Computational Studies on Catalytic Light Alkane Dehydrogenation. Martin Hangaard Hansen Paul Jennings Thomas Bligaard Jens Nørskov

Transcription

1 Computational Studies on Catalytic Light Alkane Dehydrogenation Martin Hangaard Hansen Paul Jennings Thomas Bligaard Jens Nørskov 1

2 Coking and size effect [1] Wu, Peng, Bell, Journal of Catalysis 311 (2014)

3 Graphite Nucleation [2] Saadi, Abild-Pedersen, Helveg, Sehested, Hinnemann, Appel, Nørskov, J. Phys. Chem. C 114 (2010) [3] Bengaard, Nørskov, Sehested, Clausen, Nielsen, Molenbroek, Rostrup-Nielsen, J. Catal. 209, (2002), 365 3

4 Selectivity and coking [1] Wu, Peng, Bell, Journal of Catalysis 311 (2014)

5 Undercoordinated sites Computations and UHV experiments: C-C bond scission on Ni(111) more selective on the steps.[4] Atomic models: terrace and step STM images: Ni(111) 200x200 Å Ag/Ni(111) 400x400 Å [4] Vang, Honkala, Dahl, Vestergaard, Schnadt, Lægsgaard, Clausen, Nørskov, Besenbacher, Nature Materials 4 (2005) 5

6 Role of steps on Pt Computations: C-C bond scission on Pt(111) is selective on the steps,[5] Experiment: Steps can be blocked by tin.[6] [5] Yang, Zhu, Zhou, Sui, Chen, Phys. Chem. Chem. Phys.13 (2011) [6] Virnovskaia, Morandi, Rytter, Ghiotti, Olsbye, J. Phys. Chem. C 111 (40), 2007, Stability of Sn on steps (Pt lattice constant): ΔE (ev per Sn atom) Reference energy Sn (s), Pt (s) PtSn (s), Pt (s) Pt 3 Sn (s), Pt (s) 6

7 Electronic effects of Sn in Pt Pt FCC(111) Broadening and downshift of d-band. [5] ΔE Pt 3 Sn FCC(111) E a [5] Yang, Zhu, Zhou, Sui, Chen, Phys. Chem. Chem. Phys. 13 (2011)

8 Free energy landscape Pt 3 Sn FCC (111) T=600ºC Low conversion p C2H6 = 0.03 bar p H2 = bar CH 3 CH 3 (g) CH 3 CH 3 (g) CH 3 CH 2 * CH 3 CH 2 * CH 3 CH* CH 2 CH 2 * CH 3 CH* CH 2 CH 2 * CH 2 CH* 2H* CH 2 CH 2 * * CH 2 CH 2 * * * * 8

9 Catalytic Dehydrogenation CH 4 (g) CH 3 CH 3 (g) CH 3 CH 2 * CH 3 CH* CH 3 C* CH 3 * CH 2 CH 2 (g) CH 2 CH 2 * CH 2 CH* CH 2 C* CH 2 * CHCH (g) CHCH* CHC* CH* CC* C* 19 intermediates. 34 elementary reactions. ~10 Catalyst surfaces. 9

10 Dimensionality Reduction [7] Abild-Pedersen, Greeley, Studt, Rossmeisl, Munter, Moses, Skulason, Bligaard, Nørskov PRL. 99 (2007)

11 Transition States Final state BEP [8] Wang, Petzold, Tripkovic, Kleis, Howalt, Skúlason, Fernández, Hvolbæk, Jones, Toftelund, Falsig, Bjo rketun, Studt, Abild-Pedersen, Rossmeisl, Nørskov, Bligaard, Phys. Chem. Chem. Phys. 13 (2011)

12 Production rate on closepacked Ethene Production T=600C Low conversion p C2H6 = 0.03 bar p H2 = bar CH 3 CH* formation energy [ev] MKM Solver: CATMAP [1] A. J. Medford et al. Catal Lett (2015) 145:

13 Production rate on closepacked Selectivity to Ethene CH 3 CH* formation energy [ev] T=600C Low conversion p C2H6 = 0.03 bar p H2 = bar MKM Solver: CATMAP [1] A. J. Medford et al. Catal Lett (2015) 145:

14 First Principles Screening Candidates data Screening DFT 14

15 Machine Learning Candidates, fingerprints Surrogate Model Training data Screening DFT 15

16 Linear Models Fingerprint example: x 1 pure metals bulk d-band center x 2 # valence electrons x 3 adsorbate coordination number x 4 site coordination number ect. x 5 16

17 Surrogate Model Screening Ethene Production Data added after prediction by Gaussian Process 17

18 Saving CPU time ~1300 binary alloys x 1 facet x 2 adsorbates x (3 sites + 1 slab) x 100 cpu hours = cpu hours with 200 datapoints and a surrogate model: Þ ~10x speedup. Other facets? Terminations? Ternary alloys? 18

19 Summary First Principles Computations explain: Nanoparticle size effects on coking by limited nucleus size. Sn effects on coking by step blocking. Electronic and geometric effects on selectivity. Machine learning is accelerating First principles screening for catalytic sites. Exploration of complicated reaction networks 19

20 Acknowledgements Paul C. Jennings Thomas Bligaard Jens K. Nørskov Center for Interface Science and Catalysis

21 Questions, Comments, Suggestions?

22 References [1] Sattler et al., Chem. Rev. 2014, 114, [2] A. J. Medford et al. Catal Lett (2015) 145: [3] B. Hammer & J. K. Nørskov, Adv Catal., 45, 2000 [4] F. Calle-Vallejo et al. Chem. Sci., 2013, 4, 1245 [5] F. Calle-Vallejo et al. Nat. Chem. 7, 2015 [6] A. Girard et al., Adv. Neural Information Processing Systems ; pp [7] C. E. Rasmussen & C. K. I. Williams, Gaussian Processes for Machine Learning, the MIT Press, 2006, 22

23 Alkenes Importance Ethylene production ~160 Mtons per year = 800 x tonnage of ultra large container vessel 23

24 Alkenes Importance Propylene demand [1] S.M. Sadrameli / Fuel 140 (2015) [2] S.M. Sadrameli, Fuel 173 (2016)

25 Alkenes Importance [3] J.J.H.B. Sattler et al., Chem. Rev. 114, (2014),

26 Steam Cracking Gas phase. Reactions: C-C scission H-exchange Isomerization Dehydrogenation Radicals recombination Hexamerization Temperature: 750ºC - 900ºC Alkenes yield ~ 30% [1] S.M. Sadrameli, Fuel 140 (2015) [2] S.M. Sadrameli, Fuel 173 (2016) Propylene : Ethylene ratios Yield = 0.4 : 1 Demand = 0.6 : 1 26

27 Catalytic Pathways C x H (2x + 2) C x H 2x + H 2 x [2;4] Temperature: ºC [4] T. Ren et al., Energy 31 (2006)

28 Alkanes [3] J.J.H.B. Sattler et al., Chem. Rev. 114, (2014),

29 Thermodynamics C 3 H 8 (g) C 3 H 6 (g) + H 2 (g) [3] J.J.H.B. Sattler et al., Chem. Rev. 114, (2014),

30 Thermodynamics C x H y (g) C x H y-2 (g) + H 2 (g) at 1 bar [3] J.J.H.B. Sattler et al., Chem. Rev. 114, (2014),

31 Under construction Cr-Oxide based catalyst 2014: ~ 5 Mtons propylene 2018: ~ 20 Mtons propylene from catalytic dehydrogenation. [3] J.J.H.B. Sattler et al., Chem. Rev. 114, (2014), Pt-Sn based catalyst 31

32 d-band projected onto top Pt atoms Pt FCC(111) Sn/Pt FCC(111) (Isolated Sn) More Sn => Lower d-band. Less filling of anti-bonding orbitals. Weaker chemisorption. Pt 3 Sn FCC(111) PtSn 32

33 Free energy landscape Pt(111) CH 2 CH* * CH 3 CH 2 * CH 3 CH 2 * CH 3 CH* CH 2 CH 2 * CH 2 CH 2 * * CH 3 CH 3 (g) CH 3 CH 3 (g) CH 3 CH* CH 2 CH 2 * * T=600ºC Low conversion p C2H6 = 0.03 bar p H2 = bar 33

34 Free energy landscape Pt 3 Sn (111) CH 2 CH* * CH 3 CH 2 * CH 3 CH 2 * CH 3 CH* CH 2 CH 2 * CH 2 CH 2 * * CH 3 CH 3 (g) CH 3 CH 3 (g) CH 3 CH* CH 2 CH 2 * * T=600ºC Low conversion p C2H6 = 0.03 bar p H2 = bar 34

35 Dimensionality Reduction 35