SCR-Catalyst Materials for Exhaust Gas Detection D. Schönauer-Kamin, R. Moos

Transcription

1 SCR-Catalyst Materials for Exhaust Gas Detection D. Schönauer-Kamin, R. Moos IMCS 14th, , D. Schönauer-Kamin / 1

2 Motivation SCR: selective catalytic reduction of NO x by NH 3 - NH 3 added as aqueous urea solution - catalytic reactions on SCR-catalyst - initial step: NH 3 -adsorption and -storage on the catalyst SCR-active materials: V 2 O 5 -WO 3 -TiO 2 and Fe-ZSM5 IMCS 14th, , D. Schönauer-Kamin / 2

3 Motivation SCR-catalyst materials: VWT and Fe-zeolites NH 3 -storage and catalytic reactions catalyst materials as sensors known catalytic behavior given selectivity proven long term stability stable in harsh environments detection of c gas detect the status of the catalyst layer determination of NH 3 -loading diagnosis of catalyst itself determination of the amount of stored NH 3 in situ radio-frequency technology contactless determination of the stored NH 3 -amount during operation potentiometric sensors resistive / impedimetric sensors RF antennas RF method Au electrodes catalyst coating Au-IDE functional catalyst layer solid electrolyte alumina substrate catalyst, heated IMCS 14th, , D. Schönauer-Kamin / 3

4 SCR-catalyst materials: VWT and Fe-zeolites NH 3 -storage and catalytic reactions catalyst materials as sensors known catalytic behavior given selectivity proven long term stability stable in harsh environments detection of c gas detect the status of the catalyst layer determination of NH 3 -loading diagnosis of catalyst itself determination of the amount of stored NH 3 in situ radio-frequency technology contactless determination of the stored NH 3 -amount during operation potentiometric sensors resistive / impedimetric sensors RF antennas RF method Au electrodes catalyst coating Au-IDE functional catalyst layer solid electrolyte alumina substrate catalyst, heated IMCS 14th, , D. Schönauer-Kamin / 4

5 Au electrodes Mixed potential NH 3 gas sensor catalyst coating solid electrolyte catalytic active layer: VWT / Fe-zeolite electrodes (Au/Au) solid electrolyte O 2 -ion-conducting YSZ (substrate or screen-printed layer) sensing electrode - reference electrode + U two equal noble metal electrodes: electric conductivity potential measurement porous catalytic active coating of one electrode: catalytic activity and NH 3 -selectivity long-term stability test conditions: synthetic exhaust gas test bench function of SCR-catalyst layer: catalytic properties / adsorption / selectivity base gas: 1% O 2, 6.5% CO 2, 2.5% H 2 O, N 2 addition of test gas NH 3 (1 3 ppm) sensor temperature ~ 55 C (adjusted by external furnace or platinum heater structure) IMCS 14th, , D. Schönauer-Kamin / 5 source: Schönauer, D., Sens. Act.: Chem. 14 (29)

6 c NH3 / ppm U / mv U / mv Au electrodes Mixed potential NH 3 gas sensor VWT, Au YSZ Au catalyst coating solid electrolyte 55 C base gas: 1% O 2, 6.5% CO 2, 7% H 2 O, N m 1 = 75mV/Dekade m 2 = 71 mv/dekade t / min 1 1 c NH3 / ppm - semi-logarithmic characteristic curve - sensitivity: mv / decade NH 3 - sensor does not show hysteresis (NH 3 up & down) - reproducible sensor behavior IMCS 14th, , D. Schönauer-Kamin / 6 source: Schönauer, D., Sens. Act.: Chem. 14 (29)

7 U / mv U / mv Au electrodes Mixed potential NH 3 gas sensor Fe-zeolites, Au YSZ Au catalyst coating solid electrolyte VWT C base gas: 1% O 2, 6.5% CO 2, 2.5% H 2 O, N 2 Fe-Zeolith Fe-SAPO34 Fe-SAPO / ppm c NH3 Fe-zeolites 4 2 Fe-Beta / ppm c NH3 Fe-MFI - low NH 3 -sensitivity of Fe-zeolites - VWT: highest NH 3 -sensitivity VWT: best sensing characteristics various Fe-zeolites tested: Fe-zeolite catalyst Fe-ZSM5; Fe-Beta; Fe-SAPO-5; Fe-SAPO-34 Fe-zeolites: poor sensitivity IMCS 14th, , D. Schönauer-Kamin / 7

8 Au electrodes Potentiometric SO 2 gas sensor VWT, Au NASICON Au catalyst coating solid electrolyte NASICON: Na + -ion conductor Au electrodes VWT catalyst layer 1.5 % and 3 % V 2 O 5 function of catalyst layer: catalytic properties / adsorption / selectivity test conditions: synthetic exhaust gas test bench base gas: compressed air addition of test gas SO 2 sensor temperature 5-6 C (adjusted by platinum heater structure) IMCS 14th, , D. Schönauer-Kamin / 8 source: Izu, N., J. Ceram. Soc. Jpn. 119 (211)

9 Electric potential difference, V / mv ppm 2 ppm 5 ppm 1 ppm 2 ppm 2 ppm ppm Au electrodes Potentiometric SO 2 gas sensor VWT, Au NASICON Au % V 2 2 O 5 5 in VWT c SO2 / ppm SO 2 concentration / ppm 5 C c SO2 / ppm % VWT catalyst coating solid electrolyte U / mv o C 6 o C Time / min t / min 6 C - potential difference increases with increasing c SO2 - stable 5 and 6 C U / mv C 55 C 6 C log c SO2 / min - 6 C: mv / decade SO 2 - sensitivity increases with increasing temperature IMCS 14th, , D. Schönauer-Kamin / 9 source: Izu, N., J. Ceram. Soc. Jpn. 119 (211)

10 SCR-catalyst materials: VWT and Fe-zeolites NH 3 -storage and catalytic reactions catalyst materials as sensors known catalytic behavior given selectivity proven long term stability stable in harsh environments detection of c gas detect the status of the catalyst layer determination of NH 3 -loading diagnosis of catalyst itself determination of the amount of stored NH 3 in situ radio-frequency technology contactless determination of the stored NH 3 -amount during operation potentiometric sensors resistive / impedimetric sensors RF antennas RF method Au electrodes catalyst coating Au-IDE functional catalyst layer solid electrolyte alumina substrate catalyst, heated IMCS 14th, , D. Schönauer-Kamin / 1

11 Impedimetric NH 3 gas sensor Au-IDE photolithographically line-to-space 2/2 µm or screen-printed 1/1 µm Z functional catalyst layer VWT / Fe-ZSM5 Au-IDE impedance measurement of electrical properties: impedance analyzer f = 1 MHz 1 Hz U eff = 1 V functional catalyst layer alumina substrate alumina substrate 99.6% Al 2 O 3 function of catalyst layer: sensitive film electrical properties measurement of c gas test conditions: synthetic exhaust gas test bench lean base gas: 1% O 2, 6.5% CO 2, 2.5% H 2 O, N 2 addition of test gases (NH 3, NO) sensor temperature ~ 3-5 C (adjusted by external furnace or platinum heater structure) IMCS 14th, , D. Schönauer-Kamin / 11 source: Schönauer, D., Sens. Act.: Chem. 155 (21)

12 Impedimetric NH 3 gas sensor Initial Nyquist-Plots at 5 C Au-IDE functional catalyst layer alumina substrate -Im Z / k VWT, 1/1 µm 32 ppm NH 3 33 ppm NO lean base gas -Im Z / k Re Z / k VWT 1/1: very small tail at low frequencies marginal electrode effects Diameter of semi-circle represents resistance of VWT: - small decrease with c NO addition - strong decrease with increasing c NH VWT, 2/2 µm lean base gas 33 ppm NO 1 32 ppm NH Re Z / k VWT 2/2: huge semicircle at low frequencies strong effects at the electrode interface material properties characterized by semicircle R: decreases with increasing c NH3 almost independent on c NO IMCS 14th, , D. Schönauer-Kamin / 12 source: Schönauer, D., Sens. Act.: Chem. 155 (21)

13 Impedimetric NH 3 gas sensor VWT 5 C Au-IDE functional catalyst layer alumina substrate -Im Z / M Fe-ZSM5, 2/2 µm 32 ppm NH 3 lean 33 ppm NO Re Z / M Fe-ZSM5: small tail at low frequencies: effects at the electrode interface diameter represents resistance of Fe-ZSM5 - almost independent on c NO - decreases with increasing c NH3 -Im Z / k VWT, 2/2 µm lean base gas 33 ppm NO 1 32 ppm NH Re Z / k VWT 2/2: huge semicircle at low frequencies strong effects at the electrode interface material properties characterized by semicircle Z : decreases with increasing c NH3 almost independent on c NO IMCS 14th, , D. Schönauer-Kamin / 13

14 Impedimetric NH 3 gas sensor IZI Fe-ZSM-5 / M lean 17 ppm NO 33 ppm NO 1 ppm NO lean Fe-ZSM-5, 6 Hz VWT, 26 khz 16 ppm NH 3 32 ppm NH 3 lean Time dependent impedance records at 5 C Au-IDE functional catalyst layer alumina substrate 92 ppm NH t / min IZI VWT / k f in high-frequency semicircle material properties Fe-ZSM5, 6 Hz: - no response towards NO - strong NH 3 effect Z decreases only with increasing c NH3 VWT, 26 khz: - small NO response - NH 3 effect is more pronounced Z decreases with increasing c NH3 and c NO NH 3 sensing effect: - conductivity change due to changes of bulk properties - NH 3 adsorption on catalyst surface VWT: NH 3 reacts with adsorbed oxygen species n-type semi-conducting behavior Fe-ZSM5: NH 3 adsorbs on acidic sites proton conductivity increases IMCS 14th, , D. Schönauer-Kamin / 14

15 Resistive type SO 2 sensor Au-IDE functional catalyst layer alumina substrate function of catalyst layer: sensitive film electrical properties measurement of c gas Au-IDE structure 1 / 1 µm screen-printed VWT catalyst film test conditions: synthetic exhaust gas test bench base gas: compressed air addition of SO 2 sensor temperature ~ 3-6 C (adjusted by platinum heater structure) IMCS 14th, , D. Schönauer-Kamin / 15 source: Izu, N., Sensors 11 (211)

16 Resistive type SO 2 sensor Au-IDE functional catalyst layer alumina substrate R / k 3 % V 2 O 5 in VWT ppm 6 ppm 5ppm ppm 1ppm 4 2ppm ppm 4 5ppm 2 1ppm 2ppm 35 o C 2 4 o C Time, t / min R / k Response, S =( R - R )/ R % VWT, Pt 1.5% VWT, Au 3.% VWT, Pt 3.% VWT, Au 4 o C c SO2 / ppm - R decreases strongly with increasing SO 2 concentration - semi-logarithmic dependence of S and c SO2 - SO 2 detection is possible with Au- and Pt-IDE IMCS 14th, , D. Schönauer-Kamin / 16 source: Izu, N., Sensors 11 (211)

17 SCR-catalyst materials: VWT and Fe-zeolites NH 3 -storage and catalytic reactions catalyst materials as sensors known catalytic behavior given selectivity proven long term stability stable in harsh environments detection of c gas detect the status of the catalyst layer determination of NH 3 -loading diagnosis of catalyst itself determination of the amount of stored NH 3 in situ radio-frequency technology contactless determination of the stored NH 3 -amount during operation potentiometric sensors resistive / impedimetric sensors RF antennas RF method Au electrodes catalyst coating Au-IDE functional catalyst layer solid electrolyte alumina substrate catalyst, heated IMCS 14th, , D. Schönauer-Kamin / 17

18 Radio frequency characterization material characterization in a cylindrical waveguide RF antennas catalyst, heated cylindrical waveguide: metallic catalyst housing gas flow SCR SCR catalyst: Fe-zeolite catalyst RF probe feed λ probe / NH 3 -sensor microwave cavity perturbation method scattering parameters measured by vector network analyzer e.g. reflection coefficient S 11 resonance frequency f res (at minimum of S 11 ) function of catalyst: catalyst itself is measured in-situ diagnosis of catalyst properties e.g. NH 3 loading degree IMCS 14th, , D. Schönauer-Kamin / 18 source: Reiß, S., Chem. Eng. Technol. 34 (211)

19 Radio frequency characterization NH 3 loading of Fe-zeolite catalyst S 11 / db unloaded ammonia loaded IMCS 14th, , D. Schönauer-Kamin / f / MHz frequency dependent amplitude of reflection coefficient S 11 ammonia loading resonance frequencies are reduced increased damping electrical losses increase ionic conductivity of Fe-zeolite increases due to adsorbed ammonia source: Reiß, S., Chem. Eng. Technol. 34 (211) RF antennas catalyst, heated T 3 C 5 % H2O in N2, + 5 ppm NH 3

20 Radio frequency characterization NH 3 loading and desorption RF antennas catalyst, heated f res / MHz c NH3 / ppm upstream downstream c 2 1 a b t 1 t f t 2 t 3 t t / h U / mv sensor 1 c NO / ppm T 3 C 5 % H2O in N2 IMCS 14th, , D. Schönauer-Kamin / 2 source: Reiß, S., Chem. Eng. Technol. 34 (211)

21 Radio frequency characterization characteristic curve RF antennas catalyst, heated T 3 C f res / MHz NH 3 -loading / mg - resonance frequency depends almost linearly on NH 3 loading degree - changes of electrical properties when NH 3 is adsorbed / stored in accordance to impedimetric Fe-ZSM5 analysis - possibility to determine NH 3 loading of the catalyst itself during operation IMCS 14th, , D. Schönauer-Kamin / 21 source: Reiß, S., Chem. Eng. Technol. 34 (211)

22 Conclusions SCR-catalysts can be applied for gas sensing application Potentiometric devices for NH 3 and SO 2 detection Conductometric sensors for NH 3 and SO 2 detection Direct electrical characterization of catalyst material SCR active materials can be applied as robust and stable functional sensor films electrical properties change due to adsorption phenomena, e.g. NH 3 adsorption catalytic properties are relevant RF technique applicable to SCR-catalyst NH 3 -loading of the catalyst can be determined in-situ and contactless IMCS 14th, , D. Schönauer-Kamin / 22

23 SCR-Catalyst Materials for Exhaust Gas Detection THANK YOU FOR YOUR ATTENTION! IMCS 14th, , D. Schönauer-Kamin / 23