Methane to Methanol: Tobin Marks, Northwestern University

Methane to Methanol

What’s Known and Questions/Challenges

Tobin Marks

NAS Workshop March 7-8, 2016

1. Properties of Methane

2. Naïve Generalizations

3. Conventional Approaches to Methanol

4. Homogeneous Catalytic Approaches

5. Immobilized Homogeneous Catalytic Approaches

6. Enzymatic Approaches

Properties of Methane

Selective methane activation challenging because of “noble

gas”-like electronic configuration

Large Bond Dissociation Enthalpies

Some Naïve Generalizations

Creative Catalytic Chemistry Important but Alone is Insufficient

Excellent Engineering is Essential for a Successful Process

Issues:

• Thermodynamics

• Heat and Mass Transfer Management

• Management of Toxic Intermediates and Byproducts

• Catalytic Selectivity

• Product Separation, Purification

• Catalyst Cost & Supply Security

• Catalyst Lifetime, Regeneration

• Others?

Emerging Tools for Catalyst Discovery, Optimization, Downselection

• Operando and Ex-situ Spectroscopy to Probe Catalyst Structure & Dynamics

• New Chemical/Analytical Techniques to Probe Mechanism

• High Throughput Experimentation for Optimization, Discovery

• Materials Science of Catalyst Supports, Plant Construction Materials

• Ligand Supply, Design

• High-Powered Computation for Both Understanding and Prediction

Methane

→

Methanol. Thermodynamic Considerations

Practiced on

a huge scale

ICI Process

Dream

Current Indirect US MeOH

Price ≈ $0.75/Gallon

Direct Methane to Methanol Conversion.

Heterogeneous Catalytic

Casey, P.S. et al Ind. Eng. Chem. 1994, 33, 1120-1130.

Hutchings, G.J.; Scurrell, M.S.; Woodhouse, J.R. Chem. Soc. Rev. 1989, 18, 251-283. Gesser, H. D.; Hunter, N. R.; Prakash, C. B. Chem. Rev. 1985, 85, 235

Lunsford, J. H. Catal. Today 2000, 63, 165

Alvarez-Galvan, M. C.; Mota, N.; Ojeda, M.; Rojas, S.; Navarro, R. M.; Fierro, J. L. G. Catal.

Today 2011, 171, 15

Tabata, K.; Teng, Y.; Takemoto, T.; Suzuki, E.; Bañares, M. A.; Peña, M. A.; Fierro, J. L. G.

Catal. Rev. 2002, 44, 1

Holmen, A. Catal. Today 2009, 142, 2

Brown, M. J.; Parkyns, N. D. Catal. Today 1991, 8, 305 Zhang, Q.; He, D.; Zhu, Q. J. Nat. Gas Chem. 2003, 12, 81

Many attempts using huge variety of conditions and catalysts

Very high dilution

Excess methane

Short contact times

Low temperatures

Methanol Synthesis on Cu/ZnO/Al

₂

O

₃

with H

₂

+ CO + CO

₂

 Both CO and CO₂ hydrogenation pathways, depending on rxn conditions  Cu active site; rxn temperature = 230 – 280ᵒC; 40-100 atm pressure  99% yield (when recirculating); ~ 25% conversion per pass

 Simultaneous WGS; Possible ZnO synergistic effects

Potential energy surface for methanol synthesis reactions after fitting of DFT & microkinetic model to experimental data

Agreement between experimental & computed TOF data

Grabow & Mavrikakis ACS Catal., 2011, 1, 365–384

http://bioweb.sungrant.org/Technical/Bioproducts/Bioproducts+from+Syngas/Methanol/Default.htm

Olah, G. A.; Goeppert, A.; Czaun, M.; Mathew, T.; May, R.B.; Prakash, G. K. S. J. Am. Chem. Soc. 2015, 135, 8720–8729.

Olah, G. A.; Goeppert, A.; Czaun, M.; Prakash, G. K. S. J. Am. Chem. Soc. 2013, 135, 10030–10031

Single Step Bi-reforming & Oxidative Bi-Reforming of

Methane (Natural Gas) with Steam & Carbon Dioxide to

Metgas (CO-2H

₂

) for Methanol Synthesis

NiO/MgO and CoO/MgO catalysts in tubular flow reactor up to 42 atm & 830–910°C. Catalysts for metgas production stable for 100s of hours. No obvious demonstration of MeOH formation in peer-reviewed publication.

Shilov. Homogeneous Catalytic Oxidation of Methane

Original. Pt(IV) as oxidant

Shilov discovered that the combination of [PtCl₄]2− and [PtCl₆]2−, under

conditions similar to those of CH₄ H/D exchange, oxidizes alkanes to a mixture of products, primarily alcohols and alkyl chlorides

Labinger and Bercaw JOMC, 2015, 793, 47-53; Nature 2002, 417, 507-514.

Shilov Chemistry. Homogeneous Catalytic Oxidation of Methane

Labinger & Bercaw JOMC, 2015,793,47-53

Bercaw & Labinger refinement with Cu(II) oxidant Original Cycle. Pt(IV) as oxidant

TON ≈ 100 for p-TOSH

Electrophilic Methane Functionalization → Methyl Derivatives

Periana, R. A. et al. Science 1998, 280, 560–564; Accts. Chem. Res. 2012, 45, 885-898.

Electrophilic Main Group Metals: Hg (II) & Tl(III) in Strong Acids

• HgSO₄ system catalytic in conc. H₂SO₄

• 85% Selectivity to MeSO₄H in 50% yield

• 15% selectivity to CO₂

• Air regenerates catalyst

• Catalyst inhibited by reaction product

• MeOH formation requires product

Catalytica system, uses (bipyrimidine)Pt(II) complex as catalyst and fuming sulfuric acid as solvent/oxidant; capable of efficiently functionalizing methane at temperatures ~ 200 °C.

The ‘protected’ product is not of direct use and must be separately converted to a more useful compound, such as methanol, using a scheme such as that shown in Fig. 7b. At least at present, such an integrated multistep process seems not economically competitive with the currently used technology, the indirect conversion of methane to methanol via synthesis gas.

Periana, R. A. et al. Science 1998, 280, 560–564; Accts. Chem. Res. 2012, 45, 885-898. Labinger and Bercaw JOMC, 2015, 793, 47-53; Nature 2002, 417, 507-514.

Homogeneous Methane Oxidation by H

₂

SO

₄

/SO

₃

Mediated by

Pt bipyrimidine Complexes (Periana)

Methane Oxidation by Zeolite-Supported Catalysts

M-ZSM-5, M = Fe, Cu; H

₂

O

₂

Oxidant

Hutchings G.J. et al Angew. Chem. Int. Ed. 2010, 51, 5129-5133; ACS Catal. 2013, 3, 1835-1844.

Aqueous medium, H₂O₂ oxidant

Low temperature (50ᵒC) helps selectivity

Both Fe₂ and Cu required for max selectivity Closed catalytic cycle

Cu suppresses selectivity-lowering ∙OH TOF = 2,200 – 14,000 h-1

Selectivity > 90% ( + CO₂)

Computation: Need proximate Fe centers

Transient, closely controlled ∙CH3

HCO₂H

MeCOOH

MeOH CO₂

ZSM-5; No Fe, Cu

Immobilized Periana Catalysts for Methane Oxidation

Palkovits, R.; Antonietti, M.; Kuhn, P.; Thomas, A.; Schüth, F. Angew. Chem. Int. Ed. 2009, 48, 6909-6912. Palkovits, R.; Schüth, F. et al, Chem. Commun. 2013, 49, 240-242.

Under the same conditions (fuming H₂SO₄), TON ≈ Periana catalyst MeOH selectivity ≈ 75%; rest is CO₂

Catalyst can be multiply recycled

SEM

Pt EDX map

B. N-Doped Carbon Support

MeSO₄H TON ≈ 6 - 9x of the system A above; 92 – 95% methyl selectivity,

Other product, CO₂

Lobster shell

Enzymatic Methane to Methanol Conversion

Example: Fe

₂

Dioxygenases: Methane Monooxygenase

Enzyme Structure CH₄ Activating Q Site. O-O Cleavage Homolytic?

Banergee, R.; Proshlyakov, Y.; Lipscomb, J.D.; Proshlyakov, D.A. Nature 2015, 518, 431–434 Wang, W.; Liang, A.D.; Lippard, S.J. Acc. Chem. Res., 2015, 48 , 2632–2639.

Overall reaction requires separate pathways to channel 3 reagents

1. Electrons and protons via a three-amino-acid pore adjacent to Fe₂ center 2. O₂ migrates via hydrophobic cavities

3. Methane reaches active site via hydrophobic channel or linked cavities

4. Above rates closely coupled to avoid unproductive destruction of reductant by oxidant

Thoughts. Need Your Input!

Amazing how much we have learned about key catalytic mechanisms

New tools emerging to screen catalysts, catalytic mechanisms as never before Materials science of heterogeneous catalysts advancing rapidly

Computation has made impressive advances in understanding, predicting

Are alternative oxidants such as H₂O₂, N₂O, SO₃ realistic?

Are alternative products such as CH₃SO₃H realistic?

Are there “softer” oxidants which can replace or “tame” O₂ or the above oxidants for

greater selectivity?

Advances have been made through biomimicry. Can we extend further, remembering that Nature is frequently trying to solve a different problem than we are?

Are enzymatic processes for methanol realistic? What about product separation from aqueous solutions?

Is the use of noble metal catalysts realistic?

Are homogeneous catalysts realistic? What about “single-site” heterogeneous catalysts? Are we using computation in the most effective way?