Nanostructured Heterogeneous Catalysts for the Hydrolysis of Cellulosic Materials

1. Nanostructured Heterogeneous Catalysts for the Hydrolysis of Cellulosic Materials Joshua Abbott Barnes Group Department of Chemistry University of Tennessee Knoxville, TN 12/02/2011

2. Outline • Background • Synthetic Methodology • Single Site Metal Catalysts • Catalyst Characterization • Catalytic Activity • Hybrid Organic/Inorganic Catalysts • Catalyst Characterization • Catalytic Activity • Future Work

3. Project Background and Goals • C3Bio is working to develop technologies for the conversion of lignocellulosicbiomass to hydrocarbon rich biofuels and other products currently derived from oil. • Our group is investigating the controlled degradation of cellulose. • Selective hydrolysis of cellulose would lead to products from which fuels or other fine chemicals could be manufactured. • Our goal is to create new solid acid catalysts which exhibit increased yields and selectivity to glucose or other value added products (Levulinic Acid, HMF, …). Ritter, S. K. Chemical & Engineering News. December 8, 2008, p. 15.

4. Substrate Different Phase Same Phase Homogeneous Heterogeneous Catalyst Higher Activity Difficult Separation Lower Activity Easy Separation Product

5. Limitations in current solid acid heterogeneous catalysts • Zeolites • -Microporosityprevents substrate access • Heteropolyacids • -Low Yields • Sulfonic Resins • -Stability & Durability issues • Mesoporoussilicates • -Costly templating agents in synthesis • Targeting a specific active site • Choice of catalytic precursor • Creation of a single type of site • Multiple sites lead to low selectivity • High site density is preferable • Creation and control of porosity • Ideally mesoporous (>2nm) • Active Catalyst • Higher Activity • Robust & Stable Catalyst • Reusable Goals in designing next generation solid acid catalysts

6. Synthetic Methodology Synthesis of nanostructured heterogeneous catalysts via a building block methodology • Control of the active site and its immediate environment • Single type of site • High selectivity • Control of site distribution • Building block methodology • High site density • Control of surrounding matrix • Extended control of surface area • Increased matrix rigidity

7. Me3SnO OSnMe3 + MCln Cl M OSnMe3 + Me3SnCl Me3SnO O O Cl 1. Control of active site and immediate environment Linking reaction of trimethyltinfunctionalized surfaces with metal chlorides Metathesis reaction allows for clean reaction under non forcing conditions, with an easily removable byproduct • Potential catalytically active linkers and precursers: AlCl3, GaCl3, BBr3, (C6H5CH2)SiCl3, TiCl4, ZrCl4, WOCl4

8. O O M O O M O O Si8O12(OSnMe3)8 Building Block = MCl3 (Al,Ga,B) + O M O O + Me3SnCl 2. Control of site distribution Use of a building block ensures separation of sites at high concentrations

9. TMSCl OSiMe3 O Me2SiCl2 Al O O O SiCl4 O O Si Al O O O O OSiCl3 O O Si Me Me 3. Control of surrounding matrix Secondary reactions with inert silanelinkers allow for increased matrix rigidity and increase surface area • Inert linkers: SiCl4, HSiCl3, Me2SiCl2, Me3SiCl

10. Catalyst Nanostructuring Strategy “embedded” catalyst sites MCln M M MClX M catalyst ensembles colloidal particles porous, supported catalyst particles SiCl4 building block M M SiCl4 MCln M M rigid building block platform “surface” catalyst sites = SiClx links Method of Sequential Additions

11. Catalyst Characterization • Gravimetric Analysis • Indirect method used to determine immediate environment around metal center • Estimate M : Sn ratio • Elemental Analysis (ICP-OES) • Determine M : Sn ratio • X-ray Absorption Spectroscopy (XANES and EXAFS) • Direct method used to determine immediate environment around metal centers • Brookhaven National Lab • X19A at National Synchrotron Light Source • Nitrogen Adsorption/Desorption • BET surface area • Pore structure • IR • M-O-Si vibrational frequency • Lewis or Bronsted acidic sites (pyridine adsorption) • Raman • M=O vibrational frequency • SSNMR • 13C, 29Si, 119Sn, 27Al, 11B, 51V, 17O

12. Looking at Group 13 Systems • B, Al, Ga • Solid Acid catalysts • Useful for dehydration, hydrolysis, isomerization, transesterification and hydrocarbon cracking catalysis • Our synthetic approach offers the ability to create unique purely Lewis acidic sites • The metathesis reaction theoretically yields a 3-coordinate imbedded metal center • 3 coordinate Group 13 centers are octet violators and electron deficient • How stable are the metal centers?

13. O B O O O B O O BBr3 + O B O O + 3 Me3SnBr Synthesis of a Borosilicate Catalyst Toluene 80oC 24hrs Si8O12(OSnMe3)8 Gravimetric Analysis: 2.9 ± 0.1 Eq. of Me3SnBr lost

14. Direct Characterization of Boron Centers • IR => • Feature at 1406 cm-1 is corresponds • to planar BO3 units • Lack of strong features from 1100-850 cm-1 and at 700 cm-1 indicate little to no presence of tetrahedral BO4 units 5 8 1 6 9 1 1 250 1 4 9 0 . . . 1 6 3 6 4 . 7 1 6 - 11B-MAS-7.5KHz 240 B002 - As Synthesized 230 220 210 200 190 180 170 160 • <=11B SSNMR: • Could be multiple B signals • Complexity from quadrupolar nuclei • Colaborating with Dr. Ed Hagaman at ORNL • Little to no Tetrahedral BO4 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 160 140 120 100 80 60 40 20 0 -20 -40 -60 -80 -100 -130 f1 (ppm)

15. Indirect Characterization by Pyridine Binding • Pyridine can bind to solid acid catalysts in three ways • The IR spectrum indicates only Lewis acidic binding • BO3 Signal remains, but shifts upon binding of pyridine and shifts back when pyridine is removed • Significant change in the 11B SSNMR, indicative of higher coordination Figure 8 340 11 B-MAS 320 B002 - Overlay 300 Red = B002-AS 280 Green = B002-Py 260 Blue = B002-Py-dried 240 220 200 180 160 140 120 100 80 60 40 20 0 -20 45 40 35 30 25 20 15 10 5 0 -5 -10 -15 -20 f1 (ppm)

16. O Al O O O Al O O AlCl3 + O Al O O + 3 Me3SnCl Synthesis of an Aluminosilicate Catalyst Toluene 80oC 48hrs

17. Characterization of Aluminosilicate • Gravimetric analysis indicates that more mass is lost than can be attributed • to the reaction of the three chlorides on Al. • Solution 1H NMR of the Volatiles indicates the presence of tetramethyltin. • 27Al SSNMR studies in progress. Samples are very sensitive to moisture. • Ratio of Me3SnCl: Me4Sn doesn’t seem reproducible at this point 1H NMR - Reaction Volatiles Me4Sn Me3SnCl

18. O ??? + GaCl3 Ga O O Gallium Analogues • Both Me3SnCl & Me4Sn produced FT

19. Model Data O O Fit O Ga- M+ O O O O Fit Parameters Amp: 0.95 Eo: 4.7 RGa-O: 1.87 σ2: 0.007 ± 0.0004 CNGa-O: 3.9 ± 0.1 R-Factor: 0.003 • Ga center finds a way to bond to a fourth oxygen • All chlorides on the metal center are reacted

20. Possible Side Reaction • After one equivilant of chloride has reacted, then there is enough trimethyltin chloride to turn all Al centers into 4-coordinate species Eisch, J. J. Mackenzie, K. Windisch, H.; Krüger, C. Eur. Journ. Inorg. Chem.1999, 153-162.

21. Where is tetramethyltin coming from?

22. Where is tetramethyltin coming from?

23. O Al + Al O O Cl Cl Cl Pyridine Adsorption on Building Block Aluminosilicate Transmittance L L L 1700 1650 1600 1550 1500 1450 1400 -1 cm N N Pyridine Adduct • When using AlCl3*Py, there is no evidence for tetramethyltin.

24. Catalysis Crystalline Cellulose Cellobiose dimer Glucose Monomer

25. O O M O O M O O O M O O Catalytic Protocol +

26. Catalytic Results

27. Catalytic Conclusions • Initial experiments indicated activity for conversion of cellobiose to glucose, but further studies showed that conversion was due the production of HCl via hydrolyzed M-Cl & Si-Cl bonds in the catalytic matrix. • ICP-OES studies indicated that in the presence of HCl some of the metal centers were leached from the catalysts. • In some experiments, other breakdown products were identified in low yields that indicated that the metals centers were having some influence on the conversion process. • In the end it was concluded that these catalysts were not suited for cellobiose conversion. Cellobiose Glucose

28. Sulfonic Acid Organic-Inorganic Hybrid Approach • Why are we interested • Strong Bronsted Acids • Stable in aqueous environments • Synthesis methods compatible with our methodology • Our methodology avoids templating • Challenges • Heterogeneous Sulfonic acids are well known, how are ours different? • Can we achieve higher activity, or increase site density? • Typical TEOS:RSi(OR)3 ratios from 10-5:1 so Si:R ratios of 11-6:1. A 1:1 reaction with cube BB leads to Si:R ratio of ~9:1. • Can we avoid leaching? • Reusability?

29. Commercially available heterogenzied Sulfonic acids Nafion: Diphonix: Amberlyst:

30. Synthesizing Sulfonic Acid Organic-Inorganic Hybrid Materials Literature Methods:

31. Synthsizing Sulfonic Acid Organic-Inorganic Hybrid Materials Our Methods:

32. Sample Bz002 • First Dose: 1.07:1.00 BzSiCl3:TMT • Gravimetric: 2.99±0.02 • Second Dose: Excess TMSCl – Neat 80oC • Gravimetric: ~0.25mmol Me3Sn- remaining • Sulfonation: ~3:1 ClSO3H:BzSiCl3 in CH2Cl2 @ 0oC • Remove volatiles in vacuo and heat under vacuum @100 • Final product is a fine brown/purple powder

33. IR – Before & After Sulfonation Aromatic C-H Aliphatic C-H Aromatic C-H

34. SSNMR 1H • 1H spectrum clearly shows three signals: TMS/TMT, Aromatic, Sulfonic Acid? • 13C & 29Si show little change during the sulfonation process TMS/TMT Ar-H SO3-H Before Sulfonation After Sulfonation 29Si 13C TMS/TMT Q4 TMS Aromatic -CH2- Grease T3 * *

35. Catalysis Catalyst, H2O Δ

36. Catalysis Catalyst, H2O Δ

37. Next Steps • Focus on understanding Al & Ga reactions with cube • Quantify TMT:TMTCl ratios • Examine rxns with AlCl3*Py and [Me3Sn][AlCl4] • Continued synthesis & characterization of sulfonic acid catalysts • Quantification of acid sites • Quantification of S content • Catalytic Studies • Cellobiose • Cellulose • Stability studies • Temperature & Time • Incorporation of both ionic liquid and sulfonic acid groups (Trojan Horse) • Synergistic approach to cellulose degredation