ELSEVIER
`
`Applied Catalysis B: Environmental 7 ( 1995) 137-151
`
`Conditions in which Cu-ZSM-5 outperforms
`supported vanadia catalysts in SCR of NO, by NH3
`
`James A. Sullivan, Joseph Cunningham, M.A. Morris, K. Keneavey
`Universir?_ College Cork, Cork, Ireland
`Received 29 March 1995; revised 1 July 1995; accepted I July 1995
`
`Abstract
`
`flows of a standard reactant mixture, featuring 0.6% nitric oxide, 0.6% ammonia and
`Continuous
`3.3% oxygen at moderate space velocities over 4 different catalysts, have been used to compare
`relative activities
`for selective catalytic reduction of NO, at 373-773 K. The catalysts
`tested were:
`Cu-ZSM-5
`featuring > 100% ion-exchange;
`a conventionally
`prepared vanadia-titania-tungstate
`(VTT) material and two unconventional
`catalysts prepared by vanadia deposition onto ex-sol-gel
`W03-Ti02
`supports. At catalytic temperature 473 K, higher conversion
`to N2 was achieved over Cu-
`ZSM-5
`than over
`the other
`three materials. Tests without NO at 473 K showed
`insignificant
`contributions
`to N2 formation from ammonia oxidation over any of the catalysts, whereas tests at 573,
`623,673 and 773 K revealed larger progressive
`increases
`in such contributions over Cu-ZSM-5
`than
`over the other catalysts. Values for SCR activities corrected for such contributions demonstrated
`that
`activity of Cu-ZSM-5
`for SCR conversion of the standard NO + NH, + 0, reactant mixture to N, at
`473 K was ca. twice as great as the other three catalysts at that temperature, but that increasing
`the
`reaction temperature
`to 573 K caused only a slight further increase. ‘Corrected’ SCR activities
`in the
`standard reactant mixtures were rather similar for all four materials at 573 K, but with Cu-ZSM-5
`marginally out-performed by one of two unconventional
`catalysts featuring vanadia upon an ex-sol-
`gel W03-Ti02
`support having tungsten
`incorporated
`into the TiOz anatase structure. Both of these
`unconventional
`catalysts outperformed
`a conventional ‘VTT’ catalyst. Observations upon variations
`in conversion
`to N2 with variation
`in the oxygen content of the reactant gas mixture from 1 to 6%
`established another unique feature of the Cu-ZSM-5 catalyst at 473 K, viz. the need for ca. 4.5% 0,
`to raise conversion
`to the maximum attainable over that catalyst at this temperature. No deactivation
`was observed after short-term runs at temperatures up to 823 K. Introduction of water vapour into the
`standard reactant mixture slightly enhanced
`the activity of Cu-ZSM-5 at 473 K.
`
`Keywords: Ammonia; Copper-ZSM-5; NOx reduction; Vanadia; Zeolites
`
`1. Introduction
`
`reasons, stationary power sources, such as electricity
`For efficiency/economic
`generating plants, operate in ‘lean’ conditions with an air-to-fuel ratios higher than
`
`0926-3373/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved
`SSDlO926-3373(95)00031-3
`
`Exhibit 2031.001
`
`

`
`138
`
`J.A. Sullivan et al. /Applied Catalysis B: Environmental 7 (1995) 137-151
`
`character
`thus, have a net-oxidising
`required. Emissions,
`that stoichiometrically
`with the result that potentially useful catalysts for removal of NO, pollutants therein
`must be capable of selective catalytic reduction
`(SCR) of the NO, - by an added
`reducing agent such as ammonia - whilst not significantly catalysing reduction of
`is a vanadia-
`Oz. [ 1,2]. The VTT catalyst commercially utilised for this purpose
`tungsten oxide-titania mixture in which the V205 layers deposited upon W03-Ti02
`are thought to provide active sites for the SCR process, e.g. with ammonia adsorbing
`[ 2,3]. Vanadia-
`onto V-OH sites and NO reacting with this adsorbed ammonia
`related sites considered
`important
`in the vanadia-tungstate-titania
`(VTT) catalyst
`include acidic V-OH sites, plus redox sites capable of undergoing
`-V=O
`to -V-
`OH transitions. According
`to Chen and Yang, functions of the W03 deposit include:
`broadening
`the reaction
`temperature window; enhancing
`the poison
`resistance
`towards alkali metals; lowering the ammonia oxidation activity and increasing
`the
`acidity of the catalyst
`[3]. The present work includes
`results from studies
`to
`determine whether SCR activity and other properties of VTT materials are sensi-
`tive/insensitive
`to the incorporation
`of W03
`throughout
`the titania support as
`distinct from surface-deposition.
`ions for protons of the narrow-
`copper
`Catalysts prepared by ion-exchanging
`channel zeolite aluminosilicate H-ZSM-5 are usually denoted by Cu-ZSM-5. The
`very extensive R&D attention devoted to such materials in relation to NO, removal
`from emissions to atmosphere
`from stationary or mobile power sources stems from
`evidence
`that, within differing experimental conditions,
`they may display limited
`catalytic activity not only for the selective reduction
`reaction with ammonia and
`urea [ 41, or with C i-Cs hydrocarbons
`[ 4-101, but also for dissociation
`to N2 and
`O2 [ 1 l-131. Considerations
`of Cu-ZSM-5 materials
`in the present paper will,
`however, be limited to activity for SCR with NH3 and how this compares with that
`of VTT materials.
`the two types of material might be anticipated
`Qualitative similarities between
`on the twin basis that vanadium and copper can each exhibit variable-valency,
`and
`that acidity of the titania or aluminosilicate
`support would in each case be modified
`by addition of the promoter elements. Initial objectives of the present study were
`(i) to test for the levels of SCR activity in converting
`(NO + NH3 + 0,)
`to N2 at
`temperatures 473-773 K over aliquots of Cu-ZSM-5 catalyst, and (ii) to compare
`them with activity over a conventionally prepared VTT catalyst. During the course
`of the research a paper by Komatso et al. appeared reporting rather small activity
`of Cu-ZSM-5 at 473 K either for SCR towards (NO + NH3 + 0,)
`reactants or for
`ammonia oxidation
`[ 141. However,
`the concentrations of NO and NH3 reactants
`used in that study were each a factor of six less than employed
`in the present study
`with resultant large decrease in probability
`for bimolecular
`reaction events between
`adsorbed species derived
`from NO or NH3 respectively. Results reported here
`represent much more promising
`levels of SCR activity over Cu-ZSM-5 at 473 K.
`Also presented here are results of comparative measurements upon SCR activity
`( W03-
`attained over catalysts prepared by depositing vanadia onto novel ex-sol-gel
`
`Exhibit 2031.002
`
`

`
`J.A. Sullivan et al. /Applied Cataiwis B: Environmental
`
`7 (1995) 137-151
`
`139
`
`into the TiOz lattice of these
`of 5 or 10% W03
`Incorporation
`TiOz) supports.
`materials is demonstrated by XRD together with stabilization of the Ti02 (anatase)
`structure
`to temperatures
`of ca. 1173 K [ 151. The anatase structure had been
`reported
`to increase the amount of V=O species on the surface of TiO,-supported
`vanadia catalysts by favouring precipitation of favourable crystallographic
`struc-
`[ 161.
`tures at the anatase/V,O,
`interface
`
`2. Experimental
`
`2. I. Materials preparation and characterizations
`
`The introduction of copper ions to increasing extent into a H-ZSM-5 material
`having Si/Al
`ratio = 13.4 was achieved by repeated
`ion exchange with aqueous
`solutions containing 0.05 M copper acetate. After drying in a vacuum oven at 383
`K, the ion-exchanged materials were calcined
`in O2 at 773 K for 2 h. Copper
`contents of materials
`thus prepared were determined by acid digestion and AA
`analysis which showed that 2.4% copper was the highest
`loading achieved. The
`designation Cu-ZSM-5 herein means that material, unless otherwise
`indicated. A
`VTT material of the type used commercially with 8% W03 and 4% V205 was
`prepared following the procedure described by Chen and Yang [ 171 which involved
`co-impregnation
`of an aqueous oxalic acid solution containing ammonium meta-
`vanadate and ammonium metatungstate onto predensified
`titania. The material was
`dried in vacuum at 383 K for 15 h and subsequently calcined for 20 h at 773 K in
`an O2 flow. Sol-gel procedures were adopted to achieve
`the preparation of novel
`W03-Ti02
`supports having five or ten atom-percent of tungsten incorporated
`into
`titania
`[ 151. After drying in vacuum and calcination at 773 K for 4 h, deposition
`of 4% vanadia
`thereon was achieved by wet impregnation with an oxalic acid
`solution of V20s followed by vacuum drying and calcination
`in O2 at 773 K for 16
`h. These 4% vanadia on 5% WO,-TiO, or 10% W03-Ti02 materials are hereinafter
`designated as Sample A and Sample B respectively.
`Characterization of the relative ease of reducibility of the vanadia or copper upon
`or within the ‘as-prepared’ materials were achieved by a conventional
`temperature
`programmed
`reduction
`(TPR) procedure using 3% H2 in argon, and a linear tem-
`perature ramp of 10” min ~ ’ . Powder X-ray diffraction
`(XRD) patterns from the
`‘as-prepared’,
`ex-sol-gel WO,-Ti02
`materials were
`collected
`at ambient
`temperature
`for microstructural
`characterizations
`using a Philips MCD diffracto-
`meter featuring optoelectronic
`control to ensure precise measurements of 8 values.
`Peak width positions and areas were evaluated by computer
`fitting of profiles.
`Effects of increasingly
`severe calcination upon microstructure
`of these materials
`were also investigated.
`
`Exhibit 2031.003
`
`

`
`140
`
`J.A. Sullivan et al. /Applied Catalysis B: Environmental
`
`7 (1995) 137-151
`
`2.2. Tests for SCR activity
`
`Small (25 or 10 mg) aliquots of the ‘as-prepared’ materials were supported upon
`a quartz fritted disc fused within a quartz microcatalytic
`reactor, either alone or
`admixed with silicon carbide. Two separate inlet tubes to the reactor respectively
`carried ammonia alone and a suitable premixed gaseous mixture of nitric oxide and
`oxygen
`in helium carrier gas. Flow rates from cylinders of 3%NO/He,
`3%NH,/
`He, lO%O,/He and high-purity helium were adjusted by mass-flow controllers
`to
`deliver to the sample at total flow rates of 30 or 60 ml min- ‘, a standard reactant
`gas mixture having a targeted composition of 0.6%NO + 0.6%NH3 + 3.33%02.
`Tubing from the reactor exit to the gas sampling valve and thence to the GC for
`analysis was heated to avoid deposition of ammonium compounds. Addition of
`water vapour as an extra component
`in the gaseous reactant
`flow reaching
`the
`sample was, when so desired, introduced directly into the reactor from a motorized
`syringe and vapourised
`therein to achieve selected partial pressures in the reactant
`flow. Studies on oxygen dependence were carried out in the same system by using
`the O2 and He flow controllers
`to achieve different partial pressures of O2 while
`keeping constant the overall space velocity and partial pressures of NO and NH,.
`
`3. Results
`
`3.1. Material characterizations
`
`XRD
`atom-
`Fig. 1B illustrates a series of XRD patterns obtained from the ex-sol-gel5
`% W03-Ti02
`support material after calcination at 673 K (bottom patterns), and
`also after 2 h calcinations at 773, 873, 973, 1073 K. With the exception of that for
`the 1073 K-calcined sample, the only difference apparent between the other 4 XRD
`patterns
`is some narrowing of diffraction peaks - consistent with TiOz particle
`growth, but no change in an anatase crystal structure of the W03-Ti02 material.
`Fig. 1A presents a series of XRD patterns measured upon an ex-sol-gel TiOz powder
`obtained by similar preparation, but without W03. The patterns in the two lower
`XRD’s exactly correspond
`to that for Ti02 in its anatase crystal form and further-
`more are identical
`to the bottom four XRD’s shown for W03--Ti02
`in Fig. 1B.
`From this identity
`it may be concluded
`(i) that the W03-Ti02 material had the
`TiO,-anatase crystal structure, which it retained even after calcination up to 973 K,
`and (ii) that no XRD evidence was found for any WO,-related phase after those
`calcinations. The topmost plot of Fig. 1B does, however, show evidence
`for seg-
`regation of a WO,-related phase after calcination at 1073 K, but even then the TiOz
`component apparently retained the TiO,! anatase structure. No comparable retention
`of the anatase structure was shown by the tungsten-free ex-sol-gel Ti02 material,
`since the 28 plot in Fig. 1A after 873 K calcination already demonstrated predom-
`
`Exhibit 2031.004
`
`

`
`J.A. Sullivan et al. /Applied Catal.vsis B: Environmental
`
`7 (1995) 137-151
`
`141
`
`I?NI?TRSE AT DIFFERENT ClGE TEMPSK)
`2588
`
`B.E
`
`effect of heat on 5z W sanple
`1808
`Lcountsl-
`1600-
`
`1480-
`
`E
`
`b
`
`8.0,
`I
`28
`10
`Fig. 1. XRD patterns after oxidation
`5% W03-Ti02
`ex-sol-gel.
`
`/
`
`I
`
`I
`30
`for 2 h at the indicated
`
`I
`
`I
`
`I
`48
`temperatures:
`
`I
`I
`I
`68 c-s.01 78
`SE
`( la) for TiOZ ex-sol-gel. and ( lb) for
`
`inance of the TiO,-rutile structure. Indeed features characteristic of rutile are already
`detectable even after calcination at 773 K.
`
`TPR
`Plots (a), (b) , and (c) of Fig. 2A summarise TPR profiles measured in identical
`conditions upon aliquots of the three oxide-supported
`vanadia catalysts after in-
`situ preoxidations
`in flowing O2 at 773 for 2 h followed by cooling in O2 and brief
`ramp at 10” min - ’ . Plot
`flushing in 3% Hz/Argon before commencing
`temperature
`(c) , which was obtained for a VTT sample with the same nominal 4% vanadia as
`the others, - but had been prepared by deposition on top of tungstate previously
`dispersed upon TiOz rather than within it -
`shows TPR features much smaller and
`
`Exhibit 2031.005
`
`

`
`142
`
`J.A. Sullivan et al. /Applied Catalysis B: Environmental 7 (1995) 137-151
`
`Hydrogen Uptake / Arb.Units.
`1
`
`1om
`
`900
`
`800
`
`7w
`
`600
`
`500
`
`400
`
`300
`
`200
`
`100
`
`0
`
`b
`
`I
`Irn
`
`Fig. 2. Temperature-programmed
`sample B (plot b).
`
`I
`;a0
`
`I
`3uJ
`
`I
`I
`I
`600
`500
`400
`/“C
`Temperature
`reduction profiles for Cu-ZSM-5
`(plot d), VTT (plot c), sample A (plot a) and
`
`I
`7[1)
`
`I
`800
`
`I
`900
`
`l(
`
`IO
`
`(a) and (b). These latter were obtained with
`than in TPR profiles
`less evident
`samples featuring 4% vanadia supported upon ex-sol-gel 10% W02-Ti02. Each
`exhibits one broad main-feature with maxima at 763 and 923 K for sample A and
`B respectively,
`together with a low-temperature
`shoulder (at 673 and 891 K respec-
`tively). No such features were observed
`for the ex-sol-gel
`( W02-Ti02)
`support
`in the absence of vanadia. These comparisons
`indicated that vanadia-related
`species
`supported upon and in contact with the ex-sol-gel WO,-TiO, material could be
`more easily and completely
`reduced
`than for the VTT catalyst. Conversely
`it
`appeared
`that better stabilization of oxidised vanadium species was achieved by
`tungsten-related
`species concentrated at Ti02 surfaces than by those incorporated
`into the Ti02. However,
`these differences were not further investigated, since they
`were not parallelled by large differences
`in SCR catalytic activity (vide infra) . Plot
`(d) of Fig. 2 shows a TPR profile for Cu-ZSM-5 material which exhibits two well-
`defined features peaking at 487 and 649 K. That dual-peak TPR profile is similar
`to those reported for oxidised copper species in various aluminosilicates, but which
`have been the subject of different
`interpretations
`including
`the following:
`(a) two
`peaks observed
`from Cu/Y
`zeolite
`attributed
`to
`the
`two-stage
`reduction
`CL?+ + Cu+ and Cut‘ + Cue [ 181; (b)
`the lower temperature
`feature
`in Cu-
`ZSM-5 attributed to reduction of ion-exchanged, monatomic Cu2+ species to Cu+,
`whereas the higher temperature
`feature attributed
`to reduction of an extra-frame-
`work copper component, such as copper-oxygen
`clusters
`[ 191 or Cu-O-Cu dimers
`[ 141. Efforts
`in the present study to assess which of those interpretations might
`best account for the relative sizes of the two TPR features were hampered by two
`
`Exhibit 2031.006
`
`

`
`J.A. Sullivan et al. /Applied Catalysis B: Environmental 7 (199.5) 137-151
`
`143
`
`to nitrogen from SCR reaction over
`showing % conversion of (0.6%NO + 0.6%NH, + 3.3%02)
`Fig. 3. Histogram
`in a flow of 30 ml per min at Fl W= 1200 ml min-’ g-l.
`25 mg of various catalysts
`
`factors: firstly, the strongly rising baseline evident in plot (d) , thought to arise from
`hydrogen absorption by the Zeolite and, secondly, a lack of success in efforts
`to
`apply XPS
`and AES measurements
`to monitor
`possible Cu*+ + Cu+,
`cu+ + Cue and/or Cu*+ + Cue changes after selective reductions. This lack of
`success stemmed from rapid degradation of the samples by the incident X-ray or
`electron beam, as evidenced by rapid disappearance of shake-up satellites charac-
`teristic of Cu2 + . Analysis based on summation of all XPS signal from Cu, Si, 0
`and Al, in accordance with the Kratos XSAM 800 software,
`indicated somewhat
`lower mass concentrations
`of copper
`in the topmost 30-50 A than found by acid
`digestion and AA analysis viz. 1.96% by XPS vs. 2.47% by AA, and 0.74% by
`XPS vs. 1.8% by AA for a lesser-exchanged
`sample.
`
`3.2. Comparisons of catalytic activity
`
`in bar-chart form in Fig. 3 and Fig. 4 summarise results of
`The data presented
`preliminary
`comparisons
`between
`the catalytic activities observed
`for the four
`catalysts at temperatures 373 --) 773 K and moderate Fl W ratios of 1200 and 3000
`ml min-’ g-l. A reactant mixture of composition 0.6%NO + 0.6%NH, + 3.3%02
`was used and bar-heights
`indicate
`the observed conversion
`to nitrogen expressed
`relative to the nitric oxide and ammonia contents of this standard reactant mixture.
`Each 4-bar subset within each figure facilitates comparison between relative activ-
`ities of the four different catalysts at one of the isothermal
`reaction
`temperatures
`373, 473, 573, 623, 673 and 773 K. An interesting point which emerges already
`from these figures is that for a reaction temperature of 473 the Cu-ZSM-5 exhibited
`substantially higher activity than any of the other materials at these space velocities.
`For higher reaction temperatures, however, data at these moderate space velocities
`
`Exhibit 2031.007
`
`

`
`144
`
`J.A. Sullivan et al. /Applied Catalysis B: Environmental 7 (1995) 137-151
`
`IW
`
`2w
`
`330
`
`3EQ
`
`4cm
`
`SW
`
`showing percent conversion
`Fig. 4. Histogram
`aflowof30mlperminatFIW=3OO0mlmin-’g-l.
`
`Temperature PC.
`to nitrogen from SCR reaction over 10 mg of various catalysts
`
`in
`
`did not adequately discriminate between the catalysts because of complete conver-
`sion.
`Catalytic runs were, therefore, carried out for the same four catalysts using 10
`mg of catalyst, diluted using inert silicon carbide, in a flow of 60 ml per min. This
`gave a space velocity of 6000 ml min- ’ g-’ at which conversions
`to nitrogen were
`always less than 85%. Results are presented in Fig. 5 as a histogram showing percent
`conversion as a function of catalyst and temperature. These data again show Cu-
`ZSM-5 zeolite with a significantly higher overall conversion
`than the other catalysts
`at 473 K. Increases in overall conversion
`to nitrogen over the sample B (vanadia/
`W03-TiO,)
`catalyst from 473 to 573 or 623 K was much greater than for Cu-
`
`IW
`
`ml
`
`showing percent conversion
`Fig. 5. Histogram
`aflowof60mlperminatF/W=60OOmlmin-’g-l.
`
`?m
`Temperature/%
`to nitrogen from SCR reaction over 10 mg of various catalysts
`
`950
`
`4m
`
`sxl
`
`in
`
`Exhibit 2031.008
`
`

`
`J.A. Sullivan et al. /Applied Catalysis B: Environmental 7 (1995) 137-151
`
`145
`
`MO
`
`3w
`
`350
`I “C.
`Temperature
`to nitrogen from ammonia oxidation reaction over 10 mg of various
`Fig. 6. Histogram showing percent conversion
`in a flow of 60 ml per min at F/W = 6000 ml min
`I g _ ‘.
`catalysts
`
`400
`
`MO
`
`activities over both materials at the
`in apparently comparable
`ZSM-5, resulting
`higher temperatures. Other points indicated by comparisons within this histogram
`were the higher activity of sample B relative
`to VTT at 573 and 623 K, and the
`comparable activity of the two at 673 and 773 K. On the other hand, the sample A
`catalyst had comparable
`activity with VTT at 573 K, but underwent a sharper
`decline at 673 and 773 K. Whilst the Cu-ZSM-5 again emerged as the most active
`catalyst for nitrogen product formation at 473 K. These results also suggested
`the
`need for appropriate ‘blank’ experiments
`to establish
`the extent to which direct
`oxidation of ammonia to nitrogen could be contributing
`to total nitrogen production
`at various temperatures.
`to
`Experiments
`to assess possible contributions of direct ammonia conversion
`nitrogen during the SCR process were carried out on the same catalysts under the
`same flow rates and using the same concentrations
`of ammonia and oxygen,
`i.e.
`0.6% and 3.33% respectively
`(i.e. the SCR feed gas without nitric oxide).
`the
`conversions
`to nitrogen
`(on an SCR scale) were calculated and are shown
`in
`histogram
`form on Fig. 6, again as a function of catalyst and of temperature.
`Activities of all catalysts at T < 573 K remained minimal (i.e. below 3% conversion
`on an SCR scale, < 6% true conversion). At 573 K conversion
`for all catalysts
`increased, but barely exceeded 10% converted
`(on an SCR scale). Above 570 K
`the ammonia oxidation activity of Cu-ZSM-5
`increased greatly with temperature
`and rose to 47% at 773 K, i.e. 94% of ammonia converted. Activity of the VTT
`catalyst for this reaction also increased with temperature, peaking at 30% conver-
`sion at 723 K before slightly decreasing. Similar trends as for the VTT catalyst
`were observed for sample A and sample B.
`for contributions by ammonia
`One tentative
`(vide infra) method of correcting
`oxidation
`to overall nitrogen yield in the SCR reaction has been applied to obtain
`form for A, the ‘corrected
`Fig. 7, wherein values are represented,
`in bar-chart
`
`Exhibit 2031.009
`
`

`
`146
`
`J.A. Sullivan et al. /Applied Catalysis B: Environmental 7 (1995) 137-151
`
`100
`
`300
`TemperaturePC.
`showing A, differences
`Fig. 7. Histogram
`in conversions
`for SCR and ammonia oxidation reactions over various
`catalysts at different temperatures under conditions at similar flow.
`
`350
`
`contribution by SCR to N2 production’. The A values represent
`the difference
`between
`(observed percent conversion
`in SCR reaction)
`and (observed percent
`conversion
`from ammonia oxidation only),
`in equivalent conditions. Not surpris-
`ingly the ‘corrected conversion’ data show Cu-ZSM-5
`to retain its position as best
`catalyst at 473 K, since ammonia oxidation contribution was insignificant at that
`temperature. However,
`the corrected conversion values for 573 K show vanadia/
`( ( 10%W03-Ti02) material to narrowly outperform Cu-ZSM-5, with the other two
`catalysts slightly lower again. A continued decline in A over Cu-ZSM-5
`is evident
`at 623, 673 and 773 K whereas at 573 -+ 623 K the declines
`in corresponding
`values for the other catalysts were smaller, resulting in the activity sequence, V,O,/
`10% WO,-TiO,
`> VTT > Cu-ZSM-5 > V205/5% W0JTi02.
`It is worth noting, however,
`that this way of seeking to factor out the contribution
`by ammonia oxidation does not take account of possibilities
`for competition
`between
`the ammonia oxidation and SCR reactions. The mechanism of ammonia
`oxidation
`is thought
`to involve conversion of ammonia
`to nitric oxide, and then
`further reaction of that nitric oxide with more ammonia yielding N2 [ 211. The net
`amount of ammonia oxidation will then be retarded by the presence of nitric oxide
`in the reactant stream. Therefore,
`the by-difference method used to calculate
`the
`corrected conversions
`presented
`in Fig. 7 overestimates
`the contribution
`from
`ammonia oxidation.
`to possible
`Tests were made of the relative susceptibilities of the four catalysts
`deactivation by: (A) short exposures
`to temperatures up to 873 K in the standard
`reactant mixtures; of (B) additions
`thereto of water vapour at increasing partial
`pressures. Neither
`the Cu-ZSM-5 nor the V’IT catalysts appeared susceptible
`to
`deactivation by (A), since conversion at lower temperature
`returned
`to its initial
`value following a catalytic run at 873 K. Similar short-term
`tests with the vanadia/
`( W03-TiO*)
`catalysts did indicate moderate deactivation by (A), which was
`initially surprising in view of the XRD evidence
`that these supports maintained an
`
`Exhibit 2031.010
`
`

`
`J.A. Sullivan et al. /Applied Catalysis B: Environmental
`
`7 (1995) 137-151
`
`147
`
`1M % Conversion
`
`to Nitrogen.
`
`90
`
`80
`
`7D
`
`Gil
`
`50
`
`4a
`
`M
`
`M
`
`10
`
`0
`
`0
`
`lm
`
`300
`
`403
`
`5zQ
`
`Em
`
`[ Conversion.
`
`l o o
`
`b
`
`0
`
`100
`
`2m
`
`Xl0
`Temperature
`
`/ “C
`
`403
`
`SE
`
`600
`
`cwR
`
`% Wotsr ;n Strwm.
`+ 5cR 57” ‘v=R1oN CL!. -c-w
`36. +iNN
`9%.
`(upper plots)
`the effect of 3% and 9% water vapour in the reactant stream on SCR reaction
`Fig. 8. Plot showing
`and ammonia oxidation reaction (lower plots) for: Cu-ZSM-5 8 (a); and sample B; 8 (b) catalysts. 10 mg catalyst
`in a tlow of 60 ml per min.
`
`0%
`
`-X-SCK 3%
`
`unchanged anatase structure after calcination at temperatures up to 1073 K. Results
`relating to (B ) for Cu-ZSM-5 and sample B are illustrated by an upper trio of plots
`in each of Fig. 8(a) and Fig. 8(b) . Inspection of the three upper plots in Fig. 8(a)
`shows that, relative to the values for ‘dry’ standard reactant mixture,
`the presence
`of 3 or 9% water vapour significantly
`increased the conversion
`to N2 observed over
`Cu-ZSM-5 at all temperatures
`studied. Comparison with the lower group of three
`plots on the same figure demonstrates
`that such increases could not have originated
`from an effect upon ammonia oxidation, since that was inhibited over Cu-ZSM-5
`
`Exhibit 2031.011
`
`

`
`148
`
`J.A. Sullivan et al. /Applied Catalysis B: Environmental 7 (1995) 137-151
`
`Table 1
`Corrected percent conversions
`TW
`
`to NZ product from SCR over each catalyst at the indicated reaction
`
`temperatures,
`
`T,X
`
`CuZSM
`
`VTT
`
`sample A
`
`sample B
`
`IT
`
`100
`200
`300
`400
`500
`
`a
`
`12
`54
`64
`42
`27
`
`b
`
`21
`69
`81
`53
`38
`
`C
`
`21
`69
`81
`58
`40
`
`a
`
`13
`25
`60
`43
`20
`
`b
`
`25
`31
`72
`60
`31
`
`C
`
`22
`31
`68
`53
`34
`
`a
`
`14
`28
`62
`33
`12
`
`b
`
`25
`41
`70
`=
`a
`
`C
`
`28
`34
`58
`a
`=
`
`a
`
`12
`36
`72
`58
`26
`
`b
`
`24
`36
`77
`71
`27
`
`C
`
`16
`29
`64
`60
`23
`
`Data obtained with 0%, 3%, or 9% water vapour in the reactant stream are shown in columns headed a, b or c
`respectively.
`a Measurements not taken here due to the deactivation of the sample. Sample B was changed between each run to
`account for this deactivation.
`
`to these data of the empirical correction
`by presence of water vapour. Application
`method noted above for factoring-out
`contributions by ammonia oxidation yields
`data in columns
`lb and lc of Table 1 indicative of the enhancing effect of 9%
`water vapour on SCR activity of Cu-ZSM-5 at various temperatures. Conversions
`over the VTT catalyst displayed qualitatively
`similar trends with temperature
`to
`those for Cu-ZSM-5 and application of the empirical correction method yielded
`data in columns 2b and 2c of Table 1. The differing pattern of response
`to the
`presence of Hz0 exhibited by the mixed-oxide
`supported vanadia is illustrated
`in
`Fig. 8(b) where an inhibiting effect of 9% water vapour upon conversion
`to N2
`product
`is evidenced by the upper trio of plots. Net effect on ‘corrected’ SCR
`conversion was small however since ammonia oxidation was again inhibited over
`that catalyst. Corrected conversion varied as per columns 4b and 4c of Table 1.
`Qualitatively different profiles for the dependence of percentage conversion
`to
`nitrogen upon the % oxygen content of dry (NO + NH3 + 0,)
`reactant flows were
`observed for all four catalysts at reaction
`temperatures 573 and 623 K from those
`at 473 or 378 K. At the two higher temperatures
`the percentage conversion
`rose
`rapidly as oxygen content increased from 0 towards 1% when a plateau value was
`attained with no significant further rise whilst oxygen content increased from 1 to
`6%. Plots (iii) and (iv) of Fig. 9 illustrate this type of behaviour
`in the case of Cu-
`ZSM-5. The plateau values attained at 573 and 623 K with 3.3% O2 corresponded
`to those shown in bar-chart
`form on Fig. 5. The profiles obtained
`for the four
`catalysts at temperature 378 K were very similar to one another, but very different
`from those at the two higher temperatures;
`showing only a gradual rise towards ca.
`20% conversion as oxygen content was increased
`to 6%. (An illustration of this
`type of profile is provided by plot (i) of Fig. 9 for the case of Cu-ZSM-5). For
`catalyst
`temperature 473 K, the VTT, vanadia/( 10%W03-TiOJ
`and V205/5%
`W03-Ti02
`catalysts again showed only a slow gradual
`increase whilst oxygen
`content was raised from 1% to 6%, at which content
`the N2 conversions attained
`were respectively 50% for VTT, 50% for sample B and 40% for sample A. However,
`
`Exhibit 2031.012
`
`

`
`J.A. Sullivan et al. /Applied Catalysis B: Environmenfal7 (1995) 137-151
`
`% Conversion
`
`to Nitrogen.
`
`100
`
`90
`
`80
`
`70
`
`60
`
`50
`
`40
`
`30
`
`20
`
`10
`
`0
`
`0
`
`1
`
`2
`
`% Oxygen
`
`3
`in Stream.
`
`4
`
`5
`
`Fig. 9. Plot showing
`( 10 mg) at different
`
`1
`C
`C =V=T-300 C =C=T-200 C *T-105
`IOT-350
`the effect of different
`inlet concentrations
`of oxygen upon the SCR reaction over Cu-ZSM-5
`in a flow of 60 ml min- ‘. ? ?: plot (i); ??: plot (ii); v: plot (iii); ? ?plot (iv).
`temperatures
`
`the Cu-ZSM-5 catalyst at 473 K gave rise to the markedly different profile illustrated
`by plot (ii) of Fig. 9, where it may be seen that conversion
`to N2 exhibited a marked
`rise from 20% at 1% O2 to 90% at ca. 4.5% 02,. Whatever
`its origins, two important
`operational conclusions
`follow from observation of strong positive dependence on
`P( 0,)
`: firstly, under 3.3% O2 it was a major factor in producing
`the enhanced SCR
`activity observed over Cu-ZSM-5 at 473 K relative to SCR activities over the other
`catalysts studied in those conditions; and secondly,
`that higher corrected conver-
`sions than are here reported
`in Fig. 5 using a reactant gas mixture with 3.3% O2
`would be obtainable at 473 K over Cu-ZSM-5 with O2 content
`in the range 4 to
`5%, but not over the vanadia-promoted
`catalysts.
`
`4. Discussion
`
`the
`significant differences between
`results demonstrate
`These above-mentioned
`profiles obtained at 473 K over the VTT or Cu-ZSM-5
`SCR-activity vs. P(0,)
`catalysts whenever P( 0,) was varied in the range 0 to 6%. The nature of the profiles
`over the VTT materials -with
`a very rapid increase
`in SCR activity for P(0,)
`from 0 to 1% and a levelling off at P( 0,) > 1% suggest either saturation of vanadia-
`related sites by O2 at - 1% 02, or else a change in mechanism. One possibility may
`be for a change from the Eley Rideal-type
`reaction of gaseous NO with adsorbed
`NH: species proposed over vanadia catalysts in dilute reactant conditions
`[ 22,231
`to a site-saturated
`limiting case of Langmuir-Hinshelwood-type
`mechanism
`involv-
`
`Exhibit 2031.013
`
`

`
`150
`
`J.A. Sullivan et al. /Applied Catalysis B: Environmental 7 (1995) 137-151
`
`. A Langmuir-
`from NO + O,,)
`ing reaction of NH: with adsorbed NO2 (formed
`Hinshelwood-type mechanism has been proposed over vanadia catalysts at higher
`reactant pressures
`[ 24,251. The much more gradual
`increase with P( 0,) here
`observed for SCR activity over the Cu-ZSM-5 materials (cf. Fig. 9) appears qual-
`itatively consistent with operation of a site-unsaturated Langmuir-Hinshelwood-
`type mechanism
`involving
`reaction on copper-containing
`sites of an adsorbed
`species derived from NO with an adsorbed species derived from NH3. A mechanism
`of that type has been postulated by Komatso to account for his observations, made
`in dilute reactant conditions, of an increase in SCR rate with P( 0,) over Cu-ZSM-
`5. The relevance of that hypothesis,
`involving Cu-O-Cu
`as active sites in dilute
`reactant conditions,
`to present results obtained under higher reactant concentration
`(vide infra) . However,
`the observed prolongation of P( 0,) -
`is as yet uncertain
`induced
`increase
`in SCR activity up to ca. 4.5% in those conditions
`implies that
`optimal coverage or conversion of copper-containing
`sites by oxygen to yield SCR-
`active species was not obtained until such P( 0,).
`The surprising extent
`to which SCR activity of 2.4% Cu-ZSM-5 at 473 K
`exceeded
`that of the VTT materials in our standard conditions
`(including 3.3% O2
`for each case) reinforces
`interest
`in the origins of higher conversion
`to N2 over
`such ‘overexchanged’ Cu-ZSM-5. There is general agreement on the existence of
`copper in at least two different forms in such materials, only one form being isolated
`Cu2+ ions in the aluminosilicate network. Novel identifications
`recently suggested
`for the