Researchers Develop Bacterial Enzyme-Based Catalyst for Water-Gas Shift Reaction at Ambient Conditions; New Thinking About Catalyst Design
22 September 2009
| Researchers used coupled enzymes for the WGS reaction at ambient temperature. Source: ACS. Click to enlarge. |
A team of researchers from the UK and US have developed a coupled bacterial enzyme-based catalyst for the important water-gas shift reaction (WGS) for the production of hydrogen from syngas. A paper on the work was published online in the Journal of the American Chemical Society on 15 September.
The water-gas shift (WGS) reaction for the production of hydrogen from carbon monoxide and water (CO + H2O ↔ CO2 + H2) typically requires high temperatures typically in excess of 200 °C and a metal catalyst. The team, led by Fraser Armstrong at Oxford, separated the WGS process into two half-cell electrochemical reactions (H+ reduction and CO oxidation), catalyzed by bacterial enzymes attached to a conducting particle.
The H+ reduction reaction is catalyzed by a hydrogenase, Hyd-2, from Escherichia coli, and CO oxidation is catalyzed by a carbon monoxide dehydrogenase (CODH I) from Carboxydothermus hydrogenoformans. This results in a highly efficient heterogeneous catalyst with a turnover frequency, at 30 °C, of at least 2.5 s-1 per minimum functional unit (a CODH/Hyd-2 pair) which is comparable to conventional high-temperature catalysts.
The point, said the researchers, was not to develop a replacement for robust industrial WGS catalysts, but to spur thinking about catalyst design that could match the efficiency of biological enzymes.
The experiments are unlikely to have direct relevance for energy technology as they use tiny amounts of fragile enzymes rather than robust synthetic catalysts that could be scaled up indefinitely. Even so, the study demonstrates some interesting alternative concepts for catalysis and highlights the wide gap between redox enzymes and synthetic catalysts in terms of both rates and efficiency.
Coupling via electronically conducting particles enables a catalytic redox reaction to be separated into two half-reactions having lower activation energies than the entire reaction at a single site. The H+/H2 and CO2/CO redox couples are both reversible at electrodes modified with hydrogenases and CODH, respectively, whereas the best that chemistry can currently offer are Pt metal catalysts for the hydrogen system; however, Pt is incompatible with CO and could not be used here.
Finally, the electrochemical reversibility of the CO2/CO couple catalyzed by CODH is not only a key requirement for the WGS particle catalyst but also highly inspirational in view of demonstrating the feasibility of efficient CO2/CO electrochemical cycling with CO serving as an energy store.
—Lazarus et al. 2009
Resources
Oliver Lazarus, Thomas W. Woolerton, Alison Parkin, Michael J. Lukey, Erwin Reisner, Javier Seravalli, Elizabeth Pierce, Stephen W. Ragsdale, Frank Sargent and Fraser A. Armstrong (2009) Water-Gas Shift Reaction Catalyzed by Redox Enzymes on Conducting Graphite Platelets. J. Am. Chem. Soc., Article ASAP doi: 10.1021/ja905797w
Enzymes inspire new catalyst design for hydrogen production (Chemistry World)
Perhaps humans can be fed by direct injection of hydrogen. Many local coal to Hydrogen converters need to be built so that natural gas use in the home can be replaced by hydrogen. This would cut down greatly on the radon intoroduced into homes. ..HG..
Posted by: Henry Gibson | 22 September 2009 at 10:10 AM
wtf?
From a carbon standpoint it would not be better to replace NG with H2 from coal and, seeing as we get coal from the same ground we get NG from, the hydrogen stream will also have radon in it.
There was a NG/radon study done in the UK; Levels of radon in blended gas received by most users are comparable with the levels that are present naturally in buildings as a result of ingress from the ground and this is further diluted during the combustion process. For typical rates of gas usage with an average radon level of about 200 Bq.m-3, the estimated dose from the use of natural gas is estimated at 4 µSv, less than 1% of the dose from radon exposure at the average level in UK homes.
If you're concerned about radon build-up you can deal with it with venting to the outside and changing the air in the building using a heat exchanger.
And instead of coal/hydrogen switch to something even more green, like heat pumps or solar hot water panels.
Posted by: ai_vin | 22 September 2009 at 11:03 AM
AFAIK, radon exposure in homes has nothing to do with any radon that might be present in NG. I suppose it could if the NG were being burned in room heaters that vent directly into the room, but those are against code in most places. Gas-fired central furnaces all vent to the outside. Radon typically diffuses into unsealded basements from from the soil, in areas where the soil is naturally high in uranium. The quantities are always minute, and become a problem only in tightly closed homes. The cures are to install a plastic diffusion barrier under the basement floor, and / or increase the air exchange rate for the home.
The research cited in this article is interesting from a theoretical perspective, but I don't see it as comercially significant per se. There's no market for small-scale conversion of syngas to hydrogen. For large-scale production of hydrogen from coal or biomass, there's no way that a room-temperature enzyme-based reaction can begin to compete with the cost and throughput of a conventional water gas shift reactor.
For small-scale production of hydrocarbons from water, CO2, and electricity -- which could have a potential market -- it's the reverse WSGR that's of interest. It would be cool to have a farm-scale unit that could produce diesel fuel from CO2, water, and solar electricity. But the reported mechanism won't help there.
Posted by: Silverthorn | 22 September 2009 at 05:48 PM