UMich team develops catalyst that could convert CO2 into renewable fuels such as methanol on large scale
07 May 2024
Researchers at the University of Michigan have developed a catalyst material—cobalt phthalocyanine—that converts carbon dioxide into renewable fuels such as methanol.
In a study published in the journal ACS Catalysis, U-M researchers report using cobalt phthalocyanine as a catalyst to convert carbon dioxide into methanol through multiple reaction steps. The first step converts carbon dioxide into carbon monoxide (CO) and the second step converts the CO into methanol.
While the conversion of CO2 to methanol has been industrialized, achieving this transformation on a large scale through electrochemical processes has proven to be a significant challenge.
Cobalt phthalocyanine (CoPc) is an active electrocatalyst for the sequential electrochemical reductions of CO2-to-CO and CO-to-methanol (CH3OH), and it has been shown to be active for the conversion of CO2-to-CH3OH through a cascade catalysis reaction. However, in gas-fed flow electrolyzers equipped with gas diffusion electrodes (GDEs), the reduction of CO2 by CoPc selectively produces CO with minimal CH3OH formation.
Herein, we show that the limited performance of the CO2–CO–CH3OH cascade reactions by CoPc is primarily due to the competitive binding between the CO2 and CO species. Through microkinetic analyses, we determine that the effective equilibrium constant for CO2 binding is three times higher than that for CO binding. The stronger CO2 binding suppresses the CO-to-CH3OH reaction even at moderate local CO2 concentrations.
Because the GDE configuration enhances the CO2 mass transport, gas-fed flow electrolyzers exacerbate this suppression of CH3OH formation from the CO2RR. In contrast, CH3OH formation is observed when the local concentration of the CO2 is low, compared to the local CO concentration. To promote methanol formation via CO2 reduction, we propose applying modifications to the coordination environments of CoPc to strengthen the binding of CO and regulate the transport of CO2.
—Yao et al.
Cobalt phthalocyanine acts like a molecular hook for CO2 or CO molecules. The arrangement of these molecules around the cobalt metal (the geometry) is crucial because it determines how strongly each gas molecule binds. The problem, they found, is that cobalt phthalocyanine binds much more strongly to CO2 molecules than to CO molecules. Because of this, once CO is produced in the first step, the CO is displaced by another CO2 molecule before it can be further converted to methanol.
Using advanced computational modeling, the researchers calculated that cobalt phthalocyanine binds CO2 over three times more tightly than it binds carbon monoxide. They also confirmed this through experiments measuring reaction rates when varying the amounts of CO2 and CO.
The researchers showed that the difference in binding affinity has to do with how the catalyst’s electrons interact with the CO2 and CO molecules. To solve this issue, the researchers suggest redesigning the cobalt phthalocyanine catalyst to strengthen how it interacts with CO and lessen how strongly it binds to CO2.
Resolving this roadblock could pave the way for using catalysts such as cobalt phthalocyanine to convert CO2 waste into methanol fuel efficiently on a large scale.
Resources
Libo Yao, Kevin E. Rivera-Cruz, Paul M. Zimmerman, Nirala Singh, and Charles C. L. McCrory (2024) “Electrochemical CO2 Reduction to Methanol by Cobalt Phthalocyanine: Quantifying CO2 and CO Binding Strengths and Their Influence on Methanol Production” ACS Catalysis 14 (1), 366-372 doi: 10.1021/acscatal.3c04957
"Resolving this roadblock could pave the way for using catalysts such as cobalt phthalocyanine to convert CO2 waste into methanol fuel efficiently on a large scale."
If the CO2 waste is from fossil sources this proposal is only a stop gap which will not lead to zero emissions. On the other CO2 recycling from methanol could lead to a zero emission technology.
It has been along time since I read about methanol powered turbines so I did some Internet searching. It is clear that methanol turbines with carbon capture are an active subject of research. For example I found a paper published on Mar 15, 2024 on a pre-reforming methanol powered turbine with CO2 capture (https://www.sciencedirect.com/science/article/abs/pii/S0306261923019633).
The the body of the paper is behind a pay wall but an extensive introduction is available on line. From the introduction:
"Based on a 530 MW GTCC plant, thermodynamic analysis reveals a 4.6% energy efficiency increase, a 4.3% exergy efficiency boost, and an 82.2% CO2 recovery with a 0.354 MJ/kgCO2 energy penalty. The proposed design yields 454.4 M$ more profit than the reference power plant throughout its lifespan. Additionally, sensitivity analysis indicates optimal conditions for MSR at approximately 250 °C, a 1:1 water-to-methanol ratio, and a higher reaction pressure preference."
In order for such a system to emission free the other 18% of the CO2 would have to come from the atmosphere either via biological capture or by direct air capture.
I am not trying to promote a methanol economy in which methanol is our primary energy carrier, but if there are economic niches which require long term energy storage then this technology could conceivably help to fill them.
Posted by: Roger Brown | 07 May 2024 at 07:31 AM
Cost-effective ways of converting carbon dioxide into carbon monoxide could be valuable. By reusing carbon you reduce carbon emissions into the atmosphere it does not have to be zero emissions don't let the perfect be the enemy of the good.
Posted by: SJC | 07 May 2024 at 07:48 AM
@SJC,
I don't think I declared enmity to the double use of fossil carbon. I simply declared an interest in developing a long term strategy which gets us to zero emissions.
Posted by: Roger Brown | 07 May 2024 at 08:16 AM
To get to zero emissions you need a Circular Economy that is supported by the Oil and Gas industry. The best place appears to be in Shipping & Marine fuels which due to very long distances required make electrification difficult.
Many companies in this area have endorsed “Green Methanol”, however that alone cannot meet all of the requirements of Marine applications, due to supply issues, cost, and the lower energy density of Methanol vs Bunker fuel.
There does appear to be solutions coming, like this research by the UMich team and others. Companies like Maersk and MOL Mitsui support the ideas of a Circular Economy that captures CO2 from ship engines and then is converted to Methanol.
To address energy density a liquid lignin methanol blend would improve performance and would also add an abundant “Green Source” of fuel.
There are many companies involved in these concepts. For example, Mitsubishi Gas Chemical plans to launch “Circular Carbon Methanol” Production where CO2 emissions and waste plastics are converted into methanol. Also Mitsui OSK Lines discusses the reuse of CO2 for a “circular methanol economy”.
https://www.mgc.co.jp/eng/corporate/news/files/210330e.pdf
https://www.mol-service.com/blog/environment-circulating-model-methanol-story#:~:text=The%20methanol%20thus%20produced%20in,CO2%20emissions%20during%20transport.
Finally, here are two references that show the possibility of using Lignin Methanol blends which will improve energy density and use abundant biological material.
https://shipandbunker.com/news/world/129173-maersk-plans-to-blend-lignin-with-methanol-to-increase-energy-density
“Investigation of Liquid Lignin-Methanol Blends under Realistic Two-Stroke Marine Engines Conditions”,
https://pure.tue.nl/ws/portalfiles/portal/312620086/2023-24-0085.pdf
Posted by: Gryf | 07 May 2024 at 09:38 AM
Hi Gryf.
I was interested in your comment:
' Many companies in this area have endorsed “Green Methanol”, however that alone cannot meet all of the requirements of Marine applications, due to supply issues, cost, and the lower energy density of Methanol vs Bunker fuel.'
And did a bit of digging to get a numeric handle on this.
https://www.methanol.org/wp-content/uploads/2023/05/Marine_Methanol_Report_Methanol_Institute_May_2023.pdf
(from the Executive Summary)
' Market-based measures must be deployed alongside efficiency measures to enable the transition to low carbon shipping fuels, because low and net carbon neutral maritime fuels are currently two to eight times more expensive than conventional fuels. On the current trajectory, by 2050 the total cost of ownership of vessels that run on net carbon neutral maritime fuels is likely to remain higher than that of fossil-powered vessels (see Figure 3)1
. The carbon price that experts suggest would enable net-zero shipping by 2050 ranges from $91 to $230 per ton of CO2 , depending on the policy mechanism chosen. If a flat levy is applied, the average price of CO2 would be at the higher end
of the spectrum, whilst a lower average price could be achieved under a return-and earmark scheme, whereby revenues collected are used to compensate early adopters of low carbon shipping fuels.
Methanol has a higher energy density than other alternative shipping fuels, including LNG, ammonia, and hydrogen; when considering the size of storage tanks, secondary barriers, and cofferdams. However, the energy density of methanol is lower than that of traditional shipping fuels. For example, MGO has an energy density of 36.6 GJ/m3 compared to methanol’s 15.8 GJ/m3 .This means that on a methanol- powered ship, storage and fuel tanks take about 2.4 times more space than on ships that run on MGO.
This disadvantage is mitigated by frequent bunkering and by the fact that methanol can be stored in conventional fuel storage tanks and even ballast tanks on-board a vessel, unlike fuels such as LNG and H2 that require cryogenic storage2 and have a greater impact on the loss of cargo space.'
Clearly there are significant obstacles, but they do not sound like absolute show stoppers.
A proper numeric evaluation would need not only estimates of the cost of action, but the cost of inaction, in the case of bunker oil including not only GHG costs, but the cost of health impacts from this dirty fuel.
Currently uncosted and/or uncharged costs do not mean that they are not real, and avoided,
They are simply not currently allocated correctly, where they are incurred.
But they still hit just as hard.
Posted by: Davemart | 07 May 2024 at 03:42 PM
The only proposal I have see for collecting CO2 on shipboard involves the use of solid oxide fuel cells. I do not know what the economics for collecting CO2 from a methanol/lignin blend in a traditional combustion engine would look like.
The use of lignin is also concerning. The aviation industry wants to use biomass to decarbonize air travel. People are working on developing road asphalt produced from biomass (https://www.sciencedirect.com/science/article/pii/S2095756422000228). In my mind a real concern exists about how much new demand we can place on biomass without negative impacts on food supply/ecological diversity.
Posted by: Roger Brown | 08 May 2024 at 07:44 AM
@Roger Brown
Good questions. I will break this down in parts.
First question: “ I do not know what the economics for collecting CO2 from a methanol/lignin blend in a traditional combustion engine would look like.”
This is a detailed Study by Stena Bulk, “IS CARBON CAPTURE ON SHIPS FEASIBLE?”,
https://www.ogci.com/wp-content/uploads/2023/04/OGCI_STENA_MCC_November_2021.pdf
From the Conclusion on Page 12:
“Although we demonstrated technical feasibility, capital and operating expenses remain high. Capex is driven by the relatively high costs of the storage tanks, compressors and columns, while the cost of excess fuel burned is the highest contributor to operating expenses. “
Also, this is an example of the capture CO2 emissions from an in-service vessel:
https://maritime-executive.com/article/first-carbon-capture-system-installed-on-eps-managed-tanker#:~:text=Value%20Marine's%20technology%20works%20by,CO2%20in%20a%20single%20voyage.
Posted by: Gryf | 08 May 2024 at 09:59 AM
Roger said: “a real concern exists about how much new demand we can place on biomass without negative impacts on food supply/ecological diversity.”
That is a critical issue. Biomass cannot supply 100% of the requirements for Marine fuels, Sustainable Aviation Fuel (SAF), and Asphalt uses.
That is why a Circular Economy is essential and will only work for Marine fuels(not SAF). Starting with fossil fuel sources and depending on how successful Carbon Capture works, eventually all CO2 could be from biological sources.
Also, Lignin does not impact food supply, typically Kraft lignin refers to the use of alkaline degradation as the wood process, while sulfonated lignin stems from the use of a sulfite pulping process. In other words, a waste product of the paper and pulp industry.
There are also companies working on Lignin based Marine fuels like Vertoro (not just research):
https://vertoro.com/maersk-invests-in-vertoro-to-develop-green-lignin-marine-fuels/
Another one is a Swedish company RenFuel that is converting converts forest lignin into bio-oil:
https://renfuel.se/about-us/
Posted by: Gryf | 08 May 2024 at 10:18 AM
@Gryf,
Thanks for the references.
Posted by: Roger Brown | 08 May 2024 at 12:51 PM
Gryf said:
' That is a critical issue. Biomass cannot supply 100% of the requirements for Marine fuels, Sustainable Aviation Fuel (SAF), and Asphalt uses.
That is why a Circular Economy is essential and will only work for Marine fuels(not SAF). Starting with fossil fuel sources and depending on how successful Carbon Capture works, eventually all CO2 could be from biological sources.'
Good points. A different kettle of fish to the legendary, and as far as we can see ahead, mythical, DAC.
Posted by: Davemart | 08 May 2024 at 01:47 PM
Just use Liquid Hydrogen from solar, wind, and nuclear energy for ships and not worrying about whether biomass is sufficient or not. The bunker fuel volume is 2.5% of total cargo capacity. LH2 takes up 4 times the volume of bunker fuel, meaning that there will be a 7.5% reduction in cargo capacity, although the ship can be lengthened by 5% to carry the extra LH2 fuel without impacting cargo volume. The reason that only 5% lengthening is needed for extra volume of LH2 fuel because the ship also has sizable engine compartment volume, crew quarters, and other spaces not reserved for cargo.
The added benefit of LH2 is that it is so much lighter than the bunker fuel that additional tonnage for heavier cargo will be made available, so perfect for higher density cargo.
Posted by: Roger Pham | 12 May 2024 at 03:52 PM