A Fundamental Approach to the Development of Novel Alkane Isomerization Catalysts

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Fundamental Approach to the Development of Novel Alkane

1 Abteilung Anorganische Chemie Fritz-Haber-Institut der Max-Planck-Gesellschaft Faradayweg 4-6, Berlin A Fundamental Approach to the Development of Novel Alkane Isomerization Catalysts Friederike C. Jentoft University of Reading June 4, 2007

2 Alkane Skeletal Isomerization CH 3 CH 2 CH 3 acid catalyst CH 2 CH 3 CH 3 CH CH 3 equilibrium at 300 K: 71 % isobutane Common solid acid catalysts Pt/AlCl 3 -Al 2 O 3 : Pt/zeolite: K, problems with Cl and H 2 O 533 K, unfavorable equilibrium New low temperature isomerization catalyst Pt/sulfated zirconia

3 Catalyst Comparison after G.C. Anderson, R.R. Rosin, M.A. Stine, M.J. Hunter, UOP 2004

4 Promotion of Sulfated Zirconia Pt/sulfated zirconia: 353 K Holm, Bailey 1962, US Patent 3,032,599 "SZ" isomerizes n-butane at RT Hino, Arata, JACS 1979 & Chem. Comm Rate of isomerization / µmol g -1 h SZ, 378 K 500 mg catalyst, fixed bed 1 kpa n-c 4 in N 2, atm. pressure 80 ml min -1 total flow Time on stream / min

5 Promotion of Sulfated Zirconia Pt/sulfated zirconia: 353 K Holm, Bailey 1962, US Patent 3,032,599 "SZ" isomerizes n-butane at RT Hino, Arata, JACS 1979 & Chem. Comm Fe and Mn act as promoters of SZ Hollstein et al., US Patent 4,918, Hsu et al., Chem. Comm Lange et al., Catal. Lett Rate of isomerization / µmol g -1 h Induction period Deactivation SZ, 378 K 500 mg catalyst, fixed bed 1 kpa n-c 4 in N 2, atm. pressure 80 ml min -1 total flow 2% FeSZ, 323 K 2% MnSZ, 323 K Time on stream / min

6 Promotion of Sulfated Zirconia Pt/sulfated zirconia: 353 K Holm, Bailey 1962, US Patent 3,032,599 "SZ" isomerizes n-butane at RT Hino, Arata, JACS 1979 & Chem. Comm Fe and Mn act as promoters of SZ Hollstein et al., US Patent 4,918, Hsu et al., Chem. Comm Lange et al., Catal. Lett Rate of isomerization / µmol g -1 h SZ, 378 K 2% FeSZ, 323 K 2% MnSZ, 323 K Time on stream / min SZ catalyzes cracking, alkylation, condensation, etherification, acylation, esterification, nitration, and oligomerization G.D. Yadav, J.J. Nair, Microporous Mesoporous Mat. 33 (1999) 1-48 sulfated zirconia a solid superacid (>100% H 2 SO 4 )? 500 mg catalyst, fixed bed 1 kpa n-c 4 in N 2, atm. pressure 80 ml min -1 total flow

7 Initial Ideas Brønstedacidic OH-group H O Lewis-acid site cus metal cation Zr Zr 4+ tetragonal (?!) ZrO 2 "ZrO 2 (mp 2700 C) is a white, chemically, thermally, and mechanically stable compound" Riedel, Anorganische Chemie, degruyter 2002, p. 776

8 Initial Ideas Brønstedacidic OH-group H O O S O O S O Lewis-acid site cus metal cation Zr O O O O Zr 4+ tetragonal (?!) ZrO 2 "ZrO 2 (mp 2700 C) is a white, chemically, thermally, and mechanically stable compound" Riedel, Anorganische Chemie, degruyter 2002, p. 776 sulfate generates acidity

9 Initial Ideas Brønstedacidic OH-group H O Zr Fe O S O O O Fe O O S O O tetragonal (?!) ZrO 2 Zr 4+ could not be confirmed Lewis-acid site cus metal cation "ZrO 2 (mp 2700 C) is a white, chemically, thermally, and mechanically stable compound" Riedel, Anorganische Chemie, degruyter 2002, p. 776 sulfate generates acidity Mn and Fe increase acidity of the "solid superacid" sulf. ZrO 2 evidence: activity, TPD with (subst.) benzenes Hsu et al., Chem. Comm. 1992; Lin et al., Chem. Comm extremely acidic sites can not be identified Adeeva et al., J. Catal. 1995; Wan et al., J. Catal. 1996

10 Outline 1. Preparation: calcination chemistry 2. Zirconia metastability 3. Zirconia - promoter interaction 4. Surface sites and reactivity 5. Summary 6. Outlook

11 commercial hydrous zirconia X-ray amorphous sulfated with (NH 4 ) 2 SO 4 dried at 383 K Addition of Promoters Incipient wetness Fe(III), Mn(II) nitrate Calcination sulf. ZrO 2 SZ Mn-sulf. ZrO 2 MnSZ Fe-sulf. ZrO 2 FeSZ sulfate content: 4.5 wt% SO 3 promoter content: wt% metal

Calcination Chemistry 900 800 3 K/min Temperature / K 700 600

12 Calcination Chemistry K/min Temperature / K pure SZ with Fe, Mn Time / min Volume: 17.1 ml Water loss Decomposition of NO 3- and NH 4 + Crystallization / sintering of ZrO 2 Endo-/exothermic reactions

13 Calcination Chemistry and Engineering Temperature / K K/min pure SZ with Fe, Mn Time / min Sample bed temperature / K Heating time / min g hydrous zirconia Oven temperature / K Water loss Decomposition of NO 3- and NH 4 + Crystallization / sintering of ZrO 2 Rapid overheating (up to K/s) Overshoot up to 300 K Glow phenomenon not unique to formation of ZrO 2 : Ti, Fe, Cr oxides

Effect of the Calcined Amount: MnSZ and FeSZ Heating time / min 165 170 175 180 185 190 Sample bed

14 Effect of the Calcined Amount: MnSZ and FeSZ Heating time / min Sample bed temperature / K ml 2%MnSZH 2.2 ml Oven temperature / K

15 Effect of the Calcined Amount: MnSZ and FeSZ Heating time / min Sample bed temperature / K ml 8.4 ml 2.2 ml 2%MnSZH 2.2 ml 8.4 ml 17.1 ml Oven temperature / K Strong effect of batch size Planned T max may be exceeded

Effect of the Calcined Amount: MnSZ and FeSZ Heating time / min 165 170 175 180 185 190 Sample bed temperature / K 1000 950 900 850 800 750 17.1 ml 8.4 ml 2%FeSZH 2.2 ml 17.1 ml 8.4 ml 2.2 ml 2%MnSZH 2.

16 Effect of the Calcined Amount: MnSZ and FeSZ Heating time / min Sample bed temperature / K ml 8.4 ml 2%FeSZH 2.2 ml 17.1 ml 8.4 ml 2.2 ml 2%MnSZH 2.2 ml 8.4 ml 17.1 ml Oven temperature / K Strong effect of batch size Planned T max may be exceeded Promoters: influence calcination chemistry, Fe different than Mn

17 Effect of the Calcined Amount: MnSZ and FeSZ Heating time / min Sample bed temperature / K ml 17.1 ml 8.4 ml 2.2 ml 8.4 ml 2.2 ml 2%MnSZH 2%FeSZH Oven temperature / K Temperature / K Time / min Strong effect of batch size Planned T max may be exceeded Promoters: influence calcination chemistry, Fe different than Mn

18 Influence on Catalytic Activity?! 2%FeSZ Sample bed temperature / K ml Heating time / min ml 2.2 ml 2%FeSZH 17.1 ml 8.4 ml 2.2 ml Oven temperature / K 2%MnSZ 2%MnSZH Yield isobutane (%) ml batch 8.4 ml batch 2.2 ml batch Time on stream / min 1 kpa n-c 4, 338 K Yield isobutane (%) ml batch ml batch 2.2 ml batch Time on stream / min Samples calcined in large batches more active Active phase formed during overheating non equilibrium state A. Hahn, F.C. Jentoft et al., Chem. Commun. 2001

19 Calcination - Summary Improved reproducibility; extrinsic parameter decisive: calcined amount Rapid genesis of active phase during overheating Large batch calcination produce most active catalysts

20 Calcination - Summary Improved reproducibility; extrinsic parameter decisive: calcined amount Rapid genesis of active phase during overheating Large batch calcination produce most active catalysts ln k norm (Fe,Mn)SZ literature FeSZ, MnSZ large boat 373 K Arrhenius-type graph 303 K Rate constants from literature Assuming 1 st order in n-butane Temperature -1 / K -1 F.C. Jentoft et al., invited article in preparation for Angew. Chemie

Zirconia Phase Chemistry monoclinic 1223-1473 K >2473 K

doping with of Y 3+, Mg 2+, Ca 2+ Sulfate also stabilizes

monoclinic phase C. Morterra, G. Cerrato, F. Pinna, M.

21 Zirconia Phase Chemistry monoclinic K >2473 K tetragonal cubic Tetragonal / cubic phase stabilized by doping with of Y 3+, Mg 2+, Ca 2+ Sulfate also stabilizes tetragonal phase Tetragonal phase more active than monoclinic phase C. Morterra, G. Cerrato, F. Pinna, M. Signoretto, J. Catal. 157 (1995) 109 W. Stichert and F. Schüth, J. Catal. 174 (1998) 242

or milled to obtain fine powder Samples are pressed

22 Metastable Nature of Active Sites After calcination, powders are clumped together Samples are being ground or milled to obtain fine powder Samples are pressed for catalysis, transmission spectroscopy, vacuum methods

23 Grinding of 0.5% MnSZ: : XRD and Catalysis Internal standard normalized XRD T M untreated Diffraction angle Cu Kα 2θ / M

24 Grinding of 0.5% MnSZ: : XRD and Catalysis Internal standard normalized M T untreated ground, operator 1 ground, operator 2 M Diffraction angle Cu Kα 2θ / ZrO 2 affected by mechanical stress, transformation of t-zro 2 to m-zro 2 E.D. Whitney, Trans. Faraday. Soc (footnote!) Grinding: strong operator influence

25 Grinding of 0.5% MnSZ: : XRD and Catalysis Internal standard normalized M T untreated ground, operator 1 ground, operator 2 M Diffraction angle Cu Kα 2θ / Rate of isomerization / µmol g -1 h kpa n-c4, 338 K 0.5% MnSZ, untreated ground, operator Time on stream / h ZrO 2 affected by mechanical stress, transformation of t-zro 2 to m-zro 2 E.D. Whitney, Trans. Faraday. Soc (footnote) Grinding: strong operator influence Catalytic performance also altered! B. Klose, F.C. Jentoft et al., J. Catal. 2003

26 Stability during Long-Term Storage Storage Conditions Laboratory "Berliner Luft" glovebox "tropical" 313 K, saturated H 2 O vapor

27 Stability of Sulfated Zirconia Isobutane / µmol g -1 h fresh glovebox laboratory tropical SZ } after 6 months 373 K Time on stream / h B.S. Klose, F.C. Jentoft et al., in preparation

28 Stability of Sulfated Zirconia Isobutane / µmol g -1 h fresh glovebox laboratory tropical SZ } after 6 months 373 K Intensity fresh 2 months T M M SZ, tropical Time on stream / h 6 months Diffraction angle Cu Kα 2θ / Tropical, 6 months: loss of 90% activity, 21% monoclinic phase Only fraction of tetragonal material active, particularly prone to phase transformation B.S. Klose, F.C. Jentoft et al., in preparation

29 Ion Scattering Spectroscopy: Surface Composition 2.0% MnSZ 3.5% MnSZ 2.0% FeSZ Zr Intensity / a.u. O S Mn Fe cts Energy / ev No Mn on surface at typical promoter contents

30 XRD: Phase Composition and Promoters Intensity (normalized) M M SZ, 923 K 2.0% FeSZ, 923 K Diffraction angle Cu Kα 2θ / Fe, Mn stabilize tetragonal / cubic phase J. Stöcker, Ann. Chim. 1960

31 XRD: Phase Composition and Promoters Intensity (normalized) M M 2.0% FeSZ, 923 K Diffraction angle Cu Kα 2θ / SZ, 923 K Tetragonal unit cell volume / Å SZ FeSZ MnSZ Promoter content / mol% Fe, Mn stabilize tetragonal / cubic phase J. Stöcker, Ann. Chim Unit cell of tetragonal ZrO 2 shrinks with increasing Mn content, isolated Mn 2+ in EPR spectrum

32 Analysis of Fe-Species in FeSZ with XANES Fluorescence Yield Fe K edge near edge spectra of 2% FeSZ non-washed 1 4 2, Photon Energy, kev Absorption / Fluorescence Yield Difference spectrum Fe 2 O 3 reference Photon Energy, kev Surface species can be washed off with oxalic acid, ca. 42% EPR and Mössbauer: only Fe species, Fe 2 O 3 and isolated Fe 3+ model FeSZ F.C. Jentoft et al., J. Catal. 2004

33 Preparation Method and Distribution of Promoters coprecipitation NH 4 OH calcination 923 K solutions, ZrO(NO 3 ) 2 + Fe(III), Mn(II) nitrates Temperature / K Time / min "FeZ, MnZ"

34 Preparation Method and Distribution of Promoters solutions, ZrO(NO 3 ) 2 + Fe(III), Mn(II) nitrates coprecipitation NH 4 OH Temperature / K calcination 923 K "FeZ, MnZ" Time / min Tetragonal unit cell volume / Å FeSZ, impregnated MnSZ, impregnated FeZ, MnZ, coprecipitated Promoter content / mol% Distribution of promoters on surface and into zirconia lattice strongly preparation dependent Promoter valences, zirconia crystallite size also influence unit cell F.C. Jentoft et al., J. Catal. 2004

35 Sulfation of Coprecipitated Materials & Catalysis Isobutane formation rate / µmol g -1 h kpa n-c4, 338 K 2.0MnSZ, incipient wetness impregnation 1.8MnSZ, coprecipitated and oven-dried 1.8MnSZ, coprecipitated and spray-dried Time on stream / min Active material can be generated via coprecipitation

36 Zirconia Solid State Chemistry Summary O 2- Zr 4+ Zr 4+ O 2- O 2- O 2- Zr 4+ Zr 4+ Zr 4+ Zr 4+ O 2- O 2- O 2- O 2-2Ẕr4+ 2Ẕr4+ Zr 4+ O O O 2- O 2- Active tetragonal phase formed during glow - defects? O vacancies?

37 Zirconia Solid State Chemistry Summary Zr 4+ Zr 4+ Zr 4+ O 2- O 2- O 2- O 2- Zr 4+ Zr 4+ Mn Zr O 2- O 2- O 2- O 2-2Ẕr4+ Mn 3+ 2Ẕr4+ Zr 4+ O O O 2- O 2- Active tetragonal phase formed during glow - defects? O vacancies? Incorporation of promoters M x+ with x<4 into lattice: O vacancies Many M x+ promoters known: Cr, Mn, Fe, Co, Ni, Al, Ga

38 Zirconia Solid State Chemistry Summary Zr 4+ Zr 4+ Zr 4+ O 2- O 2- O 2- O 2- Zr 4+ Zr 4+ Mn Zr O 2- O 2- O 2- O 2-2Ẕr4+ Mn 3+ 2Ẕr4+ Zr 4+ O O O 2- O 2- Active tetragonal phase formed during glow - defects? O vacancies? Incorporation of promoters M x+ with x<4 into lattice: O vacancies Many M x+ promoters known: Cr, Mn, Fe, Co, Ni, Al, Ga Active phase metastable (monoclinization)

39 Zirconia Solid State Chemistry Summary O S O S O O O O O OH Zr 4+ Zr 4+ Zr 4+ O 2- O 2- O 2- O 2- Zr 4+ Zr 4+ Mn Zr O 2- O 2- O 2- O 2-2Ẕr4+ Mn 3+ 2Ẕr4+ Zr 4+ O O O 2- O 2- Active tetragonal phase formed during glow - defects? O vacancies? Incorporation of promoters M x+ with x<4 into lattice: O vacancies Many M x+ promoters known: Cr, Mn, Fe, Co, Ni, Al, Ga Active phase metastable (monoclinization) How is the surface chemistry affected?

40 Probing Sites by Chemisorption OH Zr 4+ Zr 4+ Zr 4+ O 2- O 2- O 2- Zr 4+ Zr 4+ Zr 4+ O 2- adsorption Δ H calorimetry + NH 3 desorption T TDS/TPD H H H N OH Zr 4+ H H H N Zr 4+ Zr 4+ O 2- O 2- O 2- Zr 4+ Zr 4+ O 2- Zr 4+ IR, XPS, NMR, UV/Vis... shift of bands (probe/surface)

41 Novel Concept: Evaluation of IR Intensities 1. Hydrocarbons as probe molecules 2. Evaluation of IR Intensities I μ r 2 δ + δ - C H Site Extinction coefficients as a measure of polarization of adsorbed molecule Intensified vibrations activated bonds (reaction begin) V.B. Kazansky, I.R. Subbotina, A.A. Pronin, R. Schlögl, F.C. Jentoft, J. Phys. Chem. B 110 (2006) 7975 V.B. Kazansky, I.R. Subbotina, F.C. Jentoft, J. Catal. 240 (2006) 77 V.B. Kazansky, I.R. Subbotina, F.C. Jentoft, R. Schlögl, J. Phys. Chem. B 110 (2006) 17468

42 Spectroscopic and Adsorption Data Absorbance Wavenumber / cm -1 Band area cm -1 / cm Neopentane C(CH 3 ) 4 on FeSZ, 308 K p / hpa y = x R 2 = Adsorbed amount / mmol g Adsorbed amount / mmol g Pressure / hpa Measurement on SZ catalysts obscured by scattering effects

43 Activation of Hydrocarbons by Zeolites Ethane, CH stretching vibrations IMEC in km/mol gas phase 169 NaY 100 CaY 260 Activation of hydrocarbon by cations in zeolite (faujasite) IR intensities can be used as new criterion to evaluate activation of hydrocarbons on surfaces

44 Possibilities for Reaction Initiation reaction cycle n-butane isomerization + ads + ads hydridetransfer

45 Possibilities for Reaction Initiation + H + very strong Brønsted acid H H + -H 2 reaction cycle n-butane isomerization -H - strong Lewis acid + ads + ads -H 2 O + H + strong Brønsted acid hydridetransfer oxidized catalyst reduced catalyst oxidative dehydrogenation (stoichiometric?) possible oxidizing agents: S, Zr, promoters

46 n-butane Isomerization over MnSZ: : In Situ XAS Average Mn valence 2.8 2% 1 MnSZ kpa n-c4, at 333 K vol% n-butane Time on stream / min Conversion to isobutane (%) No change of Mn valence during reaction (after activation in He) No correlation of Mn valence to catalytic performance No stoichiometric redox reaction involving Mn R.E. Jentoft, F.C. Jentoft et al., PCCP 2005

47 Diffuse Reflectance IR Spectroscopy Reaction of SZ with n-butane 1 kpa n-c4, 573 K / RT Kubelka-Munk function 0.2 KM H-C=C CO Kubelka-Munk function KM H 2 O 5228 Kubelka-Munk function KM 2583 H 2 S Wavenumber / cm Wavenumber / cm Wavenumbers / cm -1 Batch mode experiment: heating of SZ in n-butane, spectra recorded at RT Formation of H 2 O, CO 2, H 2 S, and unsaturated hydrocarbons Redox chemistry involving sulfate! B.S. Klose, F.C. Jentoft, I.R. Subbotina, V.B. Kazansky, R. Schlögl, Langmuir 2005

48 In Situ DRIFTS: Flow Experiments kpa n-c4, 323 K Kubelka-Munk function Time on stream Wavenumber / cm -1 Bands at 1600, 1630 cm -1 increase Range of C=C stretching vibrations, but corresponding CH vibrations not observed Water bending vibration

49 Spectral and Catalytic Information Kubelka-Munk function Time on stream Wavenumber / cm -1 Rate of isomerization / µmol g -1 h MnSZ, 1 kpa n-c4, 323 K Time / h Bands at 1600, 1630 cm -1 increase Range of C=C stretching vibrations, but corresponding CH vibrations not observed Water bending vibration -H 2 O + H + Rate proportional to number of intermediates? Estimate number of intermediates from band area + ads

50 Correlation of Spectral and Catalytic Information Isobutane formed / µmol g -1 h MnSZ, 323 K SZ, 358 K Band Amount area of increase water formed / cm -1 number of carbenium ions Rate of isomerization proportional to amount of water formed (induction period) ODH one activation pathway B.S. Klose, F.C. Jentoft et al., J. Catal. 2005

51 Diffuse Reflectance IR: Effect of Promoters Kubelka-Munk function no butane 2767 SZ butane RT 373 K no butane Wavenumber / cm -1 Wavenumber / cm -1 Kubelka-Munk function MnSZ butane RT 373 K Kubelka-Munk function KM MnSZ SZ Wavenumber / cm K 373 K Promoters (Mn) increase reducibility = oxidizing power of sulfate

Summary: Catalyst Development Bulk Properties: phase composition surface area, morphology Surface Properties: acidity Oxide ZrO 2, TiO 2, Fe 2 O 3, CeO 2, Structure Reactivity

52 Summary: Catalyst Development Bulk Properties: phase composition surface area, morphology Surface Properties: acidity Oxide ZrO 2, TiO 2, Fe 2 O 3, CeO 2, Structure Reactivity Reactivity Mixed oxide/solid solution Geometric structure: phase composition lattice constants Electronic structure: oxygen vacancies Oxo-anions SO 4 2-, WO 4 2- Promoter cations M x+, x < 4

53 Current Work & Outlook Novel catalysts Preparative efforts to vary defect chemistry of zirconia Promotion by Ga (et al.) In situ electron paramagnetic resonance (TU Munich) Deactivation phenomena Stabilization of catalytic activity through Pt & H 2 Identification of carbonaceous deposits In situ UV-vis spectroscopy

An application of Nanoparticles. Application of ZrO 2 as a Catalyst and a Catalyst Support

An application of Nanoparticles Application of ZrO 2 as a Catalyst and a Catalyst Support Introduction Characteristics of ZrO 2 High T m (>3000K) Low K c High resistance for corrosion Refractories, pigments,