Poisoning/Deactivation Study ofV2O5/TiO2SCR CatalystsXiaoyu Guo, Jacob Beutler, Chase Anderson,Aaron Nackos, John Ashton, Calvin Bartholomew,William Hecker, Larry BaxterACERC ConferenceFeb 26, 2008Provo, UTOutline•Introduction•Objective and Motivation•Results and Discussion•Conclusions•AcknowledgementsIntroduction•SCR: a high efficient NOxabatement technique•A commercial post-combustion technique•Being used on 1⁄4 of the power generatedfrom coal-fired boilers•Major problem is catalyst deactivation,especially for low-rank coals and biomassExample of SCR System•Modified fromhttp://upload.wikimedia.org/wikipedia/en/5/5c/SCR2.GIFAmmoniainlet streamIntroduction•SCR: selective catalytic reduction•4NH3+ 4NO + O24N2+ 6H2O•4NH3+ 2NO2+ O23N2+ 6H2O•SCR catalyst•Supported vanadia catalyst: 1%V2O5-9%WO3/TiO2•Currently, in monolith or flat plate structure.•SCR kinetics: rNO≈k CNODeactivation Mechanisms•Plugging•Fouling/Masking•PoisoningChannel/Pore PluggingFouling/MaskingCalcium sulfate coating on catalyst surfacePoisoning•Catalytic activity linked toamount/strength ofBrønsted acid sites oncatalyst surface (Amiridis,Duevel, Wachs, 1999)•Chemical poisoning resultsfrom basicity of metal oxidedeposits (Chenet al., 1990)•Flyash from coal/biomasscontains carbonates,sulfates, and oxides ofNa,Ca,K, As, and Mg, whichare basic materialsCoal & Biomass Ash Compositions DifferPittsburgh #87.8% AshImperial W heat Straw15.4% AshRed Oak1.3% AshBlack Thunder7.2% AshSiO2Al2O3TiO2Fe2O3CaOMgONa2OP2O5K2OSO3ClBiomassCoal•Objective•Examine fresh and exposed commercial SCRcatalysts and determine the deactivation mechanism•Determine the impacts of K, Na, Ca, and SO2onvanadia catalyst properties and activities on labsynthesized catalysts•Motivation•Poisoning is a potential mechanism for SCR catalystdeactivation•SO2is generally present in boiler flue gas•Previous studies on non-sulfated catalystsObjective and MotivationSlipstream Reactor•REI operating slipstreamreactor at Rockport, IN•Reactor contains 6 separatechannels for 5 commercial,one BYU -prepared catalyst•Samples are returned foranalysisFlue GasFlue GasDuct WallDuct WallPneumatic Isolation ValveOne SCR InletHeated Sample LineSix SCR Outlet HeatedSample Lines to SequencerAmmonia InjectorSCR Reactor

2.5" out 5.0" out2.5" out5.0" out1/8" wall thickness2.25 x 2.25inner dimension4.75 x 4.75inner dimensionTop view of slipstream reactor.(Schematic courtesy of REI)Fresh and Exposed Catalysts ComparisonFresh2063 hourexposure3800 hourexposureCatalyst Characterization SystemMonolith Test ReactorFlow outPlate heater(x4)Flow inFlowThermocoupleCatalyst sampleMonolith TestReactor SchematicFlow Rate: 1000 sccmFeed:• 900 ppm NO• 900 ppm NH3• 2% O2• ~10% H2O• Balance HeTemperature: 250-325°CFresh and Exposed Catalysts PerformanceMonolith 1 kinetic dataMonolith 2 kinetic data151050

NO reduction rate constant, k (cm

3 /m

2 •s)600580560540520Temperature (K)M1 Freshfit M1 FreshM1 2063fit M1 2063M1 Biomassfit M1 BiomassM1 3800fit M1 3800302520151050

NO reduction rate constant, k (cm

3 /m

2 s)600580560540520Temperature (K)M2 Freshfit M2 FreshM2 2063fit M2 2063M2 Biomassfit M2 BiomassM2 3800fit M2 3800BET ResultsSampleM1M2BET surfacearea, m2/gAverage porediameter, nmBET surfacearea, m2/gAverage porediameter, nmFresh61.5 16.4 56.6 13.3206353.5 17.5 54.5 13.6380055.6 17.7 50.0 17.7Biomass48.2 19.9 43.9 20.0Locations of ESEM Analysis6050403020100

Weight %ONaMgAlSiPSKCaTiVFeWElementsM1 FreshM1 BioM1 2000M1 3800FlatElemental Composition vs. ExposureElemental Composition vs. Position6050403020100

Weight %ONaMgAlSiPSKCaTiVFeWElementsM1 FreshM1 3800 CenterM1 3800 EdgeM1 3800 FlatM1 3800 AshIndications from Slipstream Samples•Short exposure indicates a slight increase in activity•Pore plugging and Fouling appear to be moresignificant initially with poisoning occurring later•ESEM results indicate poisons deposit more on theoutside edge than on the inside or center of themonolith catalyst•ESEM results show sulfate accumulates on the catalystoutside surfaceIn situFTIR - MS ReactorSulfates Enhance NH3AdsorptionSulfation increases the amount of Brønsted acid sites onthe vanadia catalysts surface43210

Absorbance400035003000250020001500Wavenumber1435SulfatedFreshPeak area: 106Peak area: 59Sulfates Enhance NO Reduction ReactivitySulfation enhances NO reduction activity by increasing A, whileEaremains approximately constant before and after sulfation3530252015105

K, cm

3 /g*s570560550540530520Temperature, K24-hour sulfated 1% V2O5/TiO2Lightly sulfated 1% V2O5/TiO2Fresh 1% V2O5/TiO2A = 1716400 +/- 468000Ea = 52566 +/- 1240A = 300888 +/- 76400Ea = 45758 +/- 1160A = 182003 +/- 56700Ea = 44921 +/- 1430Ca, Na, and K Effects on NH3Adsorption0.40.30.20.10.0

Absorbance160015001400130012001100Wavenumber1%V-9%W/TiO20.5Ca 1%V-9%W/TiO20.5Na 1%V-9%W/TiO20.5K 1%V-9%W/TiO2NH3adsorption↓with↑basicity of metalsK, Na, and Ca Impacts on SCR Activity2018161412108642

k, cm

3 /g•s560540520500480460Temperature, K1V-9W/TiO20.5 Ca 1V-9W/TiO20.5Na1V-9W/TiO20.5k1V-9W/TiO2Tungsten Impact on NH3Adsorption1000ppm NH3adsorption at 50 ̊C2.01.51.00.50.0-0.5

Adsorption1800160014001200Wavenumber, cm-11%V - 9%W / TiO29%W / TiO2TiO2NOxReduction Activity Comparison20151050

k, cm

3 /g•s580560540520500480460Temperature, K1%V-9%W/TiO21%V/TiO29%W/TiO2Conclusion•Major deactivation mechanisms for vanadiacatalysts during low-rank coal combustion:•Plugging by popcorn ash•Fouling and masking by fly ash•Chemical poisoning is not important•Impacts of sulfation•Enhances NOxreduction activity•Increases ammonia adsorption•Influences rate, but not mechanismConclusion cont.•Impact of K, Na, Ca•Significant poisons•K>Na>Ca, proportional to basicity•Biomass potentially is worse than coal•Impact of Tungsten•Increase the amount of Brønsted acid sites•Does not provide activity but assists vanadia speciessignificantly in the NOxreductionCurrent work•Affect of SO2 flowing in reactant gases•Appears to significantly enhance NOx reductionactivity in preliminary experiment•More data is needed to validate effect•Problems•Forms sticky ammonium salts when mixed with NH3in stream•Must heat all lines and MS above 300°C to preventpluggingAcknowledgments•EPRI•DOE/NETL•REI•University of UtahStatistical Experimental DesignRuns Composition Factor Runs Composition FactorK Na Ca SO4K Na Ca SO41 0 0 0 0 9 00012 0.5 0 0 0 10 0.5 0 0 13 0 0.5 0 0 11 0 0.5 0 14 0 0 0.5 0 12 0 0 0.5 15 0.5 0.5 0 0 13 0.5 0.5 0 16 0.5 0 0.5 0 14 0.5 0 0.5 17 0 0.5 0.5 0 15 0 0.5 0.5 18 0.5 0.5 0.5 0 16 0.5 0.5 0.5 1Statistical Experimental DesignRuns Composition Factor Runs Composition FactorK Na Ca SO4K Na Ca SO41 0 0 0 0 9 00012 0.5 0 0 0 10 0.5 0 0 13 0 0.5 0 0 11 0 0.5 0 14 0 0 0.5 0 12 0 0 0.5 1Empirical rate constant expression⎟⎟⎟⎟⎟⎠⎞⎜⎜⎜⎜⎜⎝⎛⎟⎟⎠⎞⎜⎜⎝⎛−−⎟⎟⎠⎞⎜⎜⎝⎛−++++−−−=0000001112.01127.055.038.017.03.076.016.15.2expTTSSTTSSVNaSSVKSSVCaVNaVKk