Converting CO2 to fuel using silicon

Discussion in 'Chemistry' started by Plazma Inferno!, Aug 26, 2016.

  1. Plazma Inferno! Ding Ding Ding Ding Administrator

    The idea of converting carbon dioxide emissions to energy isn't new: there's been a global race to discover a material that can efficiently convert sunlight, carbon dioxide and water or hydrogen to fuel for decades. However, the chemical stability of carbon dioxide has made it difficult to find a practical solution.
    I already posted about various attempts of converting CO2 into a liquid fuel. A team of University of Texas at Arlington chemists and engineers demonstrated conversion of CO2 and water into liquid hydrocarbon fuel back in February. One month before them, researchers from California demonstrated that carbon dioxide captured from the air can be directly converted into methanol fuel.
    Now, a team of scientists from the University of Toronto believes they've found a way to convert about 30 billion tonnes of CO2 emissions -- that we inject into atmosphere each year -- into energy-rich fuel in a carbon-neutral cycle that uses a very abundant natural resource: silicon.
    For this task, team required a material that is a highly active and selective catalyst to enable the conversion of carbon dioxide to fuel. It also had to be made of elements that are low cost, non-toxic and readily available.
    In their paper, team reports silicon nanocrystals that meet all the criteria. The hydride-terminated silicon nanocrystals – nanostructured hydrides for short – have an average diameter of 3.5 nanometres and feature a surface area and optical absorption strength sufficient to efficiently harvest the near-infrared, visible and ultraviolet wavelengths of light from the sun together with a powerful chemical-reducing agent on the surface that efficiently and selectively converts gaseous carbon dioxide to gaseous carbon monoxide.
    The potential result: energy without harmful emissions.

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  3. exchemist Valued Senior Member

    Well, sort of interesting. But while they do not go out of their way to draw attention to the fact, this is not catalysis. The surface is oxidised to Si-OH groups and is thereafter inactive for reducing CO2. Adding hydrogen, which they tried, does not regenerate the original Si-H groups responsible for the reduction reaction. Unless a way can be found to regenerate the silicon nanocrystals, this finding will just be a chemical curiosity and will not contribute to solving our energy problems. This may not be easy: the Si-O bond is notoriously strong.
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  5. Russ_Watters Not a Trump supporter... Valued Senior Member

    "Chemical stability" is just another way of saying that carbon dioxide is what is left after you've burned your fuel. It's ash. A waste product. Not fuel. So any process that "converts" it to something burnable is literally "unburning" it. In most cases, it would probably just be better to use the energy you started with (solar is what they claim here) more directly such as with solar panels.

    Yeah, that.
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  7. exchemist Valued Senior Member

    Re your point about "unburning", this is of course exactly what photosynthesis does: driving an energetically "uphill" reduction reaction, via energy input captured from the sun. There seem to be several competing ideas on how to do this by artificial means, yielding a variety of fuels. In this case CO (come back town gas, all is forgiven?), but I have read of schemes for producing methanol and methane as well.

    I assume the point of producing a liquid or gaseous fuel, rather than electricity, is that it might enable conventional (heat-engine based) transport to function, rather than requiring total replacement of the transport fleet by electric vehicles. But I always have the question in my mind of whether the efficiency and environmental stress of such artificial photosynthesis will actually be any improvement on simply growing plants for fuel.

    I suppose at this point it is good to explore a number of competing avenues, since we do not yet know what the most practical way forward will be and we have no way (thank goodness!) to control the choices made by various societies and enterprises around the world.
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  8. Yazata Valued Senior Member

    Ask the green plants. They already remove some 250 billion tons of CO2 from the atmosphere yearly and convert it into more plants. (About half of that takes place in the oceans.)

    Coal is essentially atmospheric carbon that green plants fixed photosynthetically long ago and converted into biomass, which then was geologically converted into a more practical fuel in the long millennia since.

    Wood isn't nearly as efficient as coal, but wood-burning steam locomotives illustrate the same principle. They are mankind indirectly using atmospheric carbon dioxide as fuel too.

    Of course burning the fuel returns the carbon to the atmosphere.

    My layman's eye view is that if we are going to taking this recent global warming hysteria seriously, the goal isn't using atmospheric carbon dioxide as feedstock in making fuel. Plants are already far more efficient at doing that than we will likely ever be. The goal is to find a way to use the resulting biological product to produce useful energy without returning the carbon to the atmosphere.

    Perhaps we should also be looking at clearing fewer forests to create farmland and at reversing the damage by replanting forests previously destroyed. That will collide with the food-needs of the world's exploding population though...
    Last edited: Sep 2, 2016
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  9. billvon Valued Senior Member

    Or just leave the forests alone. Over thousands of years they build up layers of carbonaceous material under the ground - and after millions, that becomes permanently sequestered as coal. Then, as long as we leave it there, it stays away.
    Yep. Thus education. Education (especially of women) reduces birthrate.
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  10. exchemist Valued Senior Member

    Amen. Amen.

    Slightly off-topic possibly, but this is one of my strongest convictions. Education of women is in my view the single most valuable thing we can do in the world today. So many issues are addressed by it, from population to corruption to terrorism.

    I am wanting to draw up a will and I would really like to leave a bequest to a reputable and efficient charity that focuses n educating women in the developing world. Does any one have any suggestions? (...or maybe I should start a thread on it...)
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