Mixed iron–erbium vanadate NH3-SCR catalysts

• Mixed iron/erbium vanadates over TiO2–WO3–SiO2 support are active NH3-SCR catalysts.
• Iron enhances low-temperature NH3-SCR activity while erbium improves thermal stability.
• Erbium vanadate enhances thermal stability of SCR catalyst up to 800 °C by preventing anatase–rutile transformation.
• Redox and acid/base functions of the iron/erbium vanadate catalysts are important in controlling catalyst performance.

A series of SCR catalysts of mixed iron–erbium vanadates supported on TiO2–WO3–SiO2 were prepared and their reduction, textural, structural and morphological properties characterized by temperature programmed reduction, X-ray powder diffraction, B.E.T. methods and transmission electron microscopy. The influence of Fe/Er ratio in the vanadate as well as the effect of aging conditions on their activity in ammonia SCR reaction was investigated. SCR activity at medium/low temperature was found to correlate directly with the Fe loading of the catalyst, with supported FeVO4 resulting the most active material. This behavior might be correlated with the characteristics of Fe3+OV5+ bond and the acidity of the VO moiety. Supported FeVO4 suffers a strong deactivation following thermal aging due to rutile formation in TiO2-based support and consequent collapse of surface area. The effect of Er is that of blocking transformation to rutile, thus enhancing activity after thermal treatment. Mixed composition FexEr1−xVO4 with x = 0.5 represents the best compromise between activity and stability and are potential candidates for deNOx process when a higher stability is requested.

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