A SYNCHROTRON LOOK INTO THE LIFECYCLE OF PT-IN CATALYSTS

Transcription

1 LABORATORY FOR CHEMICAL TECHNOLOGY, GHENT UNIVERSITY A SYNCHROTRON LOOK INTO THE LIFECYCLE OF PT-IN CATALYSTS H. POELMAN, M. FILEZ, E. REDEKOP, V.V. GALVITA, G.B. MARIN M. MELEDINA, G. VAN TENDELOO, R.K. RAMACHANDRAN, J. DENDOOVEN, C. DETAVERNIER SOLEIL Users Meeting 2017, 19-20/1/2017 European Research Institute of Catalysis

2 INTRODUCTION Light alkenes: essential chemical building blocks Growing alkene demand Catalytic alkane dehydrogenation: highly selective * + H - H propane propylene + hydrogen Why Pt-based bimetallics? high activity and stability most promising if Pt alloys, e.g. with Sn [1], Ga [2,3], In [4] Goal: design of improved Pt-In catalysts understand changes lifecycle changes nanoscale/synchrotron characterization high precision synthesis techniques simple synthesis precise control [1] V. Galvita et al., J. Catal. 271 (2010) 209; [2] P. Siddiqi et al., J. Catal. 274 (2010) 200; [3] M. Filez et al., Chem. Mater. 26 (2014) 5936; [4] P. Sun et al., J. Catal. 282 (2011) 165 2

3 OVERVIEW Characterization methods XAS (QXAS, FT-XAS, WT-XAS) GISAXS in situ XRD SEM TEM EDX Strategies to synthesize Pt-In bimetallic catalysts ( birth ) Delivering In to Pt from the support One-pot synthesis of Pt-In Synthesis by Atomic Layer Deposition (ALD) Performance of the Pt-In bimetallic catalysts ( life and death ) Propane dehydrogenation as test reaction Redox cycles (H 2 -O 2 ) 3

4 XAS heater XAS: XANES + EXAFS sample X-rays operando FT : EXAFS R, N, σ² FT N σ² R WT : k- and R-space resolution [5] Wavelet transformation - finite wave packet - 2 degrees of freedom simultaneous spatial (~R) & elemental (~k) identification [5] M. Filez et al., Analytical Chemistry 87 (2015) 3520; doi: /acs.analchem.5b

5 CATALYST BIRTH (1.0) Layered double hydroxide (LDH) Classical calcination Pt impregnation + calcination + reduction Pt Element delivery MgAl-LDH Mg(Al)O x Pt/MgAlO x Pt impregnation + calcination + reduction calcination Mg(In)Al-LDH Mg(In)(Al)O x Pt-In/Mg(In)AlO x? 5

6 CATALYST BIRTH (1.1) Pt(acac) 2 impregnated on In-incorporated Mg(In)(Al)O x support [5] XANES - WL = +II = Pt +2 (acac) 2 Pt PtO 2 sample FT EXAFS - Pt-O model: N Pt-O = 4 C WT XAS - R ~ 1,7 Å, k ~ 5 Å -1 : Pt-O bond - Foothill: k ~ 3 Å -1 : Pt-O-C-Pt (MS) = signature acac-ligands model sample O Pt(acac) 2 adsorbed on Mg(In)(Al)O x without ligand decomposition [5] M. Filez et al., Analytical Chemistry 87 (2015) 3520; doi: /acs.analchem.5b

7 CATALYST BIRTH (1.2) Pt(acac) 2 /Mg(In)(Al)O x calcined to 650 C [5] XANES - PtO 2 -like: WL Pt 4+ PtO 2 sample PtO 2 FT EXAFS - PtO 2 -like profile Pt WT XAS - No foothill: acac decomposed - Mg/Al/O: Mg(In)(Al)O x support - No Pt no PtO 2 Mg/Al/O O sample DS O O PtO 2 ref Pt acac-ligands decompose and Pt is fully oxidized Pt 4+ atomically dispersed on Mg(In)(Al)O x support [5] M. Filez et al., Analytical Chemistry 87 (2015) 3520; doi: /acs.analchem.5b

8 CATALYST BIRTH (1.3) Pt/Mg(In)(Al)O x reduced in H 2 to 650 C [5] XANES - WL drop < metal Pt 0 - Edge shift to higher E 0 Pt-In alloying* Pt PtO 2 sample In + Pt shell sample *Bus, E., van Bokhoven, J. A. J. Phys. Chem. C 2007, 111, FT EXAFS - Double peak Pt-In ~ Pt-Pt In Pt WT XAS - R ~ 2,6 Å: Pt-Pt and Pt-In peaks - Double peak: k-space interference sample H 2 reduction triggers alloy formation: In from support mobilized, reduced and alloyed with Pt [5] M. Filez et al., Analytical Chemistry 87 (2015) 3520; doi: /acs.analchem.5b

9 CATALYST BIRTH (2.0) From multi-step towards one-pot synthesis: Mg(Pt)(In)(Al)O x [6] [6] M. Filez et al., Catalysis Science & Technology, 6 (2016) 1863; DOI: /C5CY01274K 9

10 CATALYST LIFE Performance test: Catalytic propane dehydrogenation [6] (T = 600 C, W cat /F propane, 0 = 4 kg cat s mol 1 and P propane,0 = 5 kpa, total pressure = kpa) one-pot C 3 H 6 H 2 steady-state propylene STY CH 4 LDH-derived support multi-step C 3 H 6 Initially: activity higher for multi-step Steady-state: One-pot activity > multi-step CH 4 H 2 steady-state propylene STY 10 [6] M. Filez et al., Catalysis Science & Technology, 6, , 2016, DOI: /C5CY01274K

11 CATALYST LIFE AND DEATH H 2 /O 2 cycling of Pt-In/Mg(In)(Al)O x between 700 and 540 C (2x2min) O 2 : decrease WL sintering Pt clusters (oxidized surface + metal core) H 2 : constant WL stable Pt-In alloy Rate alloying >> rate alloy decomposition + Pt oxidation 11

12 WT-XAS 1 st cycle 20 th cycle O 2 Pt-Pt Pt-O H 2 Pt-In Pt-In EXAFS model: O 2 : Pt-O + Pt-Pt shell, H 2 : Pt-In + Pt-Pt shell 12

13 QEXAFS MODELLING O 2 environment H 2 environment - Pt-Pt coordination increases - Pt-O bonds replaced by Pt-Pt - Strong In abundance around Pt - N Pt-Pt + N Pt-In ~ constant Pt NP sintering Stable PtIn 13

14 STEM-EDX Pt-In/Mg(In)(Al)O x 1 st cycle 60 th cycle O 2 H 2 Nanoscale structural changes : redox cycling increases NP size O 2 : phase segregation: Pt core - In shell structure H 2 : Pt-In alloy, In-rich shell developing 14

15 PERFORMANCE Loss in initial activity and selectivity 15

16 ATOMIC LAYER DEPOSITION [7] Precursor + reactant = deposition Self-saturating deposition Island or layer-by-layer growth Bilayer and multilayer deposition [7] Detavernier C. et al., Chem. Soc. Reviews 40 (2011) DOI: /c1cs15091j 16

17 Pt-XRF counts/unit area χ(r) [Å-3] CATALYST BIRTH (3.0) In situ Pt-ALD XRF XAS at SAMBA [8] - Pt-ALD on mesoporous SiO 2 - Precursor MeCpPtMe 3 and ozone O 3 - Nucleation and growth Mesoporous silica film Pt-O Pt-Pt 10 cycles 20 cycles 30 cycles 40 cycles 50 cycles Number of ALD cycles R [Å] In situ characterization of Pt growth [8] M. Filez et al., Catalysis Today 229 (2014) 2 13; 17

18 CATALYST BIRTH (3.1) ALD synthesis of bimetallic nanoparticles [9] - Dual deposition on planar SiO 2 : In 2 O 3 -ALD, followed by Pt-ALD - alloying upon reduction (H 2, 700 C) - XAS: PtO 2 ref Pt edge In edge Pt ref Clear alloying on both In and Pt edge: WL drop and edge shift [9] R.K. Ramachandran et al., ACS Nano, 10 (9), 2016, , DOI: /acsnano.6b

19 CATALYST BIRTH (3.1) - GISAXS: Evolution from Pt to Pt-In nanoparticles [9] R.K. Ramachandran et al., ACS Nano, 10 (9), 2016, , DOI: /acsnano.6b

20 PHASE CONTROL & SIZE CONTROL Different alloy phases depending on Pt/(Pt+In) atomic ratio Decreasing particle size for decreasing total thickness [9] R.K. Ramachandran et al., ACS Nano, 10 (9), 2016, , DOI: /acsnano.6b

21 CATALYST BIRTH (3.2) ALD: from planar to porous support Pt-In by ALD on porous SiO 2 : DF STEM TOF for propylene production First feasibility demonstrated [9] R.K. Ramachandran et al., ACS Nano, 10 (9), 2016, , DOI: /acsnano.6b

22 CONCLUDING Tuneable design of improved Pt-In catalysts requires insight into their lifecycle nanoscale and synchrotron based characterization techniques are crucial Birth Element delivery from support / one-pot synthesis: + facile synthesis, + highly performant - limited control ALD dual deposition: + highly tuneable in phase and size, + promising performance Life and Death Core shell structure evolution Alternating alloying and phase segregation Pt sintering leads to deactivation ~ process to be transferred to porous supports 22

23 Acknowledgments: Fund for Scientific Research Flanders (FWO-Vlaanderen, project: G ) Long Term Structural Methusalem Funding (Flemish Government) IAP7/05 Interuniversity Attraction Poles Programme Belgian State Belgian Science Policy Marie Curie International Incoming Fellowship for E.R. granted by the European Commission (301703) Special Research Fund BOF of Ghent University (GOA 01G01513) Fund for Scientific Research Flanders for financing ESRF-DUBBLE beamtimes European Community s Trans National Access Program CALIPSO and the Fund for Scientific Research Flanders (FWO-Vlaanderen) for financing travel costs to SOLEIL and SLS DUBBLE, SAMBA and SuperXAS staff: D. Banerjee, A. Longo, D. Hermida-Merino, W. Bras, E. Fonda, O. Safonova, M. Nachtegaal Contact: Dr. H. Poelman Phone: +32 (0) hilde.poelman@ugent.be

24 H. Poelman 1, M. Filez 1#, E. Redekop 1, V.V. Galvita 1, M. Meledina 2, G. Van Tendeloo 2, R.K. Ramachandran 3, J. Dendooven 3, C. Detavernier 3, G.B. Marin 1 1 Laboratory for Chemical Technology, Tech Lane Ghent Science Park 914, 9052 Ghent, Belgium ² Electron Microscopy for Materials Science, Groenenborgerlaan 171, 2020 Antwerp, Belgium ³ Department of Solid State Sciences, Krijgslaan 281, S1, 9000 Ghent, Belgium # Currently at Inorganic Chemistry and Catalysis group, Universiteitsweg 99, Utrecht, NL Currently at Centre for Materials Science and Nanotechnology Chemistry, PB 1126 Blindern, 0318 Oslo, N. Contact: Dr. H. Poelman Phone: +32 (0) hilde.poelman@ugent.be