Part A: Operando FT-IR Studies of heterogeneous catalytic reactions: pitfalls and benefits.

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1 Part A: Operando FT-IR Studies of heterogeneous catalytic reactions: pitfalls and benefits. Fred Meunier Institut de Recherche sur la Catalyse et l Environnement de Lyon Villeurbanne, France EUROKIN meeting, Milan 18/2/2015 1

2 Operando FT-IR Studies of heterogeneous catalytic reactions: 1. Pitfalls 2. Benefits. Pitfalls: - Temperature control - flow control in IR reaction cells 2

3 Catalytic reactor and spectroscopic IR cells U-shaped quartz reactor in a tubular furnace Transmission IR cell (ca. 20 mg wafer) Heat loss through IR windows Diffuse reflectance IR cells 3 Harrick (powder, up to 80 mg) Modified Spectra-Tech (powder, up to 60 mg)

4 4 Measure-thermocouple positioning

5 CO methanation as a bulk temperature probe IR cells bed cooler than expected 5 5

6 DRIFTS: bed surface (top) temperature Cooler HOT Cooler HOT Typical analysis depth: < few 100 μm Bed depth: 2-5 mm 6

7 Surface temperature by optical pyrometry DRIFTS cells bed surface much cooler than expected at High T 7

8 Supported CoOx for CO hydrogenation in custom-made DRIFTS cell: reduction at 450 C? Cooler Cooler Zone probed: CoOx HOT HOT Zone active catalytically: Co metal 8

9 Spectra-tech DRIFTS cell hydrodynamics: ill-defined reactor t = 0 s 3 s 6 s 9 s 12 s 15 s Meunier et al., Appl. Catal. A 340 (2008) 196 9

10 Artistic impression of a post-experiment wafer (NOx storage-reduction) Aabspec Inlet Carbonaceous deposits? Outlet 16 mm 10

Alcohol condensation at 300 C using the same catalyst Product formation rate (micromol/g/s) 4 3 Quartz tubular PFR 2 1 0

11 Alcohol condensation at 300 C using the same catalyst Product formation rate (micromol/g/s) 4 3 Quartz tubular PFR SpectraTech DRIFTS Aabspec CX Transmission Time /min Temperature (mis)control and bad hydrodynamics? 11

12 This image cannot currently be displayed. This image cannot currently be displayed. Modified DRIFTS cell from Spectra-Tech. CO + O 2 over 2% Pt/CeO CO conversion /% Modified cell Non-modified cell Metallic dome KBr window Catalyst SiC 0 Quartz wool Temperature / K Ceramic crucible Teflon tape Metal base Meunier et al., Appl. Catal. A 340 (2008) 196 Gas inlet Gas outlet

13 Validation of modified DRIFTS cell Meunier et al., Appl. Catal. A 340 (2008) 196 Au-Ce-La-O catalyst Water-gas shift: 2 % CO + 7 % H 2 O J. Catal. 247 (2007) /T (1/K) Log (rate CO 2 formation, mol/g/s) (200 C) Quartz plug flow reactor (Medford) Modified DRIFT cell (Belfast) (130 C) Ensure kinetic relevance of the IR cell-based data 13

14 Validation of modified DRIFTS cell CO hydrogenation (30% CO + 60 % H 2 at 1 bar) on 14 wt.% Co (8 nm) /Al 2 O 3 : TOF = 14 x 10-3 s -1 DeJong et al.., J. AM. CHEM. SOC. 2006, 128,

15 Operando FT-IR Studies of heterogeneous catalytic reactions: pitfalls and benefits. Benefits: - transport in zeolites - CO heat of adsorption - catalyst surface poisoning - adsorbate reactivity 15

16 Isooctane transport in large and small H-ZSM-5 17 µm 0.25 µm 1 mg powder is enough! H-ZSM-5: pore diameter ca nm kinetic diameter = 0.62 nm 16

17 Isooctane in H-ZSM-5: effect of mesoporosity Relative ic8 DRIFTS band intensity µm 0.25 µm 0 20 Desorption 40 time of ic8 60( s) ca. 4-fold reduction in the characteristic diffusion path length Meunier et al., Micropor. Mesopor. Mater. 148 (2012)

18 CO adsorption on Pt-Sn/Al 2 O 3 pre-reduced at 400 C - Feed: 2%CO/H 2 - T decreased from C C 200 C Log (1/R) 0.01 Sn-free Pt C 250 C 275 C 300 C 325 C 325 C : CO coverage = ~ IR determines Wavenumber the nature (cm -1 ) and coverage of sites 18

19 CO heat of adsorption on Pt/Al 2 O 3 and Pt-Sn/Al 2 O 3 Moscu et al, Chem. Commun., 2014, 50, Carbonyl band relative intensity Pt Pt-Sn Temperature / C Catalyst -Δ ads H (kj/mol) Pt/Al 2 O 3 E0 =180 E1 =85 Pt-Sn/Al 2 O 3 E0 = 95 E1 =75 1. CO bonding much weaker on Pt-Sn / Pt 2. Effect of surface coverage on ΔH not significant for Pt-Sn 19

20 Introduction of O2 at 225 C (Red spectrum is under CO/H2/Ar only) Moscu et al, Catal Today, 2015, in press min 10 min 4 min H2 Atmosphere CO:O2 G.A. Somorjai et al., J. Catalysis, 2014, 312, Log (1/R) 1 min Before O 2 addition Wavenumbers /cm -1

21 IR is site and coordination-specific!

22 Toluene hydrogenation: Effect of CO 2 100% 0.17 % toluene + 17 % H % CO 2 75 C Scalbert et al. PCCP, 14, 2159 (2012). Toluene conversion 80% 60% 40% 20% Pt/Al 2 O 3 KBr Rh/Al 2 O 3 0% Time on CO 2 -containing stream /min In presence of CO 2 : Pt: fast and total deactivation Rh: slow and limited deactivation: why? 22

23 Rh/Al 2 O 3 : difference DRIFTS spectra following CO 2 introduction 0.17 % toluene + 17 % H % CO Log 1/R min 183 min 23 min 4 min 1 min O C Rh 1956 Rh O C Rh Wavenumbers /cm Various Rh-CO are formed, but no CO(g) 23

24 Correlation between toluene conversion and Pt-CO Toluene conversion /% [2 % CO 2 ] [40 % CO 2 ] Pt-carbonyl band area /a.u. Conversion correlates Pt-CO signal whatever [CO 2 ] 24

Rh/Al 2 O 3 (D= 55%): linear carbonyls assignment Taimoor et al., J. Catal. 2011, 278, 153. Ferri et al., PCCP, 2002, 4, 2667.

25 Rh/Al 2 O 3 (D= 55%): linear carbonyls assignment Taimoor et al., J. Catal. 2011, 278, 153. Ferri et al., PCCP, 2002, 4, High-wavenumber carbonyls, on dense plans, displaced by toluene. Low-wavenumber carbonyls, on low coordination sites, more stable. Low dispersion samples should be more resistant to deactivation.

26 Rh/Al 2 O 3 (D=55 %) vs Rh/SiO 2 (D=19 %) Feed: 0.8 % toluene + 57 % H 2 Carbonates, Hydrogenocarbonates, Formates Log (1/R) O C 0.2 O C Rh Rh Rh Rh/Al 2 O 3 Rh/SiO Wavenumbers /cm No carbonyl nor carbonate formation on Rh/SiO 2 when CO 2 is added. Scalbert et al., J. Catal 318 (2014) 61 26

27 DRIFTS + MS + SSITKA (SSITKA: Steady-State Isotopic Transient Kinetic Analysis) Shannon and Goodwin, Chem. Rev., 90 (1995) 667. Goguet et al., J Phys. Chem. B 108 (2004) CO + H 2 O Mass spectrometer 12 CO 2 13 CO 2 Vent reactor time 13 CO + H 2 O

28 DRIFTS: Formate exchange over Pt-CeO 2 2% 12 CO + 7% H 2 O 2% 13 CO + 7% H 2 O Relative 12 C-Formates IR signal Time / min C 160 C C C 220 C 220 C Time / min Slope = k

29 Formate DRIFT signal calibration Na-formate deposition (by IWI) over the CeO 2 support Spectra recorded at 100 C under Ar 0.66 wt.% 0.33 wt.% WGS at 220 C Abs Calibration standards Formate DRIFT signal /a.u C 180 C 220 C Wavenumber /cm wt.% formate [formates] can be determined accurately

30 Pt/CeO 2 : rate of CO 2 formation vs. rate of formate decomposition Meunier et al. J. Catal. 252 (2007) 18 Rate (10-6 mol s -1 g -1 ) 12 9 CO 2 formation rate GC analysis of reactor exhaust Formate decomposition rate to CO 2 = k [formate]. 100% C 180 C 220 C Reaction temperature 30

31 Formate decomposition during CO hydrogenation on 14% Co/Al 2 O 3 30% CO + 60 % H 2 at 1 bar, 220 C Parades-Nunez et al., Catal. Today, 242 (2015) 178 Methanol Two-type of formates: fast and slow

32 Conclusions Operando FT-IR Studies of heterogeneous catalytic reactions: pitfalls and benefits. - Necessity to compare activity in IR cell and standard reactor - Understand the origin of the differences, if any. (impurities, bed by-pass, temperature gradients) - Improve cell design. - Many relevant information for kinetic modelling can be obtained (using differential conditions): transport, nature(s) and coverage of sites, heat and mode of adsorption, poisoning, adsorbate reactivity. 32

33 Daniele Tibiletti Julien Scalbert Mickael Rivallan Haoguang Li Alina Moscu Anaelle Paredes-Nunez Davide Lorito 33

Part B: Unraveling the mechanism of catalytic reactions through kinetics and thermodynamics

Part B: Unraveling the mechanism of catalytic reactions through kinetics and thermodynamics F.C. Meunier, J. Scalbert and F. Thibault-Starzyk Appl. Catal. A: Gen. (2015), in press, doi:10.1016/j.apcata.2014.12.028