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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
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