Gabasch, H.

Hävecker, M.

Knop-Gericke, A.

Sauer, H.

Schlögl, R.

Schnörch, P.

Teschner, D.

Vass, E.

English

MPG.PuRe

The role of subsurface species in heterogeneous catalytic reactions

1Russian-German-Seminar on CatalysisBridging The Gap Between Model And Real CatalysisJuly 9-12, Novosibirsk-Altai Mountains, RussiaThe role of subsurface species in heterogeneous catalytic reactionsD.Teschner, H. Gabasch, M. Hävecker, E. Vass, P. Schnörch, H. Sauer, A.Knop-Gericke, R. SchlöglFritz-Haber-Institut, Dept. Inorganic Chemistry, Faradayweg 4-6, 14195 Berlin, GermanyKnop@fhi-berlin.mpg.de2IntroductionLiterature carbon laydown selective hydrogenation“similar” catalysts different activity & selectivity(structure sensitivity?)Selectivity issue: what defines selectivity?[     ]+ H23Model of overlapping TDS peaksHydrogenation in the presence ofsubsurface H[Pd particles]  No hydrogenation withoutsubsurface H[Pd(111)]  Pentenes to pentaneDoyle AM, Shaikhutdinov SK, Jackson SD, Freund HJANGEWANDTE CHEMIE-INTERNATIONAL EDITION 42 (42): 5240-5243 2003 4Acetylene hydrogenation (TDS)Subsurface Hat low TadsTotal hydrogenation decreases strongly withoutsubsurface HKhan NA, Shaikhutdinov SK, Freund HJCATALYSIS LETTERS, 108 (3-4) 159-164, 2006  5Hydrogenation (TDS)alkynesub-surface Hsub-surface H6Summary1. Subsurface H : effective for alkene-to-alkane but also for alkyne-to-alkane transformation7Pulse experiments1-pentyne Adsorption 0.0E+002.0E-054.0E-056.0E-058.0E-051.0E-04Moles1 2 3 4 5 6 7Pulse Number1-pentyne 1-pentene trans-2-pentenecis-2-pentene pentane unknown• First pulse shows activity• 65% conversion– 38.5% 1-pentene– 6.5% trans-2-pentene– 3.5% cis-2-pentene– 6.5% pentane– 11.5% Unknown(After H2 pretreatment)                         1%Pd/Al2O3Hneeded/Pdtotal ratio: 13-to-1     Source of H? Spillover8Summary1. Subsurface H : effective for alkene-to-alkane but also for alkyne-to-alkane transformation2. Surface H : could be selective (spillover)9Hydrogenationp(C5)=10 Torr0500100015002000250030003500400045000 100 200 300 400p(H2), TorrTOF (1/h)020406080100Conversion (%)0204060801000 100 200 300 400p(H2), TorrSelectivity (%)Pentane1-Pentene2-pentenes1. 1-Pentyne hydrogenation over 1% Pd/Al2O3 in a closed loop-reactor, t=5 min. (after repeated runs at each condition)2. 1-Pentyne hydrogenation over 1% Pd/Al2O3 in continuous flowH2:C5 = 4:1 total hydrogenationH2:C5 = 3:1 selective hydrogenation10Summary1. Subsurface H : effective for alkene-to-alkane but also for alkyne-to-alkane transformation2. Surface H : could be selective (spillover)3. Different reaction orders in the different selectivity regimes & Abrupt changes between regimes11During TEOM experiment[     ]+ H2170 mins40 mins89.281.681.158.70.1trace1-pentyne10.617.116.240.1tracetrace1-pentenetrace0.20.7trace0.1trace2-pentenes0.31.12.01.299.8100n-pentane--74.942.83.6trace1-pentyne--22.454.70.5trace1-pentene--Quartz Wool, 303 K--Quartz Wool, 358 K1.90.7Al2O3, 100 % H22.30.2Pd Black, 5 % H284.511.3Pd Black, 100 % H2100tracePd/Al2O3, 100 % H2n-pentane2-pentenes12During TEOM experiment[     ]+ H2170 mins40 mins89.281.681.158.70.1trace1-pentyne10.617.116.240.1tracetrace1-pentenetrace0.20.7trace0.1trace2-pentenes0.31.12.01.299.8100n-pentane--74.942.83.6trace1-pentyne--22.454.70.5trace1-pentene--Quartz Wool, 303 K--Quartz Wool, 358 K1.90.7Al2O3, 100 % H22.30.2Pd Black, 5 % H284.511.3Pd Black, 100 % H2100tracePd/Al2O3, 100 % H2n-pentane2-pentenes13During TEOM experimentReaction with 100% H2 Reaction with 5% H2Up to x5 more carbon is retained in the selective hydrogenation regime0123456780 1 2 3AdsorbedRetained0 1 2 3AdsorbedRetainedMass change [micro g / mg catalyst]Time since introduction of 1-pentyne [hours]Pd Black14Summary1. Subsurface H : effective for alkene-to-alkane but also for alkyne-to-alkane transformation2. Surface H : could be selective (spillover)3. Different reaction orders in the different selectivity regimes & Abrupt changes between regimes4. C uptake is significantly more in the selective regime 15In situ XPS systemExperimental cellsupplied by gas lines (p0)X-rays enter the cell at 55° incidence through an SiNx window(thickness ~ 1000 Å)Analyzerinput lensFocal point of analyzerinput lensFirst differentialpumping stage (10-4p0) Second differentialpumping stage (10-6p0) Third differentialpumping stage (10-8p0) Hemisphercalelectronanalyzer(10-9p0)mass spectrometerand additional pumping16Reaction in the mbar p region (in-situ XPS)-~2~20~5SelectivityPentane [%]100~98~80~95SelectivityPentene [%]<1~2.5~5~ 10Conversion[%]Pd(111)Pd foil3% Pd/Al2O35% Pd/CNT+ H2Recation conditions: C5/H2 = 1:9, 1 mbar, 358 K17In-situ XPS: Pd 3d (hν: 720 eV)18In-situ XPS: Pd 3d depth profilingNot only adsorbate-induced surface core level shift !But on-top location!19HRTEM: lattice expansion5% Pd/CNT after reaction0.2025 nm   +4.2%   0.1944 nm    2 0 00.2027 nm   +4.3%   0.1944 nm    0 2 00.1421 nm   +3.4%   0.1374 nm    2 2 00.1434 nm   +4.4%   0.1374 nm   -2 2 0Pd nanoparticle (5nm x 6nm) with typicallattice dilatations, angular distortions arenegligiblebackground: rather disordered graphiticlayers of a CNT20In-situ XPS: C1s (Switching off experiments)1: reaction mix.2: C5 off3: H2 off4: C5 gas-phaseTeschner et al.J. Catal. 242 (2006) 26-3721In-situ XPS: Pd 3d (Switching off experiments)1: reaction mix.2: C5 off3: H2 off4: reaction; high T523 K22In-situ XPS: Pd vs. C depth profiling100 200 300 400 500 600 700 8002025303540455055606570A  Palladium Inelastic Mean Free Path [Å]Carbon Content [%]Electron Kinetic Energy [eV] Experiment: 358 K Model: 358 K Model: 3.5 ML Experiment: C5 off Model: C5 off5.25 7.15 9.05 15.15202530354045505560657075100 200 300 400 500 600 700 800 22.3513.2510.25 Electron Kinetic Energy [eV]Carbon content [%]Carbon Inelastic Mean Free Path [Å] Epxeriment: 523K Model: 523K Model: 4.2 ML7.25B0.3 nm1.4 nm14 nm23Model24Summary1. Subsurface H : effective for alkene-to-alkane but also for alkyne-to-alkane transformation2. Surface H : could be selective (spillover)3. Different reaction orders in the different selectivity regimes & Abrupt changes between regimes4. C uptake is considerably more in the selective regime 5. Pd-C surface phase forms during selective hydrogenation of pentyne & there is significant amount of subsurface C below of it6. Dynamic behaviour of Pd-C and subsurface C 250204060801000 2 4 6 8 10 12 14 16 18p(H2), mbarSelectivity (%)Pentane1-Pentene1-pentyne hydrogenation on Pd Black (done in Budapest) p(1-pentyne) = 0.66 mbarT = 35°C26And at Bessy? 270204060800 2 4 6 8 10 12 14 16 18p(H2), mbarSelectivity (%)Pentane1-Pentene2-pentenes1-pentyne hydrogenation on 1%Pd/Al2O3 (done in Budapest) Generally similar trend was observed as with bulk Pdp(1-pentyne) = 0.66 mbarT = 35°C2810305070900 20 40 60 80 100T, °CSelectivity (%)PentanePentenes1-pentyne hydrogenation on Pd Black (done in Budapest) p(1-pentyne) = 0.66 mbarp(H2) = 6.6 mbar29And at Bessy? 30Alkene and alkyne hydrogenation at BESSYPd foil, ~70°C, 1mbar (0.1 mbar CxHy + 0.9 mbar H2)31Summary¾Alkene → Alkane: no Pd-C formation¾Alkyne → Alkane: no Pd-C formation¾Alkyne → Alkene: Pd-C formationPd-C surface phase controls selectivity326420900800700600500400Temperature [K]1.20.80.4Partial Pressure [mbar*104]5.04.03.02.0• In situ measurements: 2*10-3 mbarEtheneCOCO2338 337 336 335 334 333Binding Energy [eV]358 K402 K444 KPd bulk componentPd 3d286 284 282Binding Energy [eV]374 K418 K461 KC 1s330 KCO]   488 K568 K l  t505 K540 K583 K626 K805 K3 [ ]   488 K568 K611 K654 K701 K878 K l  nentC2H4:O2=1:3, heating ramp 10K*min-133• In situ measurements:6420900800700600500400Temperature [K]1.51.00.50.0Partial Pressure [mbar*104]5.04.03.02.0Intensity [a.u.]286 284 282Binding Energy [eV]435 K495 K506 K557 K603 K646 K691 KC 1sIntensity [a.u.]338 336 334 332Binding Energy [eV]423 K482 K529 K574 K618 K661 K776 K861 KPd 3dDuring the oxidation a carbon containing phase is formed and changes theselectivity from CO2 towards COEtheneCOCO234• Detailed analysis of this carbon containingphase:6420900800700600500400Temperature [K]1.51.00.50.0Partial Pressure [mbar*104]5.04.03.02.09x10387654321Peak Intensity [a.u.]338 337 336 335 334 333 332 331Binding Energy [eV] Raw_Intensity Peak_Sum Background "Pd-Carbide" Bulk Surface9x10387654321Peak Intensity [a.u.]338 337 336 335 334 333 332 331Binding Energy [eV] Raw_Intensity Peak_Sum Background Bulk  SurfacePeak deconvolution [1][1]   J. N. Andersen,et al. Phys. Rev. B 50 1994 17525850 K: Metal 550 K: PdxCyAn additional peak which we attribute to PdxCycan clearly be identified at a BE of 335.34 eV.35• Detailed analysis of this carbon containingphase:6420900800700600500400Temperature [K]1.51.00.50.0Partial Pressure [mbar*104]5.04.03.02.0338 337 336 335 334 333 332Binding Energy [eV]Intensity [a.u.]460 eV590 eV720 eV910 eV0.70.60.50.40.30.20.10.0Normalized Peak Area [a.u]121086IMFP [Å] Surface Bulk PdxCyDepth profiles:36Conclusions• During ethene oxidation the incorporationof carbon leads to a non metallic Pd-C phase.• The new, highly symmetric Pd3d5/2 peakwas observed. The depth profiles indicatethat this new phase is not only limited to thesurface.• The appearance of this phase isaccompanied by strongly enhanced CO selectivity37M. Hävecker, Surface Analysis, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, GermanyOutlook: In situ XPS / XASThe future at BESSYInstallation of a beamline exclusively used for in situ spectroscopy in the soft X-ray rangeInstallation of infrastructure optimized for these kind of experiments on site (e.g. chemical lab, gas supply, gas analytics)ISISS:Innovative Station for In Situ Spectroscopy A project of BESSY and the Dep. Inorganic Chemistry, Fritz-Haber-Institut Later, further implementation of other in situ spectroscopy techniques: multi wavelength Raman, UV-Vis, fluorescence yield ?!Start of operation of the beamline: 200738M. Hävecker, Surface Analysis, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, GermanyOutlook: In situ XPS / XASThe future at BESSYISISS:Sketch of laboratory: dr. heinekamp, Berlin, Germany39M. Hävecker, Surface Analysis, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, GermanyOutlook: In situ XPS / XASThe future at BESSY40M. Hävecker, Surface Analysis, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, GermanyOutlook: In situ XPS / XASThe future at BESSY41M. Hävecker, Surface Analysis, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, GermanyOutlook: In situ XPS / XASThe future at BESSY42M. Hävecker, Surface Analysis, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, GermanyOutlook: In situ XPS / XASThe future at BESSY43M. Hävecker, Surface Analysis, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, GermanyOutlook: In situ XPS / XASThe future at BESSY44M. Hävecker, Surface Analysis, Dept. AC, Fritz-Haber-Institut (MPG), Berlin, GermanyOutlook: In situ XPS / XASThe future at BESSY45Thanks to:• Mounir Chamam, Attila Wootsch (Institute of Isotops, Budapest) • A. Canning, J. Gamman, S. D. Jackson• J. McGregor, L. Gladden (University of Cambridge)• A. Doyle, S. Shaikhutdinov, N. A. Khan, HJ. Freund• B. Klötzer, W.Unterberger, K. Hayek (University Innsbruck, Dept.   Physical Chemistry)• B. Aszalos-Kiss, D. Zemlianov (Purdue University)• F. Senf, R. Follath, W. Braun, J. Blume, J. Schmidt, G. Reichardt, O. Schwarzkopf (BESSY) 46• Very few methods can investigatethe solid-gas interfaceat high pressures- non-linerar optics (SFG, SHG)- scanning probe microscopies- X-ray diffractionWhy in situ XPS ?15105-40 -20 0 20temperature (ºC)vaporpressure(torr)water Tm• Photoelectron spectroscopy is very powerful⇒ Goal:  XPS at pressures of at least 5 torr• Many processes cannot beinvestigated in UHV:“Pressure Gap”- environmental chemistry- catalysis- corrosion- electrochemistry- biological samples47Fundamental limit:elastic and inelasticscattering of electronsin the gas phaseTechnical issues: - Differential pumping to keep analyzer in high vacuum- Sample preparation and control in a flow reactorIn situ XPS:  obstacles30x10-21 2520151050Ionization cross section (m2)101102103104105106Electron kinetic energy (eV)in situSEM in situTEMin situEXAFSin situXPSO2 exp. data from Schram et al. (1965) extrapolation of Schram's data48• Photons enterthrough a window• Electrons and a gasjet escape throughan aperture tovacuumIn situ XPS:  basic concept49H. Siegbahn et al., J. Electron Spectrosc. Relat. Phenom. , 319 (1973)2• H. Siegbahn et al. (1973- )• M.W. Roberts et al. (1979)• M. Faubel et al. (1987) • M. Grunze et al. (1988)• P. Oelhafen (1995)H. Siegbahn et al., J. Electron Spectrosc. Relat. Phenom. , 205 (1981)24In situ XPS instruments:  previous designsIn situ XPS using differentially pumped electrostatic lensesD.F. Ogletree, H. Bluhm, G. Lebedev, C.S. Fadley, Z. Hussain, M. Salmeron, Rev. Sci. Instrum. 73 (2002) 3872.to pump to pumpX-rays from synchrotronGas phase composition canbe measured by XPS.gas phase signal:  1 torr·mm ~ a few monolayersClose-up of sample-first aperture regiongaszdhνe-p01.00.50.0-2 -1 0 1 2z [d]p/p0z=2 mm=1 mm

The role of subsurface species in heterogeneous catalytic reactions

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MPG.PuRe

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