Temperature Selective Catalytic Reduction Of NO Research Articles

Low-Medium Temperature-Selective Catalytic Reduction of NO with NH3 over a Mn/Co-MOF-74 Catalyst.

To realize the selective catalytic reduction of NO at low–medium temperatures and avoid secondary pollution, a highly active catalyst Mn/Co-MOF-74 was synthesized. X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis, Brunauer–Emmett–Teller method, and scanning electron microscopy were employed to analyze the physicochemical properties of catalysts with different Mn/Co molar ratios and conjecture about the difference in the catalytic activity. Meanwhile, the effects of the molar ratio of Mn/Co, catalyst dosage, catalyst synthesis conditions, GHSV, and temperature on the NO conversion efficiencies were investigated and found that an optimal NO conversion efficiency of 93.5% was obtained at 200–225 °C. In the end, the stability of Mn/Co-MOF-74 was investigated and found that the catalyst has better sulfur and water resistance, and the NO conversion mechanism was speculated on the basis of characterizations and literature data.

Low temperature SCR of NO with catalysts prepared by modified ACF loading Mn and Ce: effects of modification method

Achievement of a higher NOx conversion ratio in selective catalytic reduction (SCR) at low temperature is challenging. In this work, pure activated carbon fibres (ACFs) were modified with different ratios of H2O (g), NaOH, CO2 and HNO3, respectively (named as modified ACF). The chemical and physical properties of modified ACFs were identified by Brunauer–Emmett–Teller, X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy methods. The NOx conversion ratio of ACF was improved from 56.1% to 82.4% at 80°C after modification with 30% (mass ratio) NaOH. These modified ACFs were further loaded with the mixture of MnO2 and CeO2 in the form of metal salt solutions (named as Mn0.5Ce0.5O2/modified ACF). The NOx conversion ratio of 30% SHACF remained similar at 80°C but was increased from 60.0% to 98.5% at 360°C after loading with Mn and Ce, which showed the best performance in SCR of NOx at low temperature. It could be seen that ACF delivered higher performance in low temperature SCR after being modified with the aforementioned reactants and further loading with metals. Based on chemical and physical characterization and the performance of the catalysts, the reasons for different performances of these catalysts in low temperature SCR are discussed.

Iron-doped Mn-Ce/TiO 2 catalyst for low temperature selective catalytic reduction of NO with NH 3

Abstract The catalysts of iron-doped Mn-Ce/TiO 2 (Fe-Mn-Ce/TiO 2) prepared by sol-gel method were investigated for low temperature selective catalytic reduction (SCR) of NO with NH 3. It was found that the NO conversion over Fe-Mn-Ce/TiO 2 was obviously improved after iron doping compared with that over Mn-Ce/TiO 2. Fe-Mn-Ce/TiO 2 with the molar ratio of Fe/Ti = 0.1 exhibited the highest activity. The results showed that 96.8% NO conversion was obtained over Fe(0.1)-Mn-Ce/TiO 2 at 180°C at a space velocity of 50,000 hr −1. Fe-Mn-Ce/TiO 2 exhibited much higher resistance to H 2O and SO 2 than that of Mn-Ce/TiO 2. The properties of the catalysts were characterized using X-ray diffraction (XRD), N 2 adsorption, temperature programmed desorption (NH 3-TPD and NO x-TPD), and X-ray photoelectron spectroscopy (XPS) techniques. BET, NH 3-TPD and NO x-TPD results showed that the specific surface area and NH 3 and NO x adsorption capacity of the catalysts increased with iron doping. It was known from XPS analysis that iron valence state on the surface of the catalysts were in Fe 3+ state. The doping of iron enhanced the dispersion and oxidation state of Mn and Ce on the surface of the catalysts. The oxygen concentrations on the surface of the catalysts were found to increase after iron doping. Fe-Mn-Ce/TiO 2 represented a promising catalyst for low temperature SCR of NO with NH 3 in the presence of H 2O and SO 2.

Low temperature SCR of NO with NH 3 over carbon nanotubes supported vanadium oxides

A novel multiwalled carbon nanotube (CNTs) supported vanadium catalyst was prepared. The structure of catalyst prepared was characterized by TEM, BET, FTIR, XRD and temperature-programmed desorption (TPD) methods. The results indicated that vanadium particles were highly dispersed on the wall of carbon nanotubes. The V 2O 5/CNT catalysts showed good activities in the SCR of NO with a temperature range of 373–523 K. The Lewis acid sites on the surface of V 2O 5/CNT are the active sites for the selective catalytic reduction (SCR) of NO with NH 3 at low temperatures. It was suggested that the reaction path might involve the adsorbed NH 3 species reacted with NO from gaseous phase and as well as the adsorbed NO 2 species. The diameter of CNTs showed positive effect on the activities of the catalysts. Under the reaction conditions of 463 K, 0.1 Mpa, NH 3/NO = 1, GHSV = 35,000 h −1, and V 2O 5 loading of 2.35 wt%, the outer diameter of CNTs of 60–100 nm, the NO conversion was 92%.

Surface characterization studies of TiO2 supported manganese oxide catalysts for low temperature SCR of NO with NH3

A series of TiO2 supported manganese oxide catalysts were prepared by wet-impregnation method for the low temperature selective catalytic reduction (SCR) of NO with ammonia as a reductant. A combination of various physico-chemical techniques such as N2 physisorption, O2 chemisorption, TPR, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman were used to characterize the chemical environment of these catalysts. O2 chemisorption and XRD results suggest that Mn exist in a well-dispersed state at below 16.7wt.% of Mn on TiO2 anatase (Hombikat), 7.5wt.% on TiO2 rutile (Kemira) and P-25 (80% anatase+20% rutile), and in microcrystalline phase above these loading levels on respective support materials. These results also reveal that Mn interacts very well with pure anatase phase compared to rutile. XPS results of Mn/TiO2 anatase (Hombikat) catalysts illustrated the presence of MnO2 as a major phase (peak at 642.0eV) along with Mn2O3 as the minor phase at lower loadings. The presence of Mn2O3 disappears at higher loadings. The characterization results indicated that the manganese oxide exists as an isolated species at very low loadings, highly dispersed state probably as two dimensional monolayer species at intermediate loadings, polymeric or microcrystalline form of manganese oxide at higher (above monolayer capacity) loadings was envisaged. The catalytic performance of various amounts of Mn loaded on different TiO2 supported catalysts for low temperature SCR reaction at catalyst bed temperature 175°C under power plant conditions using GHSV=50,000h−1 was studied. The catalyst with 16.7wt.% Mn/TiO2 anatase (Hombikat) was found to be highly active and selective catalyst for this reaction. The Raman studies acted as complimentary tool to XPS in order to characterize the manganese oxides (MnO, Mn2O3, Mn3O4, MnO2). Raman data show that there is a strong interaction between the Mn oxides and the support, which is responsible for the impressive catalytic performance in comparison with other systems we investigated.

05/01487 Influence of nitrogen surface functionalities onthe catalytic activity of activated carbon in low temperature SCR of NO x with NH 3: Szymanski, G. S. et al. Catalysis Today, 2004, 90, (1–2), 51–59

The effect of synthesis methods on the activity of V/Ce/WTi catalysts was investigated for the selective catalytic reduction (SCR) of NOx by NH3. V/Ce/WTi-DP (deposition precipitation) catalyst showed excellent NH3-SCR performance, especially the better medium-temperature activity and the less N2O formation than V/Ce/WTi-IMP (impregnation). These catalysts were characterized by X-ray diffraction (XRD), Brumauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (H2-TPR), and in situ DRIFTS techniques. The XPS and H2-TPR results revealed that V/Ce/WTi-DP exhibited more surface Ce species, higher level of Oα and higher reducibility of Ce species. Reflected by in situ DRIFTS results, the deposition precipitation method (DP) contributed to a greater amount of weakly adsorbed NO2, monodentate nitrate and NH3 species with better reactive activity. Meanwhile, the cis-N2O22– species, an intermediate for N2O formation, was very limited. As a result, these advantages brought about the superior SCR activity and N2 selectivity for V/Ce/WTi-DP.