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`G Model
`CATrOD -9683; No. of Pages 11
`cATroD -9683; No. of Pages 11
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`Catalysis Today xxx (2015) xxx -xxx
`Catalysis Today xxx (2015) xxx -xxx
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`Contents lists available at ScienceDirect
`Contents lists available at ScienceDirect
`
`Catalysis Today
`Catalysis Today
`
`journal homepage: www.elsevier.com /locate /cattod
`journal homepage: www.elsevier.com /locate /cattod
`
`¡CATALYSIS
`
`Effects of CO, H2 and C3H6 on Cu- SSZ -13 catalyzed NH3 -SCR
`Effects of CO, H2 and C3H6 on Cu- SSZ -13 catalyzed NH3 -SCR
`Yang Zheng, Michael P. Harold-, Dan Luss
`Yang Zheng, Michael P. Harold , Dan Luss
`Department of Chemical fr Bimolecular Engineering, University of Houston, Houston, TX 77204, USA
`Department of Chemical & Biomolecular Engineering, University of Houston, Houston, TX 77204, USA
`
`I
`
`0.
`
`A R T I C L E I N F O
`A R T
`I C L E
`I N F O
`
`A B S T R A C T
`A B S T R A C T
`
`EXHIBIT
`
`g2-0,/ --
`y-
`
`o`'1 Cj/1(.
`
`t
`
`Article history:
`Article history:
`Received 8 May 2015
`Received 8 May 2015
`Received in revised form 28 June 2015
`Received in revised form 28 June 2015
`Accepted 29 June 2015
`Accepted 29 June 2015
`Available online xxx
`Available online xxx
`
`Keywords:
`Keywords:
`NH3-SCR
`NH3-SCR
`Cu-SSZ-13
`Cu-SSZ-13
`CO
`CO
`H2
`HZ
`C3 H5
`C3 H6
`LNT+SCR
`LNT+ SCR
`
`We investigated the steady -state and transient effects of reductants (CO, H2 and C3H6) on NO2 reduction,
`We investigated the steady -state and transient effects of reductants (CO, H2 and C3H6) on NO2 reduction.
`NH3 -SCR (selective catalytic reduction), NH3 adsorption and oxidation, and N20 production on a Cu -SSZ-
`NH3 -SCR (selective catalytic reduction), NH3 adsorption and oxidation. and N20 production on a Cu -SSZ-
`13 monolithic catalyst. The three reductants affect to different extents the standard SCR (NO + NH3 + 02),
`13 monolithic catalyst. The three reductants affect to different extents the standard SCR (NO + NH3 + 02).
`fast SCR (NO + NH3 + NO2), and slow SCR (NH3 + NO2). This study underscores the importance of account-
`fast SCR (NO + NH3 + NO2), and slow SCR (NH3 + NO2). This study underscores the importance of account-
`ing for the impact of reducing agents on conventional NH3 -SCR reaction mechanism when SCR catalyst is
`ing for the impact of reducing agents on conventional NH3 -SCR reaction mechanism when SCR catalyst is
`subjected to either rich regeneration of integrated systems (LNT+ SCR, SCR on DPF) or cold -start. Propy-
`subjected to either rich regeneration of integrated systems (LNT+ SCR, SCR on DPF) or cold -start. Propy-
`lene is most effective in promoting NO2 reduction to NO by formation of organic intermediates. CO
`lene is most effective in promoting NO2 reduction to NO by formation of organic intermediates. CO
`effectively reduces nitrates to nitrites that then react with NO2, releasing NO. H2 can follow a similar
`effectively reduces nitrates to nitrites that then react with NO2. releasing NO. H2 can follow a similar
`pathway as CO but is less effective. In addition, H2 can also enable a H2 -based SCR pathway through
`pathway as CO but is less effective. In addition. H2 can also enable a H2 -based SCR pathway through
`the reduction of Cu cations to Cu° which then catalyze the NOx reduction. This pathway is particularly
`the reduction of Cu cations to Cu° which then catalyze the NOx reduction. This pathway is particularly
`evident at high temperatures and low 02 levels. As for NH3 -SCR reactions, propylene competes with NH3
`evident at high temperatures and low 02 levels. As for NH3 -SCR reactions, propylene competes with NH3
`for adsorbed NO2, which generates NO and thus increases the NO /NOx ratio. This leads to the dominance
`for adsorbed NO2, which generates NO and thus increases the NO /NOx ratio. This leads to the dominance
`of either fast or standard SCR for a slow SCR (NH3 +NO2) feed condition when C3H6 is present. CO has
`of either fast or standard SCR for a slow SCR (NH3 +NO2) feed condition when C3H6 is present. CO has
`only a minor effect on both standard and fast SCR but a promoting effect on slow SCR. The ineffective
`only a minor effect on both standard and fast SCR but a promoting effect on slow SCR. The ineffective
`reduction of NO2 to NO by H2 at low temperature (T <250 C) results in a negligible effect on slow SCR. In
`reduction of NO2 to NO by H2 at low temperature (T< 250 C) results in a negligible effect on slow SCR. In
`contrast to steady -state operation, lean /rich cycling enhances cycle -averaged NOx conversion for each of
`contrast to steady -state operation, lean /rich cycling enhances cycle- averaged NOx conversion for each of
`the NH3 -SCR reactions when adding either C3H6 or a CO + H2 mixture in the rich phase. A decreased N20
`the NH3 -SCR reactions when adding either C3H6 or a CO + H2 mixture in the rich phase. A decreased N2O
`generation rate from the slow SCR reaction is observed when any of the three reductants are present due
`generation rate from the slow SCR reaction is observed when any of the three reductants are present due
`in part to their reaction with ammonium nitrates.
`in part to their reaction with ammonium nitrates.
`
`© 2015 Elsevier B.V. All rights reserved.
`© 2015 Elsevier B.V. All rights reserved.
`
`1. Introduction
`1. Introduction
`
`Lean -burn gasoline and diesel engines achieve a higher fuel
`Lean -burn gasoline and diesel engines achieve a higher fuel
`economy than stoichiometric gasoline engines. Their use will
`economy than stoichiometric gasoline engines. Their use will
`enable vehicle manufacturers to meet the stringent 2017 -2025 US
`enable vehicle manufacturers to meet the stringent 2017 -2025 US
`EPA greenhouse gas and NHTSA (National Highway Traffic Safety
`EPA greenhouse gas and NHTSA (National Highway Traffic Safety
`Administration) fuel economy standards [1]. A major challenge of
`Administration) fuel economy standards [11. A major challenge of
`lean -burn application is the reduction of nitrogen oxides (NOx;
`lean -burn application is the reduction of nitrogen oxides (NOx;
`No + NO2) in a net oxidizing environment. Ever -tightening Tier
`NO +NO2) in a net oxidizing environment. Ever -tightening Tier
`3 and LEV Ill emission regulations exacerbate this technological
`3 and LEV IIl emission regulations exacerbate this technological
`challenge [2]. Two commercialized deNOx technologies that meet
`challenge [2]. Two commercialized deNOx technologies that meet
`the current emission standards are NOx storage and reduction
`the current emission standards are NOx storage and reduction
`(NSR) and selective catalytic reduction (SCR). The SCR technology
`(NSR) and selective catalytic reduction (SCR). The SCR technology
`reduces NOx to N2 by reaction over vanadium -based or transi-
`reduces NOx to N2 by reaction over vanadium -based or transi-
`tion metal exchanged zeolite catalysts with NH3 generated from
`tion metal exchanged zeolite catalysts with NH3 generated from
`urea hydrolysis. SCR is the leading deNOx solution for mid- or
`is the leading deNOx solution for mid- or
`urea hydrolysis. SCR
`heavy -duty vehicles and can achieve over 95% deNOx efficiency at
`heavy -duty vehicles and can achieve over 95% deNOx efficiency at
`
`Corresponding authors. Tel.: +1 713 743 4322; fax: +1 713 743 432.
`Corresponding authors. Tel.: +1 713 743 4322; fax: +1 713 743 432.
`E -mail addresses: mharold @uh.edu (M.P. Harold), dluss @uh.edu (D. Luss).
`E -mail addresses: mharold @uh.edu (M.P. Harold), dluss @uh.edu (D. Luss).
`
`http:// dx. doi. org /10.1016/j.cattod.2015.06.028
`http://dx.doi.org/10. 1 016/j.cattod.2015.06.028
`0920-5861/0 2015 Elsevier B.V. All rights reserved.
`0920-5861/C 2015 Elsevier B.V. All rights reserved.
`
`practically relevant space velocities. It requires an onboard urea
`practically relevant space velocities. It requires an onboard urea
`storage and delivery system with a minimum urea dosing tem-
`storage and delivery system with a minimum urea dosing tem-
`perature requirement of -200 C. This limits its function during
`perature requirement of --200 C. This limits its function during
`cold -start or low -load conditions. For light -duty lean -burn vehi-
`cold -start or low -load conditions. For light -duty lean -burn vehi-
`cles, NSR is preferred. It involves the storage of NOx on a lean NOx
`cles, NSR is preferred. It involves the storage of NOx on a lean NOx
`trap (LNT) catalyst under lean conditions, followed by a short, rich
`trap (LNT) catalyst under lean conditions, followed by a short, rich
`regeneration by a mixture of CO, H2 and hydrocarbons (HC) [3]. The
`regeneration by a mixture of CO, H2 and hydrocarbons (HC) [31. The
`LNT catalyst requires precious group metals (PGM) to achieve a high
`LNT catalyst requires precious group metals (PGM) to achieve a high
`NOx conversion. However, it is not as selective as SCR, producing
`NOx conversion. However, it is not as selective as SCR, producing
`byproducts such as N20 and NH3.
`byproducts such as N20 and NH3.
`The integration of SCR with NSR (or equivalently LNT) has
`The integration of SCR with NSR (or equivalently LNT) has
`aroused much interest [4 -6]. One example is the LNT+ passive
`aroused much interest [4 -6]. One example is the LNT +passive
`SCR system wherein the SCR catalyst utilizes NH3 produced by
`SCR system wherein the SCR catalyst utilizes NH3 produced by
`the upstream LNT during rich purges to achieve incremental NOx
`the upstream LNT during rich purges to achieve incremental NOx
`reduction. This system lowers the cost by the reduction of the PGM
`reduction. This system lowers the cost by the reduction of the PGM
`loading required for the LNT and elimination of the urea injec-
`loading required for the LNT and elimination of the urea injec-
`tion for the SCR system [7]. The overall NOx conversion is still
`tion for the SCR system [7]. The overall NOx conversion is still
`mostly confined in the LNT, which decreases at high temperatures
`mostly confined in the LNT, which decreases at high temperatures
`(>400 C) due to deceased NOx storage capacity and NH3 yield.
`( >400 "C) due to deceased NOx storage capacity and NH3 yield.
`A new LNT +active SCR system with urea dosing was proposed
`A new LNT+ active SCR system with urea dosing was proposed
`by researchers from SwRI [8] and Hyundai [9]. It uses a LNT to
`by researchers from SwRI [8] and Hyundai [9]. It uses a LNT to
`
`Please cite this article in press as: Y. Zheng, et al., Effects of CO, H2 and C3H6 on Cu- SSZ -13 catalyzed NH3 -SCR, Catal. Today (2015),
`Please cite this article in press as: Y. Zheng, et al., Effects of CO, H2 and C3H6 on Cu- SSZ -13 catalyzed NH3 -SCR, Catal. Today (2015),
`http://dx.doi.org/10.1016/j.cattod.2015.06.028
`http://dx.doi.org/10.1016/j.cattod.2015.06.028
`
`BASF-2022.001
`
`

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`G Model
`G Model
`CAI-MD-9683; No. of Pages 11
`CATIOD -9683; No. of Pages 11
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`2
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`Y. Zheng et a1. / Catalysis Today xxx (2015) xxx -xxx
`Y. Zheng et al. / Catalysis Todoy xxx (2015) xxx-xxx
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`overcome the SCR cold -start NOx emission, when the temperature
`overcome the SCR cold -start NOx emission, when the temperature
`is too low for urea dosing. The combined system has been demon-
`is too low for urea dosing. The combined system has been demon-
`strated to meet the LEV Ill limits. It is a promising solution for LEV
`strated to meet the LEV Ill limits. It is a promising solution for LEV
`III -compliant diesel vehicles [10].
`Ill- compliant diesel vehicles [10].
`In contrast to the stand -alone urea -SCR system designed to
`In contrast to the stand -alone urea -SCR system designed to
`operate with a lean exhaust, the combined LNT +SCR is inevitably
`operate with a lean exhaust, the combined LNT +SCR is inevitably
`exposed to a rich exhaust condition during the LNT regeneration.
`exposed to a rich exhaust condition during the LNT regeneration.
`Deep rich purges are preferred to promote NH3 generation by the
`Deep rich purges are preferred to promote NH3 generation by the
`LNT. This may generate relatively high levels of CO, H2 and HC
`LNT. This may generate relatively high levels of CO, H2 and HC
`slippage to the SCR catalyst [11,12]. A recently -commercialized
`slippage to the SCR catalyst [11,12]. A recently -commercialized
`SCR on -filter (SCRF) technology comprises a diesel particulate fil-
`SCR on -filter (SCRF) technology comprises a diesel particulate fil-
`ter (DPF) that is coated with SCR catalyst and is positioned in
`ter (DPF) that is coated with SCR catalyst and is positioned in
`close proximity to the engine to enable fast SCR light -off. The SCR
`close proximity to the engine to enable fast SCR light -off. The SCR
`component encounters a rich environment during the periodic
`component encounters a rich environment during the periodic
`DPF regeneration events [13]. Even the SCR -only system may be
`DPF regeneration events [13]. Even the SCR -only system may be
`exposed to a rich feed under certain conditions such as cold -start
`exposed to a rich feed under certain conditions such as cold -start
`period, extended vehicle idling, engine malfunction, or degraded
`period, extended vehicle idling, engine malfunction, or degraded
`upstream diesel oxidation catalysts (DOC) [14,15]. All of these
`upstream diesel oxidation catalysts (DOC) [ 14,15]. All of these
`scenarios raise questions regarding the potential impact of rich
`scenarios raise questions regarding the potential impact of rich
`reducing agents on the performance of the SCR catalyst.
`reducing agents on the performance of the SCR catalyst.
`Previous studies of the impact of various reductants on NH3 -SCR
`Previous studies of the impact of various reductants on NH3 -SCR
`performance over metal- exchanged zeolites have mainly focused
`performance over metal- exchanged zeolites have mainly focused
`on HC species poisoning. It is well known that stored HC on zeolites
`on HC species poisoning. It is well known that stored HC on zeolites
`can have a detrimental effect on both the SCR catalyst performance
`can have a detrimental effect on both the SCR catalyst performance
`and its durability [16]. He et al. reported a negative effect of C3H6
`and its durability 116]. He et al. reported a negative effect of C3H6
`due to carbon deposits during standard SCR (NO + NH3 + 02) over a
`due to carbon deposits during standard SCR (NO + NH3 + 02) over a
`Fe -beta zeolite [17]. Heo et al. attributed the competitive adsorp-
`Fe -beta zeolite [17]. Heo et al. attributed the competitive adsorp-
`tion of NH3 and C3H6 on the catalyst as well as undesired NH3
`tion of NH3 and C3H6 on the catalyst as well as undesired NH3
`consumption by side reactions to the decreased NH3 -SCR activities
`consumption by side reactions to the decreased NH3 -SCR activities
`of Fe- or Cu -ZSM -5 [ 18]. Epling et al. compared the effects of C3H6
`of Fe- or Cu -ZSM -5 [ 18]. Epling et al. compared the effects of C3H6
`and dodecane (n- C12H26) exposure over two Cu- exchanged zeolite
`and dodecane (n- C12H26) exposure over two Cu- exchanged zeolite
`catalysts; one was a small -pore zeolite ( Chabazite framework, CHA)
`catalysts; one was a small -pore zeolite (Chabazite framework, CHA)
`while the second was a standard large -pore Cu -BEA zeolite [19].
`while the second was a standard large -pore Cu -BEA zeolite [19].
`The Cu -CHA had a much better resistance to HC poisoning than the
`The Cu -CHA had a much better resistance to HC poisoning than the
`Cu -BEA by effectively suppressing HC adsorption and coke forma-
`Cu -BEA by effectively suppressing HC adsorption and coke forma-
`tion. A slightly decreased standard SCR activity was observed when
`tion. A slightly decreased standard SCR activity was observed when
`addingC3H6 to the gas fed to the Cu -CHA [ 19].This was attributed to
`adding C3H6 to the gas fed to the Cu -CHA [ 19].This was attributed to
`formation of partial oxidation intermediates. In a follow -up study,
`formation of partial oxidation intermediates. In a follow -up study,
`Kumar et al. found that even a small -pore zeolite could store non -
`Kumar et al. found that even a small -pore zeolite could store non -
`negligible amounts of carbonaceous deposits from either short -
`negligible amounts of carbonaceous deposits from either short -
`or long -chain HCs via an oxygen -dependent, thermally- activated
`or long -chain HCs via an oxygen- dependent, thermally- activated
`storage process [15]. All the above studies were conducted with
`storage process 115]. All the above studies were conducted with
`continuous exposure of the SCR catalysts to a HC. Wang et al. [20]
`continuous exposure of the SCR catalysts to a HC. Wang et al. [20]
`and Kim et al. [21 ] reported that under lean /rich cyclic conditions,
`and Kim et al. [21 ] reported that under lean /rich cyclic conditions,
`the enhanced cycle -averaged NOx conversion over a Cu -CHA cata-
`the enhanced cycle- averaged NOx conversion over a Cu -CHA cata-
`lyst by C3H6, was attributed to the mitigation of HC poisoning and
`lyst by C3H6, was attributed to the mitigation of HC poisoning and
`HC -SCR reactions.
`HC -SCR reactions.
`The factors accounting for the impact of HC on NH3 -SCR over
`The factors accounting for the impact of HC on NH3 -SCR over
`SCR zeolite catalysts include competitive adsorption, undesired
`SCR zeolite catalysts include competitive adsorption, undesired
`NH3 consumption, formation of partially oxidized intermediates
`NH3 consumption, formation of partially oxidized intermediates
`and operating conditions (continuous or cyclic). A clear elucidation
`and operating conditions (continuous or cyclic). A clear elucidation
`requires a systematic analysis. However, to date only a few studies
`requires a systematic analysis. However, to date only a few studies
`investigated the effects of other reducing regents like CO and H2 on
`investigated the effects of other reducing regents like CO and H2 on
`NH3 -SCR zeolite catalysts. Huang et al. studied the deactivation of
`NH3 -SCR zeolite catalysts. Huang et al. studied the deactivation of
`Cu- zeolites by reductive hydrothermal aging [ 14]. They found that
`Cu- zeolites by reductive hydrothermal aging [ 14]. They found that
`extended exposure to a CO /H2 mixture at 650 C resulted in per-
`extended exposure to a CO /H2 mixture at 650 C resulted in per-
`manent catalyst deactivation due to the sintering of Cu° from the
`manent catalyst deactivation due to the sintering of Cu° from the
`reduction of isolated Cue+ cations. Exposure to C3 H6 under the same
`reduction of isolated Cue+ cations. Exposure to C3 H6 under the same
`conditions resulted in a reversible deactivation after coke removal.
`conditions resulted in a reversible deactivation after coke removal.
`Smith et al. [22] recently reported that compared to C3H6, CO and H2
`Smith et al. [ 22 ] recently reported that compared to C3H6, CO and H2
`had a negligible effect on the NH3 -SCR chemistry over an Fe- zeolite
`had a negligible effect on the NH3 -SCR chemistry over an Fe- zeolite
`catalyst, with the main contribution being a slight promotion of
`catalyst, with the main contribution being a slight promotion of
`NO2 reduction to NO.
`NO2 reduction to NO.
`To the best of our knowledge, the effects of a reductant mixture
`To the best of our knowledge, the effects of a reductant mixture
`containing CO, H2 and C3H6 on the SCR performance of a small -pore
`containing CO, H2 and C3H6 on the SCR performance ofa small -pore
`Cu- chabazite catalyst under either steady -state or cyclic operations
`Cu- chabazite catalyst under either steady -state or cyclic operations
`
`have not been systematically studied. To this end, in this study we
`have not been systematically studied. To this end, in this study we
`examine the effects of each reductant through temperature ramp,
`examine the effects of each reductant through temperature ramp,
`step -response and cyclic experiments. The results can help in the
`step -response and cyclic experiments. The results can help in the
`interpretation of NH3 -SCR on Cu -CHA catalysts when subjected to
`interpretation of NH3 -SCR on Cu -CHA catalysts when subjected to
`rich exhaust exposure.
`rich exhaust exposure.
`
`2. Experimental
`2. Experimental
`
`2.1. Catalyst
`2.1. Catalyst
`
`A Cu- SSZ -13 SCR catalyst having a CHA framework was pro-
`A Cu- SSZ -13 SCR catalyst having a CHA framework was pro-
`vided by BASF (Iselin, NJ). The SCR sample had a cell density of
`vided by BASF (Iselin, NJ). The SCR sample had a cell density of
`400 cpsi and an estimated washcoat loading of about 2.4 g /in3 with
`400 cpsi and an estimated washcoat loading of about 2.4 g /in3 with
`ca. 2.5 wt.% Cu loading. For bench reactor evaluation, a core sam-
`ca. 2.5 wt.% Cu loading. For bench reactor evaluation, a core sam-
`ple was prepared (D = 0.8 cm, L=1.0 cm, 28 channels). Prior to the
`ple was prepared (D - 0.8 cm, L= 1.0 cm, 28 channels). Prior to the
`reactor tests, the catalyst was de- greened at 500 C for 5 h in a feed
`reactor tests, the catalyst was de- greened at 500 C for 5 h in a feed
`mixture containing 5% 02, 2.5% H20, 2% CO2, and balance of Ar.
`mixture containing 5% 02, 2.5% H20, 2% CO2, and balance of Ar.
`
`2.2. Temperature ramp experiments
`2.2. Temperature ramp experiments
`
`The bench -scale reactor set -up comprised a gas supply, tubu-
`The bench -scale reactor set -up comprised a gas supply, tubu-
`lar monolith reactor, and analytical and data acquisition systems.
`lar monolith reactor, and analytical and data acquisition systems.
`Gas flow rates were controlled by mass flow controllers (MKS Inc.)
`Gas flow rates were controlled by mass flow controllers (MI <S Inc.)
`before entering the inline static mixer. Water was fed by a syringe
`before entering the inline static mixer. Water was fed by a syringe
`pump (ISCO Model 500D) and vaporized in a heated line. A LabTech
`pump (ISCO Model 500D) and vaporized in a heated line. A LabTech
`interface controlled the switching valve and mass flow controllers
`interface controlled the switching valve and mass flow controllers
`for the feed streams. The monolith catalyst was wrapped with
`for the feed streams. The monolith catalyst was wrapped with
`Fiberfrax® ceramic paper and inserted inside a quartz tube (40.6 cm
`Fiberfrax® ceramic paper and inserted inside a quartz tube (40.6 cm
`long, 1.27 cm outer diameter) mounted in a tube furnace coupled to
`long, 1.27 cm outer diameter) mounted in a tube furnace coupled to
`a temperature controller. The temperature inside the reactor was
`a temperature controller. The temperature inside the reactor was
`measured
`measured
`thermo-
`thermo-
`couples (Omega Engineering Inc.). One placed 0.5 cm in front of the
`couples (Omega Engineering Inc.). One placed 0.5 cm in front of the
`monolith measured the feed temperature. The second measured
`monolith measured the feed temperature. The second measured
`the temperature in the middle of the center monolith channel. The
`the temperature in the middle of the center monolith channel. The
`gaseous effluent concentrations of NO, NO2, N20, NH3, CO, CO2 and
`gaseous effluent concentrations of NO, NO2, N20, NH3, CO, CO2 and
`H2O were measured by a calibrated FT -IR spectrometer (Thermo -
`H2O were measured by a calibrated FT -IR spectrometer (Thermo -
`Nicolet, Nexus 470).
`Nicolet, Nexus 470).
`The SCR catalyst was exposed to a constant feed composition
`The SCR catalyst was exposed to a constant feed composition
`at 500 C to establish a steady state before the temperature ramp
`at 500 C to establish a steady state before the temperature ramp
`experiments. The downward temperature ramp to 200 C was con-
`experiments. The downward temperature ramp to 200 C was con-
`ducted at a rate of -2 C /min to minimize the complicating effect
`ducted at a rate of -2 C /min to minimize the complicating effect
`of NH4NO3 formation. The ramp rate was sufficiently slow to avoid
`of NH4NO3 formation. The ramp rate was sufficiently slow to avoid
`thermal hysteresis effects and to obtain essentially steady -state
`thermal hysteresis effects and to obtain essentially steady -state
`results. [Comment: The downward ramp was found to be more
`results. [Comment: The downward ramp was found to be more
`effective in this regard than an upward ramp. For example, the NO2
`effective in this regard than an upward ramp. For example, the NO2
`SCR reaction (NO2 + NH3) is hard to reach steady -state at low tem-
`SCR reaction (NO2 + NH3) is hard to reach steady -state at low tem-
`perature (-200 C) due to the gradual accumulation of NH4NO3 on
`perature (-200 C) due to the gradual accumulation of NH4NO3 on
`the catalyst; this process deactivates the catalyst and makes it diffi-
`the catalyst; this process deactivates the catalyst and makes it diffi-
`cult to differentiate among the effects of different reducing agents.]
`cult to differentiate among the effects of different reducing agents.]
`In some experiments, a step- response method was employed in
`In some experiments, a step- response method was employed in
`order to evaluate both the transient and long -term response to gas
`order to evaluate both the transient and long -term response to gas
`concentration changes.
`concentration changes.
`the baseline NH3 -SCR
`the baseline NH3 -SCR
`feed gas composition
`composition for
`The
`feed gas
`The
`for
`reactions comprised 500 ppm NH3 and 500 ppm NO for
`reactions comprised 500 ppm NH3
`and 500 ppm NO
`for
`standard
`standard
`(NO /NOx =1;
`4NO +4NH3 + 02
`(NO /NOx =1;
`4N0 + 4NH3 + 02 - 4N2 + 6H2O),
`SCR
`SCR
`4N2 + 6H2O),
`250ppm
`250 ppm NO
`and
`and
`for
`fast
`fast
`for
`(NO /NOx =0.5;
`NO
`NO2
`NO2
`(NO /NOx = 0.5;
`SCR
`SCR
`NO +NO2 +2NH3- .2N2 +3H2O) and 500ppm NO2
`NO +NO2 +2NH3 -+2N2 +3H20) and 500ppm NO2 for
`for slow
`slow
`SCR (NO /NOx = 0; 3NO2 +4NH3
`SCR (NO /NOx = 0; 3NO2 +4NH3 -. 3.5N2 + 6H20)), in 0% or 5% 02
`3.5N2 + 6H20)), in 0% or 5% 02
`(as specified) in a carrier gas of 2.5% H2O, 2% CO2 and balance Ar,
`(as specified) in a carrier gas of 2.5% H20, 2% CO2 and balance Ar,
`at a space velocity of 120,000h -1. A reductant feed of either 1%
`at a space velocity of 120,000h -1. A reductant feed of either 1%
`CO or 1% H2 or 500ppm C3H6 was introduced as specified. The
`CO or 1% H2 or 500 ppm C3H6 was introduced as specified. The
`amount of C3H6 (500ppm) was lower than that of CO (1 %) or H2
`amount of C3H6 (500ppm) was lower than that of CO (1 %) or H2
`(1 %) on a total reductant basis (the amount of 0 species that can
`(1 %) on a total reductant basis (the amount of 0 species that can
`be consumed by reductants); i.e., 500 ppm C3H6 can consume
`be consumed by reductants); i.e., 500 ppm C3H6 can consume
`
`Please cite this article in press as: Y. Zheng, et al., Effects of CO, H2 and C3H6 on Cu- SSZ -13 catalyzed NH3 -SCR, Catal. Today (2015),
`Please cite this article in press as: Y. Zheng, et al., Effects of CO, H2 and C3H6 on Cu- SSZ -13 catalyzed NH3 -SCR, Catal. Today (2015),
`http: / /dx.doi.org /10.1016 /j.cattod.2015.06.028
`http://dx.doi.org/10.1016/j.cattod.2015.06.028
`
`BASF-2022.002
`
`

`
`Y. Zheng er al. / Catalysis Today xxx (2015) xxx -xxx
`Y. Zheng er al. / Catalysis Today xxx (2015) xxx -xxx
`
`3
`3
`
`(a) NO+CO/H2/C3H6
`(a) NO+CO/H2/C3H6
`
`!--
`
`.
`
`H2 case
`H2 case -
`
`;.
`
`CO case
`CO case
`
`3H5 case
`case
`
`(b) NO+02+CO/H2/C3H6
`(b) NO+02+CO/H2/C3H6
`
`i3H6case
`
`G Model
`G Model
`CA'1-r0D -9683; No. of Pages 11
`CMTOD -9683: No. of Pages 11
`
`100
`100
`
`o 75
`75
`P_
`:;5
`
`50
`50 -
`
`25 -
`25
`
`Os
`0
`50
`50
`
`40 -
`
`30
`30 -
`
`20 -
`20
`
`10
`10 -
`
`ad
`N
`M2
`"o
`
`ó
`
`>
`
`CO
`
`O
`
`0 It
`o
`200
`200
`
`250
`250
`
`H2 case
`H2 case
`
`CO case
`CO case
`
`k=111
`
`e
`e
`300
`300
`400
`350
`400
`350
`Feed temperature, °C
`Feed temperature, °C
`
`e
`450
`450
`
`500
`500
`
`Fig. 1. NO conversion (solid) and NH3 selectivity (dash) during reaction of NO (500 ppm) with three reductants (either 1% CO, 1% H2, or 500 ppm C3H6) in the absence of 02
`Fig. 1. NO conversion (solid) and NH3 selectivity (dash) during reaction of NO (500 ppm) with three reductants (either 1% CO, 1% H2. or 500 ppm C3 H6) in the absence of 02
`(a) and in the presence of 5% 02 (b).
`(a) and in the presence of 5% 02 (b).
`
`4500 ppm 0 species, while 1% of either- CO or H2 can consume I%
`4500ppm 0 species, while 1% of either CO or H2 can consume 1%
`0 species.
`0 species.
`
`2.3. Lean /rich cycling experiments
`2.3. Lean /rich cycling experiments
`
`Lean /rich (30/5s) cycling experiments were conducted over the
`Lean /rich (30 /5s) cycling experiments were conducted over the
`SCR catalyst. Table 1 describes the baseline cycling conditions. A
`SCR catalyst. Table I describes the baseline cycling conditions. A
`reductant of either- 1% CO or 1% H2 or 500 ppm C3H6 was added
`reductant of either 1% CO or 1% H2 or 500 ppm C3H6 was added
`to the baseline rich phase. The feed temperature was increased
`to the baseline rich phase. The feed temperature was increased
`from 200 to 450 C in steps of 50 -C. It typically took approximately
`from 200 to 450 -C in steps of 50 C. It typically took approximately
`-10 min to reach a periodic steady state. At each temperature the
`-10 min to reach a periodic steady state. At each temperature the
`cycle- averaged NOx (NO + NO2) conversion for a particular oper-
`cycle- averaged NOx (NO +NO2) conversion for a particular oper-
`ating condition was determined from the average of the final ten
`ating condition was determined from the average of the final ten
`periodic
`The fractional NOx conversion was calculated by
`periodic cycles. The fractional NO conversion was calculated by
`[FNO(t) + FN02 (t)J dt
`foT[FNO(t) + FNO2(t)] dt
`fT
`f° T [Fivo(t) + FÑo2(t) J dt
`fOT [FNO(t) + FÑ02(t)] dt
`Here tT is the duration of a lean -rich cycle. FÑO(t) and FNOZ(t) are
`Here TT is the duration of a lean -rich cycle. F¡,o(t) and FN02(t) are
`the NO and NO2 feed rates and FNO(t), FNO2(t) are the effluent molar
`the NO and NO2 feed rates and FNO(t), FNO2(t) are the effluent molar
`flow rates (mole /s).
`flow rates (mole /s).
`
`XNOa = i
`XNOx = 1
`
`T
`
`2.4. Temperature -programmed desorption (TPD) experiments
`2.4. Temperature - programmed desorption (TPD) experiments
`
`Two types of TPD experiments were performed. The first evalu-
`Two types of TPD experiments were performed. The first evalu-
`ated the effects of the three reductants on the NH3 storage capacity.
`ated the effects of the three reductants on the NH3 storage capacity.
`The catalyst was exposed to 500 ppm NH3 in a carrier gas with and
`The catalyst was exposed to 500 ppm NH3 in a carrier gas with and
`without the presence of a reductant mixture containing 1% CO, 1%
`without the presence of a reductant mixture containing 1% CO, 1%
`
`Table 1
`Table 1
`Gas condition for baseline cycling test.
`Gas condition for baseline cycling test.
`
`Gas
`Gas
`
`Lean (30 s)
`Lean (30 s)
`
`300 ppm
`300 ppm
`
`NOx'
`NOx'
`NH3
`NH3
`02
`02
`5%
`5%
`CO2
`2%
`2%
`CO2
`H20
`H20
`2.5%
`2.5%
`' NO /NOx =1 for standard, 0.5 for fast and 0 for slow SCR reactions.
`' NO /NOx -1 for standard, 0.5 for fast and 0 for slow SCR reactions.
`
`Rich (5 s)
`Rich (5 s)
`
`300 ppm
`300 ppm
`500 ppm
`500 ppm
`1%
`1%
`2%
`2%
`2.5%
`2.5%
`
`H2 and 500 ppm C3 H6 at 200 C for 30 min, followed by another 30-
`H2 and 500 ppm C3H6 at 200 C for 30 min, followed by another 30-
`min flush with carrier gas. The sample was then heated in carrier
`min flush with carrier gas. The sample was then heated in carrier
`gas at a rate of 7.5 C /min up to 500 C. The second type studied the
`gas at a rate of 7.5 C /min up to 500 C. The second type studied the
`surface reactions between NH4NO3 and reducing agents. An equal
`surface reactions between NH4NO3 and reducing agents. An equal
`amount of NH4NO3 was first loaded by co- feeding 500 ppm NH3
`amount of NH4NO3 was first loaded by co- feeding 500 ppm NH3
`and 500 ppm NO2 to the SCR catalyst at 200 C for 30 min, followed
`and 500 ppm NO2 to the SCR catalyst at 200 C for 30 min, followed
`by a 30 -min purge with carrier gas. The sample was then heated at
`by a 30 -min purge with carrier gas. The sample was then heated at
`15 C /min to 400 C in a carrier gas (baseline), or in a mixture with
`15 C /min to 400 C in a carrier gas (baseline), or in a mixture with
`either 1% CO or 1% H2 or 500 ppm C3H6. Prior to each experiment,
`either 1x CO or 1% H2 or 500ppm C3H6. Prior to each experiment,
`the catalyst was exposed to 5% 02 in a carrier gas at 500 C for 1 h.
`the catalyst was exposed to 5% 02 in a carrier gas at 500 C for 1 h.
`
`3. Results and discussion
`3. Results and discussion
`
`3.1. NO and NO2 reactions with CO, 1-12 and C3H6
`3.1. NO and NO2 reactions with CO, H2 and C3H6
`
`Fig. 1 compares the NO conversion during the reaction of NO
`Fig. 1 compares the NO conversion during the reaction of NO
`with CO, H2 or C3H6 under both anaerobic and aerobic conditions.
`with CO, H2 or C3H6 under both anaerobic and aerobic conditions.
`CO shows negligible NO conversion over the entire temperature
`CO shows negligible NO conversion over the entire temp