A New Class of Environmental Friendly Vanadate Based NH 3 SCR Catalysts Exhibiting Good Low Temperature Activity and High Temperature Stability

For the removal of NOx from the oxygen-rich diesel exhaust in mobile applications the selective catalytic reduction (SCR) is one of the most favoured technologies. Well established NH 3-SCR technique uses either V 2O 5/WO 3-TiO 2 or Zeolite based catalysts, NOx being continuously reduced by NH 3 resulting in the selective formation of nitrogen and water. A major drawback of V 2O 5 based formulations is their lower thermal stability and low temperature activity, in addition, V 2O 5 release poses serious environmental and toxicity problems. In active filter regeneration performed by post-injection of fuel the temperature may increase up to 800\ub0C resulting in drastic loss of activity (due to poor stability of V 2O 5 based formulations) as well as discharge of V 2O 5. Zeolite-based catalysts promoted by transition metal such as Fe and Cu represent an excellent solution to overcome the stability problems of V 2O 5-based catalysts with only a small activity penalty and cost raise issues but may show disadvantages in stability after hydrothermal ageing. In the present study a new class of rare earth modified Fe vanadates are shown to be valid substitutes of V 2O 5 in SCR catalyst providing i) good activity in the low temperature window (180\ub0C-300\ub0C) ii) high temperature stability up to 850\ub0C, with no major associated activity loss, iii) absence of toxicological and environmental concern

Enhanced Stability of Fe2O3-Doped FeVO4/TiO2\u2013WO3\u2013SiO2 SCR Catalysts

This work investigates the effect of addition of Fe2O3 in FeVO4 supported on TiO2-WO3-SiO2 (TWS) NH3-SCR catalysts. The catalysts were prepared by loading 8.4 wt% FeVO4 and different amounts of Fe2O3 on TWS support and the effect of ageing in the range of temperature 650-750 degrees C on the SCR reaction was studied. Fe2O3 does not give any significant contribution to SCR activity for the samples treated at lower temperature, but a remarkable difference is achieved for the samples aged at 750 degrees C. The presence of Fe2O3 at an appropriate loading significantly enhances the thermal stability of the system by contrasting the formation of rutile and lowering the formation of surface VOx species

Mixed iron\u2013erbium vanadate NH3-SCR catalysts

tA series of SCR catalysts of mixed iron\u2013erbium vanadates supported on TiO2\u2013WO3\u2013SiO2were preparedand their reduction, textural, structural and morphological properties characterized by temperature pro-grammed 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 inammonia SCR reaction was investigated. SCR activity at medium/low temperature was found to correlatedirectly with the Fe loading of the catalyst, with supported FeVO4resulting the most active material. Thisbehavior might be correlated with the characteristics of Fe3+O V5+bond and the acidity of the V Omoiety. Supported FeVO4suffers a strong deactivation following thermal aging due to rutile formation inTiO2-based support and consequent collapse of surface area. The effect of Er is that of blocking transfor-mation to rutile, thus enhancing activity after thermal treatment. Mixed composition FexEr1 12xVO4withx = 0.5 represents the best compromise between activity and stability and are potential candidates fordeNOxprocess when a higher stability is requested

Mixed iron-erbium vanadate NH3-SCR catalysts

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+-O-V5+ bond and the acidity of the V-O 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 deNO(x) process when a higher stability is requested. (C) 2014 Elsevier B.V. All rights reserved

Relationship between structures and activities of supported metal vanadates for the selective catalytic reduction of NO by NH3

Transition and rare earth metal vanadates are potential active phases for the selective catalytic reduction (SCR) of nitric oxide by ammonia for exhaust gas emission control. In this work, various metal vanadates mixed with SiO2-WO3-TiO2 (TWS) were compared to vanadia-based SCR catalysts. FeVO4-based catalysts were found to be the most active metal vanadates, followed by CeVO4 and ErVO4. In depth analysis using XRD, BET, H-2-TPR, DRUV and DRIFTS demonstrated that the vanadates partly decomposed above 600-750 degrees C to the corresponding single metal oxides, the decomposition temperature correlating with their relative stability. The activity and the estimated fraction of freed VOx from the vanadate decomposition strongly correlated with vanadia-based catalysts at comparable V-loading. Based on these findings, the enhanced thermal stability of the vanadate-based catalysts was correlated to an overall lower amount of free VOx species compared to vanadia-based catalysts. The released VOx species are responsible for the activity of the metal vanadate-based SCR catalysts and are of similar nature to those of vanadia-based catalysts. Therefore, the claimed high temperature stability advantage of supported metal vanadates is merely an effect of the degree of vanadate decomposition and is not related to their intrinsic stability

Generation of NH₃ Selective Catalytic Reduction Active Catalysts from Decomposition of Supported FeVO₄

The effect of catalyst loading, composition, and calcination temperature on NH₃ selective catalytic reduction (SCR) activity was investigated for metal vanadates of the type Fe_<i>x</i>Al_1–xVO₄ (0 ≤ <i>x</i> ≤ 1, MeVO₄) supported on TiO₂–WO₃–SiO₂ (TWS). The optimized catalyst (4.5 wt % FeVO₄/TWS calcined at 650 °C) showed an enhanced NO_<i>x</i> reduction activity compared to the reference material 2.3 wt % V₂O₅/TWS. An activation effect was observed above a calcination at 600 °C and was investigated by means of X-ray diffraction, Brunauer–Emmett–Teller, diffuse reflectance infrared Fourier transform, and X-ray absorption near edge structure analyses. It was shown that the activation is due to the decomposition of FeVO₄. VO_<i>x</i> species disperse and migrate to the support material, while the iron species sinter to Fe₂O₃ particles. We provide strong evidence that the active species responsible for NH₃–SCR in a FeVO₄/TWS catalyst is not FeVO₄ but VO_<i>x</i> species that possess a similar coordination environment to the VO_<i>x</i> species on conventional V-based catalysts. Due to the remarkable effect of the activation upon calcination, a very active and thermally stable SCR catalyst up to 700 °C was obtained