Christensen, Claus H.

Due-Hansen, Johannes

Fehrmann, Rasmus

Kustov, Arkadii

The use of bio-fuels as alternatives to traditional fossil fuels has attracted much attention recent years since bio-fuels belong to a family of renewable types of energy sources and do not contribute to the green-house effect. Selective catalytic reduction (SCR) of NOx with ammonia as reductant is the most efficient method to eliminate NOx from flue gases in stationary sources. The traditional SCR catalyst suffers significant deactivation with time due to the presence of relative large amounts of potassium in bio-fuels. A possible solution to this problem is use of highly acidic supports, which would interact with potassium stronger than active metal specie

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Downloaded from orbit.dtu.dk on: Dec 16, 2017Sulfate Promoted Zirconia as Promising Alkali-Resistant Support for Catalytic NOxRemovalDue-Hansen, Johannes; Kustov, Arkadii ; Christensen, Claus H.; Fehrmann, RasmusPublication date:2007Link back to DTU OrbitCitation (APA):Due-Hansen, J., Kustov, A., Christensen, C. H., & Fehrmann, R. (2007). Sulfate Promoted Zirconia as PromisingAlkali-Resistant Support for Catalytic NOx Removal. Poster session presented at 3rd International Conferenceon Green and Sustainable Chemistry, Delft, Netherlands.Sulfate Promoted Zirconia asPromising Alkali-Resistant Supportfor Catalytic NOx RemovalJ. Due-Hansen, A.L. Kustov, C.H. Christensen, R. FehrmannDepartment of Chemistry and Center for Sustainable and Green Chemistry,Technical University of Denmarkjdh@kemi.dtu.dk1. IntroductionTHE use of bio-fuels as alternatives to traditional fossil fuels has attractedmuch attention recent years since bio-fuels belong to a family of renew-able types of energy sources and do not contribute to the green-house effect.Selective catalytic reduction (SCR) of NOx with ammonia as reductant is themost efficient method to eliminate NOx from flue gases in stationary sources.The traditional SCR catalyst suffers significant deactivation with time dueto the presence of relative large amounts of potassium in bio-fuels. A possiblesolution to this problem is use of highly acidic supports, which would interactwith potassium stronger than active metal species.[1,2]2. ExperimentalTHE sample of sulfated zirconia with 4.1 wt% sulfate has been obtainedcommercially. The as-received support was impregnated with ammo-nium metavanadate via incipient wetness impregnation and calcined in airat 400oC, resulting in 0.5-7.5 wt% vanadium with a BET surface area of 145m2/g. The vanadia-based catalysts were impregnated with 130 µmol/g KNO3.SO2 –4 /ZrO2︸ ︷︷ ︸4.1 wt% SO2 –4NH4VO3−−−−−→IWIV2O5−SO2 –4 /ZrO2︸ ︷︷ ︸0.5-7.5 wt% VKNO3−−−−→IWIK2O−V2O5−SO2 –4 /ZrO2︸ ︷︷ ︸K/V = 0.4(1)A 3%V2O5-7%WO3/TiO2 catalyst with a BET surface area of 61 m2/g was usedas a reference.NO SCR was performed with 50 mg sample in 1000 ppm NO, 1100 ppmNH3, 3.5% O2, and 2.5% H2O, balanced with N2, total flow: 300 ml/min.3. Sample AcidityIMPREGNATION of the sulfated zirconia with vanadia results in an additionalammonia desorption peak around 390oC (Fig. 1). This peak is only ob-served in vanadia-containing samples on sulfated zirconia and not i.e. intungstated zirconia[1].100 150 200 250 300 350 400 450 500Temperature [oC]Ammonia desorbed [a.u.]390oCSO42−/ZrO2(537 µmol/g)V2O5−SO42−/ZrO2  (616 µmol/g)K2O−V2O5−SO42−/ZrO2  (452 µmol/g)Figure 1: NH3-TPD of the sulfated samples (Surface acidity in brackets),indicating a formation of a stronger acid site with addition of 1.7 wt% V4. NO SCR ActivityCATALYSTS based on sulfated zirconia exhibit good SCR properties com-pared with the titania-based reference catalyst, both depicted in Fig. 2.Especially the SCR activity after K-doping reveals the high alkali resistanceof sulfated supports over the traditional catalyst, the latter deactivating 71%at 300oC, whereas the sulfated catalyst only deactivates 29%.Optimization of the vanadia loading was performed to study the catalystsresistance toward a constant amount of potassium (130 µmol/g). The deactiva-tion of catalysts containing 0.5–7.5 wt% vanadium due to potassium poison-ing is depicted in Fig. 4, top.200 300 400 5000100200300400500Fresh NO−SCR CatalystTemperature [oC]k  [s−1 ]SulfatedReference200 300 400 5000100200300400500K−doped, K/V=0.4Temperature [oC]SulfatedReferenceFigure 2: The temperature dependency of the SCR activity of 3wt% V2O5-4.1wt% SO2 –4 /ZrO2 and a 3 wt% V2O5-WO3/TiO2 reference catalystVOOO OVOOO OVOOO+ H2OVOOO OVOOOK+ H2OVOOO O+ VOOO OK∆H=1 kJ/mol∆H=-37 kJ/molVOOO O+Figure 3: The propensity for dimerization calculated by DFT. Notice withpotassium present, the dimer is now clearly favored in enthalpy[3]Increasing the amount of vanadium, thus decreasing the K/V ratio, resultsin significant decrease in catalyst deactivation (Fig. 4, top left). At K/V = 0.2only about 10% catalyst deactivation is observed, which even decreased fur-ther with increasing vanadium concentration.0 1 2 3 4 5 6 7 8020406080100Vanadium loading [wt%]Catalyst Deactivation [%]K−doped: 130 µmol/gSCR−activity at 300oCK/V=1 K/V=0.4 K/V=0.2 K/V=0.10 0.4 0.8 1.2020406080100K/V ratio [mol/mol]0.220 1 2 3 4 5 6 7 8400500600700800900Vanadium loading [wt%]NH 3 desorbed [µmol/g]V2O5−SO42−/ZrO2K−dopedK/V=1 K/V=0.4 K/V=0.2 K/V=0.1Figure 4: Top left: Catalyst deactivation with different vanadia loadingsat 300oC; Top right: Deactivation versus the K/V molar ratio, with thresh-old at K/V = 0.22; Bottom: Amount of desorbed NH3 from the vanadia-impregnated support and the corresponding K-doped samples5. ConclusionCATALYSTS based on sulfated zirconia show good resistance towardspotassium poisoning. For samples with K/V ratios below 0.22, potassiumseems to have very low impact on the catalysts performance.Poisoning the catalysts with potassium mainly affects the strong acid sites,with NH3 desorption temperature around 390oC.References[1] Due-Hansen, J., Kustov, A.L., Rasmussen, S.B., Fehrmann, R., Christensen, C.H., Appl. Catal. B, 66(2006) 160–166.[2] Kustov, A.L., Kustova, M.Y., Fehrmann, R., Simonsen, P., Appl. Catal. B, 58 (2005) 97–104.[3] Due-Hansen, J., Boghosian, S., Kustov, A.L. Fristrup, P., Tsilomelekis, G., Ståhl, K., Christensen, C.H.,Fehrmann, R., J. Catal., submitted, april 2007.GSC-3, 3rd International Conference on Green and Sustainable Chemistry, 1-5 July 2007, Delft, The Netherlands

Sulfate Promoted Zirconia as Promising Alkali-Resistant Support for Catalytic NOx Removal

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Sulfate Promoted Zirconia as Promising Alkali-Resistant Support for Catalytic NOx Removal

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