Design of Transition-Metal/Zeolite Catalysts for Direct Conversion of Coal-Derived Carbon Dioxide to Aromatics (FE0031719)

Iman Nezam, Gabriel S. Gusmão, Wei Zhou, Matthew J. Realff, Andrew J. Medford, Christopher W. JonesGeorgia Institute of Technology, Atlanta, GA

The objective of this project is to develop a technology for the conversion of coal-derived CO2 directly into mixed aromatic chemicals that are currently sourced from petroleum. Aromatic chemicals such as benzene, toluene, and xylenes (BTX) face growing demand due to their expanding use in plastics and packaging, chiefly in poly(ethylene terephthalate) (PET). BTX is normally produced from oil in a petroleum refinery via multiple steps, involving several different reactions and separations. In this project we will explore a process intensification effort that begins the development of a new technology for the conversion of coal-derived CO2 directly into BTX in a single reactor. This approach involves hydrogenation of CO2 into methanol or short chain alkanes and related olefins, which subsequently encounter a second catalyst that converts the intermediate species to BTX in the same reactor. A BTX production technology based on this reaction scheme would significantly deviate from the state-of-the-art, allowing the use of CO2 as a feedstock, reducing the number of process steps and unit operations, and allowing smaller, more modular installations, which is commensurate with siting near large coal-fired power plants, minimizing costs of CO2 storage and transportation.

Acknowledgments

The authors acknowledge the U.S. Department of Energy for financial support through grant DE-FE0026433.

Computational Catalysis Progress

• Comprehensive DFT-based mean-field microkinetic catalytic model on Cu(111) encompassing 28 adsorbate- and 13 gas-species in 42 elementary reactions.

• Forward and reverse water-gas shift from [1] Grabow, L.C. and M. Mavrikakis, ACS Catal.

2011. Oxygenates formation: ethanol, formic acid, formaldehyde from [1], ethanol, acetic acid and acetaldehyde from Schumann, J. et al., ACS Catal. 2018. Hydrocarbons formation: methane [1] and ethane from Martin Hangaard, H. et al., J. Catal. 2019.Oxygen dissociation from Falsig, H., et al., Top. Catal. 2014.

Motivation

Two steps in a single reactor (CO2 from flue gas, some H2 source)

CO2 to Intermediates (MOH/DME): Metal Oxides (ZnZrOx)

Oligomerization + Aromatization: MFI (H-ZSM-5)

Carbon Dioxide (CO2)

• Domestic CO2 emission from coal combustion: 1500 million metric tons in 2017• Could fully support the BTX global market

Global Production (2010) 100 million metric tons

Industrial ApplicationsSolvent

Precursor to value-added chemicals

2050 Projection200 million metric tons

Current Production TechnologyCatalytic reforming of naphtha

CatalystPrecious metals supported by high surface area materials with acidity

CO2 to BTX (CO2 → Intermediate → BTX)

Experimental Progress

Benzene, Toluene, Xylene

BTX

Approach

Current Status• Maximum aromatics selectivity is obtained at T=320 oC, WHSV=7200 mL/g cat./h,

Si/Al=300: 39.7% (STY= 1.04 mmol CO2/g cat/h) • DFT-based rates have been calculated for the main intermediate species for the CO2

hydrogenation on Cu(111). DFT-energies have been extended to the 211 facet of Ag, Au, Pd, Pt, Rh and Cu.

Next steps• Studying the effect of diffusion path length on catalytic activity.• DFT-based identification of target alloy catalysts for methanol production.

CO2 H2+

Oxygenates

Methanol

Paraffins

BTXHigh selectivity range

Coke

OligomersJones’ GroupExperiments / CharacterizationSpectroscopy

Realff’s GroupTechno-economicProcess IntensificationOptimizationLCA

ZSM-5• Si/Al ratio• Crystal size

Metal Alloy Screening

ZnZrO

CO2 H2+

EXPERIMENTAL

MethanolOlefins

Olefins

THEORETICAL

Medford’s Group𝝁Kinetic models (CatMAP)

CO

Catalyst Temperature Dependence:

Cu(111)Grabow’s [1]

Cu(211)

Rh(211)

Ag(211)

Pt(211)

Au(211)

Pd(211)

Cu(111)

log

10 TO

F

Temperature [K]

P [

bar

]

Potential Energy DiagramCO2 to MethanolDFT-based formation energies for microkinetic model extended to additional transition metal catalysts

Turn-over frequencies (log10TOF) for methanol and methane on Cu(111) at static gas phase concentration 0.90:0.05:0.05 H2:CO2:CO

CO

2(g)

+ 3

H2

(g)

CO

2(g)

+ 6

H*

CO

2*+

6H

*

H-C

OO

*+

5H

*

HC

OO

*+

5H

*

HC

OO

-H*

+ 4

H*

HC

OO

H*

+ 4

H*

H-H

CO

OH

+ 3

H*

CH

3O2*+

3H

*

CH

2O

-OH

*+

3H

*

CH

2O

*+ O

H*

+ 3H

*

H-C

H2O

*+ O

H*

+ 2

H*

CH

3O-H

* +

OH

*+

H*

CH

3O

* +

OH

*+

2H

*

CH

3OH

* +

OH

*+

H*

CH

3OH

* +

H-O

H*

CH

3O

H(g

) + H

2O(g

)

CH

3O

H*

+ H

2O*

CH3OH (g) CH4 (g)

• RWGS reaction is endothermic→ Increasing CO selectivity with temperature

• Only olefins present are ethylene and propylene→ Not following the typical ASF distribution

• Aromatics are mainly C9 perhaps due to the small ZSM5 particle size (excess external surface area)

100 200 300 400

H-ZSM-5-60

H-ZSM-5-40

H-ZSM-5-20

H-ZSM-5-80

H-ZSM-5-120

H-ZSM-5-200

Temperature /oC

Inte

nsity /a.u

.

H-ZSM-5-300

H-ZSM-5-500

H-ZSM-5-800

96 µmol/g

35 µmol/g

440 µmol/g

185 µmol/g

156 µmol/g

66 µmol/g

21 µmol/g

18 µmol/g

11 µmol/g

Process Setup: Typical Products Distribution:

Zn/Zr=1/6, ZnZrOx/H-ZSM-5=1/2, Si/Al=80, H2/CO2=3 P=600 psi, T=320 oC WHSV=7200 mL/g cat./h

Zn/Zr=1/6, ZnZrOx/H-ZSM-5=1/2, Si/Al=80, H2/CO2=3 P=600 psi, WHSV=7200 mL/g cat./h

10 20 30 40 50 60

Inte

nsity /

a.u

.

2 /degree

20

40

60

80

120

200

300

500

800

Catalyst Acid Density Dependence:

• Olefin hydrogenation to paraffins becomes dominant at high temperatures

• Aromatics selectivity is maximized at 320 oC

NH3 TPD

w/o ZSM5

• Very low acid density is desired. Max aromatics selectivity at Si/Al=300

• CO selectivity is minimum at Si/Al ratio of 300-600 • High acid density promotes the

RWGS reaction• Low acid density reduces H-

transfer rate for olefins synthesis → Reduced CO selectivity