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Fe and/or Mn/SBA-15 catalysts were prepared by the impregnation method using low-cost fly ash-derived SBA-15 molecular sieve as support and tested towards NH 3 -SCR. Powder XRD, N 2 adsorption, XPS, H 2 -TPR and SEM techniques were used for catalyst characterization and investigation of relationships with the catalytic activity. The Fe-Mn/SBA-15 catalyst exhibited significantly higher NH 3 -SCR activities than Mn/SBA-15 or Fe/SBA-15 in the 150–250 °C range owing to some developed synergistic effects between Mn and Fe. In particular, the addition of Mn improved the dispersion of Fe 2 O 3 on the catalyst surface, while the addition of Fe promoted the formation of single β-MnO 2 phase. The high dispersion of Fe 2 O 3 , the appropriate Mn 4+ /Mn 3+ ratio, the concentration of adsorbed oxygen and the low-T enhanced redox activity of the Fe-Mn/SBA-15 improved its NH 3 -SCR activity. This work opens new avenues of recycling fly ash formed in coal-fired power plants (reducing environmental pollution) and developing low-cost SCR catalysts for NO x pollution control. [ABSTRACT FROM AUTHOR]

The promotional effects of Cu and Fe over the V 2 O 5 -WO 3 /TiO 2 NH 3 -SCR catalyst for the oxidation of Hg 0 and the selective catalytic reduction of NO by NH 3 were investigated in the temperature range of 280–360 °C. Cu or Fe addition, especially Cu, improved the catalytic performance of V 2 O 5 -WO 3 /TiO 2 . The results show that Cu 2 + was the main Cu species in the Cu-containing catalyst, whereas FeVO 4 was formed in the Fe-containing catalyst. Well-dispersed active species, good redox properties and abundant chemisorbed surface oxygen species on the catalyst surface were responsible for the high catalytic performances. Hg 0 oxidation over the V-based catalysts may follow a Mars-Maessen mechanism. [ABSTRACT FROM AUTHOR]

A series of vanadium based catalysts (V x Mn(4− x)Mo3Ce3/Ti) with different vanadium (x wt.%) and manganese ((4− x) wt.%) contents have been prepared by the wet impregnation method and investigated for selective catalytic reduction (SCR) of NO x by NH 3 in the presence of 8 vol.% H 2 O and 500 ppmV SO 2. The physicochemical characteristics of the catalysts were thoroughly characterized. The SCR of NO x by NH 3 (NH 3 -SCR) activity, especially the low-temperature activity, significantly increased with increasing V 2 O 5 content in the catalyst until the V 2 O 5 content reached 1.5 wt.%, which corresponds well with the redox properties of the catalyst. All of the metal oxides were well dispersed and strongly interacted with each other on the catalyst surface. V mainly exists in the V5+ state in the catalysts. The strong synergistic effect between the vanadium and cerium species led to formation of more Ce3+ species, and that between the vanadium and manganese species contributed to formation of more manganese species with low valences. All of the catalysts exhibited strong acidity, while the redox properties determined the NH 3 -SCR activity, especially the low-temperature activity. H 2 O and SO 2 had severe inhibiting effects on the activity of V1.5Mn2.5Mo3Ce3/Ti. However, good H 2 O and SO 2 resistance and high NO x conversion by V1.5Mn2.5Mo3Ce3/Ti could be achieved in the presence of SO 2 and almost no decline was observed in a long-term test at 275°C for 168 hr in the presence of SO 2 and H 2 O, which can be attributed to the sulfate species formed on the catalyst surface. Unlabelled Image [ABSTRACT FROM AUTHOR]

A NbO x /Ce 0.75 Zr 0.25 O 2 (NbCZ) catalyst was synthesized by a citric acid-aided sol-gel method. It shows that above 80% NO x conversion and above 95% N 2 selectivity for the selective catalytic reduction of NO x by ammonia over this catalyst are achieved in the temperature range 200–450 °C. Based on the DRIFTS and kinetic studies over NbCZ and Ce 0.75 Zr 0.25 O 2 , the promotion mechanism by niobia loading was elucidated with an overall reaction pathway. Two different reaction routes, “L-H” mechanism via “NH 4 NO 3 + NO” at low temperatures (<200 °C) and “E-R” mechanism via “NH 2 + NO” at high temperatures (>350 °C), are presented. The niobia addition increases the surface acidity and promotes the formation of nitrates species at low temperatures. In this way, the reaction between the ads-NH 3 and nitrates species is accelerated to form NH 4 NO 3 intermediates, which then decompose to N 2 and H 2 O. The reaction of the ads-NH 3 species with gaseous NO x at high temperatures is also promoted due to the enhanced acidity and weakened thermal stability of nitrates after niobia loading. [ABSTRACT FROM AUTHOR]