability) and also short response time and complete sensor recovery, completed by a low working temperature (220 °C), which are key factors for further development of a new commercial chemiresistor for methane detection.

Novel Nanosized Spinel MnCoFeO4 for Low-Temperature Hydrocarbon Oxidation

The present paper reports on MnCoFeO₄ spinels with peculiar composition and their catalytic behavior in the reactions of complete oxidation of hydrocarbons. The samples were synthesized by solution combustion method with sucrose and citric acid as fuels. All samples were characterized by powder X-ray diffraction, N₂-physisorption, scanning electron microscopy, thermal analysis, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy. The catalytic properties of the spinels with Mn:Co:Fe = 1:1:1 composition were studied in reactions of complete oxidation of methane, propane, butane, and propane in the presence of water as model pollutants. Both prepared catalysts are nanosized materials. The slight difference in the compositions, structure, and morphology is due to the type of fuel used in the synthesis reaction. The spinel, prepared with sucrose, shows a higher specific surface area, pore volume, higher amount of small particles fraction, higher thermal stability, and as a result, more exposed active sites on the sample surface that lead to higher catalytic activity in the studied oxidation reactions. After the catalytic tests, both samples do not undergo any substantial phase and morphological changes; thus, they could be applied in low-temperature hydrocarbon oxidation reactions.